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