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