compiler/rustc_expand/src/expand.rs

   1 use crate::base::*;
   2 use crate::config::StripUnconfigured;
   3 use crate::configure;
   4 use crate::hygiene::SyntaxContext;
   5 use crate::mbe::macro_rules::annotate_err_with_kind;
   6 use crate::module::{mod_dir_path, parse_external_mod, DirOwnership, ParsedExternalMod};
   7 use crate::placeholders::{placeholder, PlaceholderExpander};
   8
   9 use rustc_ast as ast;
  10 use rustc_ast::mut_visit::*;
  11 use rustc_ast::ptr::P;
  12 use rustc_ast::token;
  13 use rustc_ast::tokenstream::TokenStream;
  14 use rustc_ast::visit::{self, AssocCtxt, Visitor};
  15 use rustc_ast::{AstLike, AttrItem, AttrStyle, Block, Inline, ItemKind, LitKind, MacArgs};
  16 use rustc_ast::{MacCallStmt, MacStmtStyle, MetaItemKind, ModKind, NestedMetaItem};
  17 use rustc_ast::{NodeId, PatKind, Path, StmtKind, Unsafe};
  18 use rustc_ast_pretty::pprust;
  19 use rustc_attr::{self as attr, is_builtin_attr};
  20 use rustc_data_structures::map_in_place::MapInPlace;
  21 use rustc_data_structures::stack::ensure_sufficient_stack;
  22 use rustc_data_structures::sync::Lrc;
  23 use rustc_errors::{Applicability, PResult};
  24 use rustc_feature::Features;
  25 use rustc_parse::parser::{AttemptLocalParseRecovery, ForceCollect, Parser, RecoverComma};
  26 use rustc_parse::validate_attr;
  27 use rustc_session::lint::builtin::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, Symbol};
  32 use rustc_span::{ExpnId, FileName, Span, DUMMY_SP};
  33
  34 use smallvec::{smallvec, SmallVec};
  35 use std::io::ErrorKind;
  36 use std::ops::DerefMut;
  37 use std::path::PathBuf;
  38 use std::rc::Rc;
  39 use std::{iter, mem, slice};
  40
  41 macro_rules! ast_fragments {
  42     (
  43         $($Kind:ident($AstTy:ty) {
  44             $kind_name:expr;
  45             $(one fn $mut_visit_ast:ident; fn $visit_ast:ident;)?
  46             $(many fn $flat_map_ast_elt:ident; fn $visit_ast_elt:ident($($args:tt)*);)?
  47             fn $make_ast:ident;
  48         })*
  49     ) => {
  50         /// A fragment of AST that can be produced by a single macro expansion.
  51         /// Can also serve as an input and intermediate result for macro expansion operations.
  52         pub enum AstFragment {
  53             OptExpr(Option<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             $($Kind,)*
  62         }
  63
  64         impl AstFragmentKind {
  65             pub fn name(self) -> &'static str {
  66                 match self {
  67                     AstFragmentKind::OptExpr => "expression",
  68                     $(AstFragmentKind::$Kind => $kind_name,)*
  69                 }
  70             }
  71
  72             fn make_from<'a>(self, result: Box<dyn MacResult + 'a>) -> Option<AstFragment> {
  73                 match self {
  74                     AstFragmentKind::OptExpr =>
  75                         result.make_expr().map(Some).map(AstFragment::OptExpr),
  76                     $(AstFragmentKind::$Kind => result.$make_ast().map(AstFragment::$Kind),)*
  77                 }
  78             }
  79         }
  80
  81         impl AstFragment {
  82             pub fn add_placeholders(&mut self, placeholders: &[NodeId]) {
  83                 if placeholders.is_empty() {
  84                     return;
  85                 }
  86                 match self {
  87                     $($(AstFragment::$Kind(ast) => ast.extend(placeholders.iter().flat_map(|id| {
  88                         // We are repeating through arguments with `many`, to do that we have to
  89                         // mention some macro variable from those arguments even if it's not used.
  90                         macro _repeating($flat_map_ast_elt) {}
  91                         placeholder(AstFragmentKind::$Kind, *id, None).$make_ast()
  92                     })),)?)*
  93                     _ => panic!("unexpected AST fragment kind")
  94                 }
  95             }
  96
  97             pub fn make_opt_expr(self) -> Option<P<ast::Expr>> {
  98                 match self {
  99                     AstFragment::OptExpr(expr) => expr,
 100                     _ => panic!("AstFragment::make_* called on the wrong kind of fragment"),
 101                 }
 102             }
 103
 104             $(pub fn $make_ast(self) -> $AstTy {
 105                 match self {
 106                     AstFragment::$Kind(ast) => ast,
 107                     _ => panic!("AstFragment::make_* called on the wrong kind of fragment"),
 108                 }
 109             })*
 110
 111             pub fn mut_visit_with<F: MutVisitor>(&mut self, vis: &mut F) {
 112                 match self {
 113                     AstFragment::OptExpr(opt_expr) => {
 114                         visit_clobber(opt_expr, |opt_expr| {
 115                             if let Some(expr) = opt_expr {
 116                                 vis.filter_map_expr(expr)
 117                             } else {
 118                                 None
 119                             }
 120                         });
 121                     }
 122                     $($(AstFragment::$Kind(ast) => vis.$mut_visit_ast(ast),)?)*
 123                     $($(AstFragment::$Kind(ast) =>
 124                         ast.flat_map_in_place(|ast| vis.$flat_map_ast_elt(ast)),)?)*
 125                 }
 126             }
 127
 128             pub fn visit_with<'a, V: Visitor<'a>>(&'a self, visitor: &mut V) {
 129                 match *self {
 130                     AstFragment::OptExpr(Some(ref expr)) => visitor.visit_expr(expr),
 131                     AstFragment::OptExpr(None) => {}
 132                     $($(AstFragment::$Kind(ref ast) => visitor.$visit_ast(ast),)?)*
 133                     $($(AstFragment::$Kind(ref ast) => for ast_elt in &ast[..] {
 134                         visitor.$visit_ast_elt(ast_elt, $($args)*);
 135                     })?)*
 136                 }
 137             }
 138         }
 139
 140         impl<'a> MacResult for crate::mbe::macro_rules::ParserAnyMacro<'a> {
 141             $(fn $make_ast(self: Box<crate::mbe::macro_rules::ParserAnyMacro<'a>>)
 142                            -> Option<$AstTy> {
 143                 Some(self.make(AstFragmentKind::$Kind).$make_ast())
 144             })*
 145         }
 146     }
 147 }
 148
 149 ast_fragments! {
 150     Expr(P<ast::Expr>) { "expression"; one fn visit_expr; fn visit_expr; fn make_expr; }
 151     Pat(P<ast::Pat>) { "pattern"; one fn visit_pat; fn visit_pat; fn make_pat; }
 152     Ty(P<ast::Ty>) { "type"; one fn visit_ty; fn visit_ty; fn make_ty; }
 153     Stmts(SmallVec<[ast::Stmt; 1]>) {
 154         "statement"; many fn flat_map_stmt; fn visit_stmt(); fn make_stmts;
 155     }
 156     Items(SmallVec<[P<ast::Item>; 1]>) {
 157         "item"; many fn flat_map_item; fn visit_item(); fn make_items;
 158     }
 159     TraitItems(SmallVec<[P<ast::AssocItem>; 1]>) {
 160         "trait item";
 161         many fn flat_map_trait_item;
 162         fn visit_assoc_item(AssocCtxt::Trait);
 163         fn make_trait_items;
 164     }
 165     ImplItems(SmallVec<[P<ast::AssocItem>; 1]>) {
 166         "impl item";
 167         many fn flat_map_impl_item;
 168         fn visit_assoc_item(AssocCtxt::Impl);
 169         fn make_impl_items;
 170     }
 171     ForeignItems(SmallVec<[P<ast::ForeignItem>; 1]>) {
 172         "foreign item";
 173         many fn flat_map_foreign_item;
 174         fn visit_foreign_item();
 175         fn make_foreign_items;
 176     }
 177     Arms(SmallVec<[ast::Arm; 1]>) {
 178         "match arm"; many fn flat_map_arm; fn visit_arm(); fn make_arms;
 179     }
 180     Fields(SmallVec<[ast::ExprField; 1]>) {
 181         "field expression"; many fn flat_map_expr_field; fn visit_expr_field(); fn make_expr_fields;
 182     }
 183     FieldPats(SmallVec<[ast::PatField; 1]>) {
 184         "field pattern";
 185         many fn flat_map_pat_field;
 186         fn visit_pat_field();
 187         fn make_pat_fields;
 188     }
 189     GenericParams(SmallVec<[ast::GenericParam; 1]>) {
 190         "generic parameter";
 191         many fn flat_map_generic_param;
 192         fn visit_generic_param();
 193         fn make_generic_params;
 194     }
 195     Params(SmallVec<[ast::Param; 1]>) {
 196         "function parameter"; many fn flat_map_param; fn visit_param(); fn make_params;
 197     }
 198     StructFields(SmallVec<[ast::FieldDef; 1]>) {
 199         "field";
 200         many fn flat_map_field_def;
 201         fn visit_field_def();
 202         fn make_field_defs;
 203     }
 204     Variants(SmallVec<[ast::Variant; 1]>) {
 205         "variant"; many fn flat_map_variant; fn visit_variant(); fn make_variants;
 206     }
 207 }
 208
 209 pub enum SupportsMacroExpansion {
 210     No,
 211     Yes { supports_inner_attrs: bool },
 212 }
 213
 214 impl AstFragmentKind {
 215     crate fn dummy(self, span: Span) -> AstFragment {
 216         self.make_from(DummyResult::any(span)).expect("couldn't create a dummy AST fragment")
 217     }
 218
 219     pub fn supports_macro_expansion(self) -> SupportsMacroExpansion {
 220         match self {
 221             AstFragmentKind::OptExpr
 222             | AstFragmentKind::Expr
 223             | AstFragmentKind::Stmts
 224             | AstFragmentKind::Ty
 225             | AstFragmentKind::Pat => SupportsMacroExpansion::Yes { supports_inner_attrs: false },
 226             AstFragmentKind::Items
 227             | AstFragmentKind::TraitItems
 228             | AstFragmentKind::ImplItems
 229             | AstFragmentKind::ForeignItems => {
 230                 SupportsMacroExpansion::Yes { supports_inner_attrs: true }
 231             }
 232             AstFragmentKind::Arms
 233             | AstFragmentKind::Fields
 234             | AstFragmentKind::FieldPats
 235             | AstFragmentKind::GenericParams
 236             | AstFragmentKind::Params
 237             | AstFragmentKind::StructFields
 238             | AstFragmentKind::Variants => SupportsMacroExpansion::No,
 239         }
 240     }
 241
 242     fn expect_from_annotatables<I: IntoIterator<Item = Annotatable>>(
 243         self,
 244         items: I,
 245     ) -> AstFragment {
 246         let mut items = items.into_iter();
 247         match self {
 248             AstFragmentKind::Arms => {
 249                 AstFragment::Arms(items.map(Annotatable::expect_arm).collect())
 250             }
 251             AstFragmentKind::Fields => {
 252                 AstFragment::Fields(items.map(Annotatable::expect_expr_field).collect())
 253             }
 254             AstFragmentKind::FieldPats => {
 255                 AstFragment::FieldPats(items.map(Annotatable::expect_pat_field).collect())
 256             }
 257             AstFragmentKind::GenericParams => {
 258                 AstFragment::GenericParams(items.map(Annotatable::expect_generic_param).collect())
 259             }
 260             AstFragmentKind::Params => {
 261                 AstFragment::Params(items.map(Annotatable::expect_param).collect())
 262             }
 263             AstFragmentKind::StructFields => {
 264                 AstFragment::StructFields(items.map(Annotatable::expect_field_def).collect())
 265             }
 266             AstFragmentKind::Variants => {
 267                 AstFragment::Variants(items.map(Annotatable::expect_variant).collect())
 268             }
 269             AstFragmentKind::Items => {
 270                 AstFragment::Items(items.map(Annotatable::expect_item).collect())
 271             }
 272             AstFragmentKind::ImplItems => {
 273                 AstFragment::ImplItems(items.map(Annotatable::expect_impl_item).collect())
 274             }
 275             AstFragmentKind::TraitItems => {
 276                 AstFragment::TraitItems(items.map(Annotatable::expect_trait_item).collect())
 277             }
 278             AstFragmentKind::ForeignItems => {
 279                 AstFragment::ForeignItems(items.map(Annotatable::expect_foreign_item).collect())
 280             }
 281             AstFragmentKind::Stmts => {
 282                 AstFragment::Stmts(items.map(Annotatable::expect_stmt).collect())
 283             }
 284             AstFragmentKind::Expr => AstFragment::Expr(
 285                 items.next().expect("expected exactly one expression").expect_expr(),
 286             ),
 287             AstFragmentKind::OptExpr => {
 288                 AstFragment::OptExpr(items.next().map(Annotatable::expect_expr))
 289             }
 290             AstFragmentKind::Pat | AstFragmentKind::Ty => {
 291                 panic!("patterns and types aren't annotatable")
 292             }
 293         }
 294     }
 295 }
 296
 297 pub struct Invocation {
 298     pub kind: InvocationKind,
 299     pub fragment_kind: AstFragmentKind,
 300     pub expansion_data: ExpansionData,
 301 }
 302
 303 pub enum InvocationKind {
 304     Bang {
 305         mac: ast::MacCall,
 306         span: Span,
 307     },
 308     Attr {
 309         attr: ast::Attribute,
 310         // Re-insertion position for inert attributes.
 311         pos: usize,
 312         item: Annotatable,
 313         // Required for resolving derive helper attributes.
 314         derives: Vec<Path>,
 315     },
 316     Derive {
 317         path: Path,
 318         item: Annotatable,
 319     },
 320 }
 321
 322 impl InvocationKind {
 323     fn placeholder_visibility(&self) -> Option<ast::Visibility> {
 324         // HACK: For unnamed fields placeholders should have the same visibility as the actual
 325         // fields because for tuple structs/variants resolve determines visibilities of their
 326         // constructor using these field visibilities before attributes on them are are expanded.
 327         // The assumption is that the attribute expansion cannot change field visibilities,
 328         // and it holds because only inert attributes are supported in this position.
 329         match self {
 330             InvocationKind::Attr { item: Annotatable::FieldDef(field), .. }
 331             | InvocationKind::Derive { item: Annotatable::FieldDef(field), .. }
 332                 if field.ident.is_none() =>
 333             {
 334                 Some(field.vis.clone())
 335             }
 336             _ => None,
 337         }
 338     }
 339 }
 340
 341 impl Invocation {
 342     pub fn span(&self) -> Span {
 343         match &self.kind {
 344             InvocationKind::Bang { span, .. } => *span,
 345             InvocationKind::Attr { attr, .. } => attr.span,
 346             InvocationKind::Derive { path, .. } => path.span,
 347         }
 348     }
 349 }
 350
 351 pub struct MacroExpander<'a, 'b> {
 352     pub cx: &'a mut ExtCtxt<'b>,
 353     monotonic: bool, // cf. `cx.monotonic_expander()`
 354 }
 355
 356 impl<'a, 'b> MacroExpander<'a, 'b> {
 357     pub fn new(cx: &'a mut ExtCtxt<'b>, monotonic: bool) -> Self {
 358         MacroExpander { cx, monotonic }
 359     }
 360
 361     // FIXME: Avoid visiting the crate as a `Mod` item,
 362     // make crate a first class expansion target instead.
 363     pub fn expand_crate(&mut self, mut krate: ast::Crate) -> ast::Crate {
 364         let file_path = match self.cx.source_map().span_to_unmapped_path(krate.span) {
 365             FileName::Real(name) => name.into_local_path(),
 366             other => PathBuf::from(other.to_string()),
 367         };
 368         let dir_path = file_path.parent().unwrap_or(&file_path).to_owned();
 369         self.cx.root_path = dir_path.clone();
 370         self.cx.current_expansion.module = Rc::new(ModuleData {
 371             mod_path: vec![Ident::from_str(&self.cx.ecfg.crate_name)],
 372             file_path_stack: vec![file_path],
 373             dir_path,
 374         });
 375
 376         let krate_item = AstFragment::Items(smallvec![P(ast::Item {
 377             attrs: krate.attrs,
 378             span: krate.span,
 379             kind: ast::ItemKind::Mod(
 380                 Unsafe::No,
 381                 ModKind::Loaded(krate.items, Inline::Yes, krate.span)
 382             ),
 383             ident: Ident::invalid(),
 384             id: ast::DUMMY_NODE_ID,
 385             vis: ast::Visibility {
 386                 span: krate.span.shrink_to_lo(),
 387                 kind: ast::VisibilityKind::Public,
 388                 tokens: None,
 389             },
 390             tokens: None,
 391         })]);
 392
 393         match self.fully_expand_fragment(krate_item).make_items().pop().map(P::into_inner) {
 394             Some(ast::Item {
 395                 attrs,
 396                 kind: ast::ItemKind::Mod(_, ModKind::Loaded(items, ..)),
 397                 ..
 398             }) => {
 399                 krate.attrs = attrs;
 400                 krate.items = items;
 401             }
 402             None => {
 403                 // Resolution failed so we return an empty expansion
 404                 krate.attrs = vec![];
 405                 krate.items = vec![];
 406             }
 407             Some(ast::Item { span, kind, .. }) => {
 408                 krate.attrs = vec![];
 409                 krate.items = vec![];
 410                 self.cx.span_err(
 411                     span,
 412                     &format!(
 413                         "expected crate top-level item to be a module after macro expansion, found {} {}",
 414                         kind.article(), kind.descr()
 415                     ),
 416                 );
 417             }
 418         };
 419         self.cx.trace_macros_diag();
 420         krate
 421     }
 422
 423     // Recursively expand all macro invocations in this AST fragment.
 424     pub fn fully_expand_fragment(&mut self, input_fragment: AstFragment) -> AstFragment {
 425         let orig_expansion_data = self.cx.current_expansion.clone();
 426         let orig_force_mode = self.cx.force_mode;
 427         self.cx.current_expansion.depth = 0;
 428
 429         // Collect all macro invocations and replace them with placeholders.
 430         let (mut fragment_with_placeholders, mut invocations) =
 431             self.collect_invocations(input_fragment, &[]);
 432
 433         // Optimization: if we resolve all imports now,
 434         // we'll be able to immediately resolve most of imported macros.
 435         self.resolve_imports();
 436
 437         // Resolve paths in all invocations and produce output expanded fragments for them, but
 438         // do not insert them into our input AST fragment yet, only store in `expanded_fragments`.
 439         // The output fragments also go through expansion recursively until no invocations are left.
 440         // Unresolved macros produce dummy outputs as a recovery measure.
 441         invocations.reverse();
 442         let mut expanded_fragments = Vec::new();
 443         let mut undetermined_invocations = Vec::new();
 444         let (mut progress, mut force) = (false, !self.monotonic);
 445         loop {
 446             let (invoc, ext) = if let Some(invoc) = invocations.pop() {
 447                 invoc
 448             } else {
 449                 self.resolve_imports();
 450                 if undetermined_invocations.is_empty() {
 451                     break;
 452                 }
 453                 invocations = mem::take(&mut undetermined_invocations);
 454                 force = !mem::replace(&mut progress, false);
 455                 if force && self.monotonic {
 456                     self.cx.sess.delay_span_bug(
 457                         invocations.last().unwrap().0.span(),
 458                         "expansion entered force mode without producing any errors",
 459                     );
 460                 }
 461                 continue;
 462             };
 463
 464             let ext = match ext {
 465                 Some(ext) => ext,
 466                 None => {
 467                     let eager_expansion_root = if self.monotonic {
 468                         invoc.expansion_data.id
 469                     } else {
 470                         orig_expansion_data.id
 471                     };
 472                     match self.cx.resolver.resolve_macro_invocation(
 473                         &invoc,
 474                         eager_expansion_root,
 475                         force,
 476                     ) {
 477                         Ok(ext) => ext,
 478                         Err(Indeterminate) => {
 479                             // Cannot resolve, will retry this invocation later.
 480                             undetermined_invocations.push((invoc, None));
 481                             continue;
 482                         }
 483                     }
 484                 }
 485             };
 486
 487             let ExpansionData { depth, id: expn_id, .. } = invoc.expansion_data;
 488             self.cx.current_expansion = invoc.expansion_data.clone();
 489             self.cx.force_mode = force;
 490
 491             let fragment_kind = invoc.fragment_kind;
 492             let (expanded_fragment, new_invocations) = match self.expand_invoc(invoc, &ext.kind) {
 493                 ExpandResult::Ready(fragment) => {
 494                     let mut derive_invocations = Vec::new();
 495                     let derive_placeholders = self
 496                         .cx
 497                         .resolver
 498                         .take_derive_resolutions(expn_id)
 499                         .map(|derives| {
 500                             enum AnnotatableRef<'a> {
 501                                 Item(&'a P<ast::Item>),
 502                                 Stmt(&'a ast::Stmt),
 503                             }
 504                             let item = match &fragment {
 505                                 AstFragment::Items(items) => match &items[..] {
 506                                     [item] => AnnotatableRef::Item(item),
 507                                     _ => unreachable!(),
 508                                 },
 509                                 AstFragment::Stmts(stmts) => match &stmts[..] {
 510                                     [stmt] => AnnotatableRef::Stmt(stmt),
 511                                     _ => unreachable!(),
 512                                 },
 513                                 _ => unreachable!(),
 514                             };
 515
 516                             derive_invocations.reserve(derives.len());
 517                             derives
 518                                 .into_iter()
 519                                 .map(|(path, _exts)| {
 520                                     // FIXME: Consider using the derive resolutions (`_exts`)
 521                                     // instead of enqueuing the derives to be resolved again later.
 522                                     let expn_id = ExpnId::fresh(None);
 523                                     derive_invocations.push((
 524                                         Invocation {
 525                                             kind: InvocationKind::Derive {
 526                                                 path,
 527                                                 item: match item {
 528                                                     AnnotatableRef::Item(item) => {
 529                                                         Annotatable::Item(item.clone())
 530                                                     }
 531                                                     AnnotatableRef::Stmt(stmt) => {
 532                                                         Annotatable::Stmt(P(stmt.clone()))
 533                                                     }
 534                                                 },
 535                                             },
 536                                             fragment_kind,
 537                                             expansion_data: ExpansionData {
 538                                                 id: expn_id,
 539                                                 ..self.cx.current_expansion.clone()
 540                                             },
 541                                         },
 542                                         None,
 543                                     ));
 544                                     NodeId::placeholder_from_expn_id(expn_id)
 545                                 })
 546                                 .collect::<Vec<_>>()
 547                         })
 548                         .unwrap_or_default();
 549
 550                     let (fragment, collected_invocations) =
 551                         self.collect_invocations(fragment, &derive_placeholders);
 552                     // We choose to expand any derive invocations associated with this macro invocation
 553                     // *before* any macro invocations collected from the output fragment
 554                     derive_invocations.extend(collected_invocations);
 555                     (fragment, derive_invocations)
 556                 }
 557                 ExpandResult::Retry(invoc) => {
 558                     if force {
 559                         self.cx.span_bug(
 560                             invoc.span(),
 561                             "expansion entered force mode but is still stuck",
 562                         );
 563                     } else {
 564                         // Cannot expand, will retry this invocation later.
 565                         undetermined_invocations.push((invoc, Some(ext)));
 566                         continue;
 567                     }
 568                 }
 569             };
 570
 571             progress = true;
 572             if expanded_fragments.len() < depth {
 573                 expanded_fragments.push(Vec::new());
 574             }
 575             expanded_fragments[depth - 1].push((expn_id, expanded_fragment));
 576             invocations.extend(new_invocations.into_iter().rev());
 577         }
 578
 579         self.cx.current_expansion = orig_expansion_data;
 580         self.cx.force_mode = orig_force_mode;
 581
 582         // Finally incorporate all the expanded macros into the input AST fragment.
 583         let mut placeholder_expander = PlaceholderExpander::new(self.cx, self.monotonic);
 584         while let Some(expanded_fragments) = expanded_fragments.pop() {
 585             for (expn_id, expanded_fragment) in expanded_fragments.into_iter().rev() {
 586                 placeholder_expander
 587                     .add(NodeId::placeholder_from_expn_id(expn_id), expanded_fragment);
 588             }
 589         }
 590         fragment_with_placeholders.mut_visit_with(&mut placeholder_expander);
 591         fragment_with_placeholders
 592     }
 593
 594     fn resolve_imports(&mut self) {
 595         if self.monotonic {
 596             self.cx.resolver.resolve_imports();
 597         }
 598     }
 599
 600     /// Collects all macro invocations reachable at this time in this AST fragment, and replace
 601     /// them with "placeholders" - dummy macro invocations with specially crafted `NodeId`s.
 602     /// Then call into resolver that builds a skeleton ("reduced graph") of the fragment and
 603     /// prepares data for resolving paths of macro invocations.
 604     fn collect_invocations(
 605         &mut self,
 606         mut fragment: AstFragment,
 607         extra_placeholders: &[NodeId],
 608     ) -> (AstFragment, Vec<(Invocation, Option<Lrc<SyntaxExtension>>)>) {
 609         // Resolve `$crate`s in the fragment for pretty-printing.
 610         self.cx.resolver.resolve_dollar_crates();
 611
 612         let invocations = {
 613             let mut collector = InvocationCollector {
 614                 cfg: StripUnconfigured {
 615                     sess: &self.cx.sess,
 616                     features: self.cx.ecfg.features,
 617                     modified: false,
 618                 },
 619                 cx: self.cx,
 620                 invocations: Vec::new(),
 621                 monotonic: self.monotonic,
 622             };
 623             fragment.mut_visit_with(&mut collector);
 624             fragment.add_placeholders(extra_placeholders);
 625             collector.invocations
 626         };
 627
 628         if self.monotonic {
 629             self.cx
 630                 .resolver
 631                 .visit_ast_fragment_with_placeholders(self.cx.current_expansion.id, &fragment);
 632         }
 633
 634         (fragment, invocations)
 635     }
 636
 637     fn error_recursion_limit_reached(&mut self) {
 638         let expn_data = self.cx.current_expansion.id.expn_data();
 639         let suggested_limit = self.cx.ecfg.recursion_limit * 2;
 640         self.cx
 641             .struct_span_err(
 642                 expn_data.call_site,
 643                 &format!("recursion limit reached while expanding `{}`", expn_data.kind.descr()),
 644             )
 645             .help(&format!(
 646                 "consider adding a `#![recursion_limit=\"{}\"]` attribute to your crate (`{}`)",
 647                 suggested_limit, self.cx.ecfg.crate_name,
 648             ))
 649             .emit();
 650         self.cx.trace_macros_diag();
 651     }
 652
 653     /// A macro's expansion does not fit in this fragment kind.
 654     /// For example, a non-type macro in a type position.
 655     fn error_wrong_fragment_kind(&mut self, kind: AstFragmentKind, mac: &ast::MacCall, span: Span) {
 656         let msg = format!(
 657             "non-{kind} macro in {kind} position: {path}",
 658             kind = kind.name(),
 659             path = pprust::path_to_string(&mac.path),
 660         );
 661         self.cx.span_err(span, &msg);
 662         self.cx.trace_macros_diag();
 663     }
 664
 665     fn expand_invoc(
 666         &mut self,
 667         invoc: Invocation,
 668         ext: &SyntaxExtensionKind,
 669     ) -> ExpandResult<AstFragment, Invocation> {
 670         let recursion_limit =
 671             self.cx.reduced_recursion_limit.unwrap_or(self.cx.ecfg.recursion_limit);
 672         if !recursion_limit.value_within_limit(self.cx.current_expansion.depth) {
 673             if self.cx.reduced_recursion_limit.is_none() {
 674                 self.error_recursion_limit_reached();
 675             }
 676
 677             // Reduce the recursion limit by half each time it triggers.
 678             self.cx.reduced_recursion_limit = Some(recursion_limit / 2);
 679
 680             return ExpandResult::Ready(invoc.fragment_kind.dummy(invoc.span()));
 681         }
 682
 683         let (fragment_kind, span) = (invoc.fragment_kind, invoc.span());
 684         ExpandResult::Ready(match invoc.kind {
 685             InvocationKind::Bang { mac, .. } => match ext {
 686                 SyntaxExtensionKind::Bang(expander) => {
 687                     let tok_result = match expander.expand(self.cx, span, mac.args.inner_tokens()) {
 688                         Err(_) => return ExpandResult::Ready(fragment_kind.dummy(span)),
 689                         Ok(ts) => ts,
 690                     };
 691                     self.parse_ast_fragment(tok_result, fragment_kind, &mac.path, span)
 692                 }
 693                 SyntaxExtensionKind::LegacyBang(expander) => {
 694                     let prev = self.cx.current_expansion.prior_type_ascription;
 695                     self.cx.current_expansion.prior_type_ascription = mac.prior_type_ascription;
 696                     let tok_result = expander.expand(self.cx, span, mac.args.inner_tokens());
 697                     let result = if let Some(result) = fragment_kind.make_from(tok_result) {
 698                         result
 699                     } else {
 700                         self.error_wrong_fragment_kind(fragment_kind, &mac, span);
 701                         fragment_kind.dummy(span)
 702                     };
 703                     self.cx.current_expansion.prior_type_ascription = prev;
 704                     result
 705                 }
 706                 _ => unreachable!(),
 707             },
 708             InvocationKind::Attr { attr, pos, mut item, derives } => match ext {
 709                 SyntaxExtensionKind::Attr(expander) => {
 710                     self.gate_proc_macro_input(&item);
 711                     self.gate_proc_macro_attr_item(span, &item);
 712                     let tokens = match attr.style {
 713                         AttrStyle::Outer => item.into_tokens(&self.cx.sess.parse_sess),
 714                         // FIXME: Properly collect tokens for inner attributes
 715                         AttrStyle::Inner => rustc_parse::fake_token_stream(
 716                             &self.cx.sess.parse_sess,
 717                             &item.into_nonterminal(),
 718                         ),
 719                     };
 720                     let attr_item = attr.unwrap_normal_item();
 721                     if let MacArgs::Eq(..) = attr_item.args {
 722                         self.cx.span_err(span, "key-value macro attributes are not supported");
 723                     }
 724                     let inner_tokens = attr_item.args.inner_tokens();
 725                     let tok_result = match expander.expand(self.cx, span, inner_tokens, tokens) {
 726                         Err(_) => return ExpandResult::Ready(fragment_kind.dummy(span)),
 727                         Ok(ts) => ts,
 728                     };
 729                     self.parse_ast_fragment(tok_result, fragment_kind, &attr_item.path, span)
 730                 }
 731                 SyntaxExtensionKind::LegacyAttr(expander) => {
 732                     match validate_attr::parse_meta(&self.cx.sess.parse_sess, &attr) {
 733                         Ok(meta) => {
 734                             let items = match expander.expand(self.cx, span, &meta, item) {
 735                                 ExpandResult::Ready(items) => items,
 736                                 ExpandResult::Retry(item) => {
 737                                     // Reassemble the original invocation for retrying.
 738                                     return ExpandResult::Retry(Invocation {
 739                                         kind: InvocationKind::Attr { attr, pos, item, derives },
 740                                         ..invoc
 741                                     });
 742                                 }
 743                             };
 744                             if fragment_kind == AstFragmentKind::Expr && items.is_empty() {
 745                                 let msg =
 746                                     "removing an expression is not supported in this position";
 747                                 self.cx.span_err(span, msg);
 748                                 fragment_kind.dummy(span)
 749                             } else {
 750                                 fragment_kind.expect_from_annotatables(items)
 751                             }
 752                         }
 753                         Err(mut err) => {
 754                             err.emit();
 755                             fragment_kind.dummy(span)
 756                         }
 757                     }
 758                 }
 759                 SyntaxExtensionKind::NonMacroAttr { mark_used } => {
 760                     self.cx.sess.mark_attr_known(&attr);
 761                     if *mark_used {
 762                         self.cx.sess.mark_attr_used(&attr);
 763                     }
 764                     item.visit_attrs(|attrs| attrs.insert(pos, attr));
 765                     fragment_kind.expect_from_annotatables(iter::once(item))
 766                 }
 767                 _ => unreachable!(),
 768             },
 769             InvocationKind::Derive { path, item } => match ext {
 770                 SyntaxExtensionKind::Derive(expander)
 771                 | SyntaxExtensionKind::LegacyDerive(expander) => {
 772                     if let SyntaxExtensionKind::Derive(..) = ext {
 773                         self.gate_proc_macro_input(&item);
 774                     }
 775                     let meta = ast::MetaItem { kind: ast::MetaItemKind::Word, span, path };
 776                     let items = match expander.expand(self.cx, span, &meta, item) {
 777                         ExpandResult::Ready(items) => items,
 778                         ExpandResult::Retry(item) => {
 779                             // Reassemble the original invocation for retrying.
 780                             return ExpandResult::Retry(Invocation {
 781                                 kind: InvocationKind::Derive { path: meta.path, item },
 782                                 ..invoc
 783                             });
 784                         }
 785                     };
 786                     fragment_kind.expect_from_annotatables(items)
 787                 }
 788                 _ => unreachable!(),
 789             },
 790         })
 791     }
 792
 793     fn gate_proc_macro_attr_item(&self, span: Span, item: &Annotatable) {
 794         let kind = match item {
 795             Annotatable::Item(_)
 796             | Annotatable::TraitItem(_)
 797             | Annotatable::ImplItem(_)
 798             | Annotatable::ForeignItem(_) => return,
 799             Annotatable::Stmt(stmt) => {
 800                 // Attributes are stable on item statements,
 801                 // but unstable on all other kinds of statements
 802                 if stmt.is_item() {
 803                     return;
 804                 }
 805                 "statements"
 806             }
 807             Annotatable::Expr(_) => "expressions",
 808             Annotatable::Arm(..)
 809             | Annotatable::ExprField(..)
 810             | Annotatable::PatField(..)
 811             | Annotatable::GenericParam(..)
 812             | Annotatable::Param(..)
 813             | Annotatable::FieldDef(..)
 814             | Annotatable::Variant(..) => panic!("unexpected annotatable"),
 815         };
 816         if self.cx.ecfg.proc_macro_hygiene() {
 817             return;
 818         }
 819         feature_err(
 820             &self.cx.sess.parse_sess,
 821             sym::proc_macro_hygiene,
 822             span,
 823             &format!("custom attributes cannot be applied to {}", kind),
 824         )
 825         .emit();
 826     }
 827
 828     fn gate_proc_macro_input(&self, annotatable: &Annotatable) {
 829         struct GateProcMacroInput<'a> {
 830             parse_sess: &'a ParseSess,
 831         }
 832
 833         impl<'ast, 'a> Visitor<'ast> for GateProcMacroInput<'a> {
 834             fn visit_item(&mut self, item: &'ast ast::Item) {
 835                 match &item.kind {
 836                     ast::ItemKind::Mod(_, mod_kind)
 837                         if !matches!(mod_kind, ModKind::Loaded(_, Inline::Yes, _)) =>
 838                     {
 839                         feature_err(
 840                             self.parse_sess,
 841                             sym::proc_macro_hygiene,
 842                             item.span,
 843                             "non-inline modules in proc macro input are unstable",
 844                         )
 845                         .emit();
 846                     }
 847                     _ => {}
 848                 }
 849
 850                 visit::walk_item(self, item);
 851             }
 852         }
 853
 854         if !self.cx.ecfg.proc_macro_hygiene() {
 855             annotatable
 856                 .visit_with(&mut GateProcMacroInput { parse_sess: &self.cx.sess.parse_sess });
 857         }
 858     }
 859
 860     fn parse_ast_fragment(
 861         &mut self,
 862         toks: TokenStream,
 863         kind: AstFragmentKind,
 864         path: &Path,
 865         span: Span,
 866     ) -> AstFragment {
 867         let mut parser = self.cx.new_parser_from_tts(toks);
 868         match parse_ast_fragment(&mut parser, kind) {
 869             Ok(fragment) => {
 870                 ensure_complete_parse(&mut parser, path, kind.name(), span);
 871                 fragment
 872             }
 873             Err(mut err) => {
 874                 if err.span.is_dummy() {
 875                     err.set_span(span);
 876                 }
 877                 annotate_err_with_kind(&mut err, kind, span);
 878                 err.emit();
 879                 self.cx.trace_macros_diag();
 880                 kind.dummy(span)
 881             }
 882         }
 883     }
 884 }
 885
 886 pub fn parse_ast_fragment<'a>(
 887     this: &mut Parser<'a>,
 888     kind: AstFragmentKind,
 889 ) -> PResult<'a, AstFragment> {
 890     Ok(match kind {
 891         AstFragmentKind::Items => {
 892             let mut items = SmallVec::new();
 893             while let Some(item) = this.parse_item(ForceCollect::No)? {
 894                 items.push(item);
 895             }
 896             AstFragment::Items(items)
 897         }
 898         AstFragmentKind::TraitItems => {
 899             let mut items = SmallVec::new();
 900             while let Some(item) = this.parse_trait_item()? {
 901                 items.extend(item);
 902             }
 903             AstFragment::TraitItems(items)
 904         }
 905         AstFragmentKind::ImplItems => {
 906             let mut items = SmallVec::new();
 907             while let Some(item) = this.parse_impl_item()? {
 908                 items.extend(item);
 909             }
 910             AstFragment::ImplItems(items)
 911         }
 912         AstFragmentKind::ForeignItems => {
 913             let mut items = SmallVec::new();
 914             while let Some(item) = this.parse_foreign_item()? {
 915                 items.extend(item);
 916             }
 917             AstFragment::ForeignItems(items)
 918         }
 919         AstFragmentKind::Stmts => {
 920             let mut stmts = SmallVec::new();
 921             // Won't make progress on a `}`.
 922             while this.token != token::Eof && this.token != token::CloseDelim(token::Brace) {
 923                 if let Some(stmt) = this.parse_full_stmt(AttemptLocalParseRecovery::Yes)? {
 924                     stmts.push(stmt);
 925                 }
 926             }
 927             AstFragment::Stmts(stmts)
 928         }
 929         AstFragmentKind::Expr => AstFragment::Expr(this.parse_expr()?),
 930         AstFragmentKind::OptExpr => {
 931             if this.token != token::Eof {
 932                 AstFragment::OptExpr(Some(this.parse_expr()?))
 933             } else {
 934                 AstFragment::OptExpr(None)
 935             }
 936         }
 937         AstFragmentKind::Ty => AstFragment::Ty(this.parse_ty()?),
 938         AstFragmentKind::Pat => {
 939             AstFragment::Pat(this.parse_pat_allow_top_alt(None, RecoverComma::No)?)
 940         }
 941         AstFragmentKind::Arms
 942         | AstFragmentKind::Fields
 943         | AstFragmentKind::FieldPats
 944         | AstFragmentKind::GenericParams
 945         | AstFragmentKind::Params
 946         | AstFragmentKind::StructFields
 947         | AstFragmentKind::Variants => panic!("unexpected AST fragment kind"),
 948     })
 949 }
 950
 951 pub fn ensure_complete_parse<'a>(
 952     this: &mut Parser<'a>,
 953     macro_path: &Path,
 954     kind_name: &str,
 955     span: Span,
 956 ) {
 957     if this.token != token::Eof {
 958         let token = pprust::token_to_string(&this.token);
 959         let msg = format!("macro expansion ignores token `{}` and any following", token);
 960         // Avoid emitting backtrace info twice.
 961         let def_site_span = this.token.span.with_ctxt(SyntaxContext::root());
 962         let mut err = this.struct_span_err(def_site_span, &msg);
 963         err.span_label(span, "caused by the macro expansion here");
 964         let msg = format!(
 965             "the usage of `{}!` is likely invalid in {} context",
 966             pprust::path_to_string(macro_path),
 967             kind_name,
 968         );
 969         err.note(&msg);
 970         let semi_span = this.sess.source_map().next_point(span);
 971
 972         let semi_full_span = semi_span.to(this.sess.source_map().next_point(semi_span));
 973         match this.sess.source_map().span_to_snippet(semi_full_span) {
 974             Ok(ref snippet) if &snippet[..] != ";" && kind_name == "expression" => {
 975                 err.span_suggestion(
 976                     semi_span,
 977                     "you might be missing a semicolon here",
 978                     ";".to_owned(),
 979                     Applicability::MaybeIncorrect,
 980                 );
 981             }
 982             _ => {}
 983         }
 984         err.emit();
 985     }
 986 }
 987
 988 struct InvocationCollector<'a, 'b> {
 989     cx: &'a mut ExtCtxt<'b>,
 990     cfg: StripUnconfigured<'a>,
 991     invocations: Vec<(Invocation, Option<Lrc<SyntaxExtension>>)>,
 992     monotonic: bool,
 993 }
 994
 995 impl<'a, 'b> InvocationCollector<'a, 'b> {
 996     fn collect(&mut self, fragment_kind: AstFragmentKind, kind: InvocationKind) -> AstFragment {
 997         let expn_id = ExpnId::fresh(None);
 998         let vis = kind.placeholder_visibility();
 999         self.invocations.push((
1000             Invocation {
1001                 kind,
1002                 fragment_kind,
1003                 expansion_data: ExpansionData {
1004                     id: expn_id,
1005                     depth: self.cx.current_expansion.depth + 1,
1006                     ..self.cx.current_expansion.clone()
1007                 },
1008             },
1009             None,
1010         ));
1011         placeholder(fragment_kind, NodeId::placeholder_from_expn_id(expn_id), vis)
1012     }
1013
1014     fn collect_bang(
1015         &mut self,
1016         mac: ast::MacCall,
1017         span: Span,
1018         kind: AstFragmentKind,
1019     ) -> AstFragment {
1020         self.collect(kind, InvocationKind::Bang { mac, span })
1021     }
1022
1023     fn collect_attr(
1024         &mut self,
1025         (attr, pos, derives): (ast::Attribute, usize, Vec<Path>),
1026         item: Annotatable,
1027         kind: AstFragmentKind,
1028     ) -> AstFragment {
1029         self.collect(kind, InvocationKind::Attr { attr, pos, item, derives })
1030     }
1031
1032     /// If `item` is an attribute invocation, remove the attribute and return it together with
1033     /// its position and derives following it. We have to collect the derives in order to resolve
1034     /// legacy derive helpers (helpers written before derives that introduce them).
1035     fn take_first_attr(
1036         &mut self,
1037         item: &mut impl AstLike,
1038     ) -> Option<(ast::Attribute, usize, Vec<Path>)> {
1039         let mut attr = None;
1040
1041         item.visit_attrs(|attrs| {
1042             attr = attrs
1043                 .iter()
1044                 .position(|a| !self.cx.sess.is_attr_known(a) && !is_builtin_attr(a))
1045                 .map(|attr_pos| {
1046                     let attr = attrs.remove(attr_pos);
1047                     let following_derives = attrs[attr_pos..]
1048                         .iter()
1049                         .filter(|a| a.has_name(sym::derive))
1050                         .flat_map(|a| a.meta_item_list().unwrap_or_default())
1051                         .filter_map(|nested_meta| match nested_meta {
1052                             NestedMetaItem::MetaItem(ast::MetaItem {
1053                                 kind: MetaItemKind::Word,
1054                                 path,
1055                                 ..
1056                             }) => Some(path),
1057                             _ => None,
1058                         })
1059                         .collect();
1060
1061                     (attr, attr_pos, following_derives)
1062                 })
1063         });
1064
1065         attr
1066     }
1067
1068     fn configure<T: AstLike>(&mut self, node: T) -> Option<T> {
1069         self.cfg.configure(node)
1070     }
1071
1072     // Detect use of feature-gated or invalid attributes on macro invocations
1073     // since they will not be detected after macro expansion.
1074     fn check_attributes(&mut self, attrs: &[ast::Attribute]) {
1075         let features = self.cx.ecfg.features.unwrap();
1076         let mut attrs = attrs.iter().peekable();
1077         let mut span: Option<Span> = None;
1078         while let Some(attr) = attrs.next() {
1079             rustc_ast_passes::feature_gate::check_attribute(attr, self.cx.sess, features);
1080             validate_attr::check_meta(&self.cx.sess.parse_sess, attr);
1081
1082             let current_span = if let Some(sp) = span { sp.to(attr.span) } else { attr.span };
1083             span = Some(current_span);
1084
1085             if attrs.peek().map_or(false, |next_attr| next_attr.doc_str().is_some()) {
1086                 continue;
1087             }
1088
1089             if attr.doc_str().is_some() {
1090                 self.cx.sess.parse_sess.buffer_lint_with_diagnostic(
1091                     &UNUSED_DOC_COMMENTS,
1092                     current_span,
1093                     ast::CRATE_NODE_ID,
1094                     "unused doc comment",
1095                     BuiltinLintDiagnostics::UnusedDocComment(attr.span),
1096                 );
1097             }
1098         }
1099     }
1100 }
1101
1102 impl<'a, 'b> MutVisitor for InvocationCollector<'a, 'b> {
1103     fn visit_expr(&mut self, expr: &mut P<ast::Expr>) {
1104         self.cfg.configure_expr(expr);
1105         visit_clobber(expr.deref_mut(), |mut expr| {
1106             if let Some(attr) = self.take_first_attr(&mut expr) {
1107                 // Collect the invoc regardless of whether or not attributes are permitted here
1108                 // expansion will eat the attribute so it won't error later.
1109                 self.cfg.maybe_emit_expr_attr_err(&attr.0);
1110
1111                 // AstFragmentKind::Expr requires the macro to emit an expression.
1112                 return self
1113                     .collect_attr(attr, Annotatable::Expr(P(expr)), AstFragmentKind::Expr)
1114                     .make_expr()
1115                     .into_inner();
1116             }
1117
1118             if let ast::ExprKind::MacCall(mac) = expr.kind {
1119                 self.check_attributes(&expr.attrs);
1120                 self.collect_bang(mac, expr.span, AstFragmentKind::Expr).make_expr().into_inner()
1121             } else {
1122                 ensure_sufficient_stack(|| noop_visit_expr(&mut expr, self));
1123                 expr
1124             }
1125         });
1126     }
1127
1128     fn flat_map_arm(&mut self, arm: ast::Arm) -> SmallVec<[ast::Arm; 1]> {
1129         let mut arm = configure!(self, arm);
1130
1131         if let Some(attr) = self.take_first_attr(&mut arm) {
1132             return self
1133                 .collect_attr(attr, Annotatable::Arm(arm), AstFragmentKind::Arms)
1134                 .make_arms();
1135         }
1136
1137         noop_flat_map_arm(arm, self)
1138     }
1139
1140     fn flat_map_expr_field(&mut self, field: ast::ExprField) -> SmallVec<[ast::ExprField; 1]> {
1141         let mut field = configure!(self, field);
1142
1143         if let Some(attr) = self.take_first_attr(&mut field) {
1144             return self
1145                 .collect_attr(attr, Annotatable::ExprField(field), AstFragmentKind::Fields)
1146                 .make_expr_fields();
1147         }
1148
1149         noop_flat_map_expr_field(field, self)
1150     }
1151
1152     fn flat_map_pat_field(&mut self, fp: ast::PatField) -> SmallVec<[ast::PatField; 1]> {
1153         let mut fp = configure!(self, fp);
1154
1155         if let Some(attr) = self.take_first_attr(&mut fp) {
1156             return self
1157                 .collect_attr(attr, Annotatable::PatField(fp), AstFragmentKind::FieldPats)
1158                 .make_pat_fields();
1159         }
1160
1161         noop_flat_map_pat_field(fp, self)
1162     }
1163
1164     fn flat_map_param(&mut self, p: ast::Param) -> SmallVec<[ast::Param; 1]> {
1165         let mut p = configure!(self, p);
1166
1167         if let Some(attr) = self.take_first_attr(&mut p) {
1168             return self
1169                 .collect_attr(attr, Annotatable::Param(p), AstFragmentKind::Params)
1170                 .make_params();
1171         }
1172
1173         noop_flat_map_param(p, self)
1174     }
1175
1176     fn flat_map_field_def(&mut self, sf: ast::FieldDef) -> SmallVec<[ast::FieldDef; 1]> {
1177         let mut sf = configure!(self, sf);
1178
1179         if let Some(attr) = self.take_first_attr(&mut sf) {
1180             return self
1181                 .collect_attr(attr, Annotatable::FieldDef(sf), AstFragmentKind::StructFields)
1182                 .make_field_defs();
1183         }
1184
1185         noop_flat_map_field_def(sf, self)
1186     }
1187
1188     fn flat_map_variant(&mut self, variant: ast::Variant) -> SmallVec<[ast::Variant; 1]> {
1189         let mut variant = configure!(self, variant);
1190
1191         if let Some(attr) = self.take_first_attr(&mut variant) {
1192             return self
1193                 .collect_attr(attr, Annotatable::Variant(variant), AstFragmentKind::Variants)
1194                 .make_variants();
1195         }
1196
1197         noop_flat_map_variant(variant, self)
1198     }
1199
1200     fn filter_map_expr(&mut self, expr: P<ast::Expr>) -> Option<P<ast::Expr>> {
1201         let expr = configure!(self, expr);
1202         expr.filter_map(|mut expr| {
1203             if let Some(attr) = self.take_first_attr(&mut expr) {
1204                 self.cfg.maybe_emit_expr_attr_err(&attr.0);
1205
1206                 return self
1207                     .collect_attr(attr, Annotatable::Expr(P(expr)), AstFragmentKind::OptExpr)
1208                     .make_opt_expr()
1209                     .map(|expr| expr.into_inner());
1210             }
1211
1212             if let ast::ExprKind::MacCall(mac) = expr.kind {
1213                 self.check_attributes(&expr.attrs);
1214                 self.collect_bang(mac, expr.span, AstFragmentKind::OptExpr)
1215                     .make_opt_expr()
1216                     .map(|expr| expr.into_inner())
1217             } else {
1218                 Some({
1219                     noop_visit_expr(&mut expr, self);
1220                     expr
1221                 })
1222             }
1223         })
1224     }
1225
1226     fn visit_pat(&mut self, pat: &mut P<ast::Pat>) {
1227         match pat.kind {
1228             PatKind::MacCall(_) => {}
1229             _ => return noop_visit_pat(pat, self),
1230         }
1231
1232         visit_clobber(pat, |mut pat| match mem::replace(&mut pat.kind, PatKind::Wild) {
1233             PatKind::MacCall(mac) => {
1234                 self.collect_bang(mac, pat.span, AstFragmentKind::Pat).make_pat()
1235             }
1236             _ => unreachable!(),
1237         });
1238     }
1239
1240     fn flat_map_stmt(&mut self, stmt: ast::Stmt) -> SmallVec<[ast::Stmt; 1]> {
1241         let mut stmt = configure!(self, stmt);
1242
1243         // we'll expand attributes on expressions separately
1244         if !stmt.is_expr() {
1245             if let Some(attr) = self.take_first_attr(&mut stmt) {
1246                 return self
1247                     .collect_attr(attr, Annotatable::Stmt(P(stmt)), AstFragmentKind::Stmts)
1248                     .make_stmts();
1249             }
1250         }
1251
1252         if let StmtKind::MacCall(mac) = stmt.kind {
1253             let MacCallStmt { mac, style, attrs, tokens: _ } = mac.into_inner();
1254             self.check_attributes(&attrs);
1255             let mut placeholder =
1256                 self.collect_bang(mac, stmt.span, AstFragmentKind::Stmts).make_stmts();
1257
1258             // If this is a macro invocation with a semicolon, then apply that
1259             // semicolon to the final statement produced by expansion.
1260             if style == MacStmtStyle::Semicolon {
1261                 if let Some(stmt) = placeholder.pop() {
1262                     placeholder.push(stmt.add_trailing_semicolon());
1263                 }
1264             }
1265
1266             return placeholder;
1267         }
1268
1269         // The placeholder expander gives ids to statements, so we avoid folding the id here.
1270         let ast::Stmt { id, kind, span } = stmt;
1271         noop_flat_map_stmt_kind(kind, self)
1272             .into_iter()
1273             .map(|kind| ast::Stmt { id, kind, span })
1274             .collect()
1275     }
1276
1277     fn visit_block(&mut self, block: &mut P<Block>) {
1278         let orig_dir_ownership = mem::replace(
1279             &mut self.cx.current_expansion.dir_ownership,
1280             DirOwnership::UnownedViaBlock,
1281         );
1282         noop_visit_block(block, self);
1283         self.cx.current_expansion.dir_ownership = orig_dir_ownership;
1284     }
1285
1286     fn flat_map_item(&mut self, item: P<ast::Item>) -> SmallVec<[P<ast::Item>; 1]> {
1287         let mut item = configure!(self, item);
1288
1289         if let Some(attr) = self.take_first_attr(&mut item) {
1290             return self
1291                 .collect_attr(attr, Annotatable::Item(item), AstFragmentKind::Items)
1292                 .make_items();
1293         }
1294
1295         let mut attrs = mem::take(&mut item.attrs); // We do this to please borrowck.
1296         let ident = item.ident;
1297         let span = item.span;
1298
1299         match item.kind {
1300             ast::ItemKind::MacCall(..) => {
1301                 item.attrs = attrs;
1302                 self.check_attributes(&item.attrs);
1303                 item.and_then(|item| match item.kind {
1304                     ItemKind::MacCall(mac) => {
1305                         self.collect_bang(mac, span, AstFragmentKind::Items).make_items()
1306                     }
1307                     _ => unreachable!(),
1308                 })
1309             }
1310             ast::ItemKind::Mod(_, ref mut mod_kind) if ident != Ident::invalid() => {
1311                 let (file_path, dir_path, dir_ownership) = match mod_kind {
1312                     ModKind::Loaded(_, inline, _) => {
1313                         // Inline `mod foo { ... }`, but we still need to push directories.
1314                         let (dir_path, dir_ownership) = mod_dir_path(
1315                             &self.cx.sess,
1316                             ident,
1317                             &attrs,
1318                             &self.cx.current_expansion.module,
1319                             self.cx.current_expansion.dir_ownership,
1320                             *inline,
1321                         );
1322                         item.attrs = attrs;
1323                         (None, dir_path, dir_ownership)
1324                     }
1325                     ModKind::Unloaded => {
1326                         // We have an outline `mod foo;` so we need to parse the file.
1327                         let old_attrs_len = attrs.len();
1328                         let ParsedExternalMod {
1329                             mut items,
1330                             inner_span,
1331                             file_path,
1332                             dir_path,
1333                             dir_ownership,
1334                         } = parse_external_mod(
1335                             &self.cx.sess,
1336                             ident,
1337                             span,
1338                             &self.cx.current_expansion.module,
1339                             self.cx.current_expansion.dir_ownership,
1340                             &mut attrs,
1341                         );
1342
1343                         if let Some(extern_mod_loaded) = self.cx.extern_mod_loaded {
1344                             (attrs, items) = extern_mod_loaded(ident, attrs, items, inner_span);
1345                         }
1346
1347                         *mod_kind = ModKind::Loaded(items, Inline::No, inner_span);
1348                         item.attrs = attrs;
1349                         if item.attrs.len() > old_attrs_len {
1350                             // If we loaded an out-of-line module and added some inner attributes,
1351                             // then we need to re-configure it and re-collect attributes for
1352                             // resolution and expansion.
1353                             item = configure!(self, item);
1354
1355                             if let Some(attr) = self.take_first_attr(&mut item) {
1356                                 return self
1357                                     .collect_attr(
1358                                         attr,
1359                                         Annotatable::Item(item),
1360                                         AstFragmentKind::Items,
1361                                     )
1362                                     .make_items();
1363                             }
1364                         }
1365                         (Some(file_path), dir_path, dir_ownership)
1366                     }
1367                 };
1368
1369                 // Set the module info before we flat map.
1370                 let mut module = self.cx.current_expansion.module.with_dir_path(dir_path);
1371                 module.mod_path.push(ident);
1372                 if let Some(file_path) = file_path {
1373                     module.file_path_stack.push(file_path);
1374                 }
1375
1376                 let orig_module =
1377                     mem::replace(&mut self.cx.current_expansion.module, Rc::new(module));
1378                 let orig_dir_ownership =
1379                     mem::replace(&mut self.cx.current_expansion.dir_ownership, dir_ownership);
1380
1381                 let result = noop_flat_map_item(item, self);
1382
1383                 // Restore the module info.
1384                 self.cx.current_expansion.dir_ownership = orig_dir_ownership;
1385                 self.cx.current_expansion.module = orig_module;
1386
1387                 result
1388             }
1389             _ => {
1390                 item.attrs = attrs;
1391                 noop_flat_map_item(item, self)
1392             }
1393         }
1394     }
1395
1396     fn flat_map_trait_item(&mut self, item: P<ast::AssocItem>) -> SmallVec<[P<ast::AssocItem>; 1]> {
1397         let mut item = configure!(self, item);
1398
1399         if let Some(attr) = self.take_first_attr(&mut item) {
1400             return self
1401                 .collect_attr(attr, Annotatable::TraitItem(item), AstFragmentKind::TraitItems)
1402                 .make_trait_items();
1403         }
1404
1405         match item.kind {
1406             ast::AssocItemKind::MacCall(..) => {
1407                 self.check_attributes(&item.attrs);
1408                 item.and_then(|item| match item.kind {
1409                     ast::AssocItemKind::MacCall(mac) => self
1410                         .collect_bang(mac, item.span, AstFragmentKind::TraitItems)
1411                         .make_trait_items(),
1412                     _ => unreachable!(),
1413                 })
1414             }
1415             _ => noop_flat_map_assoc_item(item, self),
1416         }
1417     }
1418
1419     fn flat_map_impl_item(&mut self, item: P<ast::AssocItem>) -> SmallVec<[P<ast::AssocItem>; 1]> {
1420         let mut item = configure!(self, item);
1421
1422         if let Some(attr) = self.take_first_attr(&mut item) {
1423             return self
1424                 .collect_attr(attr, Annotatable::ImplItem(item), AstFragmentKind::ImplItems)
1425                 .make_impl_items();
1426         }
1427
1428         match item.kind {
1429             ast::AssocItemKind::MacCall(..) => {
1430                 self.check_attributes(&item.attrs);
1431                 item.and_then(|item| match item.kind {
1432                     ast::AssocItemKind::MacCall(mac) => self
1433                         .collect_bang(mac, item.span, AstFragmentKind::ImplItems)
1434                         .make_impl_items(),
1435                     _ => unreachable!(),
1436                 })
1437             }
1438             _ => noop_flat_map_assoc_item(item, self),
1439         }
1440     }
1441
1442     fn visit_ty(&mut self, ty: &mut P<ast::Ty>) {
1443         match ty.kind {
1444             ast::TyKind::MacCall(_) => {}
1445             _ => return noop_visit_ty(ty, self),
1446         };
1447
1448         visit_clobber(ty, |mut ty| match mem::replace(&mut ty.kind, ast::TyKind::Err) {
1449             ast::TyKind::MacCall(mac) => {
1450                 self.collect_bang(mac, ty.span, AstFragmentKind::Ty).make_ty()
1451             }
1452             _ => unreachable!(),
1453         });
1454     }
1455
1456     fn flat_map_foreign_item(
1457         &mut self,
1458         foreign_item: P<ast::ForeignItem>,
1459     ) -> SmallVec<[P<ast::ForeignItem>; 1]> {
1460         let mut foreign_item = configure!(self, foreign_item);
1461
1462         if let Some(attr) = self.take_first_attr(&mut foreign_item) {
1463             return self
1464                 .collect_attr(
1465                     attr,
1466                     Annotatable::ForeignItem(foreign_item),
1467                     AstFragmentKind::ForeignItems,
1468                 )
1469                 .make_foreign_items();
1470         }
1471
1472         match foreign_item.kind {
1473             ast::ForeignItemKind::MacCall(..) => {
1474                 self.check_attributes(&foreign_item.attrs);
1475                 foreign_item.and_then(|item| match item.kind {
1476                     ast::ForeignItemKind::MacCall(mac) => self
1477                         .collect_bang(mac, item.span, AstFragmentKind::ForeignItems)
1478                         .make_foreign_items(),
1479                     _ => unreachable!(),
1480                 })
1481             }
1482             _ => noop_flat_map_foreign_item(foreign_item, self),
1483         }
1484     }
1485
1486     fn flat_map_generic_param(
1487         &mut self,
1488         param: ast::GenericParam,
1489     ) -> SmallVec<[ast::GenericParam; 1]> {
1490         let mut param = configure!(self, param);
1491
1492         if let Some(attr) = self.take_first_attr(&mut param) {
1493             return self
1494                 .collect_attr(
1495                     attr,
1496                     Annotatable::GenericParam(param),
1497                     AstFragmentKind::GenericParams,
1498                 )
1499                 .make_generic_params();
1500         }
1501
1502         noop_flat_map_generic_param(param, self)
1503     }
1504
1505     fn visit_attribute(&mut self, at: &mut ast::Attribute) {
1506         // turn `#[doc(include="filename")]` attributes into `#[doc(include(file="filename",
1507         // contents="file contents")]` attributes
1508         if !self.cx.sess.check_name(at, sym::doc) {
1509             return noop_visit_attribute(at, self);
1510         }
1511
1512         if let Some(list) = at.meta_item_list() {
1513             if !list.iter().any(|it| it.has_name(sym::include)) {
1514                 return noop_visit_attribute(at, self);
1515             }
1516
1517             let mut items = vec![];
1518
1519             for mut it in list {
1520                 if !it.has_name(sym::include) {
1521                     items.push({
1522                         noop_visit_meta_list_item(&mut it, self);
1523                         it
1524                     });
1525                     continue;
1526                 }
1527
1528                 if let Some(file) = it.value_str() {
1529                     let err_count = self.cx.sess.parse_sess.span_diagnostic.err_count();
1530                     self.check_attributes(slice::from_ref(at));
1531                     if self.cx.sess.parse_sess.span_diagnostic.err_count() > err_count {
1532                         // avoid loading the file if they haven't enabled the feature
1533                         return noop_visit_attribute(at, self);
1534                     }
1535
1536                     let filename = match self.cx.resolve_path(&*file.as_str(), it.span()) {
1537                         Ok(filename) => filename,
1538                         Err(mut err) => {
1539                             err.emit();
1540                             continue;
1541                         }
1542                     };
1543
1544                     match self.cx.source_map().load_file(&filename) {
1545                         Ok(source_file) => {
1546                             let src = source_file
1547                                 .src
1548                                 .as_ref()
1549                                 .expect("freshly loaded file should have a source");
1550                             let src_interned = Symbol::intern(src.as_str());
1551
1552                             let include_info = vec![
1553                                 ast::NestedMetaItem::MetaItem(attr::mk_name_value_item_str(
1554                                     Ident::with_dummy_span(sym::file),
1555                                     file,
1556                                     DUMMY_SP,
1557                                 )),
1558                                 ast::NestedMetaItem::MetaItem(attr::mk_name_value_item_str(
1559                                     Ident::with_dummy_span(sym::contents),
1560                                     src_interned,
1561                                     DUMMY_SP,
1562                                 )),
1563                             ];
1564
1565                             let include_ident = Ident::with_dummy_span(sym::include);
1566                             let item = attr::mk_list_item(include_ident, include_info);
1567                             items.push(ast::NestedMetaItem::MetaItem(item));
1568                         }
1569                         Err(e) => {
1570                             let lit_span = it.name_value_literal_span().unwrap();
1571
1572                             if e.kind() == ErrorKind::InvalidData {
1573                                 self.cx
1574                                     .struct_span_err(
1575                                         lit_span,
1576                                         &format!("{} wasn't a utf-8 file", filename.display()),
1577                                     )
1578                                     .span_label(lit_span, "contains invalid utf-8")
1579                                     .emit();
1580                             } else {
1581                                 let mut err = self.cx.struct_span_err(
1582                                     lit_span,
1583                                     &format!("couldn't read {}: {}", filename.display(), e),
1584                                 );
1585                                 err.span_label(lit_span, "couldn't read file");
1586
1587                                 err.emit();
1588                             }
1589                         }
1590                     }
1591                 } else {
1592                     let mut err = self
1593                         .cx
1594                         .struct_span_err(it.span(), "expected path to external documentation");
1595
1596                     // Check if the user erroneously used `doc(include(...))` syntax.
1597                     let literal = it.meta_item_list().and_then(|list| {
1598                         if list.len() == 1 {
1599                             list[0].literal().map(|literal| &literal.kind)
1600                         } else {
1601                             None
1602                         }
1603                     });
1604
1605                     let (path, applicability) = match &literal {
1606                         Some(LitKind::Str(path, ..)) => {
1607                             (path.to_string(), Applicability::MachineApplicable)
1608                         }
1609                         _ => (String::from("<path>"), Applicability::HasPlaceholders),
1610                     };
1611
1612                     err.span_suggestion(
1613                         it.span(),
1614                         "provide a file path with `=`",
1615                         format!("include = \"{}\"", path),
1616                         applicability,
1617                     );
1618
1619                     err.emit();
1620                 }
1621             }
1622
1623             let meta = attr::mk_list_item(Ident::with_dummy_span(sym::doc), items);
1624             *at = ast::Attribute {
1625                 kind: ast::AttrKind::Normal(
1626                     AttrItem { path: meta.path, args: meta.kind.mac_args(meta.span), tokens: None },
1627                     None,
1628                 ),
1629                 span: at.span,
1630                 id: at.id,
1631                 style: at.style,
1632             };
1633         } else {
1634             noop_visit_attribute(at, self)
1635         }
1636     }
1637
1638     fn visit_id(&mut self, id: &mut ast::NodeId) {
1639         if self.monotonic {
1640             debug_assert_eq!(*id, ast::DUMMY_NODE_ID);
1641             *id = self.cx.resolver.next_node_id()
1642         }
1643     }
1644 }
1645
1646 pub struct ExpansionConfig<'feat> {
1647     pub crate_name: String,
1648     pub features: Option<&'feat Features>,
1649     pub recursion_limit: Limit,
1650     pub trace_mac: bool,
1651     pub should_test: bool,          // If false, strip `#[test]` nodes
1652     pub span_debug: bool,           // If true, use verbose debugging for `proc_macro::Span`
1653     pub proc_macro_backtrace: bool, // If true, show backtraces for proc-macro panics
1654 }
1655
1656 impl<'feat> ExpansionConfig<'feat> {
1657     pub fn default(crate_name: String) -> ExpansionConfig<'static> {
1658         ExpansionConfig {
1659             crate_name,
1660             features: None,
1661             recursion_limit: Limit::new(1024),
1662             trace_mac: false,
1663             should_test: false,
1664             span_debug: false,
1665             proc_macro_backtrace: false,
1666         }
1667     }
1668
1669     fn proc_macro_hygiene(&self) -> bool {
1670         self.features.map_or(false, |features| features.proc_macro_hygiene)
1671     }
1672 }