compiler/rustc_expand/src/expand.rs

   1 use crate::base::*;
   2 use crate::config::StripUnconfigured;
   3 use crate::hygiene::SyntaxContext;
   4 use crate::mbe::diagnostics::annotate_err_with_kind;
   5 use crate::module::{mod_dir_path, parse_external_mod, DirOwnership, ParsedExternalMod};
   6 use crate::placeholders::{placeholder, PlaceholderExpander};
   7
   8 use rustc_ast as ast;
   9 use rustc_ast::mut_visit::*;
  10 use rustc_ast::ptr::P;
  11 use rustc_ast::token::{self, Delimiter};
  12 use rustc_ast::tokenstream::TokenStream;
  13 use rustc_ast::visit::{self, AssocCtxt, Visitor};
  14 use rustc_ast::{AssocItemKind, AstNodeWrapper, AttrArgs, AttrStyle, AttrVec, ExprKind};
  15 use rustc_ast::{ForeignItemKind, HasAttrs, HasNodeId};
  16 use rustc_ast::{Inline, ItemKind, MacStmtStyle, MetaItemKind, ModKind};
  17 use rustc_ast::{NestedMetaItem, NodeId, PatKind, StmtKind, TyKind};
  18 use rustc_ast_pretty::pprust;
  19 use rustc_data_structures::map_in_place::MapInPlace;
  20 use rustc_data_structures::sync::Lrc;
  21 use rustc_errors::{Applicability, PResult};
  22 use rustc_feature::Features;
  23 use rustc_parse::parser::{
  24     AttemptLocalParseRecovery, CommaRecoveryMode, ForceCollect, Parser, RecoverColon, RecoverComma,
  25 };
  26 use rustc_parse::validate_attr;
  27 use rustc_session::lint::builtin::{UNUSED_ATTRIBUTES, UNUSED_DOC_COMMENTS};
  28 use rustc_session::lint::BuiltinLintDiagnostics;
  29 use rustc_session::parse::{feature_err, ParseSess};
  30 use rustc_session::Limit;
  31 use rustc_span::symbol::{sym, Ident};
  32 use rustc_span::{FileName, LocalExpnId, Span};
  33
  34 use smallvec::SmallVec;
  35 use std::ops::Deref;
  36 use std::path::PathBuf;
  37 use std::rc::Rc;
  38 use std::{iter, mem};
  39
  40 macro_rules! ast_fragments {
  41     (
  42         $($Kind:ident($AstTy:ty) {
  43             $kind_name:expr;
  44             $(one fn $mut_visit_ast:ident; fn $visit_ast:ident;)?
  45             $(many fn $flat_map_ast_elt:ident; fn $visit_ast_elt:ident($($args:tt)*);)?
  46             fn $make_ast:ident;
  47         })*
  48     ) => {
  49         /// A fragment of AST that can be produced by a single macro expansion.
  50         /// Can also serve as an input and intermediate result for macro expansion operations.
  51         pub enum AstFragment {
  52             OptExpr(Option<P<ast::Expr>>),
  53             MethodReceiverExpr(P<ast::Expr>),
  54             $($Kind($AstTy),)*
  55         }
  56
  57         /// "Discriminant" of an AST fragment.
  58         #[derive(Copy, Clone, PartialEq, Eq)]
  59         pub enum AstFragmentKind {
  60             OptExpr,
  61             MethodReceiverExpr,
  62             $($Kind,)*
  63         }
  64
  65         impl AstFragmentKind {
  66             pub fn name(self) -> &'static str {
  67                 match self {
  68                     AstFragmentKind::OptExpr => "expression",
  69                     AstFragmentKind::MethodReceiverExpr => "expression",
  70                     $(AstFragmentKind::$Kind => $kind_name,)*
  71                 }
  72             }
  73
  74             fn make_from<'a>(self, result: Box<dyn MacResult + 'a>) -> Option<AstFragment> {
  75                 match self {
  76                     AstFragmentKind::OptExpr =>
  77                         result.make_expr().map(Some).map(AstFragment::OptExpr),
  78                     AstFragmentKind::MethodReceiverExpr =>
  79                         result.make_expr().map(AstFragment::MethodReceiverExpr),
  80                     $(AstFragmentKind::$Kind => result.$make_ast().map(AstFragment::$Kind),)*
  81                 }
  82             }
  83         }
  84
  85         impl AstFragment {
  86             pub fn add_placeholders(&mut self, placeholders: &[NodeId]) {
  87                 if placeholders.is_empty() {
  88                     return;
  89                 }
  90                 match self {
  91                     $($(AstFragment::$Kind(ast) => ast.extend(placeholders.iter().flat_map(|id| {
  92                         ${ignore(flat_map_ast_elt)}
  93                         placeholder(AstFragmentKind::$Kind, *id, None).$make_ast()
  94                     })),)?)*
  95                     _ => panic!("unexpected AST fragment kind")
  96                 }
  97             }
  98
  99             pub fn make_opt_expr(self) -> Option<P<ast::Expr>> {
 100                 match self {
 101                     AstFragment::OptExpr(expr) => expr,
 102                     _ => panic!("AstFragment::make_* called on the wrong kind of fragment"),
 103                 }
 104             }
 105
 106             pub fn make_method_receiver_expr(self) -> P<ast::Expr> {
 107                 match self {
 108                     AstFragment::MethodReceiverExpr(expr) => expr,
 109                     _ => panic!("AstFragment::make_* called on the wrong kind of fragment"),
 110                 }
 111             }
 112
 113             $(pub fn $make_ast(self) -> $AstTy {
 114                 match self {
 115                     AstFragment::$Kind(ast) => ast,
 116                     _ => panic!("AstFragment::make_* called on the wrong kind of fragment"),
 117                 }
 118             })*
 119
 120             fn make_ast<T: InvocationCollectorNode>(self) -> T::OutputTy {
 121                 T::fragment_to_output(self)
 122             }
 123
 124             pub fn mut_visit_with<F: MutVisitor>(&mut self, vis: &mut F) {
 125                 match self {
 126                     AstFragment::OptExpr(opt_expr) => {
 127                         visit_clobber(opt_expr, |opt_expr| {
 128                             if let Some(expr) = opt_expr {
 129                                 vis.filter_map_expr(expr)
 130                             } else {
 131                                 None
 132                             }
 133                         });
 134                     }
 135                     AstFragment::MethodReceiverExpr(expr) => vis.visit_method_receiver_expr(expr),
 136                     $($(AstFragment::$Kind(ast) => vis.$mut_visit_ast(ast),)?)*
 137                     $($(AstFragment::$Kind(ast) =>
 138                         ast.flat_map_in_place(|ast| vis.$flat_map_ast_elt(ast)),)?)*
 139                 }
 140             }
 141
 142             pub fn visit_with<'a, V: Visitor<'a>>(&'a self, visitor: &mut V) {
 143                 match *self {
 144                     AstFragment::OptExpr(Some(ref expr)) => visitor.visit_expr(expr),
 145                     AstFragment::OptExpr(None) => {}
 146                     AstFragment::MethodReceiverExpr(ref expr) => visitor.visit_method_receiver_expr(expr),
 147                     $($(AstFragment::$Kind(ref ast) => visitor.$visit_ast(ast),)?)*
 148                     $($(AstFragment::$Kind(ref ast) => for ast_elt in &ast[..] {
 149                         visitor.$visit_ast_elt(ast_elt, $($args)*);
 150                     })?)*
 151                 }
 152             }
 153         }
 154
 155         impl<'a> MacResult for crate::mbe::macro_rules::ParserAnyMacro<'a> {
 156             $(fn $make_ast(self: Box<crate::mbe::macro_rules::ParserAnyMacro<'a>>)
 157                            -> Option<$AstTy> {
 158                 Some(self.make(AstFragmentKind::$Kind).$make_ast())
 159             })*
 160         }
 161     }
 162 }
 163
 164 ast_fragments! {
 165     Expr(P<ast::Expr>) { "expression"; one fn visit_expr; fn visit_expr; fn make_expr; }
 166     Pat(P<ast::Pat>) { "pattern"; one fn visit_pat; fn visit_pat; fn make_pat; }
 167     Ty(P<ast::Ty>) { "type"; one fn visit_ty; fn visit_ty; fn make_ty; }
 168     Stmts(SmallVec<[ast::Stmt; 1]>) {
 169         "statement"; many fn flat_map_stmt; fn visit_stmt(); fn make_stmts;
 170     }
 171     Items(SmallVec<[P<ast::Item>; 1]>) {
 172         "item"; many fn flat_map_item; fn visit_item(); fn make_items;
 173     }
 174     TraitItems(SmallVec<[P<ast::AssocItem>; 1]>) {
 175         "trait item";
 176         many fn flat_map_trait_item;
 177         fn visit_assoc_item(AssocCtxt::Trait);
 178         fn make_trait_items;
 179     }
 180     ImplItems(SmallVec<[P<ast::AssocItem>; 1]>) {
 181         "impl item";
 182         many fn flat_map_impl_item;
 183         fn visit_assoc_item(AssocCtxt::Impl);
 184         fn make_impl_items;
 185     }
 186     ForeignItems(SmallVec<[P<ast::ForeignItem>; 1]>) {
 187         "foreign item";
 188         many fn flat_map_foreign_item;
 189         fn visit_foreign_item();
 190         fn make_foreign_items;
 191     }
 192     Arms(SmallVec<[ast::Arm; 1]>) {
 193         "match arm"; many fn flat_map_arm; fn visit_arm(); fn make_arms;
 194     }
 195     ExprFields(SmallVec<[ast::ExprField; 1]>) {
 196         "field expression"; many fn flat_map_expr_field; fn visit_expr_field(); fn make_expr_fields;
 197     }
 198     PatFields(SmallVec<[ast::PatField; 1]>) {
 199         "field pattern";
 200         many fn flat_map_pat_field;
 201         fn visit_pat_field();
 202         fn make_pat_fields;
 203     }
 204     GenericParams(SmallVec<[ast::GenericParam; 1]>) {
 205         "generic parameter";
 206         many fn flat_map_generic_param;
 207         fn visit_generic_param();
 208         fn make_generic_params;
 209     }
 210     Params(SmallVec<[ast::Param; 1]>) {
 211         "function parameter"; many fn flat_map_param; fn visit_param(); fn make_params;
 212     }
 213     FieldDefs(SmallVec<[ast::FieldDef; 1]>) {
 214         "field";
 215         many fn flat_map_field_def;
 216         fn visit_field_def();
 217         fn make_field_defs;
 218     }
 219     Variants(SmallVec<[ast::Variant; 1]>) {
 220         "variant"; many fn flat_map_variant; fn visit_variant(); fn make_variants;
 221     }
 222     Crate(ast::Crate) { "crate"; one fn visit_crate; fn visit_crate; fn make_crate; }
 223 }
 224
 225 pub enum SupportsMacroExpansion {
 226     No,
 227     Yes { supports_inner_attrs: bool },
 228 }
 229
 230 impl AstFragmentKind {
 231     pub(crate) fn dummy(self, span: Span) -> AstFragment {
 232         self.make_from(DummyResult::any(span)).expect("couldn't create a dummy AST fragment")
 233     }
 234
 235     pub fn supports_macro_expansion(self) -> SupportsMacroExpansion {
 236         match self {
 237             AstFragmentKind::OptExpr
 238             | AstFragmentKind::Expr
 239             | AstFragmentKind::MethodReceiverExpr
 240             | AstFragmentKind::Stmts
 241             | AstFragmentKind::Ty
 242             | AstFragmentKind::Pat => SupportsMacroExpansion::Yes { supports_inner_attrs: false },
 243             AstFragmentKind::Items
 244             | AstFragmentKind::TraitItems
 245             | AstFragmentKind::ImplItems
 246             | AstFragmentKind::ForeignItems
 247             | AstFragmentKind::Crate => SupportsMacroExpansion::Yes { supports_inner_attrs: true },
 248             AstFragmentKind::Arms
 249             | AstFragmentKind::ExprFields
 250             | AstFragmentKind::PatFields
 251             | AstFragmentKind::GenericParams
 252             | AstFragmentKind::Params
 253             | AstFragmentKind::FieldDefs
 254             | AstFragmentKind::Variants => SupportsMacroExpansion::No,
 255         }
 256     }
 257
 258     fn expect_from_annotatables<I: IntoIterator<Item = Annotatable>>(
 259         self,
 260         items: I,
 261     ) -> AstFragment {
 262         let mut items = items.into_iter();
 263         match self {
 264             AstFragmentKind::Arms => {
 265                 AstFragment::Arms(items.map(Annotatable::expect_arm).collect())
 266             }
 267             AstFragmentKind::ExprFields => {
 268                 AstFragment::ExprFields(items.map(Annotatable::expect_expr_field).collect())
 269             }
 270             AstFragmentKind::PatFields => {
 271                 AstFragment::PatFields(items.map(Annotatable::expect_pat_field).collect())
 272             }
 273             AstFragmentKind::GenericParams => {
 274                 AstFragment::GenericParams(items.map(Annotatable::expect_generic_param).collect())
 275             }
 276             AstFragmentKind::Params => {
 277                 AstFragment::Params(items.map(Annotatable::expect_param).collect())
 278             }
 279             AstFragmentKind::FieldDefs => {
 280                 AstFragment::FieldDefs(items.map(Annotatable::expect_field_def).collect())
 281             }
 282             AstFragmentKind::Variants => {
 283                 AstFragment::Variants(items.map(Annotatable::expect_variant).collect())
 284             }
 285             AstFragmentKind::Items => {
 286                 AstFragment::Items(items.map(Annotatable::expect_item).collect())
 287             }
 288             AstFragmentKind::ImplItems => {
 289                 AstFragment::ImplItems(items.map(Annotatable::expect_impl_item).collect())
 290             }
 291             AstFragmentKind::TraitItems => {
 292                 AstFragment::TraitItems(items.map(Annotatable::expect_trait_item).collect())
 293             }
 294             AstFragmentKind::ForeignItems => {
 295                 AstFragment::ForeignItems(items.map(Annotatable::expect_foreign_item).collect())
 296             }
 297             AstFragmentKind::Stmts => {
 298                 AstFragment::Stmts(items.map(Annotatable::expect_stmt).collect())
 299             }
 300             AstFragmentKind::Expr => AstFragment::Expr(
 301                 items.next().expect("expected exactly one expression").expect_expr(),
 302             ),
 303             AstFragmentKind::MethodReceiverExpr => AstFragment::MethodReceiverExpr(
 304                 items.next().expect("expected exactly one expression").expect_expr(),
 305             ),
 306             AstFragmentKind::OptExpr => {
 307                 AstFragment::OptExpr(items.next().map(Annotatable::expect_expr))
 308             }
 309             AstFragmentKind::Crate => {
 310                 AstFragment::Crate(items.next().expect("expected exactly one crate").expect_crate())
 311             }
 312             AstFragmentKind::Pat | AstFragmentKind::Ty => {
 313                 panic!("patterns and types aren't annotatable")
 314             }
 315         }
 316     }
 317 }
 318
 319 pub struct Invocation {
 320     pub kind: InvocationKind,
 321     pub fragment_kind: AstFragmentKind,
 322     pub expansion_data: ExpansionData,
 323 }
 324
 325 pub enum InvocationKind {
 326     Bang {
 327         mac: P<ast::MacCall>,
 328         span: Span,
 329     },
 330     Attr {
 331         attr: ast::Attribute,
 332         // Re-insertion position for inert attributes.
 333         pos: usize,
 334         item: Annotatable,
 335         // Required for resolving derive helper attributes.
 336         derives: Vec<ast::Path>,
 337     },
 338     Derive {
 339         path: ast::Path,
 340         is_const: bool,
 341         item: Annotatable,
 342     },
 343 }
 344
 345 impl InvocationKind {
 346     fn placeholder_visibility(&self) -> Option<ast::Visibility> {
 347         // HACK: For unnamed fields placeholders should have the same visibility as the actual
 348         // fields because for tuple structs/variants resolve determines visibilities of their
 349         // constructor using these field visibilities before attributes on them are expanded.
 350         // The assumption is that the attribute expansion cannot change field visibilities,
 351         // and it holds because only inert attributes are supported in this position.
 352         match self {
 353             InvocationKind::Attr { item: Annotatable::FieldDef(field), .. }
 354             | InvocationKind::Derive { item: Annotatable::FieldDef(field), .. }
 355                 if field.ident.is_none() =>
 356             {
 357                 Some(field.vis.clone())
 358             }
 359             _ => None,
 360         }
 361     }
 362 }
 363
 364 impl Invocation {
 365     pub fn span(&self) -> Span {
 366         match &self.kind {
 367             InvocationKind::Bang { span, .. } => *span,
 368             InvocationKind::Attr { attr, .. } => attr.span,
 369             InvocationKind::Derive { path, .. } => path.span,
 370         }
 371     }
 372 }
 373
 374 pub struct MacroExpander<'a, 'b> {
 375     pub cx: &'a mut ExtCtxt<'b>,
 376     monotonic: bool, // cf. `cx.monotonic_expander()`
 377 }
 378
 379 impl<'a, 'b> MacroExpander<'a, 'b> {
 380     pub fn new(cx: &'a mut ExtCtxt<'b>, monotonic: bool) -> Self {
 381         MacroExpander { cx, monotonic }
 382     }
 383
 384     pub fn expand_crate(&mut self, krate: ast::Crate) -> ast::Crate {
 385         let file_path = match self.cx.source_map().span_to_filename(krate.spans.inner_span) {
 386             FileName::Real(name) => name
 387                 .into_local_path()
 388                 .expect("attempting to resolve a file path in an external file"),
 389             other => PathBuf::from(other.prefer_local().to_string()),
 390         };
 391         let dir_path = file_path.parent().unwrap_or(&file_path).to_owned();
 392         self.cx.root_path = dir_path.clone();
 393         self.cx.current_expansion.module = Rc::new(ModuleData {
 394             mod_path: vec![Ident::from_str(&self.cx.ecfg.crate_name)],
 395             file_path_stack: vec![file_path],
 396             dir_path,
 397         });
 398         let krate = self.fully_expand_fragment(AstFragment::Crate(krate)).make_crate();
 399         assert_eq!(krate.id, ast::CRATE_NODE_ID);
 400         self.cx.trace_macros_diag();
 401         krate
 402     }
 403
 404     /// Recursively expand all macro invocations in this AST fragment.
 405     pub fn fully_expand_fragment(&mut self, input_fragment: AstFragment) -> AstFragment {
 406         let orig_expansion_data = self.cx.current_expansion.clone();
 407         let orig_force_mode = self.cx.force_mode;
 408
 409         // Collect all macro invocations and replace them with placeholders.
 410         let (mut fragment_with_placeholders, mut invocations) =
 411             self.collect_invocations(input_fragment, &[]);
 412
 413         // Optimization: if we resolve all imports now,
 414         // we'll be able to immediately resolve most of imported macros.
 415         self.resolve_imports();
 416
 417         // Resolve paths in all invocations and produce output expanded fragments for them, but
 418         // do not insert them into our input AST fragment yet, only store in `expanded_fragments`.
 419         // The output fragments also go through expansion recursively until no invocations are left.
 420         // Unresolved macros produce dummy outputs as a recovery measure.
 421         invocations.reverse();
 422         let mut expanded_fragments = Vec::new();
 423         let mut undetermined_invocations = Vec::new();
 424         let (mut progress, mut force) = (false, !self.monotonic);
 425         loop {
 426             let Some((invoc, ext)) = invocations.pop() else {
 427                 self.resolve_imports();
 428                 if undetermined_invocations.is_empty() {
 429                     break;
 430                 }
 431                 invocations = mem::take(&mut undetermined_invocations);
 432                 force = !mem::replace(&mut progress, false);
 433                 if force && self.monotonic {
 434                     self.cx.sess.delay_span_bug(
 435                         invocations.last().unwrap().0.span(),
 436                         "expansion entered force mode without producing any errors",
 437                     );
 438                 }
 439                 continue;
 440             };
 441
 442             let ext = match ext {
 443                 Some(ext) => ext,
 444                 None => {
 445                     let eager_expansion_root = if self.monotonic {
 446                         invoc.expansion_data.id
 447                     } else {
 448                         orig_expansion_data.id
 449                     };
 450                     match self.cx.resolver.resolve_macro_invocation(
 451                         &invoc,
 452                         eager_expansion_root,
 453                         force,
 454                     ) {
 455                         Ok(ext) => ext,
 456                         Err(Indeterminate) => {
 457                             // Cannot resolve, will retry this invocation later.
 458                             undetermined_invocations.push((invoc, None));
 459                             continue;
 460                         }
 461                     }
 462                 }
 463             };
 464
 465             let ExpansionData { depth, id: expn_id, .. } = invoc.expansion_data;
 466             let depth = depth - orig_expansion_data.depth;
 467             self.cx.current_expansion = invoc.expansion_data.clone();
 468             self.cx.force_mode = force;
 469
 470             let fragment_kind = invoc.fragment_kind;
 471             let (expanded_fragment, new_invocations) = match self.expand_invoc(invoc, &ext.kind) {
 472                 ExpandResult::Ready(fragment) => {
 473                     let mut derive_invocations = Vec::new();
 474                     let derive_placeholders = self
 475                         .cx
 476                         .resolver
 477                         .take_derive_resolutions(expn_id)
 478                         .map(|derives| {
 479                             derive_invocations.reserve(derives.len());
 480                             derives
 481                                 .into_iter()
 482                                 .map(|(path, item, _exts, is_const)| {
 483                                     // FIXME: Consider using the derive resolutions (`_exts`)
 484                                     // instead of enqueuing the derives to be resolved again later.
 485                                     let expn_id = LocalExpnId::fresh_empty();
 486                                     derive_invocations.push((
 487                                         Invocation {
 488                                             kind: InvocationKind::Derive { path, item, is_const },
 489                                             fragment_kind,
 490                                             expansion_data: ExpansionData {
 491                                                 id: expn_id,
 492                                                 ..self.cx.current_expansion.clone()
 493                                             },
 494                                         },
 495                                         None,
 496                                     ));
 497                                     NodeId::placeholder_from_expn_id(expn_id)
 498                                 })
 499                                 .collect::<Vec<_>>()
 500                         })
 501                         .unwrap_or_default();
 502
 503                     let (fragment, collected_invocations) =
 504                         self.collect_invocations(fragment, &derive_placeholders);
 505                     // We choose to expand any derive invocations associated with this macro invocation
 506                     // *before* any macro invocations collected from the output fragment
 507                     derive_invocations.extend(collected_invocations);
 508                     (fragment, derive_invocations)
 509                 }
 510                 ExpandResult::Retry(invoc) => {
 511                     if force {
 512                         self.cx.span_bug(
 513                             invoc.span(),
 514                             "expansion entered force mode but is still stuck",
 515                         );
 516                     } else {
 517                         // Cannot expand, will retry this invocation later.
 518                         undetermined_invocations.push((invoc, Some(ext)));
 519                         continue;
 520                     }
 521                 }
 522             };
 523
 524             progress = true;
 525             if expanded_fragments.len() < depth {
 526                 expanded_fragments.push(Vec::new());
 527             }
 528             expanded_fragments[depth - 1].push((expn_id, expanded_fragment));
 529             invocations.extend(new_invocations.into_iter().rev());
 530         }
 531
 532         self.cx.current_expansion = orig_expansion_data;
 533         self.cx.force_mode = orig_force_mode;
 534
 535         // Finally incorporate all the expanded macros into the input AST fragment.
 536         let mut placeholder_expander = PlaceholderExpander::default();
 537         while let Some(expanded_fragments) = expanded_fragments.pop() {
 538             for (expn_id, expanded_fragment) in expanded_fragments.into_iter().rev() {
 539                 placeholder_expander
 540                     .add(NodeId::placeholder_from_expn_id(expn_id), expanded_fragment);
 541             }
 542         }
 543         fragment_with_placeholders.mut_visit_with(&mut placeholder_expander);
 544         fragment_with_placeholders
 545     }
 546
 547     fn resolve_imports(&mut self) {
 548         if self.monotonic {
 549             self.cx.resolver.resolve_imports();
 550         }
 551     }
 552
 553     /// Collects all macro invocations reachable at this time in this AST fragment, and replace
 554     /// them with "placeholders" - dummy macro invocations with specially crafted `NodeId`s.
 555     /// Then call into resolver that builds a skeleton ("reduced graph") of the fragment and
 556     /// prepares data for resolving paths of macro invocations.
 557     fn collect_invocations(
 558         &mut self,
 559         mut fragment: AstFragment,
 560         extra_placeholders: &[NodeId],
 561     ) -> (AstFragment, Vec<(Invocation, Option<Lrc<SyntaxExtension>>)>) {
 562         // Resolve `$crate`s in the fragment for pretty-printing.
 563         self.cx.resolver.resolve_dollar_crates();
 564
 565         let mut invocations = {
 566             let mut collector = InvocationCollector {
 567                 // Non-derive macro invocations cannot see the results of cfg expansion - they
 568                 // will either be removed along with the item, or invoked before the cfg/cfg_attr
 569                 // attribute is expanded. Therefore, we don't need to configure the tokens
 570                 // Derive macros *can* see the results of cfg-expansion - they are handled
 571                 // specially in `fully_expand_fragment`
 572                 cx: self.cx,
 573                 invocations: Vec::new(),
 574                 monotonic: self.monotonic,
 575             };
 576             fragment.mut_visit_with(&mut collector);
 577             fragment.add_placeholders(extra_placeholders);
 578             collector.invocations
 579         };
 580
 581         if self.monotonic {
 582             self.cx
 583                 .resolver
 584                 .visit_ast_fragment_with_placeholders(self.cx.current_expansion.id, &fragment);
 585
 586             if self.cx.sess.opts.unstable_opts.incremental_relative_spans {
 587                 for (invoc, _) in invocations.iter_mut() {
 588                     let expn_id = invoc.expansion_data.id;
 589                     let parent_def = self.cx.resolver.invocation_parent(expn_id);
 590                     let span = match &mut invoc.kind {
 591                         InvocationKind::Bang { ref mut span, .. } => span,
 592                         InvocationKind::Attr { attr, .. } => &mut attr.span,
 593                         InvocationKind::Derive { path, .. } => &mut path.span,
 594                     };
 595                     *span = span.with_parent(Some(parent_def));
 596                 }
 597             }
 598         }
 599
 600         (fragment, invocations)
 601     }
 602
 603     fn error_recursion_limit_reached(&mut self) {
 604         let expn_data = self.cx.current_expansion.id.expn_data();
 605         let suggested_limit = match self.cx.ecfg.recursion_limit {
 606             Limit(0) => Limit(2),
 607             limit => limit * 2,
 608         };
 609         self.cx
 610             .struct_span_err(
 611                 expn_data.call_site,
 612                 &format!("recursion limit reached while expanding `{}`", expn_data.kind.descr()),
 613             )
 614             .help(&format!(
 615                 "consider increasing the recursion limit by adding a \
 616                  `#![recursion_limit = \"{}\"]` attribute to your crate (`{}`)",
 617                 suggested_limit, self.cx.ecfg.crate_name,
 618             ))
 619             .emit();
 620         self.cx.trace_macros_diag();
 621     }
 622
 623     /// A macro's expansion does not fit in this fragment kind.
 624     /// For example, a non-type macro in a type position.
 625     fn error_wrong_fragment_kind(&mut self, kind: AstFragmentKind, mac: &ast::MacCall, span: Span) {
 626         let msg = format!(
 627             "non-{kind} macro in {kind} position: {path}",
 628             kind = kind.name(),
 629             path = pprust::path_to_string(&mac.path),
 630         );
 631         self.cx.span_err(span, &msg);
 632         self.cx.trace_macros_diag();
 633     }
 634
 635     fn expand_invoc(
 636         &mut self,
 637         invoc: Invocation,
 638         ext: &SyntaxExtensionKind,
 639     ) -> ExpandResult<AstFragment, Invocation> {
 640         let recursion_limit =
 641             self.cx.reduced_recursion_limit.unwrap_or(self.cx.ecfg.recursion_limit);
 642         if !recursion_limit.value_within_limit(self.cx.current_expansion.depth) {
 643             if self.cx.reduced_recursion_limit.is_none() {
 644                 self.error_recursion_limit_reached();
 645             }
 646
 647             // Reduce the recursion limit by half each time it triggers.
 648             self.cx.reduced_recursion_limit = Some(recursion_limit / 2);
 649
 650             return ExpandResult::Ready(invoc.fragment_kind.dummy(invoc.span()));
 651         }
 652
 653         let (fragment_kind, span) = (invoc.fragment_kind, invoc.span());
 654         ExpandResult::Ready(match invoc.kind {
 655             InvocationKind::Bang { mac, .. } => match ext {
 656                 SyntaxExtensionKind::Bang(expander) => {
 657                     let Ok(tok_result) = expander.expand(self.cx, span, mac.args.tokens.clone()) else {
 658                         return ExpandResult::Ready(fragment_kind.dummy(span));
 659                     };
 660                     self.parse_ast_fragment(tok_result, fragment_kind, &mac.path, span)
 661                 }
 662                 SyntaxExtensionKind::LegacyBang(expander) => {
 663                     let prev = self.cx.current_expansion.prior_type_ascription;
 664                     self.cx.current_expansion.prior_type_ascription = mac.prior_type_ascription;
 665                     let tok_result = expander.expand(self.cx, span, mac.args.tokens.clone());
 666                     let result = if let Some(result) = fragment_kind.make_from(tok_result) {
 667                         result
 668                     } else {
 669                         self.error_wrong_fragment_kind(fragment_kind, &mac, span);
 670                         fragment_kind.dummy(span)
 671                     };
 672                     self.cx.current_expansion.prior_type_ascription = prev;
 673                     result
 674                 }
 675                 _ => unreachable!(),
 676             },
 677             InvocationKind::Attr { attr, pos, mut item, derives } => match ext {
 678                 SyntaxExtensionKind::Attr(expander) => {
 679                     self.gate_proc_macro_input(&item);
 680                     self.gate_proc_macro_attr_item(span, &item);
 681                     let tokens = match &item {
 682                         // FIXME: Collect tokens and use them instead of generating
 683                         // fake ones. These are unstable, so it needs to be
 684                         // fixed prior to stabilization
 685                         // Fake tokens when we are invoking an inner attribute, and
 686                         // we are invoking it on an out-of-line module or crate.
 687                         Annotatable::Crate(krate) => rustc_parse::fake_token_stream_for_crate(
 688                             &self.cx.sess.parse_sess,
 689                             krate,
 690                         ),
 691                         Annotatable::Item(item_inner)
 692                             if matches!(attr.style, AttrStyle::Inner)
 693                                 && matches!(
 694                                     item_inner.kind,
 695                                     ItemKind::Mod(
 696                                         _,
 697                                         ModKind::Unloaded | ModKind::Loaded(_, Inline::No, _),
 698                                     )
 699                                 ) =>
 700                         {
 701                             rustc_parse::fake_token_stream_for_item(
 702                                 &self.cx.sess.parse_sess,
 703                                 item_inner,
 704                             )
 705                         }
 706                         _ => item.to_tokens(),
 707                     };
 708                     let attr_item = attr.unwrap_normal_item();
 709                     if let AttrArgs::Eq(..) = attr_item.args {
 710                         self.cx.span_err(span, "key-value macro attributes are not supported");
 711                     }
 712                     let inner_tokens = attr_item.args.inner_tokens();
 713                     let Ok(tok_result) = expander.expand(self.cx, span, inner_tokens, tokens) else {
 714                         return ExpandResult::Ready(fragment_kind.dummy(span));
 715                     };
 716                     self.parse_ast_fragment(tok_result, fragment_kind, &attr_item.path, span)
 717                 }
 718                 SyntaxExtensionKind::LegacyAttr(expander) => {
 719                     match validate_attr::parse_meta(&self.cx.sess.parse_sess, &attr) {
 720                         Ok(meta) => {
 721                             let items = match expander.expand(self.cx, span, &meta, item, false) {
 722                                 ExpandResult::Ready(items) => items,
 723                                 ExpandResult::Retry(item) => {
 724                                     // Reassemble the original invocation for retrying.
 725                                     return ExpandResult::Retry(Invocation {
 726                                         kind: InvocationKind::Attr { attr, pos, item, derives },
 727                                         ..invoc
 728                                     });
 729                                 }
 730                             };
 731                             if fragment_kind == AstFragmentKind::Expr && items.is_empty() {
 732                                 let msg =
 733                                     "removing an expression is not supported in this position";
 734                                 self.cx.span_err(span, msg);
 735                                 fragment_kind.dummy(span)
 736                             } else {
 737                                 fragment_kind.expect_from_annotatables(items)
 738                             }
 739                         }
 740                         Err(mut err) => {
 741                             err.emit();
 742                             fragment_kind.dummy(span)
 743                         }
 744                     }
 745                 }
 746                 SyntaxExtensionKind::NonMacroAttr => {
 747                     self.cx.expanded_inert_attrs.mark(&attr);
 748                     item.visit_attrs(|attrs| attrs.insert(pos, attr));
 749                     fragment_kind.expect_from_annotatables(iter::once(item))
 750                 }
 751                 _ => unreachable!(),
 752             },
 753             InvocationKind::Derive { path, item, is_const } => match ext {
 754                 SyntaxExtensionKind::Derive(expander)
 755                 | SyntaxExtensionKind::LegacyDerive(expander) => {
 756                     if let SyntaxExtensionKind::Derive(..) = ext {
 757                         self.gate_proc_macro_input(&item);
 758                     }
 759                     let meta = ast::MetaItem { kind: MetaItemKind::Word, span, path };
 760                     let items = match expander.expand(self.cx, span, &meta, item, is_const) {
 761                         ExpandResult::Ready(items) => items,
 762                         ExpandResult::Retry(item) => {
 763                             // Reassemble the original invocation for retrying.
 764                             return ExpandResult::Retry(Invocation {
 765                                 kind: InvocationKind::Derive { path: meta.path, item, is_const },
 766                                 ..invoc
 767                             });
 768                         }
 769                     };
 770                     fragment_kind.expect_from_annotatables(items)
 771                 }
 772                 _ => unreachable!(),
 773             },
 774         })
 775     }
 776
 777     fn gate_proc_macro_attr_item(&self, span: Span, item: &Annotatable) {
 778         let kind = match item {
 779             Annotatable::Item(_)
 780             | Annotatable::TraitItem(_)
 781             | Annotatable::ImplItem(_)
 782             | Annotatable::ForeignItem(_)
 783             | Annotatable::Crate(..) => return,
 784             Annotatable::Stmt(stmt) => {
 785                 // Attributes are stable on item statements,
 786                 // but unstable on all other kinds of statements
 787                 if stmt.is_item() {
 788                     return;
 789                 }
 790                 "statements"
 791             }
 792             Annotatable::Expr(_) => "expressions",
 793             Annotatable::Arm(..)
 794             | Annotatable::ExprField(..)
 795             | Annotatable::PatField(..)
 796             | Annotatable::GenericParam(..)
 797             | Annotatable::Param(..)
 798             | Annotatable::FieldDef(..)
 799             | Annotatable::Variant(..) => panic!("unexpected annotatable"),
 800         };
 801         if self.cx.ecfg.proc_macro_hygiene() {
 802             return;
 803         }
 804         feature_err(
 805             &self.cx.sess.parse_sess,
 806             sym::proc_macro_hygiene,
 807             span,
 808             &format!("custom attributes cannot be applied to {}", kind),
 809         )
 810         .emit();
 811     }
 812
 813     fn gate_proc_macro_input(&self, annotatable: &Annotatable) {
 814         struct GateProcMacroInput<'a> {
 815             parse_sess: &'a ParseSess,
 816         }
 817
 818         impl<'ast, 'a> Visitor<'ast> for GateProcMacroInput<'a> {
 819             fn visit_item(&mut self, item: &'ast ast::Item) {
 820                 match &item.kind {
 821                     ItemKind::Mod(_, mod_kind)
 822                         if !matches!(mod_kind, ModKind::Loaded(_, Inline::Yes, _)) =>
 823                     {
 824                         feature_err(
 825                             self.parse_sess,
 826                             sym::proc_macro_hygiene,
 827                             item.span,
 828                             "non-inline modules in proc macro input are unstable",
 829                         )
 830                         .emit();
 831                     }
 832                     _ => {}
 833                 }
 834
 835                 visit::walk_item(self, item);
 836             }
 837         }
 838
 839         if !self.cx.ecfg.proc_macro_hygiene() {
 840             annotatable
 841                 .visit_with(&mut GateProcMacroInput { parse_sess: &self.cx.sess.parse_sess });
 842         }
 843     }
 844
 845     fn parse_ast_fragment(
 846         &mut self,
 847         toks: TokenStream,
 848         kind: AstFragmentKind,
 849         path: &ast::Path,
 850         span: Span,
 851     ) -> AstFragment {
 852         let mut parser = self.cx.new_parser_from_tts(toks);
 853         match parse_ast_fragment(&mut parser, kind) {
 854             Ok(fragment) => {
 855                 ensure_complete_parse(&mut parser, path, kind.name(), span);
 856                 fragment
 857             }
 858             Err(mut err) => {
 859                 if err.span.is_dummy() {
 860                     err.set_span(span);
 861                 }
 862                 annotate_err_with_kind(&mut err, kind, span);
 863                 err.emit();
 864                 self.cx.trace_macros_diag();
 865                 kind.dummy(span)
 866             }
 867         }
 868     }
 869 }
 870
 871 pub fn parse_ast_fragment<'a>(
 872     this: &mut Parser<'a>,
 873     kind: AstFragmentKind,
 874 ) -> PResult<'a, AstFragment> {
 875     Ok(match kind {
 876         AstFragmentKind::Items => {
 877             let mut items = SmallVec::new();
 878             while let Some(item) = this.parse_item(ForceCollect::No)? {
 879                 items.push(item);
 880             }
 881             AstFragment::Items(items)
 882         }
 883         AstFragmentKind::TraitItems => {
 884             let mut items = SmallVec::new();
 885             while let Some(item) = this.parse_trait_item(ForceCollect::No)? {
 886                 items.extend(item);
 887             }
 888             AstFragment::TraitItems(items)
 889         }
 890         AstFragmentKind::ImplItems => {
 891             let mut items = SmallVec::new();
 892             while let Some(item) = this.parse_impl_item(ForceCollect::No)? {
 893                 items.extend(item);
 894             }
 895             AstFragment::ImplItems(items)
 896         }
 897         AstFragmentKind::ForeignItems => {
 898             let mut items = SmallVec::new();
 899             while let Some(item) = this.parse_foreign_item(ForceCollect::No)? {
 900                 items.extend(item);
 901             }
 902             AstFragment::ForeignItems(items)
 903         }
 904         AstFragmentKind::Stmts => {
 905             let mut stmts = SmallVec::new();
 906             // Won't make progress on a `}`.
 907             while this.token != token::Eof && this.token != token::CloseDelim(Delimiter::Brace) {
 908                 if let Some(stmt) = this.parse_full_stmt(AttemptLocalParseRecovery::Yes)? {
 909                     stmts.push(stmt);
 910                 }
 911             }
 912             AstFragment::Stmts(stmts)
 913         }
 914         AstFragmentKind::Expr => AstFragment::Expr(this.parse_expr()?),
 915         AstFragmentKind::MethodReceiverExpr => AstFragment::MethodReceiverExpr(this.parse_expr()?),
 916         AstFragmentKind::OptExpr => {
 917             if this.token != token::Eof {
 918                 AstFragment::OptExpr(Some(this.parse_expr()?))
 919             } else {
 920                 AstFragment::OptExpr(None)
 921             }
 922         }
 923         AstFragmentKind::Ty => AstFragment::Ty(this.parse_ty()?),
 924         AstFragmentKind::Pat => AstFragment::Pat(this.parse_pat_allow_top_alt(
 925             None,
 926             RecoverComma::No,
 927             RecoverColon::Yes,
 928             CommaRecoveryMode::LikelyTuple,
 929         )?),
 930         AstFragmentKind::Crate => AstFragment::Crate(this.parse_crate_mod()?),
 931         AstFragmentKind::Arms
 932         | AstFragmentKind::ExprFields
 933         | AstFragmentKind::PatFields
 934         | AstFragmentKind::GenericParams
 935         | AstFragmentKind::Params
 936         | AstFragmentKind::FieldDefs
 937         | AstFragmentKind::Variants => panic!("unexpected AST fragment kind"),
 938     })
 939 }
 940
 941 pub fn ensure_complete_parse<'a>(
 942     this: &mut Parser<'a>,
 943     macro_path: &ast::Path,
 944     kind_name: &str,
 945     span: Span,
 946 ) {
 947     if this.token != token::Eof {
 948         let token = pprust::token_to_string(&this.token);
 949         let msg = format!("macro expansion ignores token `{}` and any following", token);
 950         // Avoid emitting backtrace info twice.
 951         let def_site_span = this.token.span.with_ctxt(SyntaxContext::root());
 952         let mut err = this.struct_span_err(def_site_span, &msg);
 953         err.span_label(span, "caused by the macro expansion here");
 954         let msg = format!(
 955             "the usage of `{}!` is likely invalid in {} context",
 956             pprust::path_to_string(macro_path),
 957             kind_name,
 958         );
 959         err.note(&msg);
 960
 961         let semi_span = this.sess.source_map().next_point(span);
 962         match this.sess.source_map().span_to_snippet(semi_span) {
 963             Ok(ref snippet) if &snippet[..] != ";" && kind_name == "expression" => {
 964                 err.span_suggestion(
 965                     span.shrink_to_hi(),
 966                     "you might be missing a semicolon here",
 967                     ";",
 968                     Applicability::MaybeIncorrect,
 969                 );
 970             }
 971             _ => {}
 972         }
 973         err.emit();
 974     }
 975 }
 976
 977 /// Wraps a call to `noop_visit_*` / `noop_flat_map_*`
 978 /// for an AST node that supports attributes
 979 /// (see the `Annotatable` enum)
 980 /// This method assigns a `NodeId`, and sets that `NodeId`
 981 /// as our current 'lint node id'. If a macro call is found
 982 /// inside this AST node, we will use this AST node's `NodeId`
 983 /// to emit lints associated with that macro (allowing
 984 /// `#[allow]` / `#[deny]` to be applied close to
 985 /// the macro invocation).
 986 ///
 987 /// Do *not* call this for a macro AST node
 988 /// (e.g. `ExprKind::MacCall`) - we cannot emit lints
 989 /// at these AST nodes, since they are removed and
 990 /// replaced with the result of macro expansion.
 991 ///
 992 /// All other `NodeId`s are assigned by `visit_id`.
 993 /// * `self` is the 'self' parameter for the current method,
 994 /// * `id` is a mutable reference to the `NodeId` field
 995 ///    of the current AST node.
 996 /// * `closure` is a closure that executes the
 997 ///   `noop_visit_*` / `noop_flat_map_*` method
 998 ///   for the current AST node.
 999 macro_rules! assign_id {
1000     ($self:ident, $id:expr, $closure:expr) => {{
1001         let old_id = $self.cx.current_expansion.lint_node_id;
1002         if $self.monotonic {
1003             debug_assert_eq!(*$id, ast::DUMMY_NODE_ID);
1004             let new_id = $self.cx.resolver.next_node_id();
1005             *$id = new_id;
1006             $self.cx.current_expansion.lint_node_id = new_id;
1007         }
1008         let ret = ($closure)();
1009         $self.cx.current_expansion.lint_node_id = old_id;
1010         ret
1011     }};
1012 }
1013
1014 enum AddSemicolon {
1015     Yes,
1016     No,
1017 }
1018
1019 /// A trait implemented for all `AstFragment` nodes and providing all pieces
1020 /// of functionality used by `InvocationCollector`.
1021 trait InvocationCollectorNode: HasAttrs + HasNodeId + Sized {
1022     type OutputTy = SmallVec<[Self; 1]>;
1023     type AttrsTy: Deref<Target = [ast::Attribute]> = ast::AttrVec;
1024     const KIND: AstFragmentKind;
1025     fn to_annotatable(self) -> Annotatable;
1026     fn fragment_to_output(fragment: AstFragment) -> Self::OutputTy;
1027     fn descr() -> &'static str {
1028         unreachable!()
1029     }
1030     fn noop_flat_map<V: MutVisitor>(self, _visitor: &mut V) -> Self::OutputTy {
1031         unreachable!()
1032     }
1033     fn noop_visit<V: MutVisitor>(&mut self, _visitor: &mut V) {
1034         unreachable!()
1035     }
1036     fn is_mac_call(&self) -> bool {
1037         false
1038     }
1039     fn take_mac_call(self) -> (P<ast::MacCall>, Self::AttrsTy, AddSemicolon) {
1040         unreachable!()
1041     }
1042     fn pre_flat_map_node_collect_attr(_cfg: &StripUnconfigured<'_>, _attr: &ast::Attribute) {}
1043     fn post_flat_map_node_collect_bang(_output: &mut Self::OutputTy, _add_semicolon: AddSemicolon) {
1044     }
1045     fn wrap_flat_map_node_noop_flat_map(
1046         node: Self,
1047         collector: &mut InvocationCollector<'_, '_>,
1048         noop_flat_map: impl FnOnce(Self, &mut InvocationCollector<'_, '_>) -> Self::OutputTy,
1049     ) -> Result<Self::OutputTy, Self> {
1050         Ok(noop_flat_map(node, collector))
1051     }
1052 }
1053
1054 impl InvocationCollectorNode for P<ast::Item> {
1055     const KIND: AstFragmentKind = AstFragmentKind::Items;
1056     fn to_annotatable(self) -> Annotatable {
1057         Annotatable::Item(self)
1058     }
1059     fn fragment_to_output(fragment: AstFragment) -> Self::OutputTy {
1060         fragment.make_items()
1061     }
1062     fn noop_flat_map<V: MutVisitor>(self, visitor: &mut V) -> Self::OutputTy {
1063         noop_flat_map_item(self, visitor)
1064     }
1065     fn is_mac_call(&self) -> bool {
1066         matches!(self.kind, ItemKind::MacCall(..))
1067     }
1068     fn take_mac_call(self) -> (P<ast::MacCall>, Self::AttrsTy, AddSemicolon) {
1069         let node = self.into_inner();
1070         match node.kind {
1071             ItemKind::MacCall(mac) => (mac, node.attrs, AddSemicolon::No),
1072             _ => unreachable!(),
1073         }
1074     }
1075     fn wrap_flat_map_node_noop_flat_map(
1076         mut node: Self,
1077         collector: &mut InvocationCollector<'_, '_>,
1078         noop_flat_map: impl FnOnce(Self, &mut InvocationCollector<'_, '_>) -> Self::OutputTy,
1079     ) -> Result<Self::OutputTy, Self> {
1080         if !matches!(node.kind, ItemKind::Mod(..)) {
1081             return Ok(noop_flat_map(node, collector));
1082         }
1083
1084         // Work around borrow checker not seeing through `P`'s deref.
1085         let (ident, span, mut attrs) = (node.ident, node.span, mem::take(&mut node.attrs));
1086         let ItemKind::Mod(_, mod_kind) = &mut node.kind else {
1087             unreachable!()
1088         };
1089
1090         let ecx = &mut collector.cx;
1091         let (file_path, dir_path, dir_ownership) = match mod_kind {
1092             ModKind::Loaded(_, inline, _) => {
1093                 // Inline `mod foo { ... }`, but we still need to push directories.
1094                 let (dir_path, dir_ownership) = mod_dir_path(
1095                     &ecx.sess,
1096                     ident,
1097                     &attrs,
1098                     &ecx.current_expansion.module,
1099                     ecx.current_expansion.dir_ownership,
1100                     *inline,
1101                 );
1102                 node.attrs = attrs;
1103                 (None, dir_path, dir_ownership)
1104             }
1105             ModKind::Unloaded => {
1106                 // We have an outline `mod foo;` so we need to parse the file.
1107                 let old_attrs_len = attrs.len();
1108                 let ParsedExternalMod { items, spans, file_path, dir_path, dir_ownership } =
1109                     parse_external_mod(
1110                         &ecx.sess,
1111                         ident,
1112                         span,
1113                         &ecx.current_expansion.module,
1114                         ecx.current_expansion.dir_ownership,
1115                         &mut attrs,
1116                     );
1117
1118                 if let Some(lint_store) = ecx.lint_store {
1119                     lint_store.pre_expansion_lint(
1120                         ecx.sess,
1121                         ecx.resolver.registered_tools(),
1122                         ecx.current_expansion.lint_node_id,
1123                         &attrs,
1124                         &items,
1125                         ident.name,
1126                     );
1127                 }
1128
1129                 *mod_kind = ModKind::Loaded(items, Inline::No, spans);
1130                 node.attrs = attrs;
1131                 if node.attrs.len() > old_attrs_len {
1132                     // If we loaded an out-of-line module and added some inner attributes,
1133                     // then we need to re-configure it and re-collect attributes for
1134                     // resolution and expansion.
1135                     return Err(node);
1136                 }
1137                 (Some(file_path), dir_path, dir_ownership)
1138             }
1139         };
1140
1141         // Set the module info before we flat map.
1142         let mut module = ecx.current_expansion.module.with_dir_path(dir_path);
1143         module.mod_path.push(ident);
1144         if let Some(file_path) = file_path {
1145             module.file_path_stack.push(file_path);
1146         }
1147
1148         let orig_module = mem::replace(&mut ecx.current_expansion.module, Rc::new(module));
1149         let orig_dir_ownership =
1150             mem::replace(&mut ecx.current_expansion.dir_ownership, dir_ownership);
1151
1152         let res = Ok(noop_flat_map(node, collector));
1153
1154         collector.cx.current_expansion.dir_ownership = orig_dir_ownership;
1155         collector.cx.current_expansion.module = orig_module;
1156         res
1157     }
1158 }
1159
1160 struct TraitItemTag;
1161 impl InvocationCollectorNode for AstNodeWrapper<P<ast::AssocItem>, TraitItemTag> {
1162     type OutputTy = SmallVec<[P<ast::AssocItem>; 1]>;
1163     const KIND: AstFragmentKind = AstFragmentKind::TraitItems;
1164     fn to_annotatable(self) -> Annotatable {
1165         Annotatable::TraitItem(self.wrapped)
1166     }
1167     fn fragment_to_output(fragment: AstFragment) -> Self::OutputTy {
1168         fragment.make_trait_items()
1169     }
1170     fn noop_flat_map<V: MutVisitor>(self, visitor: &mut V) -> Self::OutputTy {
1171         noop_flat_map_assoc_item(self.wrapped, visitor)
1172     }
1173     fn is_mac_call(&self) -> bool {
1174         matches!(self.wrapped.kind, AssocItemKind::MacCall(..))
1175     }
1176     fn take_mac_call(self) -> (P<ast::MacCall>, Self::AttrsTy, AddSemicolon) {
1177         let item = self.wrapped.into_inner();
1178         match item.kind {
1179             AssocItemKind::MacCall(mac) => (mac, item.attrs, AddSemicolon::No),
1180             _ => unreachable!(),
1181         }
1182     }
1183 }
1184
1185 struct ImplItemTag;
1186 impl InvocationCollectorNode for AstNodeWrapper<P<ast::AssocItem>, ImplItemTag> {
1187     type OutputTy = SmallVec<[P<ast::AssocItem>; 1]>;
1188     const KIND: AstFragmentKind = AstFragmentKind::ImplItems;
1189     fn to_annotatable(self) -> Annotatable {
1190         Annotatable::ImplItem(self.wrapped)
1191     }
1192     fn fragment_to_output(fragment: AstFragment) -> Self::OutputTy {
1193         fragment.make_impl_items()
1194     }
1195     fn noop_flat_map<V: MutVisitor>(self, visitor: &mut V) -> Self::OutputTy {
1196         noop_flat_map_assoc_item(self.wrapped, visitor)
1197     }
1198     fn is_mac_call(&self) -> bool {
1199         matches!(self.wrapped.kind, AssocItemKind::MacCall(..))
1200     }
1201     fn take_mac_call(self) -> (P<ast::MacCall>, Self::AttrsTy, AddSemicolon) {
1202         let item = self.wrapped.into_inner();
1203         match item.kind {
1204             AssocItemKind::MacCall(mac) => (mac, item.attrs, AddSemicolon::No),
1205             _ => unreachable!(),
1206         }
1207     }
1208 }
1209
1210 impl InvocationCollectorNode for P<ast::ForeignItem> {
1211     const KIND: AstFragmentKind = AstFragmentKind::ForeignItems;
1212     fn to_annotatable(self) -> Annotatable {
1213         Annotatable::ForeignItem(self)
1214     }
1215     fn fragment_to_output(fragment: AstFragment) -> Self::OutputTy {
1216         fragment.make_foreign_items()
1217     }
1218     fn noop_flat_map<V: MutVisitor>(self, visitor: &mut V) -> Self::OutputTy {
1219         noop_flat_map_foreign_item(self, visitor)
1220     }
1221     fn is_mac_call(&self) -> bool {
1222         matches!(self.kind, ForeignItemKind::MacCall(..))
1223     }
1224     fn take_mac_call(self) -> (P<ast::MacCall>, Self::AttrsTy, AddSemicolon) {
1225         let node = self.into_inner();
1226         match node.kind {
1227             ForeignItemKind::MacCall(mac) => (mac, node.attrs, AddSemicolon::No),
1228             _ => unreachable!(),
1229         }
1230     }
1231 }
1232
1233 impl InvocationCollectorNode for ast::Variant {
1234     const KIND: AstFragmentKind = AstFragmentKind::Variants;
1235     fn to_annotatable(self) -> Annotatable {
1236         Annotatable::Variant(self)
1237     }
1238     fn fragment_to_output(fragment: AstFragment) -> Self::OutputTy {
1239         fragment.make_variants()
1240     }
1241     fn noop_flat_map<V: MutVisitor>(self, visitor: &mut V) -> Self::OutputTy {
1242         noop_flat_map_variant(self, visitor)
1243     }
1244 }
1245
1246 impl InvocationCollectorNode for ast::FieldDef {
1247     const KIND: AstFragmentKind = AstFragmentKind::FieldDefs;
1248     fn to_annotatable(self) -> Annotatable {
1249         Annotatable::FieldDef(self)
1250     }
1251     fn fragment_to_output(fragment: AstFragment) -> Self::OutputTy {
1252         fragment.make_field_defs()
1253     }
1254     fn noop_flat_map<V: MutVisitor>(self, visitor: &mut V) -> Self::OutputTy {
1255         noop_flat_map_field_def(self, visitor)
1256     }
1257 }
1258
1259 impl InvocationCollectorNode for ast::PatField {
1260     const KIND: AstFragmentKind = AstFragmentKind::PatFields;
1261     fn to_annotatable(self) -> Annotatable {
1262         Annotatable::PatField(self)
1263     }
1264     fn fragment_to_output(fragment: AstFragment) -> Self::OutputTy {
1265         fragment.make_pat_fields()
1266     }
1267     fn noop_flat_map<V: MutVisitor>(self, visitor: &mut V) -> Self::OutputTy {
1268         noop_flat_map_pat_field(self, visitor)
1269     }
1270 }
1271
1272 impl InvocationCollectorNode for ast::ExprField {
1273     const KIND: AstFragmentKind = AstFragmentKind::ExprFields;
1274     fn to_annotatable(self) -> Annotatable {
1275         Annotatable::ExprField(self)
1276     }
1277     fn fragment_to_output(fragment: AstFragment) -> Self::OutputTy {
1278         fragment.make_expr_fields()
1279     }
1280     fn noop_flat_map<V: MutVisitor>(self, visitor: &mut V) -> Self::OutputTy {
1281         noop_flat_map_expr_field(self, visitor)
1282     }
1283 }
1284
1285 impl InvocationCollectorNode for ast::Param {
1286     const KIND: AstFragmentKind = AstFragmentKind::Params;
1287     fn to_annotatable(self) -> Annotatable {
1288         Annotatable::Param(self)
1289     }
1290     fn fragment_to_output(fragment: AstFragment) -> Self::OutputTy {
1291         fragment.make_params()
1292     }
1293     fn noop_flat_map<V: MutVisitor>(self, visitor: &mut V) -> Self::OutputTy {
1294         noop_flat_map_param(self, visitor)
1295     }
1296 }
1297
1298 impl InvocationCollectorNode for ast::GenericParam {
1299     const KIND: AstFragmentKind = AstFragmentKind::GenericParams;
1300     fn to_annotatable(self) -> Annotatable {
1301         Annotatable::GenericParam(self)
1302     }
1303     fn fragment_to_output(fragment: AstFragment) -> Self::OutputTy {
1304         fragment.make_generic_params()
1305     }
1306     fn noop_flat_map<V: MutVisitor>(self, visitor: &mut V) -> Self::OutputTy {
1307         noop_flat_map_generic_param(self, visitor)
1308     }
1309 }
1310
1311 impl InvocationCollectorNode for ast::Arm {
1312     const KIND: AstFragmentKind = AstFragmentKind::Arms;
1313     fn to_annotatable(self) -> Annotatable {
1314         Annotatable::Arm(self)
1315     }
1316     fn fragment_to_output(fragment: AstFragment) -> Self::OutputTy {
1317         fragment.make_arms()
1318     }
1319     fn noop_flat_map<V: MutVisitor>(self, visitor: &mut V) -> Self::OutputTy {
1320         noop_flat_map_arm(self, visitor)
1321     }
1322 }
1323
1324 impl InvocationCollectorNode for ast::Stmt {
1325     type AttrsTy = ast::AttrVec;
1326     const KIND: AstFragmentKind = AstFragmentKind::Stmts;
1327     fn to_annotatable(self) -> Annotatable {
1328         Annotatable::Stmt(P(self))
1329     }
1330     fn fragment_to_output(fragment: AstFragment) -> Self::OutputTy {
1331         fragment.make_stmts()
1332     }
1333     fn noop_flat_map<V: MutVisitor>(self, visitor: &mut V) -> Self::OutputTy {
1334         noop_flat_map_stmt(self, visitor)
1335     }
1336     fn is_mac_call(&self) -> bool {
1337         match &self.kind {
1338             StmtKind::MacCall(..) => true,
1339             StmtKind::Item(item) => matches!(item.kind, ItemKind::MacCall(..)),
1340             StmtKind::Semi(expr) => matches!(expr.kind, ExprKind::MacCall(..)),
1341             StmtKind::Expr(..) => unreachable!(),
1342             StmtKind::Local(..) | StmtKind::Empty => false,
1343         }
1344     }
1345     fn take_mac_call(self) -> (P<ast::MacCall>, Self::AttrsTy, AddSemicolon) {
1346         // We pull macro invocations (both attributes and fn-like macro calls) out of their
1347         // `StmtKind`s and treat them as statement macro invocations, not as items or expressions.
1348         let (add_semicolon, mac, attrs) = match self.kind {
1349             StmtKind::MacCall(mac) => {
1350                 let ast::MacCallStmt { mac, style, attrs, .. } = mac.into_inner();
1351                 (style == MacStmtStyle::Semicolon, mac, attrs)
1352             }
1353             StmtKind::Item(item) => match item.into_inner() {
1354                 ast::Item { kind: ItemKind::MacCall(mac), attrs, .. } => {
1355                     (mac.args.need_semicolon(), mac, attrs)
1356                 }
1357                 _ => unreachable!(),
1358             },
1359             StmtKind::Semi(expr) => match expr.into_inner() {
1360                 ast::Expr { kind: ExprKind::MacCall(mac), attrs, .. } => {
1361                     (mac.args.need_semicolon(), mac, attrs)
1362                 }
1363                 _ => unreachable!(),
1364             },
1365             _ => unreachable!(),
1366         };
1367         (mac, attrs, if add_semicolon { AddSemicolon::Yes } else { AddSemicolon::No })
1368     }
1369     fn post_flat_map_node_collect_bang(stmts: &mut Self::OutputTy, add_semicolon: AddSemicolon) {
1370         // If this is a macro invocation with a semicolon, then apply that
1371         // semicolon to the final statement produced by expansion.
1372         if matches!(add_semicolon, AddSemicolon::Yes) {
1373             if let Some(stmt) = stmts.pop() {
1374                 stmts.push(stmt.add_trailing_semicolon());
1375             }
1376         }
1377     }
1378 }
1379
1380 impl InvocationCollectorNode for ast::Crate {
1381     type OutputTy = ast::Crate;
1382     const KIND: AstFragmentKind = AstFragmentKind::Crate;
1383     fn to_annotatable(self) -> Annotatable {
1384         Annotatable::Crate(self)
1385     }
1386     fn fragment_to_output(fragment: AstFragment) -> Self::OutputTy {
1387         fragment.make_crate()
1388     }
1389     fn noop_visit<V: MutVisitor>(&mut self, visitor: &mut V) {
1390         noop_visit_crate(self, visitor)
1391     }
1392 }
1393
1394 impl InvocationCollectorNode for P<ast::Ty> {
1395     type OutputTy = P<ast::Ty>;
1396     const KIND: AstFragmentKind = AstFragmentKind::Ty;
1397     fn to_annotatable(self) -> Annotatable {
1398         unreachable!()
1399     }
1400     fn fragment_to_output(fragment: AstFragment) -> Self::OutputTy {
1401         fragment.make_ty()
1402     }
1403     fn noop_visit<V: MutVisitor>(&mut self, visitor: &mut V) {
1404         noop_visit_ty(self, visitor)
1405     }
1406     fn is_mac_call(&self) -> bool {
1407         matches!(self.kind, ast::TyKind::MacCall(..))
1408     }
1409     fn take_mac_call(self) -> (P<ast::MacCall>, Self::AttrsTy, AddSemicolon) {
1410         let node = self.into_inner();
1411         match node.kind {
1412             TyKind::MacCall(mac) => (mac, AttrVec::new(), AddSemicolon::No),
1413             _ => unreachable!(),
1414         }
1415     }
1416 }
1417
1418 impl InvocationCollectorNode for P<ast::Pat> {
1419     type OutputTy = P<ast::Pat>;
1420     const KIND: AstFragmentKind = AstFragmentKind::Pat;
1421     fn to_annotatable(self) -> Annotatable {
1422         unreachable!()
1423     }
1424     fn fragment_to_output(fragment: AstFragment) -> Self::OutputTy {
1425         fragment.make_pat()
1426     }
1427     fn noop_visit<V: MutVisitor>(&mut self, visitor: &mut V) {
1428         noop_visit_pat(self, visitor)
1429     }
1430     fn is_mac_call(&self) -> bool {
1431         matches!(self.kind, PatKind::MacCall(..))
1432     }
1433     fn take_mac_call(self) -> (P<ast::MacCall>, Self::AttrsTy, AddSemicolon) {
1434         let node = self.into_inner();
1435         match node.kind {
1436             PatKind::MacCall(mac) => (mac, AttrVec::new(), AddSemicolon::No),
1437             _ => unreachable!(),
1438         }
1439     }
1440 }
1441
1442 impl InvocationCollectorNode for P<ast::Expr> {
1443     type OutputTy = P<ast::Expr>;
1444     type AttrsTy = ast::AttrVec;
1445     const KIND: AstFragmentKind = AstFragmentKind::Expr;
1446     fn to_annotatable(self) -> Annotatable {
1447         Annotatable::Expr(self)
1448     }
1449     fn fragment_to_output(fragment: AstFragment) -> Self::OutputTy {
1450         fragment.make_expr()
1451     }
1452     fn descr() -> &'static str {
1453         "an expression"
1454     }
1455     fn noop_visit<V: MutVisitor>(&mut self, visitor: &mut V) {
1456         noop_visit_expr(self, visitor)
1457     }
1458     fn is_mac_call(&self) -> bool {
1459         matches!(self.kind, ExprKind::MacCall(..))
1460     }
1461     fn take_mac_call(self) -> (P<ast::MacCall>, Self::AttrsTy, AddSemicolon) {
1462         let node = self.into_inner();
1463         match node.kind {
1464             ExprKind::MacCall(mac) => (mac, node.attrs, AddSemicolon::No),
1465             _ => unreachable!(),
1466         }
1467     }
1468 }
1469
1470 struct OptExprTag;
1471 impl InvocationCollectorNode for AstNodeWrapper<P<ast::Expr>, OptExprTag> {
1472     type OutputTy = Option<P<ast::Expr>>;
1473     type AttrsTy = ast::AttrVec;
1474     const KIND: AstFragmentKind = AstFragmentKind::OptExpr;
1475     fn to_annotatable(self) -> Annotatable {
1476         Annotatable::Expr(self.wrapped)
1477     }
1478     fn fragment_to_output(fragment: AstFragment) -> Self::OutputTy {
1479         fragment.make_opt_expr()
1480     }
1481     fn noop_flat_map<V: MutVisitor>(mut self, visitor: &mut V) -> Self::OutputTy {
1482         noop_visit_expr(&mut self.wrapped, visitor);
1483         Some(self.wrapped)
1484     }
1485     fn is_mac_call(&self) -> bool {
1486         matches!(self.wrapped.kind, ast::ExprKind::MacCall(..))
1487     }
1488     fn take_mac_call(self) -> (P<ast::MacCall>, Self::AttrsTy, AddSemicolon) {
1489         let node = self.wrapped.into_inner();
1490         match node.kind {
1491             ExprKind::MacCall(mac) => (mac, node.attrs, AddSemicolon::No),
1492             _ => unreachable!(),
1493         }
1494     }
1495     fn pre_flat_map_node_collect_attr(cfg: &StripUnconfigured<'_>, attr: &ast::Attribute) {
1496         cfg.maybe_emit_expr_attr_err(&attr);
1497     }
1498 }
1499
1500 /// This struct is a hack to workaround unstable of `stmt_expr_attributes`.
1501 /// It can be removed once that feature is stabilized.
1502 struct MethodReceiverTag;
1503 impl DummyAstNode for MethodReceiverTag {
1504     fn dummy() -> MethodReceiverTag {
1505         MethodReceiverTag
1506     }
1507 }
1508 impl InvocationCollectorNode for AstNodeWrapper<P<ast::Expr>, MethodReceiverTag> {
1509     type OutputTy = Self;
1510     type AttrsTy = ast::AttrVec;
1511     const KIND: AstFragmentKind = AstFragmentKind::MethodReceiverExpr;
1512     fn descr() -> &'static str {
1513         "an expression"
1514     }
1515     fn to_annotatable(self) -> Annotatable {
1516         Annotatable::Expr(self.wrapped)
1517     }
1518     fn fragment_to_output(fragment: AstFragment) -> Self::OutputTy {
1519         AstNodeWrapper::new(fragment.make_method_receiver_expr(), MethodReceiverTag)
1520     }
1521     fn noop_visit<V: MutVisitor>(&mut self, visitor: &mut V) {
1522         noop_visit_expr(&mut self.wrapped, visitor)
1523     }
1524     fn is_mac_call(&self) -> bool {
1525         matches!(self.wrapped.kind, ast::ExprKind::MacCall(..))
1526     }
1527     fn take_mac_call(self) -> (P<ast::MacCall>, Self::AttrsTy, AddSemicolon) {
1528         let node = self.wrapped.into_inner();
1529         match node.kind {
1530             ExprKind::MacCall(mac) => (mac, node.attrs, AddSemicolon::No),
1531             _ => unreachable!(),
1532         }
1533     }
1534 }
1535
1536 struct InvocationCollector<'a, 'b> {
1537     cx: &'a mut ExtCtxt<'b>,
1538     invocations: Vec<(Invocation, Option<Lrc<SyntaxExtension>>)>,
1539     monotonic: bool,
1540 }
1541
1542 impl<'a, 'b> InvocationCollector<'a, 'b> {
1543     fn cfg(&self) -> StripUnconfigured<'_> {
1544         StripUnconfigured {
1545             sess: &self.cx.sess,
1546             features: self.cx.ecfg.features,
1547             config_tokens: false,
1548             lint_node_id: self.cx.current_expansion.lint_node_id,
1549         }
1550     }
1551
1552     fn collect(&mut self, fragment_kind: AstFragmentKind, kind: InvocationKind) -> AstFragment {
1553         let expn_id = LocalExpnId::fresh_empty();
1554         let vis = kind.placeholder_visibility();
1555         self.invocations.push((
1556             Invocation {
1557                 kind,
1558                 fragment_kind,
1559                 expansion_data: ExpansionData {
1560                     id: expn_id,
1561                     depth: self.cx.current_expansion.depth + 1,
1562                     ..self.cx.current_expansion.clone()
1563                 },
1564             },
1565             None,
1566         ));
1567         placeholder(fragment_kind, NodeId::placeholder_from_expn_id(expn_id), vis)
1568     }
1569
1570     fn collect_bang(&mut self, mac: P<ast::MacCall>, kind: AstFragmentKind) -> AstFragment {
1571         // cache the macro call span so that it can be
1572         // easily adjusted for incremental compilation
1573         let span = mac.span();
1574         self.collect(kind, InvocationKind::Bang { mac, span })
1575     }
1576
1577     fn collect_attr(
1578         &mut self,
1579         (attr, pos, derives): (ast::Attribute, usize, Vec<ast::Path>),
1580         item: Annotatable,
1581         kind: AstFragmentKind,
1582     ) -> AstFragment {
1583         self.collect(kind, InvocationKind::Attr { attr, pos, item, derives })
1584     }
1585
1586     /// If `item` is an attribute invocation, remove the attribute and return it together with
1587     /// its position and derives following it. We have to collect the derives in order to resolve
1588     /// legacy derive helpers (helpers written before derives that introduce them).
1589     fn take_first_attr(
1590         &self,
1591         item: &mut impl HasAttrs,
1592     ) -> Option<(ast::Attribute, usize, Vec<ast::Path>)> {
1593         let mut attr = None;
1594
1595         let mut cfg_pos = None;
1596         let mut attr_pos = None;
1597         for (pos, attr) in item.attrs().iter().enumerate() {
1598             if !attr.is_doc_comment() && !self.cx.expanded_inert_attrs.is_marked(attr) {
1599                 let name = attr.ident().map(|ident| ident.name);
1600                 if name == Some(sym::cfg) || name == Some(sym::cfg_attr) {
1601                     cfg_pos = Some(pos); // a cfg attr found, no need to search anymore
1602                     break;
1603                 } else if attr_pos.is_none()
1604                     && !name.map_or(false, rustc_feature::is_builtin_attr_name)
1605                 {
1606                     attr_pos = Some(pos); // a non-cfg attr found, still may find a cfg attr
1607                 }
1608             }
1609         }
1610
1611         item.visit_attrs(|attrs| {
1612             attr = Some(match (cfg_pos, attr_pos) {
1613                 (Some(pos), _) => (attrs.remove(pos), pos, Vec::new()),
1614                 (_, Some(pos)) => {
1615                     let attr = attrs.remove(pos);
1616                     let following_derives = attrs[pos..]
1617                         .iter()
1618                         .filter(|a| a.has_name(sym::derive))
1619                         .flat_map(|a| a.meta_item_list().unwrap_or_default())
1620                         .filter_map(|nested_meta| match nested_meta {
1621                             NestedMetaItem::MetaItem(ast::MetaItem {
1622                                 kind: MetaItemKind::Word,
1623                                 path,
1624                                 ..
1625                             }) => Some(path),
1626                             _ => None,
1627                         })
1628                         .collect();
1629
1630                     (attr, pos, following_derives)
1631                 }
1632                 _ => return,
1633             });
1634         });
1635
1636         attr
1637     }
1638
1639     // Detect use of feature-gated or invalid attributes on macro invocations
1640     // since they will not be detected after macro expansion.
1641     fn check_attributes(&self, attrs: &[ast::Attribute], call: &ast::MacCall) {
1642         let features = self.cx.ecfg.features.unwrap();
1643         let mut attrs = attrs.iter().peekable();
1644         let mut span: Option<Span> = None;
1645         while let Some(attr) = attrs.next() {
1646             rustc_ast_passes::feature_gate::check_attribute(attr, self.cx.sess, features);
1647             validate_attr::check_attr(&self.cx.sess.parse_sess, attr);
1648
1649             let current_span = if let Some(sp) = span { sp.to(attr.span) } else { attr.span };
1650             span = Some(current_span);
1651
1652             if attrs.peek().map_or(false, |next_attr| next_attr.doc_str().is_some()) {
1653                 continue;
1654             }
1655
1656             if attr.is_doc_comment() {
1657                 self.cx.sess.parse_sess.buffer_lint_with_diagnostic(
1658                     &UNUSED_DOC_COMMENTS,
1659                     current_span,
1660                     self.cx.current_expansion.lint_node_id,
1661                     "unused doc comment",
1662                     BuiltinLintDiagnostics::UnusedDocComment(attr.span),
1663                 );
1664             } else if rustc_attr::is_builtin_attr(attr) {
1665                 let attr_name = attr.ident().unwrap().name;
1666                 // `#[cfg]` and `#[cfg_attr]` are special - they are
1667                 // eagerly evaluated.
1668                 if attr_name != sym::cfg && attr_name != sym::cfg_attr {
1669                     self.cx.sess.parse_sess.buffer_lint_with_diagnostic(
1670                         &UNUSED_ATTRIBUTES,
1671                         attr.span,
1672                         self.cx.current_expansion.lint_node_id,
1673                         &format!("unused attribute `{}`", attr_name),
1674                         BuiltinLintDiagnostics::UnusedBuiltinAttribute {
1675                             attr_name,
1676                             macro_name: pprust::path_to_string(&call.path),
1677                             invoc_span: call.path.span,
1678                         },
1679                     );
1680                 }
1681             }
1682         }
1683     }
1684
1685     fn expand_cfg_true(
1686         &mut self,
1687         node: &mut impl HasAttrs,
1688         attr: ast::Attribute,
1689         pos: usize,
1690     ) -> bool {
1691         let res = self.cfg().cfg_true(&attr);
1692         if res {
1693             // FIXME: `cfg(TRUE)` attributes do not currently remove themselves during expansion,
1694             // and some tools like rustdoc and clippy rely on that. Find a way to remove them
1695             // while keeping the tools working.
1696             self.cx.expanded_inert_attrs.mark(&attr);
1697             node.visit_attrs(|attrs| attrs.insert(pos, attr));
1698         }
1699         res
1700     }
1701
1702     fn expand_cfg_attr(&self, node: &mut impl HasAttrs, attr: ast::Attribute, pos: usize) {
1703         node.visit_attrs(|attrs| {
1704             // Repeated `insert` calls is inefficient, but the number of
1705             // insertions is almost always 0 or 1 in practice.
1706             for cfg in self.cfg().expand_cfg_attr(attr, false).into_iter().rev() {
1707                 attrs.insert(pos, cfg)
1708             }
1709         });
1710     }
1711
1712     fn flat_map_node<Node: InvocationCollectorNode<OutputTy: Default>>(
1713         &mut self,
1714         mut node: Node,
1715     ) -> Node::OutputTy {
1716         loop {
1717             return match self.take_first_attr(&mut node) {
1718                 Some((attr, pos, derives)) => match attr.name_or_empty() {
1719                     sym::cfg => {
1720                         if self.expand_cfg_true(&mut node, attr, pos) {
1721                             continue;
1722                         }
1723                         Default::default()
1724                     }
1725                     sym::cfg_attr => {
1726                         self.expand_cfg_attr(&mut node, attr, pos);
1727                         continue;
1728                     }
1729                     _ => {
1730                         Node::pre_flat_map_node_collect_attr(&self.cfg(), &attr);
1731                         self.collect_attr((attr, pos, derives), node.to_annotatable(), Node::KIND)
1732                             .make_ast::<Node>()
1733                     }
1734                 },
1735                 None if node.is_mac_call() => {
1736                     let (mac, attrs, add_semicolon) = node.take_mac_call();
1737                     self.check_attributes(&attrs, &mac);
1738                     let mut res = self.collect_bang(mac, Node::KIND).make_ast::<Node>();
1739                     Node::post_flat_map_node_collect_bang(&mut res, add_semicolon);
1740                     res
1741                 }
1742                 None => {
1743                     match Node::wrap_flat_map_node_noop_flat_map(node, self, |mut node, this| {
1744                         assign_id!(this, node.node_id_mut(), || node.noop_flat_map(this))
1745                     }) {
1746                         Ok(output) => output,
1747                         Err(returned_node) => {
1748                             node = returned_node;
1749                             continue;
1750                         }
1751                     }
1752                 }
1753             };
1754         }
1755     }
1756
1757     fn visit_node<Node: InvocationCollectorNode<OutputTy = Node> + DummyAstNode>(
1758         &mut self,
1759         node: &mut Node,
1760     ) {
1761         loop {
1762             return match self.take_first_attr(node) {
1763                 Some((attr, pos, derives)) => match attr.name_or_empty() {
1764                     sym::cfg => {
1765                         let span = attr.span;
1766                         if self.expand_cfg_true(node, attr, pos) {
1767                             continue;
1768                         }
1769                         let msg =
1770                             format!("removing {} is not supported in this position", Node::descr());
1771                         self.cx.span_err(span, &msg);
1772                         continue;
1773                     }
1774                     sym::cfg_attr => {
1775                         self.expand_cfg_attr(node, attr, pos);
1776                         continue;
1777                     }
1778                     _ => visit_clobber(node, |node| {
1779                         self.collect_attr((attr, pos, derives), node.to_annotatable(), Node::KIND)
1780                             .make_ast::<Node>()
1781                     }),
1782                 },
1783                 None if node.is_mac_call() => {
1784                     visit_clobber(node, |node| {
1785                         // Do not clobber unless it's actually a macro (uncommon case).
1786                         let (mac, attrs, _) = node.take_mac_call();
1787                         self.check_attributes(&attrs, &mac);
1788                         self.collect_bang(mac, Node::KIND).make_ast::<Node>()
1789                     })
1790                 }
1791                 None => {
1792                     assign_id!(self, node.node_id_mut(), || node.noop_visit(self))
1793                 }
1794             };
1795         }
1796     }
1797 }
1798
1799 impl<'a, 'b> MutVisitor for InvocationCollector<'a, 'b> {
1800     fn flat_map_item(&mut self, node: P<ast::Item>) -> SmallVec<[P<ast::Item>; 1]> {
1801         self.flat_map_node(node)
1802     }
1803
1804     fn flat_map_trait_item(&mut self, node: P<ast::AssocItem>) -> SmallVec<[P<ast::AssocItem>; 1]> {
1805         self.flat_map_node(AstNodeWrapper::new(node, TraitItemTag))
1806     }
1807
1808     fn flat_map_impl_item(&mut self, node: P<ast::AssocItem>) -> SmallVec<[P<ast::AssocItem>; 1]> {
1809         self.flat_map_node(AstNodeWrapper::new(node, ImplItemTag))
1810     }
1811
1812     fn flat_map_foreign_item(
1813         &mut self,
1814         node: P<ast::ForeignItem>,
1815     ) -> SmallVec<[P<ast::ForeignItem>; 1]> {
1816         self.flat_map_node(node)
1817     }
1818
1819     fn flat_map_variant(&mut self, node: ast::Variant) -> SmallVec<[ast::Variant; 1]> {
1820         self.flat_map_node(node)
1821     }
1822
1823     fn flat_map_field_def(&mut self, node: ast::FieldDef) -> SmallVec<[ast::FieldDef; 1]> {
1824         self.flat_map_node(node)
1825     }
1826
1827     fn flat_map_pat_field(&mut self, node: ast::PatField) -> SmallVec<[ast::PatField; 1]> {
1828         self.flat_map_node(node)
1829     }
1830
1831     fn flat_map_expr_field(&mut self, node: ast::ExprField) -> SmallVec<[ast::ExprField; 1]> {
1832         self.flat_map_node(node)
1833     }
1834
1835     fn flat_map_param(&mut self, node: ast::Param) -> SmallVec<[ast::Param; 1]> {
1836         self.flat_map_node(node)
1837     }
1838
1839     fn flat_map_generic_param(
1840         &mut self,
1841         node: ast::GenericParam,
1842     ) -> SmallVec<[ast::GenericParam; 1]> {
1843         self.flat_map_node(node)
1844     }
1845
1846     fn flat_map_arm(&mut self, node: ast::Arm) -> SmallVec<[ast::Arm; 1]> {
1847         self.flat_map_node(node)
1848     }
1849
1850     fn flat_map_stmt(&mut self, node: ast::Stmt) -> SmallVec<[ast::Stmt; 1]> {
1851         // FIXME: invocations in semicolon-less expressions positions are expanded as expressions,
1852         // changing that requires some compatibility measures.
1853         if node.is_expr() {
1854             // The only way that we can end up with a `MacCall` expression statement,
1855             // (as opposed to a `StmtKind::MacCall`) is if we have a macro as the
1856             // trailing expression in a block (e.g. `fn foo() { my_macro!() }`).
1857             // Record this information, so that we can report a more specific
1858             // `SEMICOLON_IN_EXPRESSIONS_FROM_MACROS` lint if needed.
1859             // See #78991 for an investigation of treating macros in this position
1860             // as statements, rather than expressions, during parsing.
1861             return match &node.kind {
1862                 StmtKind::Expr(expr)
1863                     if matches!(**expr, ast::Expr { kind: ExprKind::MacCall(..), .. }) =>
1864                 {
1865                     self.cx.current_expansion.is_trailing_mac = true;
1866                     // Don't use `assign_id` for this statement - it may get removed
1867                     // entirely due to a `#[cfg]` on the contained expression
1868                     let res = noop_flat_map_stmt(node, self);
1869                     self.cx.current_expansion.is_trailing_mac = false;
1870                     res
1871                 }
1872                 _ => noop_flat_map_stmt(node, self),
1873             };
1874         }
1875
1876         self.flat_map_node(node)
1877     }
1878
1879     fn visit_crate(&mut self, node: &mut ast::Crate) {
1880         self.visit_node(node)
1881     }
1882
1883     fn visit_ty(&mut self, node: &mut P<ast::Ty>) {
1884         self.visit_node(node)
1885     }
1886
1887     fn visit_pat(&mut self, node: &mut P<ast::Pat>) {
1888         self.visit_node(node)
1889     }
1890
1891     fn visit_expr(&mut self, node: &mut P<ast::Expr>) {
1892         // FIXME: Feature gating is performed inconsistently between `Expr` and `OptExpr`.
1893         if let Some(attr) = node.attrs.first() {
1894             self.cfg().maybe_emit_expr_attr_err(attr);
1895         }
1896         self.visit_node(node)
1897     }
1898
1899     fn visit_method_receiver_expr(&mut self, node: &mut P<ast::Expr>) {
1900         visit_clobber(node, |node| {
1901             let mut wrapper = AstNodeWrapper::new(node, MethodReceiverTag);
1902             self.visit_node(&mut wrapper);
1903             wrapper.wrapped
1904         })
1905     }
1906
1907     fn filter_map_expr(&mut self, node: P<ast::Expr>) -> Option<P<ast::Expr>> {
1908         self.flat_map_node(AstNodeWrapper::new(node, OptExprTag))
1909     }
1910
1911     fn visit_block(&mut self, node: &mut P<ast::Block>) {
1912         let orig_dir_ownership = mem::replace(
1913             &mut self.cx.current_expansion.dir_ownership,
1914             DirOwnership::UnownedViaBlock,
1915         );
1916         noop_visit_block(node, self);
1917         self.cx.current_expansion.dir_ownership = orig_dir_ownership;
1918     }
1919
1920     fn visit_id(&mut self, id: &mut NodeId) {
1921         // We may have already assigned a `NodeId`
1922         // by calling `assign_id`
1923         if self.monotonic && *id == ast::DUMMY_NODE_ID {
1924             *id = self.cx.resolver.next_node_id();
1925         }
1926     }
1927 }
1928
1929 pub struct ExpansionConfig<'feat> {
1930     pub crate_name: String,
1931     pub features: Option<&'feat Features>,
1932     pub recursion_limit: Limit,
1933     pub trace_mac: bool,
1934     /// If false, strip `#[test]` nodes
1935     pub should_test: bool,
1936     /// If true, use verbose debugging for `proc_macro::Span`
1937     pub span_debug: bool,
1938     /// If true, show backtraces for proc-macro panics
1939     pub proc_macro_backtrace: bool,
1940 }
1941
1942 impl<'feat> ExpansionConfig<'feat> {
1943     pub fn default(crate_name: String) -> ExpansionConfig<'static> {
1944         ExpansionConfig {
1945             crate_name,
1946             features: None,
1947             recursion_limit: Limit::new(1024),
1948             trace_mac: false,
1949             should_test: false,
1950             span_debug: false,
1951             proc_macro_backtrace: false,
1952         }
1953     }
1954
1955     fn proc_macro_hygiene(&self) -> bool {
1956         self.features.map_or(false, |features| features.proc_macro_hygiene)
1957     }
1958 }