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