compiler/rustc_resolve/src/macros.rs

   1 //! A bunch of methods and structures more or less related to resolving macros and
   2 //! interface provided by `Resolver` to macro expander.
   3
   4 use crate::imports::ImportResolver;
   5 use crate::Namespace::*;
   6 use crate::{BuiltinMacroState, Determinacy};
   7 use crate::{DeriveData, Finalize, ParentScope, ResolutionError, Resolver, ScopeSet};
   8 use crate::{ModuleKind, ModuleOrUniformRoot, NameBinding, PathResult, Segment};
   9 use rustc_ast::{self as ast, Inline, ItemKind, ModKind, NodeId};
  10 use rustc_ast_pretty::pprust;
  11 use rustc_attr::StabilityLevel;
  12 use rustc_data_structures::fx::FxHashSet;
  13 use rustc_data_structures::intern::Interned;
  14 use rustc_data_structures::sync::Lrc;
  15 use rustc_errors::{struct_span_err, Applicability};
  16 use rustc_expand::base::{Annotatable, DeriveResolutions, Indeterminate, ResolverExpand};
  17 use rustc_expand::base::{SyntaxExtension, SyntaxExtensionKind};
  18 use rustc_expand::compile_declarative_macro;
  19 use rustc_expand::expand::{AstFragment, Invocation, InvocationKind, SupportsMacroExpansion};
  20 use rustc_hir::def::{self, DefKind, NonMacroAttrKind};
  21 use rustc_hir::def_id::{CrateNum, LocalDefId};
  22 use rustc_middle::middle::stability;
  23 use rustc_middle::ty::RegisteredTools;
  24 use rustc_session::lint::builtin::{LEGACY_DERIVE_HELPERS, SOFT_UNSTABLE};
  25 use rustc_session::lint::builtin::{UNUSED_MACROS, UNUSED_MACRO_RULES};
  26 use rustc_session::lint::BuiltinLintDiagnostics;
  27 use rustc_session::parse::feature_err;
  28 use rustc_session::Session;
  29 use rustc_span::edition::Edition;
  30 use rustc_span::hygiene::{self, ExpnData, ExpnKind, LocalExpnId};
  31 use rustc_span::hygiene::{AstPass, MacroKind};
  32 use rustc_span::symbol::{kw, sym, Ident, Symbol};
  33 use rustc_span::{Span, DUMMY_SP};
  34 use std::cell::Cell;
  35 use std::mem;
  36
  37 type Res = def::Res<NodeId>;
  38
  39 /// Binding produced by a `macro_rules` item.
  40 /// Not modularized, can shadow previous `macro_rules` bindings, etc.
  41 #[derive(Debug)]
  42 pub struct MacroRulesBinding<'a> {
  43     pub(crate) binding: &'a NameBinding<'a>,
  44     /// `macro_rules` scope into which the `macro_rules` item was planted.
  45     pub(crate) parent_macro_rules_scope: MacroRulesScopeRef<'a>,
  46     pub(crate) ident: Ident,
  47 }
  48
  49 /// The scope introduced by a `macro_rules!` macro.
  50 /// This starts at the macro's definition and ends at the end of the macro's parent
  51 /// module (named or unnamed), or even further if it escapes with `#[macro_use]`.
  52 /// Some macro invocations need to introduce `macro_rules` scopes too because they
  53 /// can potentially expand into macro definitions.
  54 #[derive(Copy, Clone, Debug)]
  55 pub enum MacroRulesScope<'a> {
  56     /// Empty "root" scope at the crate start containing no names.
  57     Empty,
  58     /// The scope introduced by a `macro_rules!` macro definition.
  59     Binding(&'a MacroRulesBinding<'a>),
  60     /// The scope introduced by a macro invocation that can potentially
  61     /// create a `macro_rules!` macro definition.
  62     Invocation(LocalExpnId),
  63 }
  64
  65 /// `macro_rules!` scopes are always kept by reference and inside a cell.
  66 /// The reason is that we update scopes with value `MacroRulesScope::Invocation(invoc_id)`
  67 /// in-place after `invoc_id` gets expanded.
  68 /// This helps to avoid uncontrollable growth of `macro_rules!` scope chains,
  69 /// which usually grow linearly with the number of macro invocations
  70 /// in a module (including derives) and hurt performance.
  71 pub(crate) type MacroRulesScopeRef<'a> = Interned<'a, Cell<MacroRulesScope<'a>>>;
  72
  73 /// Macro namespace is separated into two sub-namespaces, one for bang macros and
  74 /// one for attribute-like macros (attributes, derives).
  75 /// We ignore resolutions from one sub-namespace when searching names in scope for another.
  76 pub(crate) fn sub_namespace_match(
  77     candidate: Option<MacroKind>,
  78     requirement: Option<MacroKind>,
  79 ) -> bool {
  80     #[derive(PartialEq)]
  81     enum SubNS {
  82         Bang,
  83         AttrLike,
  84     }
  85     let sub_ns = |kind| match kind {
  86         MacroKind::Bang => SubNS::Bang,
  87         MacroKind::Attr | MacroKind::Derive => SubNS::AttrLike,
  88     };
  89     let candidate = candidate.map(sub_ns);
  90     let requirement = requirement.map(sub_ns);
  91     // "No specific sub-namespace" means "matches anything" for both requirements and candidates.
  92     candidate.is_none() || requirement.is_none() || candidate == requirement
  93 }
  94
  95 // We don't want to format a path using pretty-printing,
  96 // `format!("{}", path)`, because that tries to insert
  97 // line-breaks and is slow.
  98 fn fast_print_path(path: &ast::Path) -> Symbol {
  99     if path.segments.len() == 1 {
 100         path.segments[0].ident.name
 101     } else {
 102         let mut path_str = String::with_capacity(64);
 103         for (i, segment) in path.segments.iter().enumerate() {
 104             if i != 0 {
 105                 path_str.push_str("::");
 106             }
 107             if segment.ident.name != kw::PathRoot {
 108                 path_str.push_str(segment.ident.as_str())
 109             }
 110         }
 111         Symbol::intern(&path_str)
 112     }
 113 }
 114
 115 pub(crate) fn registered_tools(sess: &Session, attrs: &[ast::Attribute]) -> FxHashSet<Ident> {
 116     let mut registered_tools = FxHashSet::default();
 117     for attr in sess.filter_by_name(attrs, sym::register_tool) {
 118         for nested_meta in attr.meta_item_list().unwrap_or_default() {
 119             match nested_meta.ident() {
 120                 Some(ident) => {
 121                     if let Some(old_ident) = registered_tools.replace(ident) {
 122                         let msg = format!("{} `{}` was already registered", "tool", ident);
 123                         sess.struct_span_err(ident.span, &msg)
 124                             .span_label(old_ident.span, "already registered here")
 125                             .emit();
 126                     }
 127                 }
 128                 None => {
 129                     let msg = format!("`{}` only accepts identifiers", sym::register_tool);
 130                     let span = nested_meta.span();
 131                     sess.struct_span_err(span, &msg).span_label(span, "not an identifier").emit();
 132                 }
 133             }
 134         }
 135     }
 136     // We implicitly add `rustfmt` and `clippy` to known tools,
 137     // but it's not an error to register them explicitly.
 138     let predefined_tools = [sym::clippy, sym::rustfmt];
 139     registered_tools.extend(predefined_tools.iter().cloned().map(Ident::with_dummy_span));
 140     registered_tools
 141 }
 142
 143 // Some feature gates for inner attributes are reported as lints for backward compatibility.
 144 fn soft_custom_inner_attributes_gate(path: &ast::Path, invoc: &Invocation) -> bool {
 145     match &path.segments[..] {
 146         // `#![test]`
 147         [seg] if seg.ident.name == sym::test => return true,
 148         // `#![rustfmt::skip]` on out-of-line modules
 149         [seg1, seg2] if seg1.ident.name == sym::rustfmt && seg2.ident.name == sym::skip => {
 150             if let InvocationKind::Attr { item, .. } = &invoc.kind {
 151                 if let Annotatable::Item(item) = item {
 152                     if let ItemKind::Mod(_, ModKind::Loaded(_, Inline::No, _)) = item.kind {
 153                         return true;
 154                     }
 155                 }
 156             }
 157         }
 158         _ => {}
 159     }
 160     false
 161 }
 162
 163 impl<'a> ResolverExpand for Resolver<'a> {
 164     fn next_node_id(&mut self) -> NodeId {
 165         self.next_node_id()
 166     }
 167
 168     fn invocation_parent(&self, id: LocalExpnId) -> LocalDefId {
 169         self.invocation_parents[&id].0
 170     }
 171
 172     fn resolve_dollar_crates(&mut self) {
 173         hygiene::update_dollar_crate_names(|ctxt| {
 174             let ident = Ident::new(kw::DollarCrate, DUMMY_SP.with_ctxt(ctxt));
 175             match self.resolve_crate_root(ident).kind {
 176                 ModuleKind::Def(.., name) if name != kw::Empty => name,
 177                 _ => kw::Crate,
 178             }
 179         });
 180     }
 181
 182     fn visit_ast_fragment_with_placeholders(
 183         &mut self,
 184         expansion: LocalExpnId,
 185         fragment: &AstFragment,
 186     ) {
 187         // Integrate the new AST fragment into all the definition and module structures.
 188         // We are inside the `expansion` now, but other parent scope components are still the same.
 189         let parent_scope = ParentScope { expansion, ..self.invocation_parent_scopes[&expansion] };
 190         let output_macro_rules_scope = self.build_reduced_graph(fragment, parent_scope);
 191         self.output_macro_rules_scopes.insert(expansion, output_macro_rules_scope);
 192
 193         parent_scope.module.unexpanded_invocations.borrow_mut().remove(&expansion);
 194     }
 195
 196     fn register_builtin_macro(&mut self, name: Symbol, ext: SyntaxExtensionKind) {
 197         if self.builtin_macros.insert(name, BuiltinMacroState::NotYetSeen(ext)).is_some() {
 198             self.session
 199                 .diagnostic()
 200                 .bug(&format!("built-in macro `{}` was already registered", name));
 201         }
 202     }
 203
 204     // Create a new Expansion with a definition site of the provided module, or
 205     // a fake empty `#[no_implicit_prelude]` module if no module is provided.
 206     fn expansion_for_ast_pass(
 207         &mut self,
 208         call_site: Span,
 209         pass: AstPass,
 210         features: &[Symbol],
 211         parent_module_id: Option<NodeId>,
 212     ) -> LocalExpnId {
 213         let parent_module =
 214             parent_module_id.map(|module_id| self.local_def_id(module_id).to_def_id());
 215         let expn_id = LocalExpnId::fresh(
 216             ExpnData::allow_unstable(
 217                 ExpnKind::AstPass(pass),
 218                 call_site,
 219                 self.session.edition(),
 220                 features.into(),
 221                 None,
 222                 parent_module,
 223             ),
 224             self.create_stable_hashing_context(),
 225         );
 226
 227         let parent_scope =
 228             parent_module.map_or(self.empty_module, |def_id| self.expect_module(def_id));
 229         self.ast_transform_scopes.insert(expn_id, parent_scope);
 230
 231         expn_id
 232     }
 233
 234     fn resolve_imports(&mut self) {
 235         ImportResolver { r: self }.resolve_imports()
 236     }
 237
 238     fn resolve_macro_invocation(
 239         &mut self,
 240         invoc: &Invocation,
 241         eager_expansion_root: LocalExpnId,
 242         force: bool,
 243     ) -> Result<Lrc<SyntaxExtension>, Indeterminate> {
 244         let invoc_id = invoc.expansion_data.id;
 245         let parent_scope = match self.invocation_parent_scopes.get(&invoc_id) {
 246             Some(parent_scope) => *parent_scope,
 247             None => {
 248                 // If there's no entry in the table, then we are resolving an eagerly expanded
 249                 // macro, which should inherit its parent scope from its eager expansion root -
 250                 // the macro that requested this eager expansion.
 251                 let parent_scope = *self
 252                     .invocation_parent_scopes
 253                     .get(&eager_expansion_root)
 254                     .expect("non-eager expansion without a parent scope");
 255                 self.invocation_parent_scopes.insert(invoc_id, parent_scope);
 256                 parent_scope
 257             }
 258         };
 259
 260         let (path, kind, inner_attr, derives) = match invoc.kind {
 261             InvocationKind::Attr { ref attr, ref derives, .. } => (
 262                 &attr.get_normal_item().path,
 263                 MacroKind::Attr,
 264                 attr.style == ast::AttrStyle::Inner,
 265                 self.arenas.alloc_ast_paths(derives),
 266             ),
 267             InvocationKind::Bang { ref mac, .. } => (&mac.path, MacroKind::Bang, false, &[][..]),
 268             InvocationKind::Derive { ref path, .. } => (path, MacroKind::Derive, false, &[][..]),
 269         };
 270
 271         // Derives are not included when `invocations` are collected, so we have to add them here.
 272         let parent_scope = &ParentScope { derives, ..parent_scope };
 273         let supports_macro_expansion = invoc.fragment_kind.supports_macro_expansion();
 274         let node_id = invoc.expansion_data.lint_node_id;
 275         let (ext, res) = self.smart_resolve_macro_path(
 276             path,
 277             kind,
 278             supports_macro_expansion,
 279             inner_attr,
 280             parent_scope,
 281             node_id,
 282             force,
 283             soft_custom_inner_attributes_gate(path, invoc),
 284         )?;
 285
 286         let span = invoc.span();
 287         let def_id = res.opt_def_id();
 288         invoc_id.set_expn_data(
 289             ext.expn_data(
 290                 parent_scope.expansion,
 291                 span,
 292                 fast_print_path(path),
 293                 def_id,
 294                 def_id.map(|def_id| self.macro_def_scope(def_id).nearest_parent_mod()),
 295             ),
 296             self.create_stable_hashing_context(),
 297         );
 298
 299         Ok(ext)
 300     }
 301
 302     fn record_macro_rule_usage(&mut self, id: NodeId, rule_i: usize) {
 303         let did = self.local_def_id(id);
 304         self.unused_macro_rules.remove(&(did, rule_i));
 305     }
 306
 307     fn check_unused_macros(&mut self) {
 308         for (_, &(node_id, ident)) in self.unused_macros.iter() {
 309             self.lint_buffer.buffer_lint(
 310                 UNUSED_MACROS,
 311                 node_id,
 312                 ident.span,
 313                 &format!("unused macro definition: `{}`", ident.name),
 314             );
 315         }
 316         for (&(def_id, arm_i), &(ident, rule_span)) in self.unused_macro_rules.iter() {
 317             if self.unused_macros.contains_key(&def_id) {
 318                 // We already lint the entire macro as unused
 319                 continue;
 320             }
 321             let node_id = self.def_id_to_node_id[def_id];
 322             self.lint_buffer.buffer_lint(
 323                 UNUSED_MACRO_RULES,
 324                 node_id,
 325                 rule_span,
 326                 &format!(
 327                     "{} rule of macro `{}` is never used",
 328                     crate::diagnostics::ordinalize(arm_i + 1),
 329                     ident.name
 330                 ),
 331             );
 332         }
 333     }
 334
 335     fn has_derive_copy(&self, expn_id: LocalExpnId) -> bool {
 336         self.containers_deriving_copy.contains(&expn_id)
 337     }
 338
 339     fn resolve_derives(
 340         &mut self,
 341         expn_id: LocalExpnId,
 342         force: bool,
 343         derive_paths: &dyn Fn() -> DeriveResolutions,
 344     ) -> Result<(), Indeterminate> {
 345         // Block expansion of the container until we resolve all derives in it.
 346         // This is required for two reasons:
 347         // - Derive helper attributes are in scope for the item to which the `#[derive]`
 348         //   is applied, so they have to be produced by the container's expansion rather
 349         //   than by individual derives.
 350         // - Derives in the container need to know whether one of them is a built-in `Copy`.
 351         // Temporarily take the data to avoid borrow checker conflicts.
 352         let mut derive_data = mem::take(&mut self.derive_data);
 353         let entry = derive_data.entry(expn_id).or_insert_with(|| DeriveData {
 354             resolutions: derive_paths(),
 355             helper_attrs: Vec::new(),
 356             has_derive_copy: false,
 357         });
 358         let parent_scope = self.invocation_parent_scopes[&expn_id];
 359         for (i, (path, _, opt_ext, _)) in entry.resolutions.iter_mut().enumerate() {
 360             if opt_ext.is_none() {
 361                 *opt_ext = Some(
 362                     match self.resolve_macro_path(
 363                         &path,
 364                         Some(MacroKind::Derive),
 365                         &parent_scope,
 366                         true,
 367                         force,
 368                     ) {
 369                         Ok((Some(ext), _)) => {
 370                             if !ext.helper_attrs.is_empty() {
 371                                 let last_seg = path.segments.last().unwrap();
 372                                 let span = last_seg.ident.span.normalize_to_macros_2_0();
 373                                 entry.helper_attrs.extend(
 374                                     ext.helper_attrs
 375                                         .iter()
 376                                         .map(|name| (i, Ident::new(*name, span))),
 377                                 );
 378                             }
 379                             entry.has_derive_copy |= ext.builtin_name == Some(sym::Copy);
 380                             ext
 381                         }
 382                         Ok(_) | Err(Determinacy::Determined) => self.dummy_ext(MacroKind::Derive),
 383                         Err(Determinacy::Undetermined) => {
 384                             assert!(self.derive_data.is_empty());
 385                             self.derive_data = derive_data;
 386                             return Err(Indeterminate);
 387                         }
 388                     },
 389                 );
 390             }
 391         }
 392         // Sort helpers in a stable way independent from the derive resolution order.
 393         entry.helper_attrs.sort_by_key(|(i, _)| *i);
 394         self.helper_attrs
 395             .insert(expn_id, entry.helper_attrs.iter().map(|(_, ident)| *ident).collect());
 396         // Mark this derive as having `Copy` either if it has `Copy` itself or if its parent derive
 397         // has `Copy`, to support cases like `#[derive(Clone, Copy)] #[derive(Debug)]`.
 398         if entry.has_derive_copy || self.has_derive_copy(parent_scope.expansion) {
 399             self.containers_deriving_copy.insert(expn_id);
 400         }
 401         assert!(self.derive_data.is_empty());
 402         self.derive_data = derive_data;
 403         Ok(())
 404     }
 405
 406     fn take_derive_resolutions(&mut self, expn_id: LocalExpnId) -> Option<DeriveResolutions> {
 407         self.derive_data.remove(&expn_id).map(|data| data.resolutions)
 408     }
 409
 410     // The function that implements the resolution logic of `#[cfg_accessible(path)]`.
 411     // Returns true if the path can certainly be resolved in one of three namespaces,
 412     // returns false if the path certainly cannot be resolved in any of the three namespaces.
 413     // Returns `Indeterminate` if we cannot give a certain answer yet.
 414     fn cfg_accessible(
 415         &mut self,
 416         expn_id: LocalExpnId,
 417         path: &ast::Path,
 418     ) -> Result<bool, Indeterminate> {
 419         let span = path.span;
 420         let path = &Segment::from_path(path);
 421         let parent_scope = self.invocation_parent_scopes[&expn_id];
 422
 423         let mut indeterminate = false;
 424         for ns in [TypeNS, ValueNS, MacroNS].iter().copied() {
 425             match self.maybe_resolve_path(path, Some(ns), &parent_scope) {
 426                 PathResult::Module(ModuleOrUniformRoot::Module(_)) => return Ok(true),
 427                 PathResult::NonModule(partial_res) if partial_res.unresolved_segments() == 0 => {
 428                     return Ok(true);
 429                 }
 430                 PathResult::NonModule(..) |
 431                 // HACK(Urgau): This shouldn't be necessary
 432                 PathResult::Failed { is_error_from_last_segment: false, .. } => {
 433                     self.session
 434                         .struct_span_err(span, "not sure whether the path is accessible or not")
 435                         .note("the type may have associated items, but we are currently not checking them")
 436                         .emit();
 437
 438                     // If we get a partially resolved NonModule in one namespace, we should get the
 439                     // same result in any other namespaces, so we can return early.
 440                     return Ok(false);
 441                 }
 442                 PathResult::Indeterminate => indeterminate = true,
 443                 // We can only be sure that a path doesn't exist after having tested all the
 444                 // possibilities, only at that time we can return false.
 445                 PathResult::Failed { .. } => {}
 446                 PathResult::Module(_) => panic!("unexpected path resolution"),
 447             }
 448         }
 449
 450         if indeterminate {
 451             return Err(Indeterminate);
 452         }
 453
 454         Ok(false)
 455     }
 456
 457     fn get_proc_macro_quoted_span(&self, krate: CrateNum, id: usize) -> Span {
 458         self.cstore().get_proc_macro_quoted_span_untracked(krate, id, self.session)
 459     }
 460
 461     fn declare_proc_macro(&mut self, id: NodeId) {
 462         self.proc_macros.push(id)
 463     }
 464
 465     fn registered_tools(&self) -> &RegisteredTools {
 466         &self.registered_tools
 467     }
 468 }
 469
 470 impl<'a> Resolver<'a> {
 471     /// Resolve macro path with error reporting and recovery.
 472     /// Uses dummy syntax extensions for unresolved macros or macros with unexpected resolutions
 473     /// for better error recovery.
 474     fn smart_resolve_macro_path(
 475         &mut self,
 476         path: &ast::Path,
 477         kind: MacroKind,
 478         supports_macro_expansion: SupportsMacroExpansion,
 479         inner_attr: bool,
 480         parent_scope: &ParentScope<'a>,
 481         node_id: NodeId,
 482         force: bool,
 483         soft_custom_inner_attributes_gate: bool,
 484     ) -> Result<(Lrc<SyntaxExtension>, Res), Indeterminate> {
 485         let (ext, res) = match self.resolve_macro_path(path, Some(kind), parent_scope, true, force)
 486         {
 487             Ok((Some(ext), res)) => (ext, res),
 488             Ok((None, res)) => (self.dummy_ext(kind), res),
 489             Err(Determinacy::Determined) => (self.dummy_ext(kind), Res::Err),
 490             Err(Determinacy::Undetermined) => return Err(Indeterminate),
 491         };
 492
 493         // Report errors for the resolved macro.
 494         for segment in &path.segments {
 495             if let Some(args) = &segment.args {
 496                 self.session.span_err(args.span(), "generic arguments in macro path");
 497             }
 498             if kind == MacroKind::Attr && segment.ident.as_str().starts_with("rustc") {
 499                 self.session.span_err(
 500                     segment.ident.span,
 501                     "attributes starting with `rustc` are reserved for use by the `rustc` compiler",
 502                 );
 503             }
 504         }
 505
 506         match res {
 507             Res::Def(DefKind::Macro(_), def_id) => {
 508                 if let Some(def_id) = def_id.as_local() {
 509                     self.unused_macros.remove(&def_id);
 510                     if self.proc_macro_stubs.contains(&def_id) {
 511                         self.session.span_err(
 512                             path.span,
 513                             "can't use a procedural macro from the same crate that defines it",
 514                         );
 515                     }
 516                 }
 517             }
 518             Res::NonMacroAttr(..) | Res::Err => {}
 519             _ => panic!("expected `DefKind::Macro` or `Res::NonMacroAttr`"),
 520         };
 521
 522         self.check_stability_and_deprecation(&ext, path, node_id);
 523
 524         let unexpected_res = if ext.macro_kind() != kind {
 525             Some((kind.article(), kind.descr_expected()))
 526         } else if matches!(res, Res::Def(..)) {
 527             match supports_macro_expansion {
 528                 SupportsMacroExpansion::No => Some(("a", "non-macro attribute")),
 529                 SupportsMacroExpansion::Yes { supports_inner_attrs } => {
 530                     if inner_attr && !supports_inner_attrs {
 531                         Some(("a", "non-macro inner attribute"))
 532                     } else {
 533                         None
 534                     }
 535                 }
 536             }
 537         } else {
 538             None
 539         };
 540         if let Some((article, expected)) = unexpected_res {
 541             let path_str = pprust::path_to_string(path);
 542             let msg = format!("expected {}, found {} `{}`", expected, res.descr(), path_str);
 543             self.session
 544                 .struct_span_err(path.span, &msg)
 545                 .span_label(path.span, format!("not {} {}", article, expected))
 546                 .emit();
 547             return Ok((self.dummy_ext(kind), Res::Err));
 548         }
 549
 550         // We are trying to avoid reporting this error if other related errors were reported.
 551         if res != Res::Err
 552             && inner_attr
 553             && !self.session.features_untracked().custom_inner_attributes
 554         {
 555             let msg = match res {
 556                 Res::Def(..) => "inner macro attributes are unstable",
 557                 Res::NonMacroAttr(..) => "custom inner attributes are unstable",
 558                 _ => unreachable!(),
 559             };
 560             if soft_custom_inner_attributes_gate {
 561                 self.session.parse_sess.buffer_lint(SOFT_UNSTABLE, path.span, node_id, msg);
 562             } else {
 563                 feature_err(&self.session.parse_sess, sym::custom_inner_attributes, path.span, msg)
 564                     .emit();
 565             }
 566         }
 567
 568         Ok((ext, res))
 569     }
 570
 571     pub fn resolve_macro_path(
 572         &mut self,
 573         path: &ast::Path,
 574         kind: Option<MacroKind>,
 575         parent_scope: &ParentScope<'a>,
 576         trace: bool,
 577         force: bool,
 578     ) -> Result<(Option<Lrc<SyntaxExtension>>, Res), Determinacy> {
 579         let path_span = path.span;
 580         let mut path = Segment::from_path(path);
 581
 582         // Possibly apply the macro helper hack
 583         if kind == Some(MacroKind::Bang)
 584             && path.len() == 1
 585             && path[0].ident.span.ctxt().outer_expn_data().local_inner_macros
 586         {
 587             let root = Ident::new(kw::DollarCrate, path[0].ident.span);
 588             path.insert(0, Segment::from_ident(root));
 589         }
 590
 591         let res = if path.len() > 1 {
 592             let res = match self.maybe_resolve_path(&path, Some(MacroNS), parent_scope) {
 593                 PathResult::NonModule(path_res) if let Some(res) = path_res.full_res() => Ok(res),
 594                 PathResult::Indeterminate if !force => return Err(Determinacy::Undetermined),
 595                 PathResult::NonModule(..)
 596                 | PathResult::Indeterminate
 597                 | PathResult::Failed { .. } => Err(Determinacy::Determined),
 598                 PathResult::Module(..) => unreachable!(),
 599             };
 600
 601             if trace {
 602                 let kind = kind.expect("macro kind must be specified if tracing is enabled");
 603                 self.multi_segment_macro_resolutions.push((
 604                     path,
 605                     path_span,
 606                     kind,
 607                     *parent_scope,
 608                     res.ok(),
 609                 ));
 610             }
 611
 612             self.prohibit_imported_non_macro_attrs(None, res.ok(), path_span);
 613             res
 614         } else {
 615             let scope_set = kind.map_or(ScopeSet::All(MacroNS, false), ScopeSet::Macro);
 616             let binding = self.early_resolve_ident_in_lexical_scope(
 617                 path[0].ident,
 618                 scope_set,
 619                 parent_scope,
 620                 None,
 621                 force,
 622                 None,
 623             );
 624             if let Err(Determinacy::Undetermined) = binding {
 625                 return Err(Determinacy::Undetermined);
 626             }
 627
 628             if trace {
 629                 let kind = kind.expect("macro kind must be specified if tracing is enabled");
 630                 self.single_segment_macro_resolutions.push((
 631                     path[0].ident,
 632                     kind,
 633                     *parent_scope,
 634                     binding.ok(),
 635                 ));
 636             }
 637
 638             let res = binding.map(|binding| binding.res());
 639             self.prohibit_imported_non_macro_attrs(binding.ok(), res.ok(), path_span);
 640             res
 641         };
 642
 643         res.map(|res| (self.get_macro(res).map(|macro_data| macro_data.ext), res))
 644     }
 645
 646     pub(crate) fn finalize_macro_resolutions(&mut self) {
 647         let check_consistency = |this: &mut Self,
 648                                  path: &[Segment],
 649                                  span,
 650                                  kind: MacroKind,
 651                                  initial_res: Option<Res>,
 652                                  res: Res| {
 653             if let Some(initial_res) = initial_res {
 654                 if res != initial_res {
 655                     // Make sure compilation does not succeed if preferred macro resolution
 656                     // has changed after the macro had been expanded. In theory all such
 657                     // situations should be reported as errors, so this is a bug.
 658                     this.session.delay_span_bug(span, "inconsistent resolution for a macro");
 659                 }
 660             } else {
 661                 // It's possible that the macro was unresolved (indeterminate) and silently
 662                 // expanded into a dummy fragment for recovery during expansion.
 663                 // Now, post-expansion, the resolution may succeed, but we can't change the
 664                 // past and need to report an error.
 665                 // However, non-speculative `resolve_path` can successfully return private items
 666                 // even if speculative `resolve_path` returned nothing previously, so we skip this
 667                 // less informative error if the privacy error is reported elsewhere.
 668                 if this.privacy_errors.is_empty() {
 669                     let msg = format!(
 670                         "cannot determine resolution for the {} `{}`",
 671                         kind.descr(),
 672                         Segment::names_to_string(path)
 673                     );
 674                     let msg_note = "import resolution is stuck, try simplifying macro imports";
 675                     this.session.struct_span_err(span, &msg).note(msg_note).emit();
 676                 }
 677             }
 678         };
 679
 680         let macro_resolutions = mem::take(&mut self.multi_segment_macro_resolutions);
 681         for (mut path, path_span, kind, parent_scope, initial_res) in macro_resolutions {
 682             // FIXME: Path resolution will ICE if segment IDs present.
 683             for seg in &mut path {
 684                 seg.id = None;
 685             }
 686             match self.resolve_path(
 687                 &path,
 688                 Some(MacroNS),
 689                 &parent_scope,
 690                 Some(Finalize::new(ast::CRATE_NODE_ID, path_span)),
 691                 None,
 692             ) {
 693                 PathResult::NonModule(path_res) if let Some(res) = path_res.full_res() => {
 694                     check_consistency(self, &path, path_span, kind, initial_res, res)
 695                 }
 696                 path_res @ PathResult::NonModule(..) | path_res @ PathResult::Failed { .. } => {
 697                     let mut suggestion = None;
 698                     let (span, label) = if let PathResult::Failed { span, label, .. } = path_res {
 699                         // try to suggest if it's not a macro, maybe a function
 700                         if let PathResult::NonModule(partial_res) = self.maybe_resolve_path(&path, Some(ValueNS), &parent_scope)
 701                             && partial_res.unresolved_segments() == 0 {
 702                             let sm = self.session.source_map();
 703                             let exclamation_span = sm.next_point(span);
 704                             suggestion = Some((
 705                                 vec![(exclamation_span, "".to_string())],
 706                                     format!("{} is not a macro, but a {}, try to remove `!`", Segment::names_to_string(&path), partial_res.base_res().descr()),
 707                                     Applicability::MaybeIncorrect
 708                                 ));
 709                         }
 710                         (span, label)
 711                     } else {
 712                         (
 713                             path_span,
 714                             format!(
 715                                 "partially resolved path in {} {}",
 716                                 kind.article(),
 717                                 kind.descr()
 718                             ),
 719                         )
 720                     };
 721                     self.report_error(
 722                         span,
 723                         ResolutionError::FailedToResolve { label, suggestion },
 724                     );
 725                 }
 726                 PathResult::Module(..) | PathResult::Indeterminate => unreachable!(),
 727             }
 728         }
 729
 730         let macro_resolutions = mem::take(&mut self.single_segment_macro_resolutions);
 731         for (ident, kind, parent_scope, initial_binding) in macro_resolutions {
 732             match self.early_resolve_ident_in_lexical_scope(
 733                 ident,
 734                 ScopeSet::Macro(kind),
 735                 &parent_scope,
 736                 Some(Finalize::new(ast::CRATE_NODE_ID, ident.span)),
 737                 true,
 738                 None,
 739             ) {
 740                 Ok(binding) => {
 741                     let initial_res = initial_binding.map(|initial_binding| {
 742                         self.record_use(ident, initial_binding, false);
 743                         initial_binding.res()
 744                     });
 745                     let res = binding.res();
 746                     let seg = Segment::from_ident(ident);
 747                     check_consistency(self, &[seg], ident.span, kind, initial_res, res);
 748                     if res == Res::NonMacroAttr(NonMacroAttrKind::DeriveHelperCompat) {
 749                         let node_id = self
 750                             .invocation_parents
 751                             .get(&parent_scope.expansion)
 752                             .map_or(ast::CRATE_NODE_ID, |id| self.def_id_to_node_id[id.0]);
 753                         self.lint_buffer.buffer_lint_with_diagnostic(
 754                             LEGACY_DERIVE_HELPERS,
 755                             node_id,
 756                             ident.span,
 757                             "derive helper attribute is used before it is introduced",
 758                             BuiltinLintDiagnostics::LegacyDeriveHelpers(binding.span),
 759                         );
 760                     }
 761                 }
 762                 Err(..) => {
 763                     let expected = kind.descr_expected();
 764                     let msg = format!("cannot find {} `{}` in this scope", expected, ident);
 765                     let mut err = self.session.struct_span_err(ident.span, &msg);
 766                     self.unresolved_macro_suggestions(&mut err, kind, &parent_scope, ident);
 767                     err.emit();
 768                 }
 769             }
 770         }
 771
 772         let builtin_attrs = mem::take(&mut self.builtin_attrs);
 773         for (ident, parent_scope) in builtin_attrs {
 774             let _ = self.early_resolve_ident_in_lexical_scope(
 775                 ident,
 776                 ScopeSet::Macro(MacroKind::Attr),
 777                 &parent_scope,
 778                 Some(Finalize::new(ast::CRATE_NODE_ID, ident.span)),
 779                 true,
 780                 None,
 781             );
 782         }
 783     }
 784
 785     fn check_stability_and_deprecation(
 786         &mut self,
 787         ext: &SyntaxExtension,
 788         path: &ast::Path,
 789         node_id: NodeId,
 790     ) {
 791         let span = path.span;
 792         if let Some(stability) = &ext.stability {
 793             if let StabilityLevel::Unstable { reason, issue, is_soft, implied_by } = stability.level
 794             {
 795                 let feature = stability.feature;
 796
 797                 let is_allowed = |feature| {
 798                     self.active_features.contains(&feature) || span.allows_unstable(feature)
 799                 };
 800                 let allowed_by_implication =
 801                     implied_by.map(|feature| is_allowed(feature)).unwrap_or(false);
 802                 if !is_allowed(feature) && !allowed_by_implication {
 803                     let lint_buffer = &mut self.lint_buffer;
 804                     let soft_handler =
 805                         |lint, span, msg: &_| lint_buffer.buffer_lint(lint, node_id, span, msg);
 806                     stability::report_unstable(
 807                         self.session,
 808                         feature,
 809                         reason.to_opt_reason(),
 810                         issue,
 811                         None,
 812                         is_soft,
 813                         span,
 814                         soft_handler,
 815                     );
 816                 }
 817             }
 818         }
 819         if let Some(depr) = &ext.deprecation {
 820             let path = pprust::path_to_string(&path);
 821             let (message, lint) = stability::deprecation_message_and_lint(depr, "macro", &path);
 822             stability::early_report_deprecation(
 823                 &mut self.lint_buffer,
 824                 &message,
 825                 depr.suggestion,
 826                 lint,
 827                 span,
 828                 node_id,
 829             );
 830         }
 831     }
 832
 833     fn prohibit_imported_non_macro_attrs(
 834         &self,
 835         binding: Option<&'a NameBinding<'a>>,
 836         res: Option<Res>,
 837         span: Span,
 838     ) {
 839         if let Some(Res::NonMacroAttr(kind)) = res {
 840             if kind != NonMacroAttrKind::Tool && binding.map_or(true, |b| b.is_import()) {
 841                 let msg =
 842                     format!("cannot use {} {} through an import", kind.article(), kind.descr());
 843                 let mut err = self.session.struct_span_err(span, &msg);
 844                 if let Some(binding) = binding {
 845                     err.span_note(binding.span, &format!("the {} imported here", kind.descr()));
 846                 }
 847                 err.emit();
 848             }
 849         }
 850     }
 851
 852     pub(crate) fn check_reserved_macro_name(&mut self, ident: Ident, res: Res) {
 853         // Reserve some names that are not quite covered by the general check
 854         // performed on `Resolver::builtin_attrs`.
 855         if ident.name == sym::cfg || ident.name == sym::cfg_attr {
 856             let macro_kind = self.get_macro(res).map(|macro_data| macro_data.ext.macro_kind());
 857             if macro_kind.is_some() && sub_namespace_match(macro_kind, Some(MacroKind::Attr)) {
 858                 self.session.span_err(
 859                     ident.span,
 860                     &format!("name `{}` is reserved in attribute namespace", ident),
 861                 );
 862             }
 863         }
 864     }
 865
 866     /// Compile the macro into a `SyntaxExtension` and its rule spans.
 867     ///
 868     /// Possibly replace its expander to a pre-defined one for built-in macros.
 869     pub(crate) fn compile_macro(
 870         &mut self,
 871         item: &ast::Item,
 872         edition: Edition,
 873     ) -> (SyntaxExtension, Vec<(usize, Span)>) {
 874         let (mut result, mut rule_spans) = compile_declarative_macro(
 875             &self.session,
 876             self.session.features_untracked(),
 877             item,
 878             edition,
 879         );
 880
 881         if let Some(builtin_name) = result.builtin_name {
 882             // The macro was marked with `#[rustc_builtin_macro]`.
 883             if let Some(builtin_macro) = self.builtin_macros.get_mut(&builtin_name) {
 884                 // The macro is a built-in, replace its expander function
 885                 // while still taking everything else from the source code.
 886                 // If we already loaded this builtin macro, give a better error message than 'no such builtin macro'.
 887                 match mem::replace(builtin_macro, BuiltinMacroState::AlreadySeen(item.span)) {
 888                     BuiltinMacroState::NotYetSeen(ext) => {
 889                         result.kind = ext;
 890                         rule_spans = Vec::new();
 891                         if item.id != ast::DUMMY_NODE_ID {
 892                             self.builtin_macro_kinds
 893                                 .insert(self.local_def_id(item.id), result.macro_kind());
 894                         }
 895                     }
 896                     BuiltinMacroState::AlreadySeen(span) => {
 897                         struct_span_err!(
 898                             self.session,
 899                             item.span,
 900                             E0773,
 901                             "attempted to define built-in macro more than once"
 902                         )
 903                         .span_note(span, "previously defined here")
 904                         .emit();
 905                     }
 906                 }
 907             } else {
 908                 let msg = format!("cannot find a built-in macro with name `{}`", item.ident);
 909                 self.session.span_err(item.span, &msg);
 910             }
 911         }
 912
 913         (result, rule_spans)
 914     }
 915 }