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::imports::ImportResolver;
   5 use crate::Namespace::*;
   6 use crate::{AmbiguityError, AmbiguityErrorMisc, AmbiguityKind, Determinacy};
   7 use crate::{CrateLint, ParentScope, ResolutionError, Resolver, Scope, ScopeSet, Weak};
   8 use crate::{ModuleKind, ModuleOrUniformRoot, NameBinding, PathResult, Segment, ToNameBinding};
   9 use rustc_ast::{self as ast, NodeId};
  10 use rustc_ast_lowering::ResolverAstLowering;
  11 use rustc_ast_pretty::pprust;
  12 use rustc_attr::StabilityLevel;
  13 use rustc_data_structures::fx::FxHashSet;
  14 use rustc_expand::base::{Indeterminate, InvocationRes, ResolverExpand, SyntaxExtension};
  15 use rustc_expand::compile_declarative_macro;
  16 use rustc_expand::expand::{AstFragment, AstFragmentKind, Invocation, InvocationKind};
  17 use rustc_feature::is_builtin_attr_name;
  18 use rustc_hir::def::{self, DefKind, NonMacroAttrKind};
  19 use rustc_hir::def_id;
  20 use rustc_middle::middle::stability;
  21 use rustc_middle::{span_bug, ty};
  22 use rustc_session::lint::builtin::UNUSED_MACROS;
  23 use rustc_session::Session;
  24 use rustc_span::edition::Edition;
  25 use rustc_span::hygiene::{self, ExpnData, ExpnId, ExpnKind};
  26 use rustc_span::symbol::{kw, sym, Ident, Symbol};
  27 use rustc_span::{Span, DUMMY_SP};
  28
  29 use rustc_data_structures::sync::Lrc;
  30 use rustc_span::hygiene::{AstPass, MacroKind};
  31 use std::{mem, ptr};
  32
  33 type Res = def::Res<NodeId>;
  34
  35 /// Binding produced by a `macro_rules` item.
  36 /// Not modularized, can shadow previous `macro_rules` bindings, etc.
  37 #[derive(Debug)]
  38 pub struct MacroRulesBinding<'a> {
  39     crate binding: &'a NameBinding<'a>,
  40     /// `macro_rules` scope into which the `macro_rules` item was planted.
  41     crate parent_macro_rules_scope: MacroRulesScope<'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 `macro_rules` scopes too because they
  49 /// can potentially expand into macro definitions.
  50 #[derive(Copy, Clone, Debug)]
  51 pub enum MacroRulesScope<'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 MacroRulesBinding<'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 {
  67         Bang,
  68         AttrLike,
  69     }
  70     let sub_ns = |kind| match kind {
  71         MacroKind::Bang => SubNS::Bang,
  72         MacroKind::Attr | MacroKind::Derive => SubNS::AttrLike,
  73     };
  74     let candidate = candidate.map(sub_ns);
  75     let requirement = requirement.map(sub_ns);
  76     // "No specific sub-namespace" means "matches anything" for both requirements and candidates.
  77     candidate.is_none() || requirement.is_none() || candidate == requirement
  78 }
  79
  80 // We don't want to format a path using pretty-printing,
  81 // `format!("{}", path)`, because that tries to insert
  82 // line-breaks and is slow.
  83 fn fast_print_path(path: &ast::Path) -> Symbol {
  84     if path.segments.len() == 1 {
  85         path.segments[0].ident.name
  86     } else {
  87         let mut path_str = String::with_capacity(64);
  88         for (i, segment) in path.segments.iter().enumerate() {
  89             if i != 0 {
  90                 path_str.push_str("::");
  91             }
  92             if segment.ident.name != kw::PathRoot {
  93                 path_str.push_str(&segment.ident.as_str())
  94             }
  95         }
  96         Symbol::intern(&path_str)
  97     }
  98 }
  99
 100 /// The code common between processing `#![register_tool]` and `#![register_attr]`.
 101 fn registered_idents(
 102     sess: &Session,
 103     attrs: &[ast::Attribute],
 104     attr_name: Symbol,
 105     descr: &str,
 106 ) -> FxHashSet<Ident> {
 107     let mut registered = FxHashSet::default();
 108     for attr in sess.filter_by_name(attrs, attr_name) {
 109         for nested_meta in attr.meta_item_list().unwrap_or_default() {
 110             match nested_meta.ident() {
 111                 Some(ident) => {
 112                     if let Some(old_ident) = registered.replace(ident) {
 113                         let msg = format!("{} `{}` was already registered", descr, ident);
 114                         sess.struct_span_err(ident.span, &msg)
 115                             .span_label(old_ident.span, "already registered here")
 116                             .emit();
 117                     }
 118                 }
 119                 None => {
 120                     let msg = format!("`{}` only accepts identifiers", attr_name);
 121                     let span = nested_meta.span();
 122                     sess.struct_span_err(span, &msg).span_label(span, "not an identifier").emit();
 123                 }
 124             }
 125         }
 126     }
 127     registered
 128 }
 129
 130 crate fn registered_attrs_and_tools(
 131     sess: &Session,
 132     attrs: &[ast::Attribute],
 133 ) -> (FxHashSet<Ident>, FxHashSet<Ident>) {
 134     let registered_attrs = registered_idents(sess, attrs, sym::register_attr, "attribute");
 135     let mut registered_tools = registered_idents(sess, attrs, sym::register_tool, "tool");
 136     // We implicitly add `rustfmt` and `clippy` to known tools,
 137     // but it's not an error to register them explicitly.
 138     let predefined_tools = [sym::clippy, sym::rustfmt];
 139     registered_tools.extend(predefined_tools.iter().cloned().map(Ident::with_dummy_span));
 140     (registered_attrs, registered_tools)
 141 }
 142
 143 impl<'a> ResolverExpand for Resolver<'a> {
 144     fn next_node_id(&mut self) -> NodeId {
 145         self.next_node_id()
 146     }
 147
 148     fn resolve_dollar_crates(&mut self) {
 149         hygiene::update_dollar_crate_names(|ctxt| {
 150             let ident = Ident::new(kw::DollarCrate, DUMMY_SP.with_ctxt(ctxt));
 151             match self.resolve_crate_root(ident).kind {
 152                 ModuleKind::Def(.., name) if name != kw::Invalid => name,
 153                 _ => kw::Crate,
 154             }
 155         });
 156     }
 157
 158     fn visit_ast_fragment_with_placeholders(&mut self, expansion: ExpnId, fragment: &AstFragment) {
 159         // Integrate the new AST fragment into all the definition and module structures.
 160         // We are inside the `expansion` now, but other parent scope components are still the same.
 161         let parent_scope = ParentScope { expansion, ..self.invocation_parent_scopes[&expansion] };
 162         let output_macro_rules_scope = self.build_reduced_graph(fragment, parent_scope);
 163         self.output_macro_rules_scopes.insert(expansion, output_macro_rules_scope);
 164
 165         parent_scope.module.unexpanded_invocations.borrow_mut().remove(&expansion);
 166     }
 167
 168     fn register_builtin_macro(&mut self, ident: Ident, ext: SyntaxExtension) {
 169         if self.builtin_macros.insert(ident.name, ext).is_some() {
 170             self.session
 171                 .span_err(ident.span, &format!("built-in macro `{}` was already defined", ident));
 172         }
 173     }
 174
 175     // Create a new Expansion with a definition site of the provided module, or
 176     // a fake empty `#[no_implicit_prelude]` module if no module is provided.
 177     fn expansion_for_ast_pass(
 178         &mut self,
 179         call_site: Span,
 180         pass: AstPass,
 181         features: &[Symbol],
 182         parent_module_id: Option<NodeId>,
 183     ) -> ExpnId {
 184         let expn_id = ExpnId::fresh(Some(ExpnData::allow_unstable(
 185             ExpnKind::AstPass(pass),
 186             call_site,
 187             self.session.edition(),
 188             features.into(),
 189             None,
 190         )));
 191
 192         let parent_scope = if let Some(module_id) = parent_module_id {
 193             let parent_def_id = self.local_def_id(module_id);
 194             self.definitions.add_parent_module_of_macro_def(expn_id, parent_def_id.to_def_id());
 195             self.module_map[&parent_def_id]
 196         } else {
 197             self.definitions.add_parent_module_of_macro_def(
 198                 expn_id,
 199                 def_id::DefId::local(def_id::CRATE_DEF_INDEX),
 200             );
 201             self.empty_module
 202         };
 203         self.ast_transform_scopes.insert(expn_id, parent_scope);
 204         expn_id
 205     }
 206
 207     fn resolve_imports(&mut self) {
 208         ImportResolver { r: self }.resolve_imports()
 209     }
 210
 211     fn resolve_macro_invocation(
 212         &mut self,
 213         invoc: &Invocation,
 214         eager_expansion_root: ExpnId,
 215         force: bool,
 216     ) -> Result<InvocationRes, Indeterminate> {
 217         let invoc_id = invoc.expansion_data.id;
 218         let parent_scope = match self.invocation_parent_scopes.get(&invoc_id) {
 219             Some(parent_scope) => *parent_scope,
 220             None => {
 221                 // If there's no entry in the table, then we are resolving an eagerly expanded
 222                 // macro, which should inherit its parent scope from its eager expansion root -
 223                 // the macro that requested this eager expansion.
 224                 let parent_scope = *self
 225                     .invocation_parent_scopes
 226                     .get(&eager_expansion_root)
 227                     .expect("non-eager expansion without a parent scope");
 228                 self.invocation_parent_scopes.insert(invoc_id, parent_scope);
 229                 parent_scope
 230             }
 231         };
 232
 233         let (path, kind, derives, after_derive) = match invoc.kind {
 234             InvocationKind::Attr { ref attr, ref derives, after_derive, .. } => (
 235                 &attr.get_normal_item().path,
 236                 MacroKind::Attr,
 237                 self.arenas.alloc_ast_paths(derives),
 238                 after_derive,
 239             ),
 240             InvocationKind::Bang { ref mac, .. } => (&mac.path, MacroKind::Bang, &[][..], false),
 241             InvocationKind::Derive { ref path, .. } => (path, MacroKind::Derive, &[][..], false),
 242             InvocationKind::DeriveContainer { ref derives, .. } => {
 243                 // Block expansion of the container until we resolve all derives in it.
 244                 // This is required for two reasons:
 245                 // - Derive helper attributes are in scope for the item to which the `#[derive]`
 246                 //   is applied, so they have to be produced by the container's expansion rather
 247                 //   than by individual derives.
 248                 // - Derives in the container need to know whether one of them is a built-in `Copy`.
 249                 // FIXME: Try to avoid repeated resolutions for derives here and in expansion.
 250                 let mut exts = Vec::new();
 251                 let mut helper_attrs = Vec::new();
 252                 for path in derives {
 253                     exts.push(
 254                         match self.resolve_macro_path(
 255                             path,
 256                             Some(MacroKind::Derive),
 257                             &parent_scope,
 258                             true,
 259                             force,
 260                         ) {
 261                             Ok((Some(ext), _)) => {
 262                                 let span = path
 263                                     .segments
 264                                     .last()
 265                                     .unwrap()
 266                                     .ident
 267                                     .span
 268                                     .normalize_to_macros_2_0();
 269                                 helper_attrs.extend(
 270                                     ext.helper_attrs.iter().map(|name| Ident::new(*name, span)),
 271                                 );
 272                                 if ext.is_derive_copy {
 273                                     self.add_derive_copy(invoc_id);
 274                                 }
 275                                 ext
 276                             }
 277                             Ok(_) | Err(Determinacy::Determined) => {
 278                                 self.dummy_ext(MacroKind::Derive)
 279                             }
 280                             Err(Determinacy::Undetermined) => return Err(Indeterminate),
 281                         },
 282                     )
 283                 }
 284                 self.helper_attrs.insert(invoc_id, helper_attrs);
 285                 return Ok(InvocationRes::DeriveContainer(exts));
 286             }
 287         };
 288
 289         // Derives are not included when `invocations` are collected, so we have to add them here.
 290         let parent_scope = &ParentScope { derives, ..parent_scope };
 291         let node_id = self.lint_node_id(eager_expansion_root);
 292         let (ext, res) = self.smart_resolve_macro_path(path, kind, parent_scope, node_id, force)?;
 293
 294         let span = invoc.span();
 295         invoc_id.set_expn_data(ext.expn_data(
 296             parent_scope.expansion,
 297             span,
 298             fast_print_path(path),
 299             res.opt_def_id(),
 300         ));
 301
 302         if let Res::Def(_, _) = res {
 303             if after_derive {
 304                 self.session.span_err(span, "macro attributes must be placed before `#[derive]`");
 305             }
 306             let normal_module_def_id = self.macro_def_scope(invoc_id).normal_ancestor_id;
 307             self.definitions.add_parent_module_of_macro_def(invoc_id, normal_module_def_id);
 308         }
 309
 310         match invoc.fragment_kind {
 311             AstFragmentKind::Arms
 312             | AstFragmentKind::Fields
 313             | AstFragmentKind::FieldPats
 314             | AstFragmentKind::GenericParams
 315             | AstFragmentKind::Params
 316             | AstFragmentKind::StructFields
 317             | AstFragmentKind::Variants => {
 318                 if let Res::Def(..) = res {
 319                     self.session.span_err(
 320                         span,
 321                         &format!(
 322                             "expected an inert attribute, found {} {}",
 323                             res.article(),
 324                             res.descr()
 325                         ),
 326                     );
 327                     return Ok(InvocationRes::Single(self.dummy_ext(kind)));
 328                 }
 329             }
 330             _ => {}
 331         }
 332
 333         Ok(InvocationRes::Single(ext))
 334     }
 335
 336     fn check_unused_macros(&mut self) {
 337         for (_, &(node_id, span)) in self.unused_macros.iter() {
 338             self.lint_buffer.buffer_lint(UNUSED_MACROS, node_id, span, "unused macro definition");
 339         }
 340     }
 341
 342     fn lint_node_id(&mut self, expn_id: ExpnId) -> NodeId {
 343         self.invocation_parents
 344             .get(&expn_id)
 345             .map_or(ast::CRATE_NODE_ID, |id| self.def_id_to_node_id[*id])
 346     }
 347
 348     fn has_derive_copy(&self, expn_id: ExpnId) -> bool {
 349         self.containers_deriving_copy.contains(&expn_id)
 350     }
 351
 352     fn add_derive_copy(&mut self, expn_id: ExpnId) {
 353         self.containers_deriving_copy.insert(expn_id);
 354     }
 355
 356     // The function that implements the resolution logic of `#[cfg_accessible(path)]`.
 357     // Returns true if the path can certainly be resolved in one of three namespaces,
 358     // returns false if the path certainly cannot be resolved in any of the three namespaces.
 359     // Returns `Indeterminate` if we cannot give a certain answer yet.
 360     fn cfg_accessible(&mut self, expn_id: ExpnId, path: &ast::Path) -> Result<bool, Indeterminate> {
 361         let span = path.span;
 362         let path = &Segment::from_path(path);
 363         let parent_scope = self.invocation_parent_scopes[&expn_id];
 364
 365         let mut indeterminate = false;
 366         for ns in [TypeNS, ValueNS, MacroNS].iter().copied() {
 367             match self.resolve_path(path, Some(ns), &parent_scope, false, span, CrateLint::No) {
 368                 PathResult::Module(ModuleOrUniformRoot::Module(_)) => return Ok(true),
 369                 PathResult::NonModule(partial_res) if partial_res.unresolved_segments() == 0 => {
 370                     return Ok(true);
 371                 }
 372                 PathResult::Indeterminate => indeterminate = true,
 373                 // FIXME: `resolve_path` is not ready to report partially resolved paths
 374                 // correctly, so we just report an error if the path was reported as unresolved.
 375                 // This needs to be fixed for `cfg_accessible` to be useful.
 376                 PathResult::NonModule(..) | PathResult::Failed { .. } => {}
 377                 PathResult::Module(_) => panic!("unexpected path resolution"),
 378             }
 379         }
 380
 381         if indeterminate {
 382             return Err(Indeterminate);
 383         }
 384
 385         self.session
 386             .struct_span_err(span, "not sure whether the path is accessible or not")
 387             .span_note(span, "`cfg_accessible` is not fully implemented")
 388             .emit();
 389         Ok(false)
 390     }
 391 }
 392
 393 impl<'a> Resolver<'a> {
 394     /// Resolve macro path with error reporting and recovery.
 395     fn smart_resolve_macro_path(
 396         &mut self,
 397         path: &ast::Path,
 398         kind: MacroKind,
 399         parent_scope: &ParentScope<'a>,
 400         node_id: NodeId,
 401         force: bool,
 402     ) -> Result<(Lrc<SyntaxExtension>, Res), Indeterminate> {
 403         let (ext, res) = match self.resolve_macro_path(path, Some(kind), parent_scope, true, force)
 404         {
 405             Ok((Some(ext), res)) => (ext, res),
 406             // Use dummy syntax extensions for unresolved macros for better recovery.
 407             Ok((None, res)) => (self.dummy_ext(kind), res),
 408             Err(Determinacy::Determined) => (self.dummy_ext(kind), Res::Err),
 409             Err(Determinacy::Undetermined) => return Err(Indeterminate),
 410         };
 411
 412         // Report errors for the resolved macro.
 413         for segment in &path.segments {
 414             if let Some(args) = &segment.args {
 415                 self.session.span_err(args.span(), "generic arguments in macro path");
 416             }
 417             if kind == MacroKind::Attr && segment.ident.as_str().starts_with("rustc") {
 418                 self.session.span_err(
 419                     segment.ident.span,
 420                     "attributes starting with `rustc` are reserved for use by the `rustc` compiler",
 421                 );
 422             }
 423         }
 424
 425         match res {
 426             Res::Def(DefKind::Macro(_), def_id) => {
 427                 if let Some(def_id) = def_id.as_local() {
 428                     self.unused_macros.remove(&def_id);
 429                     if self.proc_macro_stubs.contains(&def_id) {
 430                         self.session.span_err(
 431                             path.span,
 432                             "can't use a procedural macro from the same crate that defines it",
 433                         );
 434                     }
 435                 }
 436             }
 437             Res::NonMacroAttr(..) | Res::Err => {}
 438             _ => panic!("expected `DefKind::Macro` or `Res::NonMacroAttr`"),
 439         };
 440
 441         self.check_stability_and_deprecation(&ext, path, node_id);
 442
 443         Ok(if ext.macro_kind() != kind {
 444             let expected = kind.descr_expected();
 445             let path_str = pprust::path_to_string(path);
 446             let msg = format!("expected {}, found {} `{}`", expected, res.descr(), path_str);
 447             self.session
 448                 .struct_span_err(path.span, &msg)
 449                 .span_label(path.span, format!("not {} {}", kind.article(), expected))
 450                 .emit();
 451             // Use dummy syntax extensions for unexpected macro kinds for better recovery.
 452             (self.dummy_ext(kind), Res::Err)
 453         } else {
 454             (ext, res)
 455         })
 456     }
 457
 458     pub fn resolve_macro_path(
 459         &mut self,
 460         path: &ast::Path,
 461         kind: Option<MacroKind>,
 462         parent_scope: &ParentScope<'a>,
 463         trace: bool,
 464         force: bool,
 465     ) -> Result<(Option<Lrc<SyntaxExtension>>, Res), Determinacy> {
 466         let path_span = path.span;
 467         let mut path = Segment::from_path(path);
 468
 469         // Possibly apply the macro helper hack
 470         if kind == Some(MacroKind::Bang)
 471             && path.len() == 1
 472             && path[0].ident.span.ctxt().outer_expn_data().local_inner_macros
 473         {
 474             let root = Ident::new(kw::DollarCrate, path[0].ident.span);
 475             path.insert(0, Segment::from_ident(root));
 476         }
 477
 478         let res = if path.len() > 1 {
 479             let res = match self.resolve_path(
 480                 &path,
 481                 Some(MacroNS),
 482                 parent_scope,
 483                 false,
 484                 path_span,
 485                 CrateLint::No,
 486             ) {
 487                 PathResult::NonModule(path_res) if path_res.unresolved_segments() == 0 => {
 488                     Ok(path_res.base_res())
 489                 }
 490                 PathResult::Indeterminate if !force => return Err(Determinacy::Undetermined),
 491                 PathResult::NonModule(..)
 492                 | PathResult::Indeterminate
 493                 | PathResult::Failed { .. } => Err(Determinacy::Determined),
 494                 PathResult::Module(..) => unreachable!(),
 495             };
 496
 497             if trace {
 498                 let kind = kind.expect("macro kind must be specified if tracing is enabled");
 499                 self.multi_segment_macro_resolutions.push((
 500                     path,
 501                     path_span,
 502                     kind,
 503                     *parent_scope,
 504                     res.ok(),
 505                 ));
 506             }
 507
 508             self.prohibit_imported_non_macro_attrs(None, res.ok(), path_span);
 509             res
 510         } else {
 511             let scope_set = kind.map_or(ScopeSet::All(MacroNS, false), ScopeSet::Macro);
 512             let binding = self.early_resolve_ident_in_lexical_scope(
 513                 path[0].ident,
 514                 scope_set,
 515                 parent_scope,
 516                 false,
 517                 force,
 518                 path_span,
 519             );
 520             if let Err(Determinacy::Undetermined) = binding {
 521                 return Err(Determinacy::Undetermined);
 522             }
 523
 524             if trace {
 525                 let kind = kind.expect("macro kind must be specified if tracing is enabled");
 526                 self.single_segment_macro_resolutions.push((
 527                     path[0].ident,
 528                     kind,
 529                     *parent_scope,
 530                     binding.ok(),
 531                 ));
 532             }
 533
 534             let res = binding.map(|binding| binding.res());
 535             self.prohibit_imported_non_macro_attrs(binding.ok(), res.ok(), path_span);
 536             res
 537         };
 538
 539         res.map(|res| (self.get_macro(res), res))
 540     }
 541
 542     // Resolve an identifier in lexical scope.
 543     // This is a variation of `fn resolve_ident_in_lexical_scope` that can be run during
 544     // expansion and import resolution (perhaps they can be merged in the future).
 545     // The function is used for resolving initial segments of macro paths (e.g., `foo` in
 546     // `foo::bar!(); or `foo!();`) and also for import paths on 2018 edition.
 547     crate fn early_resolve_ident_in_lexical_scope(
 548         &mut self,
 549         orig_ident: Ident,
 550         scope_set: ScopeSet,
 551         parent_scope: &ParentScope<'a>,
 552         record_used: bool,
 553         force: bool,
 554         path_span: Span,
 555     ) -> Result<&'a NameBinding<'a>, Determinacy> {
 556         bitflags::bitflags! {
 557             struct Flags: u8 {
 558                 const MACRO_RULES          = 1 << 0;
 559                 const MODULE               = 1 << 1;
 560                 const DERIVE_HELPER_COMPAT = 1 << 2;
 561                 const MISC_SUGGEST_CRATE   = 1 << 3;
 562                 const MISC_SUGGEST_SELF    = 1 << 4;
 563                 const MISC_FROM_PRELUDE    = 1 << 5;
 564             }
 565         }
 566
 567         assert!(force || !record_used); // `record_used` implies `force`
 568
 569         // Make sure `self`, `super` etc produce an error when passed to here.
 570         if orig_ident.is_path_segment_keyword() {
 571             return Err(Determinacy::Determined);
 572         }
 573
 574         let (ns, macro_kind, is_import) = match scope_set {
 575             ScopeSet::All(ns, is_import) => (ns, None, is_import),
 576             ScopeSet::AbsolutePath(ns) => (ns, None, false),
 577             ScopeSet::Macro(macro_kind) => (MacroNS, Some(macro_kind), false),
 578         };
 579
 580         // This is *the* result, resolution from the scope closest to the resolved identifier.
 581         // However, sometimes this result is "weak" because it comes from a glob import or
 582         // a macro expansion, and in this case it cannot shadow names from outer scopes, e.g.
 583         // mod m { ... } // solution in outer scope
 584         // {
 585         //     use prefix::*; // imports another `m` - innermost solution
 586         //                    // weak, cannot shadow the outer `m`, need to report ambiguity error
 587         //     m::mac!();
 588         // }
 589         // So we have to save the innermost solution and continue searching in outer scopes
 590         // to detect potential ambiguities.
 591         let mut innermost_result: Option<(&NameBinding<'_>, Flags)> = None;
 592         let mut determinacy = Determinacy::Determined;
 593
 594         // Go through all the scopes and try to resolve the name.
 595         let break_result = self.visit_scopes(
 596             scope_set,
 597             parent_scope,
 598             orig_ident,
 599             |this, scope, use_prelude, ident| {
 600                 let ok = |res, span, arenas| {
 601                     Ok((
 602                         (res, ty::Visibility::Public, span, ExpnId::root()).to_name_binding(arenas),
 603                         Flags::empty(),
 604                     ))
 605                 };
 606                 let result = match scope {
 607                     Scope::DeriveHelpers(expn_id) => {
 608                         if let Some(attr) = this
 609                             .helper_attrs
 610                             .get(&expn_id)
 611                             .and_then(|attrs| attrs.iter().rfind(|i| ident == **i))
 612                         {
 613                             let binding = (
 614                                 Res::NonMacroAttr(NonMacroAttrKind::DeriveHelper),
 615                                 ty::Visibility::Public,
 616                                 attr.span,
 617                                 expn_id,
 618                             )
 619                                 .to_name_binding(this.arenas);
 620                             Ok((binding, Flags::empty()))
 621                         } else {
 622                             Err(Determinacy::Determined)
 623                         }
 624                     }
 625                     Scope::DeriveHelpersCompat => {
 626                         let mut result = Err(Determinacy::Determined);
 627                         for derive in parent_scope.derives {
 628                             let parent_scope = &ParentScope { derives: &[], ..*parent_scope };
 629                             match this.resolve_macro_path(
 630                                 derive,
 631                                 Some(MacroKind::Derive),
 632                                 parent_scope,
 633                                 true,
 634                                 force,
 635                             ) {
 636                                 Ok((Some(ext), _)) => {
 637                                     if ext.helper_attrs.contains(&ident.name) {
 638                                         let binding = (
 639                                             Res::NonMacroAttr(NonMacroAttrKind::DeriveHelper),
 640                                             ty::Visibility::Public,
 641                                             derive.span,
 642                                             ExpnId::root(),
 643                                         )
 644                                             .to_name_binding(this.arenas);
 645                                         result = Ok((binding, Flags::DERIVE_HELPER_COMPAT));
 646                                         break;
 647                                     }
 648                                 }
 649                                 Ok(_) | Err(Determinacy::Determined) => {}
 650                                 Err(Determinacy::Undetermined) => {
 651                                     result = Err(Determinacy::Undetermined)
 652                                 }
 653                             }
 654                         }
 655                         result
 656                     }
 657                     Scope::MacroRules(macro_rules_scope) => match macro_rules_scope {
 658                         MacroRulesScope::Binding(macro_rules_binding)
 659                             if ident == macro_rules_binding.ident =>
 660                         {
 661                             Ok((macro_rules_binding.binding, Flags::MACRO_RULES))
 662                         }
 663                         MacroRulesScope::Invocation(invoc_id)
 664                             if !this.output_macro_rules_scopes.contains_key(&invoc_id) =>
 665                         {
 666                             Err(Determinacy::Undetermined)
 667                         }
 668                         _ => Err(Determinacy::Determined),
 669                     },
 670                     Scope::CrateRoot => {
 671                         let root_ident = Ident::new(kw::PathRoot, ident.span);
 672                         let root_module = this.resolve_crate_root(root_ident);
 673                         let binding = this.resolve_ident_in_module_ext(
 674                             ModuleOrUniformRoot::Module(root_module),
 675                             ident,
 676                             ns,
 677                             parent_scope,
 678                             record_used,
 679                             path_span,
 680                         );
 681                         match binding {
 682                             Ok(binding) => Ok((binding, Flags::MODULE | Flags::MISC_SUGGEST_CRATE)),
 683                             Err((Determinacy::Undetermined, Weak::No)) => {
 684                                 return Some(Err(Determinacy::determined(force)));
 685                             }
 686                             Err((Determinacy::Undetermined, Weak::Yes)) => {
 687                                 Err(Determinacy::Undetermined)
 688                             }
 689                             Err((Determinacy::Determined, _)) => Err(Determinacy::Determined),
 690                         }
 691                     }
 692                     Scope::Module(module) => {
 693                         let adjusted_parent_scope = &ParentScope { module, ..*parent_scope };
 694                         let binding = this.resolve_ident_in_module_unadjusted_ext(
 695                             ModuleOrUniformRoot::Module(module),
 696                             ident,
 697                             ns,
 698                             adjusted_parent_scope,
 699                             true,
 700                             record_used,
 701                             path_span,
 702                         );
 703                         match binding {
 704                             Ok(binding) => {
 705                                 let misc_flags = if ptr::eq(module, this.graph_root) {
 706                                     Flags::MISC_SUGGEST_CRATE
 707                                 } else if module.is_normal() {
 708                                     Flags::MISC_SUGGEST_SELF
 709                                 } else {
 710                                     Flags::empty()
 711                                 };
 712                                 Ok((binding, Flags::MODULE | misc_flags))
 713                             }
 714                             Err((Determinacy::Undetermined, Weak::No)) => {
 715                                 return Some(Err(Determinacy::determined(force)));
 716                             }
 717                             Err((Determinacy::Undetermined, Weak::Yes)) => {
 718                                 Err(Determinacy::Undetermined)
 719                             }
 720                             Err((Determinacy::Determined, _)) => Err(Determinacy::Determined),
 721                         }
 722                     }
 723                     Scope::RegisteredAttrs => match this.registered_attrs.get(&ident).cloned() {
 724                         Some(ident) => ok(
 725                             Res::NonMacroAttr(NonMacroAttrKind::Registered),
 726                             ident.span,
 727                             this.arenas,
 728                         ),
 729                         None => Err(Determinacy::Determined),
 730                     },
 731                     Scope::MacroUsePrelude => {
 732                         match this.macro_use_prelude.get(&ident.name).cloned() {
 733                             Some(binding) => Ok((binding, Flags::MISC_FROM_PRELUDE)),
 734                             None => Err(Determinacy::determined(
 735                                 this.graph_root.unexpanded_invocations.borrow().is_empty(),
 736                             )),
 737                         }
 738                     }
 739                     Scope::BuiltinAttrs => {
 740                         if is_builtin_attr_name(ident.name) {
 741                             ok(Res::NonMacroAttr(NonMacroAttrKind::Builtin), DUMMY_SP, this.arenas)
 742                         } else {
 743                             Err(Determinacy::Determined)
 744                         }
 745                     }
 746                     Scope::ExternPrelude => match this.extern_prelude_get(ident, !record_used) {
 747                         Some(binding) => Ok((binding, Flags::empty())),
 748                         None => Err(Determinacy::determined(
 749                             this.graph_root.unexpanded_invocations.borrow().is_empty(),
 750                         )),
 751                     },
 752                     Scope::ToolPrelude => match this.registered_tools.get(&ident).cloned() {
 753                         Some(ident) => ok(Res::ToolMod, ident.span, this.arenas),
 754                         None => Err(Determinacy::Determined),
 755                     },
 756                     Scope::StdLibPrelude => {
 757                         let mut result = Err(Determinacy::Determined);
 758                         if let Some(prelude) = this.prelude {
 759                             if let Ok(binding) = this.resolve_ident_in_module_unadjusted(
 760                                 ModuleOrUniformRoot::Module(prelude),
 761                                 ident,
 762                                 ns,
 763                                 parent_scope,
 764                                 false,
 765                                 path_span,
 766                             ) {
 767                                 if use_prelude || this.is_builtin_macro(binding.res()) {
 768                                     result = Ok((binding, Flags::MISC_FROM_PRELUDE));
 769                                 }
 770                             }
 771                         }
 772                         result
 773                     }
 774                     Scope::BuiltinTypes => {
 775                         match this.primitive_type_table.primitive_types.get(&ident.name).cloned() {
 776                             Some(prim_ty) => ok(Res::PrimTy(prim_ty), DUMMY_SP, this.arenas),
 777                             None => Err(Determinacy::Determined),
 778                         }
 779                     }
 780                 };
 781
 782                 match result {
 783                     Ok((binding, flags))
 784                         if sub_namespace_match(binding.macro_kind(), macro_kind) =>
 785                     {
 786                         if !record_used {
 787                             return Some(Ok(binding));
 788                         }
 789
 790                         if let Some((innermost_binding, innermost_flags)) = innermost_result {
 791                             // Found another solution, if the first one was "weak", report an error.
 792                             let (res, innermost_res) = (binding.res(), innermost_binding.res());
 793                             if res != innermost_res {
 794                                 let builtin = Res::NonMacroAttr(NonMacroAttrKind::Builtin);
 795                                 let is_derive_helper_compat = |res, flags: Flags| {
 796                                     res == Res::NonMacroAttr(NonMacroAttrKind::DeriveHelper)
 797                                         && flags.contains(Flags::DERIVE_HELPER_COMPAT)
 798                                 };
 799
 800                                 let ambiguity_error_kind = if is_import {
 801                                     Some(AmbiguityKind::Import)
 802                                 } else if innermost_res == builtin || res == builtin {
 803                                     Some(AmbiguityKind::BuiltinAttr)
 804                                 } else if is_derive_helper_compat(innermost_res, innermost_flags)
 805                                     || is_derive_helper_compat(res, flags)
 806                                 {
 807                                     Some(AmbiguityKind::DeriveHelper)
 808                                 } else if innermost_flags.contains(Flags::MACRO_RULES)
 809                                     && flags.contains(Flags::MODULE)
 810                                     && !this.disambiguate_macro_rules_vs_modularized(
 811                                         innermost_binding,
 812                                         binding,
 813                                     )
 814                                     || flags.contains(Flags::MACRO_RULES)
 815                                         && innermost_flags.contains(Flags::MODULE)
 816                                         && !this.disambiguate_macro_rules_vs_modularized(
 817                                             binding,
 818                                             innermost_binding,
 819                                         )
 820                                 {
 821                                     Some(AmbiguityKind::MacroRulesVsModularized)
 822                                 } else if innermost_binding.is_glob_import() {
 823                                     Some(AmbiguityKind::GlobVsOuter)
 824                                 } else if innermost_binding
 825                                     .may_appear_after(parent_scope.expansion, binding)
 826                                 {
 827                                     Some(AmbiguityKind::MoreExpandedVsOuter)
 828                                 } else {
 829                                     None
 830                                 };
 831                                 if let Some(kind) = ambiguity_error_kind {
 832                                     let misc = |f: Flags| {
 833                                         if f.contains(Flags::MISC_SUGGEST_CRATE) {
 834                                             AmbiguityErrorMisc::SuggestCrate
 835                                         } else if f.contains(Flags::MISC_SUGGEST_SELF) {
 836                                             AmbiguityErrorMisc::SuggestSelf
 837                                         } else if f.contains(Flags::MISC_FROM_PRELUDE) {
 838                                             AmbiguityErrorMisc::FromPrelude
 839                                         } else {
 840                                             AmbiguityErrorMisc::None
 841                                         }
 842                                     };
 843                                     this.ambiguity_errors.push(AmbiguityError {
 844                                         kind,
 845                                         ident: orig_ident,
 846                                         b1: innermost_binding,
 847                                         b2: binding,
 848                                         misc1: misc(innermost_flags),
 849                                         misc2: misc(flags),
 850                                     });
 851                                     return Some(Ok(innermost_binding));
 852                                 }
 853                             }
 854                         } else {
 855                             // Found the first solution.
 856                             innermost_result = Some((binding, flags));
 857                         }
 858                     }
 859                     Ok(..) | Err(Determinacy::Determined) => {}
 860                     Err(Determinacy::Undetermined) => determinacy = Determinacy::Undetermined,
 861                 }
 862
 863                 None
 864             },
 865         );
 866
 867         if let Some(break_result) = break_result {
 868             return break_result;
 869         }
 870
 871         // The first found solution was the only one, return it.
 872         if let Some((binding, _)) = innermost_result {
 873             return Ok(binding);
 874         }
 875
 876         Err(Determinacy::determined(determinacy == Determinacy::Determined || force))
 877     }
 878
 879     crate fn finalize_macro_resolutions(&mut self) {
 880         let check_consistency = |this: &mut Self,
 881                                  path: &[Segment],
 882                                  span,
 883                                  kind: MacroKind,
 884                                  initial_res: Option<Res>,
 885                                  res: Res| {
 886             if let Some(initial_res) = initial_res {
 887                 if res != initial_res && res != Res::Err && this.ambiguity_errors.is_empty() {
 888                     // Make sure compilation does not succeed if preferred macro resolution
 889                     // has changed after the macro had been expanded. In theory all such
 890                     // situations should be reported as ambiguity errors, so this is a bug.
 891                     span_bug!(span, "inconsistent resolution for a macro");
 892                 }
 893             } else {
 894                 // It's possible that the macro was unresolved (indeterminate) and silently
 895                 // expanded into a dummy fragment for recovery during expansion.
 896                 // Now, post-expansion, the resolution may succeed, but we can't change the
 897                 // past and need to report an error.
 898                 // However, non-speculative `resolve_path` can successfully return private items
 899                 // even if speculative `resolve_path` returned nothing previously, so we skip this
 900                 // less informative error if the privacy error is reported elsewhere.
 901                 if this.privacy_errors.is_empty() {
 902                     let msg = format!(
 903                         "cannot determine resolution for the {} `{}`",
 904                         kind.descr(),
 905                         Segment::names_to_string(path)
 906                     );
 907                     let msg_note = "import resolution is stuck, try simplifying macro imports";
 908                     this.session.struct_span_err(span, &msg).note(msg_note).emit();
 909                 }
 910             }
 911         };
 912
 913         let macro_resolutions = mem::take(&mut self.multi_segment_macro_resolutions);
 914         for (mut path, path_span, kind, parent_scope, initial_res) in macro_resolutions {
 915             // FIXME: Path resolution will ICE if segment IDs present.
 916             for seg in &mut path {
 917                 seg.id = None;
 918             }
 919             match self.resolve_path(
 920                 &path,
 921                 Some(MacroNS),
 922                 &parent_scope,
 923                 true,
 924                 path_span,
 925                 CrateLint::No,
 926             ) {
 927                 PathResult::NonModule(path_res) if path_res.unresolved_segments() == 0 => {
 928                     let res = path_res.base_res();
 929                     check_consistency(self, &path, path_span, kind, initial_res, res);
 930                 }
 931                 path_res @ PathResult::NonModule(..) | path_res @ PathResult::Failed { .. } => {
 932                     let (span, label) = if let PathResult::Failed { span, label, .. } = path_res {
 933                         (span, label)
 934                     } else {
 935                         (
 936                             path_span,
 937                             format!(
 938                                 "partially resolved path in {} {}",
 939                                 kind.article(),
 940                                 kind.descr()
 941                             ),
 942                         )
 943                     };
 944                     self.report_error(
 945                         span,
 946                         ResolutionError::FailedToResolve { label, suggestion: None },
 947                     );
 948                 }
 949                 PathResult::Module(..) | PathResult::Indeterminate => unreachable!(),
 950             }
 951         }
 952
 953         let macro_resolutions = mem::take(&mut self.single_segment_macro_resolutions);
 954         for (ident, kind, parent_scope, initial_binding) in macro_resolutions {
 955             match self.early_resolve_ident_in_lexical_scope(
 956                 ident,
 957                 ScopeSet::Macro(kind),
 958                 &parent_scope,
 959                 true,
 960                 true,
 961                 ident.span,
 962             ) {
 963                 Ok(binding) => {
 964                     let initial_res = initial_binding.map(|initial_binding| {
 965                         self.record_use(ident, MacroNS, initial_binding, false);
 966                         initial_binding.res()
 967                     });
 968                     let res = binding.res();
 969                     let seg = Segment::from_ident(ident);
 970                     check_consistency(self, &[seg], ident.span, kind, initial_res, res);
 971                 }
 972                 Err(..) => {
 973                     let expected = kind.descr_expected();
 974                     let msg = format!("cannot find {} `{}` in this scope", expected, ident);
 975                     let mut err = self.session.struct_span_err(ident.span, &msg);
 976                     self.unresolved_macro_suggestions(&mut err, kind, &parent_scope, ident);
 977                     err.emit();
 978                 }
 979             }
 980         }
 981
 982         let builtin_attrs = mem::take(&mut self.builtin_attrs);
 983         for (ident, parent_scope) in builtin_attrs {
 984             let _ = self.early_resolve_ident_in_lexical_scope(
 985                 ident,
 986                 ScopeSet::Macro(MacroKind::Attr),
 987                 &parent_scope,
 988                 true,
 989                 true,
 990                 ident.span,
 991             );
 992         }
 993     }
 994
 995     fn check_stability_and_deprecation(
 996         &mut self,
 997         ext: &SyntaxExtension,
 998         path: &ast::Path,
 999         node_id: NodeId,
1000     ) {
1001         let span = path.span;
1002         if let Some(stability) = &ext.stability {
1003             if let StabilityLevel::Unstable { reason, issue, is_soft } = stability.level {
1004                 let feature = stability.feature;
1005                 if !self.active_features.contains(&feature) && !span.allows_unstable(feature) {
1006                     let lint_buffer = &mut self.lint_buffer;
1007                     let soft_handler =
1008                         |lint, span, msg: &_| lint_buffer.buffer_lint(lint, node_id, span, msg);
1009                     stability::report_unstable(
1010                         self.session,
1011                         feature,
1012                         reason,
1013                         issue,
1014                         is_soft,
1015                         span,
1016                         soft_handler,
1017                     );
1018                 }
1019             }
1020         }
1021         if let Some(depr) = &ext.deprecation {
1022             let path = pprust::path_to_string(&path);
1023             let (message, lint) = stability::deprecation_message(depr, "macro", &path);
1024             stability::early_report_deprecation(
1025                 &mut self.lint_buffer,
1026                 &message,
1027                 depr.suggestion,
1028                 lint,
1029                 span,
1030             );
1031         }
1032     }
1033
1034     fn prohibit_imported_non_macro_attrs(
1035         &self,
1036         binding: Option<&'a NameBinding<'a>>,
1037         res: Option<Res>,
1038         span: Span,
1039     ) {
1040         if let Some(Res::NonMacroAttr(kind)) = res {
1041             if kind != NonMacroAttrKind::Tool && binding.map_or(true, |b| b.is_import()) {
1042                 let msg =
1043                     format!("cannot use {} {} through an import", kind.article(), kind.descr());
1044                 let mut err = self.session.struct_span_err(span, &msg);
1045                 if let Some(binding) = binding {
1046                     err.span_note(binding.span, &format!("the {} imported here", kind.descr()));
1047                 }
1048                 err.emit();
1049             }
1050         }
1051     }
1052
1053     crate fn check_reserved_macro_name(&mut self, ident: Ident, res: Res) {
1054         // Reserve some names that are not quite covered by the general check
1055         // performed on `Resolver::builtin_attrs`.
1056         if ident.name == sym::cfg || ident.name == sym::cfg_attr || ident.name == sym::derive {
1057             let macro_kind = self.get_macro(res).map(|ext| ext.macro_kind());
1058             if macro_kind.is_some() && sub_namespace_match(macro_kind, Some(MacroKind::Attr)) {
1059                 self.session.span_err(
1060                     ident.span,
1061                     &format!("name `{}` is reserved in attribute namespace", ident),
1062                 );
1063             }
1064         }
1065     }
1066
1067     /// Compile the macro into a `SyntaxExtension` and possibly replace
1068     /// its expander to a pre-defined one for built-in macros.
1069     crate fn compile_macro(&mut self, item: &ast::Item, edition: Edition) -> SyntaxExtension {
1070         let mut result = compile_declarative_macro(
1071             &self.session,
1072             self.session.features_untracked(),
1073             item,
1074             edition,
1075         );
1076
1077         if result.is_builtin {
1078             // The macro was marked with `#[rustc_builtin_macro]`.
1079             if let Some(ext) = self.builtin_macros.remove(&item.ident.name) {
1080                 // The macro is a built-in, replace its expander function
1081                 // while still taking everything else from the source code.
1082                 result.kind = ext.kind;
1083             } else {
1084                 let msg = format!("cannot find a built-in macro with name `{}`", item.ident);
1085                 self.session.span_err(item.span, &msg);
1086             }
1087         }
1088
1089         result
1090     }
1091 }