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::{AmbiguityError, AmbiguityErrorMisc, AmbiguityKind, BuiltinMacroState, Determinacy};
   7 use crate::{CrateLint, DeriveData, ParentScope, ResolutionError, Resolver, Scope, ScopeSet, Weak};
   8 use crate::{ModuleKind, ModuleOrUniformRoot, NameBinding, PathResult, Segment, ToNameBinding};
   9 use rustc_ast::{self as ast, Inline, ItemKind, ModKind, NodeId};
  10 use rustc_ast_lowering::ResolverAstLowering;
  11 use rustc_ast_pretty::pprust;
  12 use rustc_attr::StabilityLevel;
  13 use rustc_data_structures::fx::FxHashSet;
  14 use rustc_data_structures::ptr_key::PtrKey;
  15 use rustc_data_structures::sync::Lrc;
  16 use rustc_errors::struct_span_err;
  17 use rustc_expand::base::{Annotatable, DeriveResolutions, Indeterminate, ResolverExpand};
  18 use rustc_expand::base::{SyntaxExtension, SyntaxExtensionKind};
  19 use rustc_expand::compile_declarative_macro;
  20 use rustc_expand::expand::{AstFragment, Invocation, InvocationKind, SupportsMacroExpansion};
  21 use rustc_feature::is_builtin_attr_name;
  22 use rustc_hir::def::{self, DefKind, NonMacroAttrKind};
  23 use rustc_hir::def_id::{CrateNum, LocalDefId};
  24 use rustc_hir::PrimTy;
  25 use rustc_middle::middle::stability;
  26 use rustc_middle::ty;
  27 use rustc_session::lint::builtin::{LEGACY_DERIVE_HELPERS, PROC_MACRO_DERIVE_RESOLUTION_FALLBACK};
  28 use rustc_session::lint::builtin::{SOFT_UNSTABLE, UNUSED_MACROS};
  29 use rustc_session::lint::BuiltinLintDiagnostics;
  30 use rustc_session::parse::feature_err;
  31 use rustc_session::Session;
  32 use rustc_span::edition::Edition;
  33 use rustc_span::hygiene::{self, ExpnData, ExpnKind, LocalExpnId};
  34 use rustc_span::hygiene::{AstPass, MacroKind};
  35 use rustc_span::symbol::{kw, sym, Ident, Symbol};
  36 use rustc_span::{Span, DUMMY_SP};
  37 use std::cell::Cell;
  38 use std::{mem, ptr};
  39
  40 type Res = def::Res<NodeId>;
  41
  42 /// Binding produced by a `macro_rules` item.
  43 /// Not modularized, can shadow previous `macro_rules` bindings, etc.
  44 #[derive(Debug)]
  45 pub struct MacroRulesBinding<'a> {
  46     crate binding: &'a NameBinding<'a>,
  47     /// `macro_rules` scope into which the `macro_rules` item was planted.
  48     crate parent_macro_rules_scope: MacroRulesScopeRef<'a>,
  49     crate ident: Ident,
  50 }
  51
  52 /// The scope introduced by a `macro_rules!` macro.
  53 /// This starts at the macro's definition and ends at the end of the macro's parent
  54 /// module (named or unnamed), or even further if it escapes with `#[macro_use]`.
  55 /// Some macro invocations need to introduce `macro_rules` scopes too because they
  56 /// can potentially expand into macro definitions.
  57 #[derive(Copy, Clone, Debug)]
  58 pub enum MacroRulesScope<'a> {
  59     /// Empty "root" scope at the crate start containing no names.
  60     Empty,
  61     /// The scope introduced by a `macro_rules!` macro definition.
  62     Binding(&'a MacroRulesBinding<'a>),
  63     /// The scope introduced by a macro invocation that can potentially
  64     /// create a `macro_rules!` macro definition.
  65     Invocation(LocalExpnId),
  66 }
  67
  68 /// `macro_rules!` scopes are always kept by reference and inside a cell.
  69 /// The reason is that we update scopes with value `MacroRulesScope::Invocation(invoc_id)`
  70 /// in-place after `invoc_id` gets expanded.
  71 /// This helps to avoid uncontrollable growth of `macro_rules!` scope chains,
  72 /// which usually grow lineraly with the number of macro invocations
  73 /// in a module (including derives) and hurt performance.
  74 pub(crate) type MacroRulesScopeRef<'a> = PtrKey<'a, Cell<MacroRulesScope<'a>>>;
  75
  76 // Macro namespace is separated into two sub-namespaces, one for bang macros and
  77 // one for attribute-like macros (attributes, derives).
  78 // We ignore resolutions from one sub-namespace when searching names in scope for another.
  79 fn sub_namespace_match(candidate: Option<MacroKind>, requirement: Option<MacroKind>) -> 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 /// The code common between processing `#![register_tool]` and `#![register_attr]`.
 116 fn registered_idents(
 117     sess: &Session,
 118     attrs: &[ast::Attribute],
 119     attr_name: Symbol,
 120     descr: &str,
 121 ) -> FxHashSet<Ident> {
 122     let mut registered = FxHashSet::default();
 123     for attr in sess.filter_by_name(attrs, attr_name) {
 124         for nested_meta in attr.meta_item_list().unwrap_or_default() {
 125             match nested_meta.ident() {
 126                 Some(ident) => {
 127                     if let Some(old_ident) = registered.replace(ident) {
 128                         let msg = format!("{} `{}` was already registered", descr, ident);
 129                         sess.struct_span_err(ident.span, &msg)
 130                             .span_label(old_ident.span, "already registered here")
 131                             .emit();
 132                     }
 133                 }
 134                 None => {
 135                     let msg = format!("`{}` only accepts identifiers", attr_name);
 136                     let span = nested_meta.span();
 137                     sess.struct_span_err(span, &msg).span_label(span, "not an identifier").emit();
 138                 }
 139             }
 140         }
 141     }
 142     registered
 143 }
 144
 145 crate fn registered_attrs_and_tools(
 146     sess: &Session,
 147     attrs: &[ast::Attribute],
 148 ) -> (FxHashSet<Ident>, FxHashSet<Ident>) {
 149     let registered_attrs = registered_idents(sess, attrs, sym::register_attr, "attribute");
 150     let mut registered_tools = registered_idents(sess, attrs, sym::register_tool, "tool");
 151     // We implicitly add `rustfmt` and `clippy` to known tools,
 152     // but it's not an error to register them explicitly.
 153     let predefined_tools = [sym::clippy, sym::rustfmt];
 154     registered_tools.extend(predefined_tools.iter().cloned().map(Ident::with_dummy_span));
 155     (registered_attrs, registered_tools)
 156 }
 157
 158 // Some feature gates for inner attributes are reported as lints for backward compatibility.
 159 fn soft_custom_inner_attributes_gate(path: &ast::Path, invoc: &Invocation) -> bool {
 160     match &path.segments[..] {
 161         // `#![test]`
 162         [seg] if seg.ident.name == sym::test => return true,
 163         // `#![rustfmt::skip]` on out-of-line modules
 164         [seg1, seg2] if seg1.ident.name == sym::rustfmt && seg2.ident.name == sym::skip => {
 165             if let InvocationKind::Attr { item, .. } = &invoc.kind {
 166                 if let Annotatable::Item(item) = item {
 167                     if let ItemKind::Mod(_, ModKind::Loaded(_, Inline::No, _)) = item.kind {
 168                         return true;
 169                     }
 170                 }
 171             }
 172         }
 173         _ => {}
 174     }
 175     false
 176 }
 177
 178 impl<'a> ResolverExpand for Resolver<'a> {
 179     fn next_node_id(&mut self) -> NodeId {
 180         self.next_node_id()
 181     }
 182
 183     fn invocation_parent(&self, id: LocalExpnId) -> LocalDefId {
 184         self.invocation_parents[&id].0
 185     }
 186
 187     fn resolve_dollar_crates(&mut self) {
 188         hygiene::update_dollar_crate_names(|ctxt| {
 189             let ident = Ident::new(kw::DollarCrate, DUMMY_SP.with_ctxt(ctxt));
 190             match self.resolve_crate_root(ident).kind {
 191                 ModuleKind::Def(.., name) if name != kw::Empty => name,
 192                 _ => kw::Crate,
 193             }
 194         });
 195     }
 196
 197     fn visit_ast_fragment_with_placeholders(
 198         &mut self,
 199         expansion: LocalExpnId,
 200         fragment: &AstFragment,
 201     ) {
 202         // Integrate the new AST fragment into all the definition and module structures.
 203         // We are inside the `expansion` now, but other parent scope components are still the same.
 204         let parent_scope = ParentScope { expansion, ..self.invocation_parent_scopes[&expansion] };
 205         let output_macro_rules_scope = self.build_reduced_graph(fragment, parent_scope);
 206         self.output_macro_rules_scopes.insert(expansion, output_macro_rules_scope);
 207
 208         parent_scope.module.unexpanded_invocations.borrow_mut().remove(&expansion);
 209     }
 210
 211     fn register_builtin_macro(&mut self, name: Symbol, ext: SyntaxExtensionKind) {
 212         if self.builtin_macros.insert(name, BuiltinMacroState::NotYetSeen(ext)).is_some() {
 213             self.session
 214                 .diagnostic()
 215                 .bug(&format!("built-in macro `{}` was already registered", name));
 216         }
 217     }
 218
 219     // Create a new Expansion with a definition site of the provided module, or
 220     // a fake empty `#[no_implicit_prelude]` module if no module is provided.
 221     fn expansion_for_ast_pass(
 222         &mut self,
 223         call_site: Span,
 224         pass: AstPass,
 225         features: &[Symbol],
 226         parent_module_id: Option<NodeId>,
 227     ) -> LocalExpnId {
 228         let parent_module =
 229             parent_module_id.map(|module_id| self.local_def_id(module_id).to_def_id());
 230         let expn_id = LocalExpnId::fresh(
 231             ExpnData::allow_unstable(
 232                 ExpnKind::AstPass(pass),
 233                 call_site,
 234                 self.session.edition(),
 235                 features.into(),
 236                 None,
 237                 parent_module,
 238             ),
 239             self.create_stable_hashing_context(),
 240         );
 241
 242         let parent_scope =
 243             parent_module.map_or(self.empty_module, |def_id| self.expect_module(def_id));
 244         self.ast_transform_scopes.insert(expn_id, parent_scope);
 245
 246         expn_id
 247     }
 248
 249     fn resolve_imports(&mut self) {
 250         ImportResolver { r: self }.resolve_imports()
 251     }
 252
 253     fn resolve_macro_invocation(
 254         &mut self,
 255         invoc: &Invocation,
 256         eager_expansion_root: LocalExpnId,
 257         force: bool,
 258     ) -> Result<Lrc<SyntaxExtension>, Indeterminate> {
 259         let invoc_id = invoc.expansion_data.id;
 260         let parent_scope = match self.invocation_parent_scopes.get(&invoc_id) {
 261             Some(parent_scope) => *parent_scope,
 262             None => {
 263                 // If there's no entry in the table, then we are resolving an eagerly expanded
 264                 // macro, which should inherit its parent scope from its eager expansion root -
 265                 // the macro that requested this eager expansion.
 266                 let parent_scope = *self
 267                     .invocation_parent_scopes
 268                     .get(&eager_expansion_root)
 269                     .expect("non-eager expansion without a parent scope");
 270                 self.invocation_parent_scopes.insert(invoc_id, parent_scope);
 271                 parent_scope
 272             }
 273         };
 274
 275         let (path, kind, inner_attr, derives) = match invoc.kind {
 276             InvocationKind::Attr { ref attr, ref derives, .. } => (
 277                 &attr.get_normal_item().path,
 278                 MacroKind::Attr,
 279                 attr.style == ast::AttrStyle::Inner,
 280                 self.arenas.alloc_ast_paths(derives),
 281             ),
 282             InvocationKind::Bang { ref mac, .. } => (&mac.path, MacroKind::Bang, false, &[][..]),
 283             InvocationKind::Derive { ref path, .. } => (path, MacroKind::Derive, false, &[][..]),
 284         };
 285
 286         // Derives are not included when `invocations` are collected, so we have to add them here.
 287         let parent_scope = &ParentScope { derives, ..parent_scope };
 288         let supports_macro_expansion = invoc.fragment_kind.supports_macro_expansion();
 289         let node_id = invoc.expansion_data.lint_node_id;
 290         let (ext, res) = self.smart_resolve_macro_path(
 291             path,
 292             kind,
 293             supports_macro_expansion,
 294             inner_attr,
 295             parent_scope,
 296             node_id,
 297             force,
 298             soft_custom_inner_attributes_gate(path, invoc),
 299         )?;
 300
 301         let span = invoc.span();
 302         let def_id = res.opt_def_id();
 303         invoc_id.set_expn_data(
 304             ext.expn_data(
 305                 parent_scope.expansion,
 306                 span,
 307                 fast_print_path(path),
 308                 def_id,
 309                 def_id.map(|def_id| self.macro_def_scope(def_id).nearest_parent_mod()),
 310             ),
 311             self.create_stable_hashing_context(),
 312         );
 313
 314         Ok(ext)
 315     }
 316
 317     fn check_unused_macros(&mut self) {
 318         for (_, &(node_id, ident)) in self.unused_macros.iter() {
 319             self.lint_buffer.buffer_lint(
 320                 UNUSED_MACROS,
 321                 node_id,
 322                 ident.span,
 323                 &format!("unused macro definition: `{}`", ident.as_str()),
 324             );
 325         }
 326     }
 327
 328     fn has_derive_copy(&self, expn_id: LocalExpnId) -> bool {
 329         self.containers_deriving_copy.contains(&expn_id)
 330     }
 331
 332     fn resolve_derives(
 333         &mut self,
 334         expn_id: LocalExpnId,
 335         force: bool,
 336         derive_paths: &dyn Fn() -> DeriveResolutions,
 337     ) -> Result<(), Indeterminate> {
 338         // Block expansion of the container until we resolve all derives in it.
 339         // This is required for two reasons:
 340         // - Derive helper attributes are in scope for the item to which the `#[derive]`
 341         //   is applied, so they have to be produced by the container's expansion rather
 342         //   than by individual derives.
 343         // - Derives in the container need to know whether one of them is a built-in `Copy`.
 344         // Temporarily take the data to avoid borrow checker conflicts.
 345         let mut derive_data = mem::take(&mut self.derive_data);
 346         let entry = derive_data.entry(expn_id).or_insert_with(|| DeriveData {
 347             resolutions: derive_paths(),
 348             helper_attrs: Vec::new(),
 349             has_derive_copy: false,
 350         });
 351         let parent_scope = self.invocation_parent_scopes[&expn_id];
 352         for (i, (path, _, opt_ext)) in entry.resolutions.iter_mut().enumerate() {
 353             if opt_ext.is_none() {
 354                 *opt_ext = Some(
 355                     match self.resolve_macro_path(
 356                         &path,
 357                         Some(MacroKind::Derive),
 358                         &parent_scope,
 359                         true,
 360                         force,
 361                     ) {
 362                         Ok((Some(ext), _)) => {
 363                             if !ext.helper_attrs.is_empty() {
 364                                 let last_seg = path.segments.last().unwrap();
 365                                 let span = last_seg.ident.span.normalize_to_macros_2_0();
 366                                 entry.helper_attrs.extend(
 367                                     ext.helper_attrs
 368                                         .iter()
 369                                         .map(|name| (i, Ident::new(*name, span))),
 370                                 );
 371                             }
 372                             entry.has_derive_copy |= ext.builtin_name == Some(sym::Copy);
 373                             ext
 374                         }
 375                         Ok(_) | Err(Determinacy::Determined) => self.dummy_ext(MacroKind::Derive),
 376                         Err(Determinacy::Undetermined) => {
 377                             assert!(self.derive_data.is_empty());
 378                             self.derive_data = derive_data;
 379                             return Err(Indeterminate);
 380                         }
 381                     },
 382                 );
 383             }
 384         }
 385         // Sort helpers in a stable way independent from the derive resolution order.
 386         entry.helper_attrs.sort_by_key(|(i, _)| *i);
 387         self.helper_attrs
 388             .insert(expn_id, entry.helper_attrs.iter().map(|(_, ident)| *ident).collect());
 389         // Mark this derive as having `Copy` either if it has `Copy` itself or if its parent derive
 390         // has `Copy`, to support cases like `#[derive(Clone, Copy)] #[derive(Debug)]`.
 391         if entry.has_derive_copy || self.has_derive_copy(parent_scope.expansion) {
 392             self.containers_deriving_copy.insert(expn_id);
 393         }
 394         assert!(self.derive_data.is_empty());
 395         self.derive_data = derive_data;
 396         Ok(())
 397     }
 398
 399     fn take_derive_resolutions(&mut self, expn_id: LocalExpnId) -> Option<DeriveResolutions> {
 400         self.derive_data.remove(&expn_id).map(|data| data.resolutions)
 401     }
 402
 403     // The function that implements the resolution logic of `#[cfg_accessible(path)]`.
 404     // Returns true if the path can certainly be resolved in one of three namespaces,
 405     // returns false if the path certainly cannot be resolved in any of the three namespaces.
 406     // Returns `Indeterminate` if we cannot give a certain answer yet.
 407     fn cfg_accessible(
 408         &mut self,
 409         expn_id: LocalExpnId,
 410         path: &ast::Path,
 411     ) -> Result<bool, Indeterminate> {
 412         let span = path.span;
 413         let path = &Segment::from_path(path);
 414         let parent_scope = self.invocation_parent_scopes[&expn_id];
 415
 416         let mut indeterminate = false;
 417         for ns in [TypeNS, ValueNS, MacroNS].iter().copied() {
 418             match self.resolve_path(path, Some(ns), &parent_scope, false, span, CrateLint::No) {
 419                 PathResult::Module(ModuleOrUniformRoot::Module(_)) => return Ok(true),
 420                 PathResult::NonModule(partial_res) if partial_res.unresolved_segments() == 0 => {
 421                     return Ok(true);
 422                 }
 423                 PathResult::Indeterminate => indeterminate = true,
 424                 // FIXME: `resolve_path` is not ready to report partially resolved paths
 425                 // correctly, so we just report an error if the path was reported as unresolved.
 426                 // This needs to be fixed for `cfg_accessible` to be useful.
 427                 PathResult::NonModule(..) | PathResult::Failed { .. } => {}
 428                 PathResult::Module(_) => panic!("unexpected path resolution"),
 429             }
 430         }
 431
 432         if indeterminate {
 433             return Err(Indeterminate);
 434         }
 435
 436         self.session
 437             .struct_span_err(span, "not sure whether the path is accessible or not")
 438             .span_note(span, "`cfg_accessible` is not fully implemented")
 439             .emit();
 440         Ok(false)
 441     }
 442
 443     fn get_proc_macro_quoted_span(&self, krate: CrateNum, id: usize) -> Span {
 444         self.crate_loader.cstore().get_proc_macro_quoted_span_untracked(krate, id, self.session)
 445     }
 446
 447     fn declare_proc_macro(&mut self, id: NodeId) {
 448         self.proc_macros.push(id)
 449     }
 450 }
 451
 452 impl<'a> Resolver<'a> {
 453     /// Resolve macro path with error reporting and recovery.
 454     /// Uses dummy syntax extensions for unresolved macros or macros with unexpected resolutions
 455     /// for better error recovery.
 456     fn smart_resolve_macro_path(
 457         &mut self,
 458         path: &ast::Path,
 459         kind: MacroKind,
 460         supports_macro_expansion: SupportsMacroExpansion,
 461         inner_attr: bool,
 462         parent_scope: &ParentScope<'a>,
 463         node_id: NodeId,
 464         force: bool,
 465         soft_custom_inner_attributes_gate: bool,
 466     ) -> Result<(Lrc<SyntaxExtension>, Res), Indeterminate> {
 467         let (ext, res) = match self.resolve_macro_path(path, Some(kind), parent_scope, true, force)
 468         {
 469             Ok((Some(ext), res)) => (ext, res),
 470             Ok((None, res)) => (self.dummy_ext(kind), res),
 471             Err(Determinacy::Determined) => (self.dummy_ext(kind), Res::Err),
 472             Err(Determinacy::Undetermined) => return Err(Indeterminate),
 473         };
 474
 475         // Report errors for the resolved macro.
 476         for segment in &path.segments {
 477             if let Some(args) = &segment.args {
 478                 self.session.span_err(args.span(), "generic arguments in macro path");
 479             }
 480             if kind == MacroKind::Attr && segment.ident.as_str().starts_with("rustc") {
 481                 self.session.span_err(
 482                     segment.ident.span,
 483                     "attributes starting with `rustc` are reserved for use by the `rustc` compiler",
 484                 );
 485             }
 486         }
 487
 488         match res {
 489             Res::Def(DefKind::Macro(_), def_id) => {
 490                 if let Some(def_id) = def_id.as_local() {
 491                     self.unused_macros.remove(&def_id);
 492                     if self.proc_macro_stubs.contains(&def_id) {
 493                         self.session.span_err(
 494                             path.span,
 495                             "can't use a procedural macro from the same crate that defines it",
 496                         );
 497                     }
 498                 }
 499             }
 500             Res::NonMacroAttr(..) | Res::Err => {}
 501             _ => panic!("expected `DefKind::Macro` or `Res::NonMacroAttr`"),
 502         };
 503
 504         self.check_stability_and_deprecation(&ext, path, node_id);
 505
 506         let unexpected_res = if ext.macro_kind() != kind {
 507             Some((kind.article(), kind.descr_expected()))
 508         } else if matches!(res, Res::Def(..)) {
 509             match supports_macro_expansion {
 510                 SupportsMacroExpansion::No => Some(("a", "non-macro attribute")),
 511                 SupportsMacroExpansion::Yes { supports_inner_attrs } => {
 512                     if inner_attr && !supports_inner_attrs {
 513                         Some(("a", "non-macro inner attribute"))
 514                     } else {
 515                         None
 516                     }
 517                 }
 518             }
 519         } else {
 520             None
 521         };
 522         if let Some((article, expected)) = unexpected_res {
 523             let path_str = pprust::path_to_string(path);
 524             let msg = format!("expected {}, found {} `{}`", expected, res.descr(), path_str);
 525             self.session
 526                 .struct_span_err(path.span, &msg)
 527                 .span_label(path.span, format!("not {} {}", article, expected))
 528                 .emit();
 529             return Ok((self.dummy_ext(kind), Res::Err));
 530         }
 531
 532         // We are trying to avoid reporting this error if other related errors were reported.
 533         if res != Res::Err
 534             && inner_attr
 535             && !self.session.features_untracked().custom_inner_attributes
 536         {
 537             let msg = match res {
 538                 Res::Def(..) => "inner macro attributes are unstable",
 539                 Res::NonMacroAttr(..) => "custom inner attributes are unstable",
 540                 _ => unreachable!(),
 541             };
 542             if soft_custom_inner_attributes_gate {
 543                 self.session.parse_sess.buffer_lint(SOFT_UNSTABLE, path.span, node_id, msg);
 544             } else {
 545                 feature_err(&self.session.parse_sess, sym::custom_inner_attributes, path.span, msg)
 546                     .emit();
 547             }
 548         }
 549
 550         Ok((ext, res))
 551     }
 552
 553     pub fn resolve_macro_path(
 554         &mut self,
 555         path: &ast::Path,
 556         kind: Option<MacroKind>,
 557         parent_scope: &ParentScope<'a>,
 558         trace: bool,
 559         force: bool,
 560     ) -> Result<(Option<Lrc<SyntaxExtension>>, Res), Determinacy> {
 561         let path_span = path.span;
 562         let mut path = Segment::from_path(path);
 563
 564         // Possibly apply the macro helper hack
 565         if kind == Some(MacroKind::Bang)
 566             && path.len() == 1
 567             && path[0].ident.span.ctxt().outer_expn_data().local_inner_macros
 568         {
 569             let root = Ident::new(kw::DollarCrate, path[0].ident.span);
 570             path.insert(0, Segment::from_ident(root));
 571         }
 572
 573         let res = if path.len() > 1 {
 574             let res = match self.resolve_path(
 575                 &path,
 576                 Some(MacroNS),
 577                 parent_scope,
 578                 false,
 579                 path_span,
 580                 CrateLint::No,
 581             ) {
 582                 PathResult::NonModule(path_res) if path_res.unresolved_segments() == 0 => {
 583                     Ok(path_res.base_res())
 584                 }
 585                 PathResult::Indeterminate if !force => return Err(Determinacy::Undetermined),
 586                 PathResult::NonModule(..)
 587                 | PathResult::Indeterminate
 588                 | PathResult::Failed { .. } => Err(Determinacy::Determined),
 589                 PathResult::Module(..) => unreachable!(),
 590             };
 591
 592             if trace {
 593                 let kind = kind.expect("macro kind must be specified if tracing is enabled");
 594                 self.multi_segment_macro_resolutions.push((
 595                     path,
 596                     path_span,
 597                     kind,
 598                     *parent_scope,
 599                     res.ok(),
 600                 ));
 601             }
 602
 603             self.prohibit_imported_non_macro_attrs(None, res.ok(), path_span);
 604             res
 605         } else {
 606             let scope_set = kind.map_or(ScopeSet::All(MacroNS, false), ScopeSet::Macro);
 607             let binding = self.early_resolve_ident_in_lexical_scope(
 608                 path[0].ident,
 609                 scope_set,
 610                 parent_scope,
 611                 false,
 612                 force,
 613                 path_span,
 614             );
 615             if let Err(Determinacy::Undetermined) = binding {
 616                 return Err(Determinacy::Undetermined);
 617             }
 618
 619             if trace {
 620                 let kind = kind.expect("macro kind must be specified if tracing is enabled");
 621                 self.single_segment_macro_resolutions.push((
 622                     path[0].ident,
 623                     kind,
 624                     *parent_scope,
 625                     binding.ok(),
 626                 ));
 627             }
 628
 629             let res = binding.map(|binding| binding.res());
 630             self.prohibit_imported_non_macro_attrs(binding.ok(), res.ok(), path_span);
 631             res
 632         };
 633
 634         res.map(|res| (self.get_macro(res), res))
 635     }
 636
 637     // Resolve an identifier in lexical scope.
 638     // This is a variation of `fn resolve_ident_in_lexical_scope` that can be run during
 639     // expansion and import resolution (perhaps they can be merged in the future).
 640     // The function is used for resolving initial segments of macro paths (e.g., `foo` in
 641     // `foo::bar!(); or `foo!();`) and also for import paths on 2018 edition.
 642     crate fn early_resolve_ident_in_lexical_scope(
 643         &mut self,
 644         orig_ident: Ident,
 645         scope_set: ScopeSet<'a>,
 646         parent_scope: &ParentScope<'a>,
 647         record_used: bool,
 648         force: bool,
 649         path_span: Span,
 650     ) -> Result<&'a NameBinding<'a>, Determinacy> {
 651         bitflags::bitflags! {
 652             struct Flags: u8 {
 653                 const MACRO_RULES          = 1 << 0;
 654                 const MODULE               = 1 << 1;
 655                 const MISC_SUGGEST_CRATE   = 1 << 2;
 656                 const MISC_SUGGEST_SELF    = 1 << 3;
 657                 const MISC_FROM_PRELUDE    = 1 << 4;
 658             }
 659         }
 660
 661         assert!(force || !record_used); // `record_used` implies `force`
 662
 663         // Make sure `self`, `super` etc produce an error when passed to here.
 664         if orig_ident.is_path_segment_keyword() {
 665             return Err(Determinacy::Determined);
 666         }
 667
 668         let (ns, macro_kind, is_import) = match scope_set {
 669             ScopeSet::All(ns, is_import) => (ns, None, is_import),
 670             ScopeSet::AbsolutePath(ns) => (ns, None, false),
 671             ScopeSet::Macro(macro_kind) => (MacroNS, Some(macro_kind), false),
 672             ScopeSet::Late(ns, ..) => (ns, None, false),
 673         };
 674
 675         // This is *the* result, resolution from the scope closest to the resolved identifier.
 676         // However, sometimes this result is "weak" because it comes from a glob import or
 677         // a macro expansion, and in this case it cannot shadow names from outer scopes, e.g.
 678         // mod m { ... } // solution in outer scope
 679         // {
 680         //     use prefix::*; // imports another `m` - innermost solution
 681         //                    // weak, cannot shadow the outer `m`, need to report ambiguity error
 682         //     m::mac!();
 683         // }
 684         // So we have to save the innermost solution and continue searching in outer scopes
 685         // to detect potential ambiguities.
 686         let mut innermost_result: Option<(&NameBinding<'_>, Flags)> = None;
 687         let mut determinacy = Determinacy::Determined;
 688
 689         // Go through all the scopes and try to resolve the name.
 690         let break_result = self.visit_scopes(
 691             scope_set,
 692             parent_scope,
 693             orig_ident.span.ctxt(),
 694             |this, scope, use_prelude, ctxt| {
 695                 let ident = Ident::new(orig_ident.name, orig_ident.span.with_ctxt(ctxt));
 696                 let ok = |res, span, arenas| {
 697                     Ok((
 698                         (res, ty::Visibility::Public, span, LocalExpnId::ROOT)
 699                             .to_name_binding(arenas),
 700                         Flags::empty(),
 701                     ))
 702                 };
 703                 let result = match scope {
 704                     Scope::DeriveHelpers(expn_id) => {
 705                         if let Some(attr) = this
 706                             .helper_attrs
 707                             .get(&expn_id)
 708                             .and_then(|attrs| attrs.iter().rfind(|i| ident == **i))
 709                         {
 710                             let binding = (
 711                                 Res::NonMacroAttr(NonMacroAttrKind::DeriveHelper),
 712                                 ty::Visibility::Public,
 713                                 attr.span,
 714                                 expn_id,
 715                             )
 716                                 .to_name_binding(this.arenas);
 717                             Ok((binding, Flags::empty()))
 718                         } else {
 719                             Err(Determinacy::Determined)
 720                         }
 721                     }
 722                     Scope::DeriveHelpersCompat => {
 723                         let mut result = Err(Determinacy::Determined);
 724                         for derive in parent_scope.derives {
 725                             let parent_scope = &ParentScope { derives: &[], ..*parent_scope };
 726                             match this.resolve_macro_path(
 727                                 derive,
 728                                 Some(MacroKind::Derive),
 729                                 parent_scope,
 730                                 true,
 731                                 force,
 732                             ) {
 733                                 Ok((Some(ext), _)) => {
 734                                     if ext.helper_attrs.contains(&ident.name) {
 735                                         result = ok(
 736                                             Res::NonMacroAttr(NonMacroAttrKind::DeriveHelperCompat),
 737                                             derive.span,
 738                                             this.arenas,
 739                                         );
 740                                         break;
 741                                     }
 742                                 }
 743                                 Ok(_) | Err(Determinacy::Determined) => {}
 744                                 Err(Determinacy::Undetermined) => {
 745                                     result = Err(Determinacy::Undetermined)
 746                                 }
 747                             }
 748                         }
 749                         result
 750                     }
 751                     Scope::MacroRules(macro_rules_scope) => match macro_rules_scope.get() {
 752                         MacroRulesScope::Binding(macro_rules_binding)
 753                             if ident == macro_rules_binding.ident =>
 754                         {
 755                             Ok((macro_rules_binding.binding, Flags::MACRO_RULES))
 756                         }
 757                         MacroRulesScope::Invocation(_) => Err(Determinacy::Undetermined),
 758                         _ => Err(Determinacy::Determined),
 759                     },
 760                     Scope::CrateRoot => {
 761                         let root_ident = Ident::new(kw::PathRoot, ident.span);
 762                         let root_module = this.resolve_crate_root(root_ident);
 763                         let binding = this.resolve_ident_in_module_ext(
 764                             ModuleOrUniformRoot::Module(root_module),
 765                             ident,
 766                             ns,
 767                             parent_scope,
 768                             record_used,
 769                             path_span,
 770                         );
 771                         match binding {
 772                             Ok(binding) => Ok((binding, Flags::MODULE | Flags::MISC_SUGGEST_CRATE)),
 773                             Err((Determinacy::Undetermined, Weak::No)) => {
 774                                 return Some(Err(Determinacy::determined(force)));
 775                             }
 776                             Err((Determinacy::Undetermined, Weak::Yes)) => {
 777                                 Err(Determinacy::Undetermined)
 778                             }
 779                             Err((Determinacy::Determined, _)) => Err(Determinacy::Determined),
 780                         }
 781                     }
 782                     Scope::Module(module, derive_fallback_lint_id) => {
 783                         let adjusted_parent_scope = &ParentScope { module, ..*parent_scope };
 784                         let binding = this.resolve_ident_in_module_unadjusted_ext(
 785                             ModuleOrUniformRoot::Module(module),
 786                             ident,
 787                             ns,
 788                             adjusted_parent_scope,
 789                             !matches!(scope_set, ScopeSet::Late(..)),
 790                             record_used,
 791                             path_span,
 792                         );
 793                         match binding {
 794                             Ok(binding) => {
 795                                 if let Some(lint_id) = derive_fallback_lint_id {
 796                                     this.lint_buffer.buffer_lint_with_diagnostic(
 797                                         PROC_MACRO_DERIVE_RESOLUTION_FALLBACK,
 798                                         lint_id,
 799                                         orig_ident.span,
 800                                         &format!(
 801                                             "cannot find {} `{}` in this scope",
 802                                             ns.descr(),
 803                                             ident
 804                                         ),
 805                                         BuiltinLintDiagnostics::ProcMacroDeriveResolutionFallback(
 806                                             orig_ident.span,
 807                                         ),
 808                                     );
 809                                 }
 810                                 let misc_flags = if ptr::eq(module, this.graph_root) {
 811                                     Flags::MISC_SUGGEST_CRATE
 812                                 } else if module.is_normal() {
 813                                     Flags::MISC_SUGGEST_SELF
 814                                 } else {
 815                                     Flags::empty()
 816                                 };
 817                                 Ok((binding, Flags::MODULE | misc_flags))
 818                             }
 819                             Err((Determinacy::Undetermined, Weak::No)) => {
 820                                 return Some(Err(Determinacy::determined(force)));
 821                             }
 822                             Err((Determinacy::Undetermined, Weak::Yes)) => {
 823                                 Err(Determinacy::Undetermined)
 824                             }
 825                             Err((Determinacy::Determined, _)) => Err(Determinacy::Determined),
 826                         }
 827                     }
 828                     Scope::RegisteredAttrs => match this.registered_attrs.get(&ident).cloned() {
 829                         Some(ident) => ok(
 830                             Res::NonMacroAttr(NonMacroAttrKind::Registered),
 831                             ident.span,
 832                             this.arenas,
 833                         ),
 834                         None => Err(Determinacy::Determined),
 835                     },
 836                     Scope::MacroUsePrelude => {
 837                         match this.macro_use_prelude.get(&ident.name).cloned() {
 838                             Some(binding) => Ok((binding, Flags::MISC_FROM_PRELUDE)),
 839                             None => Err(Determinacy::determined(
 840                                 this.graph_root.unexpanded_invocations.borrow().is_empty(),
 841                             )),
 842                         }
 843                     }
 844                     Scope::BuiltinAttrs => {
 845                         if is_builtin_attr_name(ident.name) {
 846                             ok(
 847                                 Res::NonMacroAttr(NonMacroAttrKind::Builtin(ident.name)),
 848                                 DUMMY_SP,
 849                                 this.arenas,
 850                             )
 851                         } else {
 852                             Err(Determinacy::Determined)
 853                         }
 854                     }
 855                     Scope::ExternPrelude => match this.extern_prelude_get(ident, !record_used) {
 856                         Some(binding) => Ok((binding, Flags::empty())),
 857                         None => Err(Determinacy::determined(
 858                             this.graph_root.unexpanded_invocations.borrow().is_empty(),
 859                         )),
 860                     },
 861                     Scope::ToolPrelude => match this.registered_tools.get(&ident).cloned() {
 862                         Some(ident) => ok(Res::ToolMod, ident.span, this.arenas),
 863                         None => Err(Determinacy::Determined),
 864                     },
 865                     Scope::StdLibPrelude => {
 866                         let mut result = Err(Determinacy::Determined);
 867                         if let Some(prelude) = this.prelude {
 868                             if let Ok(binding) = this.resolve_ident_in_module_unadjusted(
 869                                 ModuleOrUniformRoot::Module(prelude),
 870                                 ident,
 871                                 ns,
 872                                 parent_scope,
 873                                 false,
 874                                 path_span,
 875                             ) {
 876                                 if use_prelude || this.is_builtin_macro(binding.res()) {
 877                                     result = Ok((binding, Flags::MISC_FROM_PRELUDE));
 878                                 }
 879                             }
 880                         }
 881                         result
 882                     }
 883                     Scope::BuiltinTypes => match PrimTy::from_name(ident.name) {
 884                         Some(prim_ty) => ok(Res::PrimTy(prim_ty), DUMMY_SP, this.arenas),
 885                         None => Err(Determinacy::Determined),
 886                     },
 887                 };
 888
 889                 match result {
 890                     Ok((binding, flags))
 891                         if sub_namespace_match(binding.macro_kind(), macro_kind) =>
 892                     {
 893                         if !record_used || matches!(scope_set, ScopeSet::Late(..)) {
 894                             return Some(Ok(binding));
 895                         }
 896
 897                         if let Some((innermost_binding, innermost_flags)) = innermost_result {
 898                             // Found another solution, if the first one was "weak", report an error.
 899                             let (res, innermost_res) = (binding.res(), innermost_binding.res());
 900                             if res != innermost_res {
 901                                 let is_builtin = |res| {
 902                                     matches!(res, Res::NonMacroAttr(NonMacroAttrKind::Builtin(..)))
 903                                 };
 904                                 let derive_helper =
 905                                     Res::NonMacroAttr(NonMacroAttrKind::DeriveHelper);
 906                                 let derive_helper_compat =
 907                                     Res::NonMacroAttr(NonMacroAttrKind::DeriveHelperCompat);
 908
 909                                 let ambiguity_error_kind = if is_import {
 910                                     Some(AmbiguityKind::Import)
 911                                 } else if is_builtin(innermost_res) || is_builtin(res) {
 912                                     Some(AmbiguityKind::BuiltinAttr)
 913                                 } else if innermost_res == derive_helper_compat
 914                                     || res == derive_helper_compat && innermost_res != derive_helper
 915                                 {
 916                                     Some(AmbiguityKind::DeriveHelper)
 917                                 } else if innermost_flags.contains(Flags::MACRO_RULES)
 918                                     && flags.contains(Flags::MODULE)
 919                                     && !this.disambiguate_macro_rules_vs_modularized(
 920                                         innermost_binding,
 921                                         binding,
 922                                     )
 923                                     || flags.contains(Flags::MACRO_RULES)
 924                                         && innermost_flags.contains(Flags::MODULE)
 925                                         && !this.disambiguate_macro_rules_vs_modularized(
 926                                             binding,
 927                                             innermost_binding,
 928                                         )
 929                                 {
 930                                     Some(AmbiguityKind::MacroRulesVsModularized)
 931                                 } else if innermost_binding.is_glob_import() {
 932                                     Some(AmbiguityKind::GlobVsOuter)
 933                                 } else if innermost_binding
 934                                     .may_appear_after(parent_scope.expansion, binding)
 935                                 {
 936                                     Some(AmbiguityKind::MoreExpandedVsOuter)
 937                                 } else {
 938                                     None
 939                                 };
 940                                 if let Some(kind) = ambiguity_error_kind {
 941                                     let misc = |f: Flags| {
 942                                         if f.contains(Flags::MISC_SUGGEST_CRATE) {
 943                                             AmbiguityErrorMisc::SuggestCrate
 944                                         } else if f.contains(Flags::MISC_SUGGEST_SELF) {
 945                                             AmbiguityErrorMisc::SuggestSelf
 946                                         } else if f.contains(Flags::MISC_FROM_PRELUDE) {
 947                                             AmbiguityErrorMisc::FromPrelude
 948                                         } else {
 949                                             AmbiguityErrorMisc::None
 950                                         }
 951                                     };
 952                                     this.ambiguity_errors.push(AmbiguityError {
 953                                         kind,
 954                                         ident: orig_ident,
 955                                         b1: innermost_binding,
 956                                         b2: binding,
 957                                         misc1: misc(innermost_flags),
 958                                         misc2: misc(flags),
 959                                     });
 960                                     return Some(Ok(innermost_binding));
 961                                 }
 962                             }
 963                         } else {
 964                             // Found the first solution.
 965                             innermost_result = Some((binding, flags));
 966                         }
 967                     }
 968                     Ok(..) | Err(Determinacy::Determined) => {}
 969                     Err(Determinacy::Undetermined) => determinacy = Determinacy::Undetermined,
 970                 }
 971
 972                 None
 973             },
 974         );
 975
 976         if let Some(break_result) = break_result {
 977             return break_result;
 978         }
 979
 980         // The first found solution was the only one, return it.
 981         if let Some((binding, _)) = innermost_result {
 982             return Ok(binding);
 983         }
 984
 985         Err(Determinacy::determined(determinacy == Determinacy::Determined || force))
 986     }
 987
 988     crate fn finalize_macro_resolutions(&mut self) {
 989         let check_consistency = |this: &mut Self,
 990                                  path: &[Segment],
 991                                  span,
 992                                  kind: MacroKind,
 993                                  initial_res: Option<Res>,
 994                                  res: Res| {
 995             if let Some(initial_res) = initial_res {
 996                 if res != initial_res {
 997                     // Make sure compilation does not succeed if preferred macro resolution
 998                     // has changed after the macro had been expanded. In theory all such
 999                     // situations should be reported as errors, so this is a bug.
1000                     this.session.delay_span_bug(span, "inconsistent resolution for a macro");
1001                 }
1002             } else {
1003                 // It's possible that the macro was unresolved (indeterminate) and silently
1004                 // expanded into a dummy fragment for recovery during expansion.
1005                 // Now, post-expansion, the resolution may succeed, but we can't change the
1006                 // past and need to report an error.
1007                 // However, non-speculative `resolve_path` can successfully return private items
1008                 // even if speculative `resolve_path` returned nothing previously, so we skip this
1009                 // less informative error if the privacy error is reported elsewhere.
1010                 if this.privacy_errors.is_empty() {
1011                     let msg = format!(
1012                         "cannot determine resolution for the {} `{}`",
1013                         kind.descr(),
1014                         Segment::names_to_string(path)
1015                     );
1016                     let msg_note = "import resolution is stuck, try simplifying macro imports";
1017                     this.session.struct_span_err(span, &msg).note(msg_note).emit();
1018                 }
1019             }
1020         };
1021
1022         let macro_resolutions = mem::take(&mut self.multi_segment_macro_resolutions);
1023         for (mut path, path_span, kind, parent_scope, initial_res) in macro_resolutions {
1024             // FIXME: Path resolution will ICE if segment IDs present.
1025             for seg in &mut path {
1026                 seg.id = None;
1027             }
1028             match self.resolve_path(
1029                 &path,
1030                 Some(MacroNS),
1031                 &parent_scope,
1032                 true,
1033                 path_span,
1034                 CrateLint::No,
1035             ) {
1036                 PathResult::NonModule(path_res) if path_res.unresolved_segments() == 0 => {
1037                     let res = path_res.base_res();
1038                     check_consistency(self, &path, path_span, kind, initial_res, res);
1039                 }
1040                 path_res @ PathResult::NonModule(..) | path_res @ PathResult::Failed { .. } => {
1041                     let (span, label) = if let PathResult::Failed { span, label, .. } = path_res {
1042                         (span, label)
1043                     } else {
1044                         (
1045                             path_span,
1046                             format!(
1047                                 "partially resolved path in {} {}",
1048                                 kind.article(),
1049                                 kind.descr()
1050                             ),
1051                         )
1052                     };
1053                     self.report_error(
1054                         span,
1055                         ResolutionError::FailedToResolve { label, suggestion: None },
1056                     );
1057                 }
1058                 PathResult::Module(..) | PathResult::Indeterminate => unreachable!(),
1059             }
1060         }
1061
1062         let macro_resolutions = mem::take(&mut self.single_segment_macro_resolutions);
1063         for (ident, kind, parent_scope, initial_binding) in macro_resolutions {
1064             match self.early_resolve_ident_in_lexical_scope(
1065                 ident,
1066                 ScopeSet::Macro(kind),
1067                 &parent_scope,
1068                 true,
1069                 true,
1070                 ident.span,
1071             ) {
1072                 Ok(binding) => {
1073                     let initial_res = initial_binding.map(|initial_binding| {
1074                         self.record_use(ident, initial_binding, false);
1075                         initial_binding.res()
1076                     });
1077                     let res = binding.res();
1078                     let seg = Segment::from_ident(ident);
1079                     check_consistency(self, &[seg], ident.span, kind, initial_res, res);
1080                     if res == Res::NonMacroAttr(NonMacroAttrKind::DeriveHelperCompat) {
1081                         let node_id = self
1082                             .invocation_parents
1083                             .get(&parent_scope.expansion)
1084                             .map_or(ast::CRATE_NODE_ID, |id| self.def_id_to_node_id[id.0]);
1085                         self.lint_buffer.buffer_lint_with_diagnostic(
1086                             LEGACY_DERIVE_HELPERS,
1087                             node_id,
1088                             ident.span,
1089                             "derive helper attribute is used before it is introduced",
1090                             BuiltinLintDiagnostics::LegacyDeriveHelpers(binding.span),
1091                         );
1092                     }
1093                 }
1094                 Err(..) => {
1095                     let expected = kind.descr_expected();
1096                     let msg = format!("cannot find {} `{}` in this scope", expected, ident);
1097                     let mut err = self.session.struct_span_err(ident.span, &msg);
1098                     self.unresolved_macro_suggestions(&mut err, kind, &parent_scope, ident);
1099                     err.emit();
1100                 }
1101             }
1102         }
1103
1104         let builtin_attrs = mem::take(&mut self.builtin_attrs);
1105         for (ident, parent_scope) in builtin_attrs {
1106             let _ = self.early_resolve_ident_in_lexical_scope(
1107                 ident,
1108                 ScopeSet::Macro(MacroKind::Attr),
1109                 &parent_scope,
1110                 true,
1111                 true,
1112                 ident.span,
1113             );
1114         }
1115     }
1116
1117     fn check_stability_and_deprecation(
1118         &mut self,
1119         ext: &SyntaxExtension,
1120         path: &ast::Path,
1121         node_id: NodeId,
1122     ) {
1123         let span = path.span;
1124         if let Some(stability) = &ext.stability {
1125             if let StabilityLevel::Unstable { reason, issue, is_soft } = stability.level {
1126                 let feature = stability.feature;
1127                 if !self.active_features.contains(&feature) && !span.allows_unstable(feature) {
1128                     let lint_buffer = &mut self.lint_buffer;
1129                     let soft_handler =
1130                         |lint, span, msg: &_| lint_buffer.buffer_lint(lint, node_id, span, msg);
1131                     stability::report_unstable(
1132                         self.session,
1133                         feature,
1134                         reason,
1135                         issue,
1136                         is_soft,
1137                         span,
1138                         soft_handler,
1139                     );
1140                 }
1141             }
1142         }
1143         if let Some(depr) = &ext.deprecation {
1144             let path = pprust::path_to_string(&path);
1145             let (message, lint) = stability::deprecation_message_and_lint(depr, "macro", &path);
1146             stability::early_report_deprecation(
1147                 &mut self.lint_buffer,
1148                 &message,
1149                 depr.suggestion,
1150                 lint,
1151                 span,
1152                 node_id,
1153             );
1154         }
1155     }
1156
1157     fn prohibit_imported_non_macro_attrs(
1158         &self,
1159         binding: Option<&'a NameBinding<'a>>,
1160         res: Option<Res>,
1161         span: Span,
1162     ) {
1163         if let Some(Res::NonMacroAttr(kind)) = res {
1164             if kind != NonMacroAttrKind::Tool && binding.map_or(true, |b| b.is_import()) {
1165                 let msg =
1166                     format!("cannot use {} {} through an import", kind.article(), kind.descr());
1167                 let mut err = self.session.struct_span_err(span, &msg);
1168                 if let Some(binding) = binding {
1169                     err.span_note(binding.span, &format!("the {} imported here", kind.descr()));
1170                 }
1171                 err.emit();
1172             }
1173         }
1174     }
1175
1176     crate fn check_reserved_macro_name(&mut self, ident: Ident, res: Res) {
1177         // Reserve some names that are not quite covered by the general check
1178         // performed on `Resolver::builtin_attrs`.
1179         if ident.name == sym::cfg || ident.name == sym::cfg_attr {
1180             let macro_kind = self.get_macro(res).map(|ext| ext.macro_kind());
1181             if macro_kind.is_some() && sub_namespace_match(macro_kind, Some(MacroKind::Attr)) {
1182                 self.session.span_err(
1183                     ident.span,
1184                     &format!("name `{}` is reserved in attribute namespace", ident),
1185                 );
1186             }
1187         }
1188     }
1189
1190     /// Compile the macro into a `SyntaxExtension` and possibly replace
1191     /// its expander to a pre-defined one for built-in macros.
1192     crate fn compile_macro(&mut self, item: &ast::Item, edition: Edition) -> SyntaxExtension {
1193         let mut result = compile_declarative_macro(
1194             &self.session,
1195             self.session.features_untracked(),
1196             item,
1197             edition,
1198         );
1199
1200         if let Some(builtin_name) = result.builtin_name {
1201             // The macro was marked with `#[rustc_builtin_macro]`.
1202             if let Some(builtin_macro) = self.builtin_macros.get_mut(&builtin_name) {
1203                 // The macro is a built-in, replace its expander function
1204                 // while still taking everything else from the source code.
1205                 // If we already loaded this builtin macro, give a better error message than 'no such builtin macro'.
1206                 match mem::replace(builtin_macro, BuiltinMacroState::AlreadySeen(item.span)) {
1207                     BuiltinMacroState::NotYetSeen(ext) => result.kind = ext,
1208                     BuiltinMacroState::AlreadySeen(span) => {
1209                         struct_span_err!(
1210                             self.session,
1211                             item.span,
1212                             E0773,
1213                             "attempted to define built-in macro more than once"
1214                         )
1215                         .span_note(span, "previously defined here")
1216                         .emit();
1217                     }
1218                 }
1219             } else {
1220                 let msg = format!("cannot find a built-in macro with name `{}`", item.ident);
1221                 self.session.span_err(item.span, &msg);
1222             }
1223         }
1224
1225         result
1226     }
1227 }