src/librustc_resolve/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::{AmbiguityError, AmbiguityKind, AmbiguityErrorMisc, Determinacy};
   5 use crate::{CrateLint, Resolver, ResolutionError, Scope, ScopeSet, ParentScope, Weak};
   6 use crate::{ModuleKind, NameBinding, PathResult, Segment, ToNameBinding};
   7 use crate::{ModuleOrUniformRoot, KNOWN_TOOLS};
   8 use crate::Namespace::*;
   9 use crate::resolve_imports::ImportResolver;
  10 use rustc::hir::def::{self, DefKind, NonMacroAttrKind};
  11 use rustc::hir::def_id;
  12 use rustc::middle::stability;
  13 use rustc::{ty, lint, span_bug};
  14 use syntax::ast::{self, NodeId, Ident};
  15 use syntax::attr::StabilityLevel;
  16 use syntax::edition::Edition;
  17 use syntax::feature_gate::{emit_feature_err, is_builtin_attr_name};
  18 use syntax::feature_gate::GateIssue;
  19 use syntax::print::pprust;
  20 use syntax::symbol::{Symbol, kw, sym};
  21 use syntax_expand::base::{self, InvocationRes, Indeterminate};
  22 use syntax_expand::base::SyntaxExtension;
  23 use syntax_expand::expand::{AstFragment, AstFragmentKind, Invocation, InvocationKind};
  24 use syntax_expand::compile_declarative_macro;
  25 use syntax_pos::hygiene::{self, ExpnId, ExpnData, ExpnKind};
  26 use syntax_pos::{Span, DUMMY_SP};
  27
  28 use std::{mem, ptr};
  29 use rustc_data_structures::sync::Lrc;
  30 use syntax_pos::hygiene::{MacroKind, AstPass};
  31
  32 type Res = def::Res<NodeId>;
  33
  34 /// Binding produced by a `macro_rules` item.
  35 /// Not modularized, can shadow previous legacy bindings, etc.
  36 #[derive(Debug)]
  37 pub struct LegacyBinding<'a> {
  38     crate binding: &'a NameBinding<'a>,
  39     /// Legacy scope into which the `macro_rules` item was planted.
  40     crate parent_legacy_scope: LegacyScope<'a>,
  41     crate ident: Ident,
  42 }
  43
  44 /// The scope introduced by a `macro_rules!` macro.
  45 /// This starts at the macro's definition and ends at the end of the macro's parent
  46 /// module (named or unnamed), or even further if it escapes with `#[macro_use]`.
  47 /// Some macro invocations need to introduce legacy scopes too because they
  48 /// can potentially expand into macro definitions.
  49 #[derive(Copy, Clone, Debug)]
  50 pub enum LegacyScope<'a> {
  51     /// Empty "root" scope at the crate start containing no names.
  52     Empty,
  53     /// The scope introduced by a `macro_rules!` macro definition.
  54     Binding(&'a LegacyBinding<'a>),
  55     /// The scope introduced by a macro invocation that can potentially
  56     /// create a `macro_rules!` macro definition.
  57     Invocation(ExpnId),
  58 }
  59
  60 // Macro namespace is separated into two sub-namespaces, one for bang macros and
  61 // one for attribute-like macros (attributes, derives).
  62 // We ignore resolutions from one sub-namespace when searching names in scope for another.
  63 fn sub_namespace_match(candidate: Option<MacroKind>, requirement: Option<MacroKind>) -> bool {
  64     #[derive(PartialEq)]
  65     enum SubNS { Bang, AttrLike }
  66     let sub_ns = |kind| match kind {
  67         MacroKind::Bang => SubNS::Bang,
  68         MacroKind::Attr | MacroKind::Derive => SubNS::AttrLike,
  69     };
  70     let candidate = candidate.map(sub_ns);
  71     let requirement = requirement.map(sub_ns);
  72     // "No specific sub-namespace" means "matches anything" for both requirements and candidates.
  73     candidate.is_none() || requirement.is_none() || candidate == requirement
  74 }
  75
  76 // We don't want to format a path using pretty-printing,
  77 // `format!("{}", path)`, because that tries to insert
  78 // line-breaks and is slow.
  79 fn fast_print_path(path: &ast::Path) -> Symbol {
  80     if path.segments.len() == 1 {
  81         return path.segments[0].ident.name
  82     } else {
  83         let mut path_str = String::with_capacity(64);
  84         for (i, segment) in path.segments.iter().enumerate() {
  85             if i != 0 {
  86                 path_str.push_str("::");
  87             }
  88             if segment.ident.name != kw::PathRoot {
  89                 path_str.push_str(&segment.ident.as_str())
  90             }
  91         }
  92         Symbol::intern(&path_str)
  93     }
  94 }
  95
  96 impl<'a> base::Resolver for Resolver<'a> {
  97     fn next_node_id(&mut self) -> NodeId {
  98         self.session.next_node_id()
  99     }
 100
 101     fn resolve_dollar_crates(&mut self) {
 102         hygiene::update_dollar_crate_names(|ctxt| {
 103             let ident = Ident::new(kw::DollarCrate, DUMMY_SP.with_ctxt(ctxt));
 104             match self.resolve_crate_root(ident).kind {
 105                 ModuleKind::Def(.., name) if name != kw::Invalid => name,
 106                 _ => kw::Crate,
 107             }
 108         });
 109     }
 110
 111     fn visit_ast_fragment_with_placeholders(&mut self, expansion: ExpnId, fragment: &AstFragment) {
 112         // Integrate the new AST fragment into all the definition and module structures.
 113         // We are inside the `expansion` now, but other parent scope components are still the same.
 114         let parent_scope = ParentScope { expansion, ..self.invocation_parent_scopes[&expansion] };
 115         let output_legacy_scope = self.build_reduced_graph(fragment, parent_scope);
 116         self.output_legacy_scopes.insert(expansion, output_legacy_scope);
 117
 118         parent_scope.module.unexpanded_invocations.borrow_mut().remove(&expansion);
 119     }
 120
 121     fn register_builtin_macro(&mut self, ident: ast::Ident, ext: SyntaxExtension) {
 122         if self.builtin_macros.insert(ident.name, ext).is_some() {
 123             self.session.span_err(ident.span,
 124                                   &format!("built-in macro `{}` was already defined", ident));
 125         }
 126     }
 127
 128     // Create a new Expansion with a definition site of the provided module, or
 129     // a fake empty `#[no_implicit_prelude]` module if no module is provided.
 130     fn expansion_for_ast_pass(
 131         &mut self,
 132         call_site: Span,
 133         pass: AstPass,
 134         features: &[Symbol],
 135         parent_module_id: Option<NodeId>,
 136     ) -> ExpnId {
 137         let expn_id = ExpnId::fresh(Some(ExpnData::allow_unstable(
 138             ExpnKind::AstPass(pass),
 139             call_site,
 140             self.session.edition(),
 141             features.into(),
 142         )));
 143
 144         let parent_scope = if let Some(module_id) = parent_module_id {
 145             let parent_def_id = self.definitions.local_def_id(module_id);
 146             self.definitions.add_parent_module_of_macro_def(expn_id, parent_def_id);
 147             self.module_map[&parent_def_id]
 148         } else {
 149             self.definitions.add_parent_module_of_macro_def(
 150                 expn_id,
 151                 def_id::DefId::local(def_id::CRATE_DEF_INDEX),
 152             );
 153             self.empty_module
 154         };
 155         self.ast_transform_scopes.insert(expn_id, parent_scope);
 156         expn_id
 157     }
 158
 159     fn resolve_imports(&mut self) {
 160         ImportResolver { r: self }.resolve_imports()
 161     }
 162
 163     fn resolve_macro_invocation(
 164         &mut self, invoc: &Invocation, eager_expansion_root: ExpnId, force: bool
 165     ) -> Result<InvocationRes, Indeterminate> {
 166         let invoc_id = invoc.expansion_data.id;
 167         let parent_scope = match self.invocation_parent_scopes.get(&invoc_id) {
 168             Some(parent_scope) => *parent_scope,
 169             None => {
 170                 // If there's no entry in the table, then we are resolving an eagerly expanded
 171                 // macro, which should inherit its parent scope from its eager expansion root -
 172                 // the macro that requested this eager expansion.
 173                 let parent_scope = *self.invocation_parent_scopes.get(&eager_expansion_root)
 174                     .expect("non-eager expansion without a parent scope");
 175                 self.invocation_parent_scopes.insert(invoc_id, parent_scope);
 176                 parent_scope
 177             }
 178         };
 179
 180         let (path, kind, derives, after_derive) = match invoc.kind {
 181             InvocationKind::Attr { ref attr, ref derives, after_derive, .. } =>
 182                 (&attr.get_normal_item().path,
 183                  MacroKind::Attr,
 184                  self.arenas.alloc_ast_paths(derives),
 185                  after_derive),
 186             InvocationKind::Bang { ref mac, .. } =>
 187                 (&mac.path, MacroKind::Bang, &[][..], false),
 188             InvocationKind::Derive { ref path, .. } =>
 189                 (path, MacroKind::Derive, &[][..], false),
 190             InvocationKind::DeriveContainer { ref derives, .. } => {
 191                 // Block expansion of the container until we resolve all derives in it.
 192                 // This is required for two reasons:
 193                 // - Derive helper attributes are in scope for the item to which the `#[derive]`
 194                 //   is applied, so they have to be produced by the container's expansion rather
 195                 //   than by individual derives.
 196                 // - Derives in the container need to know whether one of them is a built-in `Copy`.
 197                 // FIXME: Try to avoid repeated resolutions for derives here and in expansion.
 198                 let mut exts = Vec::new();
 199                 for path in derives {
 200                     exts.push(match self.resolve_macro_path(
 201                         path, Some(MacroKind::Derive), &parent_scope, true, force
 202                     ) {
 203                         Ok((Some(ext), _)) => ext,
 204                         Ok(_) | Err(Determinacy::Determined) => self.dummy_ext(MacroKind::Derive),
 205                         Err(Determinacy::Undetermined) => return Err(Indeterminate),
 206                     })
 207                 }
 208                 return Ok(InvocationRes::DeriveContainer(exts));
 209             }
 210         };
 211
 212         // Derives are not included when `invocations` are collected, so we have to add them here.
 213         let parent_scope = &ParentScope { derives, ..parent_scope };
 214         let (ext, res) = self.smart_resolve_macro_path(path, kind, parent_scope, force)?;
 215
 216         let span = invoc.span();
 217         invoc_id.set_expn_data(ext.expn_data(parent_scope.expansion, span, fast_print_path(path)));
 218
 219         if let Res::Def(_, def_id) = res {
 220             if after_derive {
 221                 self.session.span_err(span, "macro attributes must be placed before `#[derive]`");
 222             }
 223             self.macro_defs.insert(invoc_id, def_id);
 224             let normal_module_def_id = self.macro_def_scope(invoc_id).normal_ancestor_id;
 225             self.definitions.add_parent_module_of_macro_def(invoc_id, normal_module_def_id);
 226         }
 227
 228         match invoc.fragment_kind {
 229             AstFragmentKind::Arms
 230                 | AstFragmentKind::Fields
 231                 | AstFragmentKind::FieldPats
 232                 | AstFragmentKind::GenericParams
 233                 | AstFragmentKind::Params
 234                 | AstFragmentKind::StructFields
 235                 | AstFragmentKind::Variants =>
 236             {
 237                 if let Res::Def(..) = res {
 238                     self.session.span_err(
 239                         span,
 240                         &format!("expected an inert attribute, found {} {}",
 241                                  res.article(), res.descr()),
 242                     );
 243                     return Ok(InvocationRes::Single(self.dummy_ext(kind)));
 244                 }
 245             },
 246             _ => {}
 247         }
 248
 249         Ok(InvocationRes::Single(ext))
 250     }
 251
 252     fn check_unused_macros(&mut self) {
 253         for (&node_id, &span) in self.unused_macros.iter() {
 254             self.lint_buffer.buffer_lint(
 255                 lint::builtin::UNUSED_MACROS, node_id, span, "unused macro definition"
 256             );
 257         }
 258     }
 259
 260     fn has_derive_copy(&self, expn_id: ExpnId) -> bool {
 261         self.containers_deriving_copy.contains(&expn_id)
 262     }
 263
 264     fn add_derive_copy(&mut self, expn_id: ExpnId) {
 265         self.containers_deriving_copy.insert(expn_id);
 266     }
 267 }
 268
 269 impl<'a> Resolver<'a> {
 270     /// Resolve macro path with error reporting and recovery.
 271     fn smart_resolve_macro_path(
 272         &mut self,
 273         path: &ast::Path,
 274         kind: MacroKind,
 275         parent_scope: &ParentScope<'a>,
 276         force: bool,
 277     ) -> Result<(Lrc<SyntaxExtension>, Res), Indeterminate> {
 278         let (ext, res) = match self.resolve_macro_path(path, Some(kind), parent_scope,
 279                                                        true, force) {
 280             Ok((Some(ext), res)) => (ext, res),
 281             // Use dummy syntax extensions for unresolved macros for better recovery.
 282             Ok((None, res)) => (self.dummy_ext(kind), res),
 283             Err(Determinacy::Determined) => (self.dummy_ext(kind), Res::Err),
 284             Err(Determinacy::Undetermined) => return Err(Indeterminate),
 285         };
 286
 287         // Report errors and enforce feature gates for the resolved macro.
 288         let features = self.session.features_untracked();
 289         for segment in &path.segments {
 290             if let Some(args) = &segment.args {
 291                 self.session.span_err(args.span(), "generic arguments in macro path");
 292             }
 293             if kind == MacroKind::Attr && !features.rustc_attrs &&
 294                segment.ident.as_str().starts_with("rustc") {
 295                 let msg =
 296                     "attributes starting with `rustc` are reserved for use by the `rustc` compiler";
 297                 emit_feature_err(
 298                     &self.session.parse_sess,
 299                     sym::rustc_attrs,
 300                     segment.ident.span,
 301                     GateIssue::Language,
 302                     msg,
 303                 );
 304             }
 305         }
 306
 307         match res {
 308             Res::Def(DefKind::Macro(_), def_id) => {
 309                 if let Some(node_id) = self.definitions.as_local_node_id(def_id) {
 310                     self.unused_macros.remove(&node_id);
 311                     if self.proc_macro_stubs.contains(&node_id) {
 312                         self.session.span_err(
 313                             path.span,
 314                             "can't use a procedural macro from the same crate that defines it",
 315                         );
 316                     }
 317                 }
 318             }
 319             Res::NonMacroAttr(..) | Res::Err => {}
 320             _ => panic!("expected `DefKind::Macro` or `Res::NonMacroAttr`"),
 321         };
 322
 323         self.check_stability_and_deprecation(&ext, path);
 324
 325         Ok(if ext.macro_kind() != kind {
 326             let expected = kind.descr_expected();
 327             let path_str = pprust::path_to_string(path);
 328             let msg = format!("expected {}, found {} `{}`", expected, res.descr(), path_str);
 329             self.session.struct_span_err(path.span, &msg)
 330                         .span_label(path.span, format!("not {} {}", kind.article(), expected))
 331                         .emit();
 332             // Use dummy syntax extensions for unexpected macro kinds for better recovery.
 333             (self.dummy_ext(kind), Res::Err)
 334         } else {
 335             (ext, res)
 336         })
 337     }
 338
 339     pub fn resolve_macro_path(
 340         &mut self,
 341         path: &ast::Path,
 342         kind: Option<MacroKind>,
 343         parent_scope: &ParentScope<'a>,
 344         trace: bool,
 345         force: bool,
 346     ) -> Result<(Option<Lrc<SyntaxExtension>>, Res), Determinacy> {
 347         let path_span = path.span;
 348         let mut path = Segment::from_path(path);
 349
 350         // Possibly apply the macro helper hack
 351         if kind == Some(MacroKind::Bang) && path.len() == 1 &&
 352            path[0].ident.span.ctxt().outer_expn_data().local_inner_macros {
 353             let root = Ident::new(kw::DollarCrate, path[0].ident.span);
 354             path.insert(0, Segment::from_ident(root));
 355         }
 356
 357         let res = if path.len() > 1 {
 358             let res = match self.resolve_path(&path, Some(MacroNS), parent_scope,
 359                                               false, path_span, CrateLint::No) {
 360                 PathResult::NonModule(path_res) if path_res.unresolved_segments() == 0 => {
 361                     Ok(path_res.base_res())
 362                 }
 363                 PathResult::Indeterminate if !force => return Err(Determinacy::Undetermined),
 364                 PathResult::NonModule(..)
 365                 | PathResult::Indeterminate
 366                 | PathResult::Failed { .. } => Err(Determinacy::Determined),
 367                 PathResult::Module(..) => unreachable!(),
 368             };
 369
 370             if trace {
 371                 let kind = kind.expect("macro kind must be specified if tracing is enabled");
 372                 self.multi_segment_macro_resolutions
 373                     .push((path, path_span, kind, *parent_scope, res.ok()));
 374             }
 375
 376             self.prohibit_imported_non_macro_attrs(None, res.ok(), path_span);
 377             res
 378         } else {
 379             let scope_set = kind.map_or(ScopeSet::All(MacroNS, false), ScopeSet::Macro);
 380             let binding = self.early_resolve_ident_in_lexical_scope(
 381                 path[0].ident, scope_set, parent_scope, false, force, path_span
 382             );
 383             if let Err(Determinacy::Undetermined) = binding {
 384                 return Err(Determinacy::Undetermined);
 385             }
 386
 387             if trace {
 388                 let kind = kind.expect("macro kind must be specified if tracing is enabled");
 389                 self.single_segment_macro_resolutions
 390                     .push((path[0].ident, kind, *parent_scope, binding.ok()));
 391             }
 392
 393             let res = binding.map(|binding| binding.res());
 394             self.prohibit_imported_non_macro_attrs(binding.ok(), res.ok(), path_span);
 395             res
 396         };
 397
 398         res.map(|res| (self.get_macro(res), res))
 399     }
 400
 401     // Resolve an identifier in lexical scope.
 402     // This is a variation of `fn resolve_ident_in_lexical_scope` that can be run during
 403     // expansion and import resolution (perhaps they can be merged in the future).
 404     // The function is used for resolving initial segments of macro paths (e.g., `foo` in
 405     // `foo::bar!(); or `foo!();`) and also for import paths on 2018 edition.
 406     crate fn early_resolve_ident_in_lexical_scope(
 407         &mut self,
 408         orig_ident: Ident,
 409         scope_set: ScopeSet,
 410         parent_scope: &ParentScope<'a>,
 411         record_used: bool,
 412         force: bool,
 413         path_span: Span,
 414     ) -> Result<&'a NameBinding<'a>, Determinacy> {
 415         bitflags::bitflags! {
 416             struct Flags: u8 {
 417                 const MACRO_RULES        = 1 << 0;
 418                 const MODULE             = 1 << 1;
 419                 const PRELUDE            = 1 << 2;
 420                 const MISC_SUGGEST_CRATE = 1 << 3;
 421                 const MISC_SUGGEST_SELF  = 1 << 4;
 422                 const MISC_FROM_PRELUDE  = 1 << 5;
 423             }
 424         }
 425
 426         assert!(force || !record_used); // `record_used` implies `force`
 427
 428         // Make sure `self`, `super` etc produce an error when passed to here.
 429         if orig_ident.is_path_segment_keyword() {
 430             return Err(Determinacy::Determined);
 431         }
 432
 433         let (ns, macro_kind, is_import) = match scope_set {
 434             ScopeSet::All(ns, is_import) => (ns, None, is_import),
 435             ScopeSet::AbsolutePath(ns) => (ns, None, false),
 436             ScopeSet::Macro(macro_kind) => (MacroNS, Some(macro_kind), false),
 437         };
 438
 439         // This is *the* result, resolution from the scope closest to the resolved identifier.
 440         // However, sometimes this result is "weak" because it comes from a glob import or
 441         // a macro expansion, and in this case it cannot shadow names from outer scopes, e.g.
 442         // mod m { ... } // solution in outer scope
 443         // {
 444         //     use prefix::*; // imports another `m` - innermost solution
 445         //                    // weak, cannot shadow the outer `m`, need to report ambiguity error
 446         //     m::mac!();
 447         // }
 448         // So we have to save the innermost solution and continue searching in outer scopes
 449         // to detect potential ambiguities.
 450         let mut innermost_result: Option<(&NameBinding<'_>, Flags)> = None;
 451         let mut determinacy = Determinacy::Determined;
 452
 453         // Go through all the scopes and try to resolve the name.
 454         let break_result = self.visit_scopes(scope_set, parent_scope, orig_ident,
 455                                              |this, scope, use_prelude, ident| {
 456             let result = match scope {
 457                 Scope::DeriveHelpers => {
 458                     let mut result = Err(Determinacy::Determined);
 459                     for derive in parent_scope.derives {
 460                         let parent_scope = &ParentScope { derives: &[], ..*parent_scope };
 461                         match this.resolve_macro_path(derive, Some(MacroKind::Derive),
 462                                                       parent_scope, true, force) {
 463                             Ok((Some(ext), _)) => if ext.helper_attrs.contains(&ident.name) {
 464                                 let binding = (Res::NonMacroAttr(NonMacroAttrKind::DeriveHelper),
 465                                                ty::Visibility::Public, derive.span, ExpnId::root())
 466                                                .to_name_binding(this.arenas);
 467                                 result = Ok((binding, Flags::empty()));
 468                                 break;
 469                             }
 470                             Ok(_) | Err(Determinacy::Determined) => {}
 471                             Err(Determinacy::Undetermined) =>
 472                                 result = Err(Determinacy::Undetermined),
 473                         }
 474                     }
 475                     result
 476                 }
 477                 Scope::MacroRules(legacy_scope) => match legacy_scope {
 478                     LegacyScope::Binding(legacy_binding) if ident == legacy_binding.ident =>
 479                         Ok((legacy_binding.binding, Flags::MACRO_RULES)),
 480                     LegacyScope::Invocation(invoc_id)
 481                         if !this.output_legacy_scopes.contains_key(&invoc_id) =>
 482                             Err(Determinacy::Undetermined),
 483                     _ => Err(Determinacy::Determined),
 484                 }
 485                 Scope::CrateRoot => {
 486                     let root_ident = Ident::new(kw::PathRoot, ident.span);
 487                     let root_module = this.resolve_crate_root(root_ident);
 488                     let binding = this.resolve_ident_in_module_ext(
 489                         ModuleOrUniformRoot::Module(root_module),
 490                         ident,
 491                         ns,
 492                         parent_scope,
 493                         record_used,
 494                         path_span,
 495                     );
 496                     match binding {
 497                         Ok(binding) => Ok((binding, Flags::MODULE | Flags::MISC_SUGGEST_CRATE)),
 498                         Err((Determinacy::Undetermined, Weak::No)) =>
 499                             return Some(Err(Determinacy::determined(force))),
 500                         Err((Determinacy::Undetermined, Weak::Yes)) =>
 501                             Err(Determinacy::Undetermined),
 502                         Err((Determinacy::Determined, _)) => Err(Determinacy::Determined),
 503                     }
 504                 }
 505                 Scope::Module(module) => {
 506                     let adjusted_parent_scope = &ParentScope { module, ..*parent_scope };
 507                     let binding = this.resolve_ident_in_module_unadjusted_ext(
 508                         ModuleOrUniformRoot::Module(module),
 509                         ident,
 510                         ns,
 511                         adjusted_parent_scope,
 512                         true,
 513                         record_used,
 514                         path_span,
 515                     );
 516                     match binding {
 517                         Ok(binding) => {
 518                             let misc_flags = if ptr::eq(module, this.graph_root) {
 519                                 Flags::MISC_SUGGEST_CRATE
 520                             } else if module.is_normal() {
 521                                 Flags::MISC_SUGGEST_SELF
 522                             } else {
 523                                 Flags::empty()
 524                             };
 525                             Ok((binding, Flags::MODULE | misc_flags))
 526                         }
 527                         Err((Determinacy::Undetermined, Weak::No)) =>
 528                             return Some(Err(Determinacy::determined(force))),
 529                         Err((Determinacy::Undetermined, Weak::Yes)) =>
 530                             Err(Determinacy::Undetermined),
 531                         Err((Determinacy::Determined, _)) => Err(Determinacy::Determined),
 532                     }
 533                 }
 534                 Scope::MacroUsePrelude => match this.macro_use_prelude.get(&ident.name).cloned() {
 535                     Some(binding) => Ok((binding, Flags::PRELUDE | Flags::MISC_FROM_PRELUDE)),
 536                     None => Err(Determinacy::determined(
 537                         this.graph_root.unexpanded_invocations.borrow().is_empty()
 538                     ))
 539                 }
 540                 Scope::BuiltinAttrs => if is_builtin_attr_name(ident.name) {
 541                     let binding = (Res::NonMacroAttr(NonMacroAttrKind::Builtin),
 542                                    ty::Visibility::Public, DUMMY_SP, ExpnId::root())
 543                                    .to_name_binding(this.arenas);
 544                     Ok((binding, Flags::PRELUDE))
 545                 } else {
 546                     Err(Determinacy::Determined)
 547                 }
 548                 Scope::LegacyPluginHelpers => if this.session.plugin_attributes.borrow().iter()
 549                                                      .any(|(name, _)| ident.name == *name) {
 550                     let binding = (Res::NonMacroAttr(NonMacroAttrKind::LegacyPluginHelper),
 551                                    ty::Visibility::Public, DUMMY_SP, ExpnId::root())
 552                                    .to_name_binding(this.arenas);
 553                     Ok((binding, Flags::PRELUDE))
 554                 } else {
 555                     Err(Determinacy::Determined)
 556                 }
 557                 Scope::ExternPrelude => match this.extern_prelude_get(ident, !record_used) {
 558                     Some(binding) => Ok((binding, Flags::PRELUDE)),
 559                     None => Err(Determinacy::determined(
 560                         this.graph_root.unexpanded_invocations.borrow().is_empty()
 561                     )),
 562                 }
 563                 Scope::ToolPrelude => if KNOWN_TOOLS.contains(&ident.name) {
 564                     let binding = (Res::ToolMod, ty::Visibility::Public, DUMMY_SP, ExpnId::root())
 565                                    .to_name_binding(this.arenas);
 566                     Ok((binding, Flags::PRELUDE))
 567                 } else {
 568                     Err(Determinacy::Determined)
 569                 }
 570                 Scope::StdLibPrelude => {
 571                     let mut result = Err(Determinacy::Determined);
 572                     if let Some(prelude) = this.prelude {
 573                         if let Ok(binding) = this.resolve_ident_in_module_unadjusted(
 574                             ModuleOrUniformRoot::Module(prelude),
 575                             ident,
 576                             ns,
 577                             parent_scope,
 578                             false,
 579                             path_span,
 580                         ) {
 581                             if use_prelude || this.is_builtin_macro(binding.res()) {
 582                                 result = Ok((binding, Flags::PRELUDE | Flags::MISC_FROM_PRELUDE));
 583                             }
 584                         }
 585                     }
 586                     result
 587                 }
 588                 Scope::BuiltinTypes => match this.primitive_type_table.primitive_types
 589                                                  .get(&ident.name).cloned() {
 590                     Some(prim_ty) => {
 591                         let binding = (Res::PrimTy(prim_ty), ty::Visibility::Public,
 592                                        DUMMY_SP, ExpnId::root()).to_name_binding(this.arenas);
 593                         Ok((binding, Flags::PRELUDE))
 594                     }
 595                     None => Err(Determinacy::Determined)
 596                 }
 597             };
 598
 599             match result {
 600                 Ok((binding, flags)) if sub_namespace_match(binding.macro_kind(), macro_kind) => {
 601                     if !record_used {
 602                         return Some(Ok(binding));
 603                     }
 604
 605                     if let Some((innermost_binding, innermost_flags)) = innermost_result {
 606                         // Found another solution, if the first one was "weak", report an error.
 607                         let (res, innermost_res) = (binding.res(), innermost_binding.res());
 608                         if res != innermost_res {
 609                             let builtin = Res::NonMacroAttr(NonMacroAttrKind::Builtin);
 610                             let derive_helper = Res::NonMacroAttr(NonMacroAttrKind::DeriveHelper);
 611                             let legacy_helper =
 612                                 Res::NonMacroAttr(NonMacroAttrKind::LegacyPluginHelper);
 613
 614                             let ambiguity_error_kind = if is_import {
 615                                 Some(AmbiguityKind::Import)
 616                             } else if innermost_res == builtin || res == builtin {
 617                                 Some(AmbiguityKind::BuiltinAttr)
 618                             } else if innermost_res == derive_helper || res == derive_helper {
 619                                 Some(AmbiguityKind::DeriveHelper)
 620                             } else if innermost_res == legacy_helper &&
 621                                       flags.contains(Flags::PRELUDE) ||
 622                                       res == legacy_helper &&
 623                                       innermost_flags.contains(Flags::PRELUDE) {
 624                                 Some(AmbiguityKind::LegacyHelperVsPrelude)
 625                             } else if innermost_flags.contains(Flags::MACRO_RULES) &&
 626                                       flags.contains(Flags::MODULE) &&
 627                                       !this.disambiguate_legacy_vs_modern(innermost_binding,
 628                                                                           binding) ||
 629                                       flags.contains(Flags::MACRO_RULES) &&
 630                                       innermost_flags.contains(Flags::MODULE) &&
 631                                       !this.disambiguate_legacy_vs_modern(binding,
 632                                                                           innermost_binding) {
 633                                 Some(AmbiguityKind::LegacyVsModern)
 634                             } else if innermost_binding.is_glob_import() {
 635                                 Some(AmbiguityKind::GlobVsOuter)
 636                             } else if innermost_binding.may_appear_after(parent_scope.expansion,
 637                                                                          binding) {
 638                                 Some(AmbiguityKind::MoreExpandedVsOuter)
 639                             } else {
 640                                 None
 641                             };
 642                             if let Some(kind) = ambiguity_error_kind {
 643                                 let misc = |f: Flags| if f.contains(Flags::MISC_SUGGEST_CRATE) {
 644                                     AmbiguityErrorMisc::SuggestCrate
 645                                 } else if f.contains(Flags::MISC_SUGGEST_SELF) {
 646                                     AmbiguityErrorMisc::SuggestSelf
 647                                 } else if f.contains(Flags::MISC_FROM_PRELUDE) {
 648                                     AmbiguityErrorMisc::FromPrelude
 649                                 } else {
 650                                     AmbiguityErrorMisc::None
 651                                 };
 652                                 this.ambiguity_errors.push(AmbiguityError {
 653                                     kind,
 654                                     ident: orig_ident,
 655                                     b1: innermost_binding,
 656                                     b2: binding,
 657                                     misc1: misc(innermost_flags),
 658                                     misc2: misc(flags),
 659                                 });
 660                                 return Some(Ok(innermost_binding));
 661                             }
 662                         }
 663                     } else {
 664                         // Found the first solution.
 665                         innermost_result = Some((binding, flags));
 666                     }
 667                 }
 668                 Ok(..) | Err(Determinacy::Determined) => {}
 669                 Err(Determinacy::Undetermined) => determinacy = Determinacy::Undetermined
 670             }
 671
 672             None
 673         });
 674
 675         if let Some(break_result) = break_result {
 676             return break_result;
 677         }
 678
 679         // The first found solution was the only one, return it.
 680         if let Some((binding, _)) = innermost_result {
 681             return Ok(binding);
 682         }
 683
 684         let determinacy = Determinacy::determined(determinacy == Determinacy::Determined || force);
 685         if determinacy == Determinacy::Determined && macro_kind == Some(MacroKind::Attr) &&
 686            self.session.features_untracked().custom_attribute {
 687             // For single-segment attributes interpret determinate "no resolution" as a custom
 688             // attribute. (Lexical resolution implies the first segment and attr kind should imply
 689             // the last segment, so we are certainly working with a single-segment attribute here.)
 690             assert!(ns == MacroNS);
 691             let binding = (Res::NonMacroAttr(NonMacroAttrKind::Custom),
 692                            ty::Visibility::Public, orig_ident.span, ExpnId::root())
 693                            .to_name_binding(self.arenas);
 694             Ok(binding)
 695         } else {
 696             Err(determinacy)
 697         }
 698     }
 699
 700     crate fn finalize_macro_resolutions(&mut self) {
 701         let check_consistency = |this: &mut Self, path: &[Segment], span, kind: MacroKind,
 702                                  initial_res: Option<Res>, res: Res| {
 703             if let Some(initial_res) = initial_res {
 704                 if res != initial_res && res != Res::Err && this.ambiguity_errors.is_empty() {
 705                     // Make sure compilation does not succeed if preferred macro resolution
 706                     // has changed after the macro had been expanded. In theory all such
 707                     // situations should be reported as ambiguity errors, so this is a bug.
 708                     if initial_res == Res::NonMacroAttr(NonMacroAttrKind::Custom) {
 709                         // Yeah, legacy custom attributes are implemented using forced resolution
 710                         // (which is a best effort error recovery tool, basically), so we can't
 711                         // promise their resolution won't change later.
 712                         let msg = format!("inconsistent resolution for a macro: first {}, then {}",
 713                                           initial_res.descr(), res.descr());
 714                         this.session.span_err(span, &msg);
 715                     } else {
 716                         span_bug!(span, "inconsistent resolution for a macro");
 717                     }
 718                 }
 719             } else {
 720                 // It's possible that the macro was unresolved (indeterminate) and silently
 721                 // expanded into a dummy fragment for recovery during expansion.
 722                 // Now, post-expansion, the resolution may succeed, but we can't change the
 723                 // past and need to report an error.
 724                 // However, non-speculative `resolve_path` can successfully return private items
 725                 // even if speculative `resolve_path` returned nothing previously, so we skip this
 726                 // less informative error if the privacy error is reported elsewhere.
 727                 if this.privacy_errors.is_empty() {
 728                     let msg = format!("cannot determine resolution for the {} `{}`",
 729                                         kind.descr(), Segment::names_to_string(path));
 730                     let msg_note = "import resolution is stuck, try simplifying macro imports";
 731                     this.session.struct_span_err(span, &msg).note(msg_note).emit();
 732                 }
 733             }
 734         };
 735
 736         let macro_resolutions = mem::take(&mut self.multi_segment_macro_resolutions);
 737         for (mut path, path_span, kind, parent_scope, initial_res) in macro_resolutions {
 738             // FIXME: Path resolution will ICE if segment IDs present.
 739             for seg in &mut path { seg.id = None; }
 740             match self.resolve_path(
 741                 &path, Some(MacroNS), &parent_scope, true, path_span, CrateLint::No
 742             ) {
 743                 PathResult::NonModule(path_res) if path_res.unresolved_segments() == 0 => {
 744                     let res = path_res.base_res();
 745                     check_consistency(self, &path, path_span, kind, initial_res, res);
 746                 }
 747                 path_res @ PathResult::NonModule(..) | path_res @ PathResult::Failed { .. } => {
 748                     let (span, label) = if let PathResult::Failed { span, label, .. } = path_res {
 749                         (span, label)
 750                     } else {
 751                         (path_span, format!("partially resolved path in {} {}",
 752                                             kind.article(), kind.descr()))
 753                     };
 754                     self.report_error(span, ResolutionError::FailedToResolve {
 755                         label,
 756                         suggestion: None
 757                     });
 758                 }
 759                 PathResult::Module(..) | PathResult::Indeterminate => unreachable!(),
 760             }
 761         }
 762
 763         let macro_resolutions = mem::take(&mut self.single_segment_macro_resolutions);
 764         for (ident, kind, parent_scope, initial_binding) in macro_resolutions {
 765             match self.early_resolve_ident_in_lexical_scope(ident, ScopeSet::Macro(kind),
 766                                                             &parent_scope, true, true, ident.span) {
 767                 Ok(binding) => {
 768                     let initial_res = initial_binding.map(|initial_binding| {
 769                         self.record_use(ident, MacroNS, initial_binding, false);
 770                         initial_binding.res()
 771                     });
 772                     let res = binding.res();
 773                     let seg = Segment::from_ident(ident);
 774                     check_consistency(self, &[seg], ident.span, kind, initial_res, res);
 775                 }
 776                 Err(..) => {
 777                     let expected = kind.descr_expected();
 778                     let msg = format!("cannot find {} `{}` in this scope", expected, ident);
 779                     let mut err = self.session.struct_span_err(ident.span, &msg);
 780                     self.unresolved_macro_suggestions(&mut err, kind, &parent_scope, ident);
 781                     err.emit();
 782                 }
 783             }
 784         }
 785
 786         let builtin_attrs = mem::take(&mut self.builtin_attrs);
 787         for (ident, parent_scope) in builtin_attrs {
 788             let _ = self.early_resolve_ident_in_lexical_scope(
 789                 ident, ScopeSet::Macro(MacroKind::Attr), &parent_scope, true, true, ident.span
 790             );
 791         }
 792     }
 793
 794     fn check_stability_and_deprecation(&mut self, ext: &SyntaxExtension, path: &ast::Path) {
 795         let span = path.span;
 796         if let Some(stability) = &ext.stability {
 797             if let StabilityLevel::Unstable { reason, issue, is_soft } = stability.level {
 798                 let feature = stability.feature;
 799                 if !self.active_features.contains(&feature) && !span.allows_unstable(feature) {
 800                     let node_id = ast::CRATE_NODE_ID;
 801                     let lint_buffer = &mut self.lint_buffer;
 802                     let soft_handler = |lint, span, msg: &_| {
 803                         lint_buffer.buffer_lint(lint, node_id, span, msg)
 804                     };
 805                     stability::report_unstable(
 806                         self.session, feature, reason, issue, is_soft, span, soft_handler
 807                     );
 808                 }
 809             }
 810             if let Some(depr) = &stability.rustc_depr {
 811                 let path = pprust::path_to_string(path);
 812                 let (message, lint) = stability::rustc_deprecation_message(depr, &path);
 813                 stability::early_report_deprecation(
 814                     &mut self.lint_buffer, &message, depr.suggestion, lint, span
 815                 );
 816             }
 817         }
 818         if let Some(depr) = &ext.deprecation {
 819             let path = pprust::path_to_string(&path);
 820             let (message, lint) = stability::deprecation_message(depr, &path);
 821             stability::early_report_deprecation(&mut self.lint_buffer, &message, None, lint, span);
 822         }
 823     }
 824
 825     fn prohibit_imported_non_macro_attrs(&self, binding: Option<&'a NameBinding<'a>>,
 826                                          res: Option<Res>, span: Span) {
 827         if let Some(Res::NonMacroAttr(kind)) = res {
 828             if kind != NonMacroAttrKind::Tool && binding.map_or(true, |b| b.is_import()) {
 829                 let msg = format!("cannot use a {} through an import", kind.descr());
 830                 let mut err = self.session.struct_span_err(span, &msg);
 831                 if let Some(binding) = binding {
 832                     err.span_note(binding.span, &format!("the {} imported here", kind.descr()));
 833                 }
 834                 err.emit();
 835             }
 836         }
 837     }
 838
 839     crate fn check_reserved_macro_name(&mut self, ident: Ident, res: Res) {
 840         // Reserve some names that are not quite covered by the general check
 841         // performed on `Resolver::builtin_attrs`.
 842         if ident.name == sym::cfg || ident.name == sym::cfg_attr || ident.name == sym::derive {
 843             let macro_kind = self.get_macro(res).map(|ext| ext.macro_kind());
 844             if macro_kind.is_some() && sub_namespace_match(macro_kind, Some(MacroKind::Attr)) {
 845                 self.session.span_err(
 846                     ident.span, &format!("name `{}` is reserved in attribute namespace", ident)
 847                 );
 848             }
 849         }
 850     }
 851
 852     /// Compile the macro into a `SyntaxExtension` and possibly replace it with a pre-defined
 853     /// extension partially or entirely for built-in macros and legacy plugin macros.
 854     crate fn compile_macro(&mut self, item: &ast::Item, edition: Edition) -> SyntaxExtension {
 855         let mut result = compile_declarative_macro(
 856             &self.session.parse_sess, self.session.features_untracked(), item, edition
 857         );
 858
 859         if result.is_builtin {
 860             // The macro was marked with `#[rustc_builtin_macro]`.
 861             if let Some(ext) = self.builtin_macros.remove(&item.ident.name) {
 862                 if ext.is_builtin {
 863                     // The macro is a built-in, replace only the expander function.
 864                     result.kind = ext.kind;
 865                 } else {
 866                     // The macro is from a plugin, the in-source definition is dummy,
 867                     // take all the data from the resolver.
 868                     result = ext;
 869                 }
 870             } else {
 871                 let msg = format!("cannot find a built-in macro with name `{}`", item.ident);
 872                 self.session.span_err(item.span, &msg);
 873             }
 874         }
 875
 876         result
 877     }
 878 }