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