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