src/librustc_resolve/macros.rs

   1 // Copyright 2016 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 use {AmbiguityError, CrateLint, Resolver, ResolutionError, is_known_tool, resolve_error};
  12 use {Module, ModuleKind, NameBinding, NameBindingKind, PathResult, ToNameBinding};
  13 use ModuleOrUniformRoot;
  14 use Namespace::{self, *};
  15 use build_reduced_graph::{BuildReducedGraphVisitor, IsMacroExport};
  16 use resolve_imports::ImportResolver;
  17 use rustc::hir::def_id::{DefId, CRATE_DEF_INDEX, DefIndex,
  18                          CrateNum, DefIndexAddressSpace};
  19 use rustc::hir::def::{Def, NonMacroAttrKind};
  20 use rustc::hir::map::{self, DefCollector};
  21 use rustc::{ty, lint};
  22 use syntax::ast::{self, Name, Ident};
  23 use syntax::attr;
  24 use syntax::errors::DiagnosticBuilder;
  25 use syntax::ext::base::{self, Determinacy};
  26 use syntax::ext::base::{MacroKind, SyntaxExtension, Resolver as SyntaxResolver};
  27 use syntax::ext::expand::{AstFragment, Invocation, InvocationKind};
  28 use syntax::ext::hygiene::{self, Mark};
  29 use syntax::ext::tt::macro_rules;
  30 use syntax::feature_gate::{self, feature_err, emit_feature_err, is_builtin_attr_name, GateIssue};
  31 use syntax::feature_gate::EXPLAIN_DERIVE_UNDERSCORE;
  32 use syntax::fold::{self, Folder};
  33 use syntax::parse::parser::PathStyle;
  34 use syntax::parse::token::{self, Token};
  35 use syntax::ptr::P;
  36 use syntax::symbol::{Symbol, keywords};
  37 use syntax::tokenstream::{TokenStream, TokenTree, Delimited, DelimSpan};
  38 use syntax::util::lev_distance::find_best_match_for_name;
  39 use syntax_pos::{Span, DUMMY_SP};
  40 use errors::Applicability;
  41
  42 use std::cell::Cell;
  43 use std::mem;
  44 use rustc_data_structures::sync::Lrc;
  45
  46 #[derive(Clone)]
  47 pub struct InvocationData<'a> {
  48     def_index: DefIndex,
  49     /// Module in which the macro was invoked.
  50     crate module: Cell<Module<'a>>,
  51     /// Legacy scope in which the macro was invoked.
  52     /// The invocation path is resolved in this scope.
  53     crate parent_legacy_scope: Cell<LegacyScope<'a>>,
  54     /// Legacy scope *produced* by expanding this macro invocation,
  55     /// includes all the macro_rules items, other invocations, etc generated by it.
  56     /// Set to the parent scope if the macro is not expanded yet (as if the macro produced nothing).
  57     crate output_legacy_scope: Cell<LegacyScope<'a>>,
  58 }
  59
  60 impl<'a> InvocationData<'a> {
  61     pub fn root(graph_root: Module<'a>) -> Self {
  62         InvocationData {
  63             module: Cell::new(graph_root),
  64             def_index: CRATE_DEF_INDEX,
  65             parent_legacy_scope: Cell::new(LegacyScope::Empty),
  66             output_legacy_scope: Cell::new(LegacyScope::Empty),
  67         }
  68     }
  69 }
  70
  71 /// Binding produced by a `macro_rules` item.
  72 /// Not modularized, can shadow previous legacy bindings, etc.
  73 pub struct LegacyBinding<'a> {
  74     binding: &'a NameBinding<'a>,
  75     /// Legacy scope into which the `macro_rules` item was planted.
  76     parent_legacy_scope: LegacyScope<'a>,
  77     ident: Ident,
  78 }
  79
  80 /// Scope introduced by a `macro_rules!` macro.
  81 /// Starts at the macro's definition and ends at the end of the macro's parent module
  82 /// (named or unnamed), or even further if it escapes with `#[macro_use]`.
  83 /// Some macro invocations need to introduce legacy scopes too because they
  84 /// potentially can expand into macro definitions.
  85 #[derive(Copy, Clone)]
  86 pub enum LegacyScope<'a> {
  87     /// Created when invocation data is allocated in the arena,
  88     /// must be replaced with a proper scope later.
  89     Uninitialized,
  90     /// Empty "root" scope at the crate start containing no names.
  91     Empty,
  92     /// Scope introduced by a `macro_rules!` macro definition.
  93     Binding(&'a LegacyBinding<'a>),
  94     /// Scope introduced by a macro invocation that can potentially
  95     /// create a `macro_rules!` macro definition.
  96     Invocation(&'a InvocationData<'a>),
  97 }
  98
  99 /// Everything you need to resolve a macro path.
 100 #[derive(Clone)]
 101 pub struct ParentScope<'a> {
 102     crate module: Module<'a>,
 103     crate expansion: Mark,
 104     crate legacy: LegacyScope<'a>,
 105     crate derives: Vec<ast::Path>,
 106 }
 107
 108 // Macro namespace is separated into two sub-namespaces, one for bang macros and
 109 // one for attribute-like macros (attributes, derives).
 110 // We ignore resolutions from one sub-namespace when searching names in scope for another.
 111 fn sub_namespace_mismatch(requirement: Option<MacroKind>, candidate: Option<MacroKind>) -> bool {
 112     #[derive(PartialEq)]
 113     enum SubNS { Bang, AttrLike }
 114     let sub_ns = |kind| match kind {
 115         MacroKind::Bang => Some(SubNS::Bang),
 116         MacroKind::Attr | MacroKind::Derive => Some(SubNS::AttrLike),
 117         MacroKind::ProcMacroStub => None,
 118     };
 119     let requirement = requirement.and_then(|kind| sub_ns(kind));
 120     let candidate = candidate.and_then(|kind| sub_ns(kind));
 121     // "No specific sub-namespace" means "matches anything" for both requirements and candidates.
 122     candidate.is_some() && requirement.is_some() && candidate != requirement
 123 }
 124
 125 impl<'a, 'crateloader: 'a> base::Resolver for Resolver<'a, 'crateloader> {
 126     fn next_node_id(&mut self) -> ast::NodeId {
 127         self.session.next_node_id()
 128     }
 129
 130     fn get_module_scope(&mut self, id: ast::NodeId) -> Mark {
 131         let mark = Mark::fresh(Mark::root());
 132         let module = self.module_map[&self.definitions.local_def_id(id)];
 133         self.invocations.insert(mark, self.arenas.alloc_invocation_data(InvocationData {
 134             module: Cell::new(module),
 135             def_index: module.def_id().unwrap().index,
 136             parent_legacy_scope: Cell::new(LegacyScope::Empty),
 137             output_legacy_scope: Cell::new(LegacyScope::Empty),
 138         }));
 139         mark
 140     }
 141
 142     fn eliminate_crate_var(&mut self, item: P<ast::Item>) -> P<ast::Item> {
 143         struct EliminateCrateVar<'b, 'a: 'b, 'crateloader: 'a>(
 144             &'b mut Resolver<'a, 'crateloader>, Span
 145         );
 146
 147         impl<'a, 'b, 'crateloader> Folder for EliminateCrateVar<'a, 'b, 'crateloader> {
 148             fn fold_path(&mut self, path: ast::Path) -> ast::Path {
 149                 match self.fold_qpath(None, path) {
 150                     (None, path) => path,
 151                     _ => unreachable!(),
 152                 }
 153             }
 154
 155             fn fold_qpath(&mut self, mut qself: Option<ast::QSelf>, mut path: ast::Path)
 156                           -> (Option<ast::QSelf>, ast::Path) {
 157                 qself = qself.map(|ast::QSelf { ty, path_span, position }| {
 158                     ast::QSelf {
 159                         ty: self.fold_ty(ty),
 160                         path_span: self.new_span(path_span),
 161                         position,
 162                     }
 163                 });
 164
 165                 if path.segments[0].ident.name == keywords::DollarCrate.name() {
 166                     let module = self.0.resolve_crate_root(path.segments[0].ident);
 167                     path.segments[0].ident.name = keywords::CrateRoot.name();
 168                     if !module.is_local() {
 169                         let span = path.segments[0].ident.span;
 170                         path.segments.insert(1, match module.kind {
 171                             ModuleKind::Def(_, name) => ast::PathSegment::from_ident(
 172                                 ast::Ident::with_empty_ctxt(name).with_span_pos(span)
 173                             ),
 174                             _ => unreachable!(),
 175                         });
 176                         if let Some(qself) = &mut qself {
 177                             qself.position += 1;
 178                         }
 179                     }
 180                 }
 181                 (qself, path)
 182             }
 183
 184             fn fold_mac(&mut self, mac: ast::Mac) -> ast::Mac {
 185                 fold::noop_fold_mac(mac, self)
 186             }
 187         }
 188
 189         let ret = EliminateCrateVar(self, item.span).fold_item(item);
 190         assert!(ret.len() == 1);
 191         ret.into_iter().next().unwrap()
 192     }
 193
 194     fn is_whitelisted_legacy_custom_derive(&self, name: Name) -> bool {
 195         self.whitelisted_legacy_custom_derives.contains(&name)
 196     }
 197
 198     fn visit_ast_fragment_with_placeholders(&mut self, mark: Mark, fragment: &AstFragment,
 199                                             derives: &[Mark]) {
 200         let invocation = self.invocations[&mark];
 201         self.collect_def_ids(mark, invocation, fragment);
 202
 203         self.current_module = invocation.module.get();
 204         self.current_module.unresolved_invocations.borrow_mut().remove(&mark);
 205         self.current_module.unresolved_invocations.borrow_mut().extend(derives);
 206         for &derive in derives {
 207             self.invocations.insert(derive, invocation);
 208         }
 209         let mut visitor = BuildReducedGraphVisitor {
 210             resolver: self,
 211             current_legacy_scope: invocation.parent_legacy_scope.get(),
 212             expansion: mark,
 213         };
 214         fragment.visit_with(&mut visitor);
 215         invocation.output_legacy_scope.set(visitor.current_legacy_scope);
 216     }
 217
 218     fn add_builtin(&mut self, ident: ast::Ident, ext: Lrc<SyntaxExtension>) {
 219         let def_id = DefId {
 220             krate: CrateNum::BuiltinMacros,
 221             index: DefIndex::from_array_index(self.macro_map.len(),
 222                                               DefIndexAddressSpace::Low),
 223         };
 224         let kind = ext.kind();
 225         self.macro_map.insert(def_id, ext);
 226         let binding = self.arenas.alloc_name_binding(NameBinding {
 227             kind: NameBindingKind::Def(Def::Macro(def_id, kind), false),
 228             span: DUMMY_SP,
 229             vis: ty::Visibility::Invisible,
 230             expansion: Mark::root(),
 231         });
 232         if self.builtin_macros.insert(ident.name, binding).is_some() {
 233             self.session.span_err(ident.span,
 234                                   &format!("built-in macro `{}` was already defined", ident));
 235         }
 236     }
 237
 238     fn resolve_imports(&mut self) {
 239         ImportResolver { resolver: self }.resolve_imports()
 240     }
 241
 242     // Resolves attribute and derive legacy macros from `#![plugin(..)]`.
 243     fn find_legacy_attr_invoc(&mut self, attrs: &mut Vec<ast::Attribute>, allow_derive: bool)
 244                               -> Option<ast::Attribute> {
 245         if !allow_derive {
 246             return None;
 247         }
 248
 249         // Check for legacy derives
 250         for i in 0..attrs.len() {
 251             let name = attrs[i].name();
 252
 253             if name == "derive" {
 254                 let result = attrs[i].parse_list(&self.session.parse_sess, |parser| {
 255                     parser.parse_path_allowing_meta(PathStyle::Mod)
 256                 });
 257
 258                 let mut traits = match result {
 259                     Ok(traits) => traits,
 260                     Err(mut e) => {
 261                         e.cancel();
 262                         continue
 263                     }
 264                 };
 265
 266                 for j in 0..traits.len() {
 267                     if traits[j].segments.len() > 1 {
 268                         continue
 269                     }
 270                     let trait_name = traits[j].segments[0].ident.name;
 271                     let legacy_name = Symbol::intern(&format!("derive_{}", trait_name));
 272                     if !self.builtin_macros.contains_key(&legacy_name) {
 273                         continue
 274                     }
 275                     let span = traits.remove(j).span;
 276                     self.gate_legacy_custom_derive(legacy_name, span);
 277                     if traits.is_empty() {
 278                         attrs.remove(i);
 279                     } else {
 280                         let mut tokens = Vec::new();
 281                         for (j, path) in traits.iter().enumerate() {
 282                             if j > 0 {
 283                                 tokens.push(TokenTree::Token(attrs[i].span, Token::Comma).into());
 284                             }
 285                             for (k, segment) in path.segments.iter().enumerate() {
 286                                 if k > 0 {
 287                                     tokens.push(TokenTree::Token(path.span, Token::ModSep).into());
 288                                 }
 289                                 let tok = Token::from_ast_ident(segment.ident);
 290                                 tokens.push(TokenTree::Token(path.span, tok).into());
 291                             }
 292                         }
 293                         let delim_span = DelimSpan::from_single(attrs[i].span);
 294                         attrs[i].tokens = TokenTree::Delimited(delim_span, Delimited {
 295                             delim: token::Paren,
 296                             tts: TokenStream::concat(tokens).into(),
 297                         }).into();
 298                     }
 299                     return Some(ast::Attribute {
 300                         path: ast::Path::from_ident(Ident::new(legacy_name, span)),
 301                         tokens: TokenStream::empty(),
 302                         id: attr::mk_attr_id(),
 303                         style: ast::AttrStyle::Outer,
 304                         is_sugared_doc: false,
 305                         span,
 306                     });
 307                 }
 308             }
 309         }
 310
 311         None
 312     }
 313
 314     fn resolve_macro_invocation(&mut self, invoc: &Invocation, invoc_id: Mark, force: bool)
 315                                 -> Result<Option<Lrc<SyntaxExtension>>, Determinacy> {
 316         let (path, kind, derives_in_scope, after_derive) = match invoc.kind {
 317             InvocationKind::Attr { attr: None, .. } =>
 318                 return Ok(None),
 319             InvocationKind::Attr { attr: Some(ref attr), ref traits, after_derive, .. } =>
 320                 (&attr.path, MacroKind::Attr, traits.clone(), after_derive),
 321             InvocationKind::Bang { ref mac, .. } =>
 322                 (&mac.node.path, MacroKind::Bang, Vec::new(), false),
 323             InvocationKind::Derive { ref path, .. } =>
 324                 (path, MacroKind::Derive, Vec::new(), false),
 325         };
 326
 327         let parent_scope = self.invoc_parent_scope(invoc_id, derives_in_scope);
 328         let (def, ext) = self.resolve_macro_to_def(path, kind, &parent_scope, force)?;
 329
 330         if let Def::Macro(def_id, _) = def {
 331             if after_derive {
 332                 self.session.span_err(invoc.span(),
 333                                       "macro attributes must be placed before `#[derive]`");
 334             }
 335             self.macro_defs.insert(invoc.expansion_data.mark, def_id);
 336             let normal_module_def_id =
 337                 self.macro_def_scope(invoc.expansion_data.mark).normal_ancestor_id;
 338             self.definitions.add_parent_module_of_macro_def(invoc.expansion_data.mark,
 339                                                             normal_module_def_id);
 340             invoc.expansion_data.mark.set_default_transparency(ext.default_transparency());
 341             invoc.expansion_data.mark.set_is_builtin(def_id.krate == CrateNum::BuiltinMacros);
 342         }
 343
 344         Ok(Some(ext))
 345     }
 346
 347     fn resolve_macro_path(&mut self, path: &ast::Path, kind: MacroKind, invoc_id: Mark,
 348                           derives_in_scope: Vec<ast::Path>, force: bool)
 349                           -> Result<Lrc<SyntaxExtension>, Determinacy> {
 350         let parent_scope = self.invoc_parent_scope(invoc_id, derives_in_scope);
 351         Ok(self.resolve_macro_to_def(path, kind, &parent_scope, force)?.1)
 352     }
 353
 354     fn check_unused_macros(&self) {
 355         for did in self.unused_macros.iter() {
 356             let id_span = match *self.macro_map[did] {
 357                 SyntaxExtension::NormalTT { def_info, .. } |
 358                 SyntaxExtension::DeclMacro { def_info, .. } => def_info,
 359                 _ => None,
 360             };
 361             if let Some((id, span)) = id_span {
 362                 let lint = lint::builtin::UNUSED_MACROS;
 363                 let msg = "unused macro definition";
 364                 self.session.buffer_lint(lint, id, span, msg);
 365             } else {
 366                 bug!("attempted to create unused macro error, but span not available");
 367             }
 368         }
 369     }
 370 }
 371
 372 impl<'a, 'cl> Resolver<'a, 'cl> {
 373     pub fn dummy_parent_scope(&mut self) -> ParentScope<'a> {
 374         self.invoc_parent_scope(Mark::root(), Vec::new())
 375     }
 376
 377     fn invoc_parent_scope(&mut self, invoc_id: Mark, derives: Vec<ast::Path>) -> ParentScope<'a> {
 378         let invoc = self.invocations[&invoc_id];
 379         ParentScope {
 380             module: invoc.module.get().nearest_item_scope(),
 381             expansion: invoc_id.parent(),
 382             legacy: invoc.parent_legacy_scope.get(),
 383             derives,
 384         }
 385     }
 386
 387     fn resolve_macro_to_def(
 388         &mut self,
 389         path: &ast::Path,
 390         kind: MacroKind,
 391         parent_scope: &ParentScope<'a>,
 392         force: bool,
 393     ) -> Result<(Def, Lrc<SyntaxExtension>), Determinacy> {
 394         let def = self.resolve_macro_to_def_inner(path, kind, parent_scope, force);
 395
 396         // Report errors and enforce feature gates for the resolved macro.
 397         if def != Err(Determinacy::Undetermined) {
 398             // Do not report duplicated errors on every undetermined resolution.
 399             for segment in &path.segments {
 400                 if let Some(args) = &segment.args {
 401                     self.session.span_err(args.span(), "generic arguments in macro path");
 402                 }
 403             }
 404         }
 405
 406         let def = def?;
 407
 408         match def {
 409             Def::Macro(def_id, macro_kind) => {
 410                 self.unused_macros.remove(&def_id);
 411                 if macro_kind == MacroKind::ProcMacroStub {
 412                     let msg = "can't use a procedural macro from the same crate that defines it";
 413                     self.session.span_err(path.span, msg);
 414                     return Err(Determinacy::Determined);
 415                 }
 416             }
 417             Def::NonMacroAttr(attr_kind) => {
 418                 if kind == MacroKind::Attr {
 419                     let features = self.session.features_untracked();
 420                     if attr_kind == NonMacroAttrKind::Custom {
 421                         assert!(path.segments.len() == 1);
 422                         let name = path.segments[0].ident.name.as_str();
 423                         if name.starts_with("rustc_") {
 424                             if !features.rustc_attrs {
 425                                 let msg = "unless otherwise specified, attributes with the prefix \
 426                                            `rustc_` are reserved for internal compiler diagnostics";
 427                                 feature_err(&self.session.parse_sess, "rustc_attrs", path.span,
 428                                             GateIssue::Language, &msg).emit();
 429                             }
 430                         } else if name.starts_with("derive_") {
 431                             if !features.custom_derive {
 432                                 feature_err(&self.session.parse_sess, "custom_derive", path.span,
 433                                             GateIssue::Language, EXPLAIN_DERIVE_UNDERSCORE).emit();
 434                             }
 435                         } else if !features.custom_attribute {
 436                             let msg = format!("The attribute `{}` is currently unknown to the \
 437                                                compiler and may have meaning added to it in the \
 438                                                future", path);
 439                             feature_err(&self.session.parse_sess, "custom_attribute", path.span,
 440                                         GateIssue::Language, &msg).emit();
 441                         }
 442                     }
 443                 } else {
 444                     // Not only attributes, but anything in macro namespace can result in
 445                     // `Def::NonMacroAttr` definition (e.g. `inline!()`), so we must report
 446                     // an error for those cases.
 447                     let msg = format!("expected a macro, found {}", def.kind_name());
 448                     self.session.span_err(path.span, &msg);
 449                     return Err(Determinacy::Determined);
 450                 }
 451             }
 452             _ => panic!("expected `Def::Macro` or `Def::NonMacroAttr`"),
 453         }
 454
 455         Ok((def, self.get_macro(def)))
 456     }
 457
 458     pub fn resolve_macro_to_def_inner(
 459         &mut self,
 460         path: &ast::Path,
 461         kind: MacroKind,
 462         parent_scope: &ParentScope<'a>,
 463         force: bool,
 464     ) -> Result<Def, Determinacy> {
 465         let ast::Path { ref segments, span } = *path;
 466         let mut path: Vec<_> = segments.iter().map(|seg| seg.ident).collect();
 467
 468         // Possibly apply the macro helper hack
 469         if kind == MacroKind::Bang && path.len() == 1 &&
 470            path[0].span.ctxt().outer().expn_info().map_or(false, |info| info.local_inner_macros) {
 471             let root = Ident::new(keywords::DollarCrate.name(), path[0].span);
 472             path.insert(0, root);
 473         }
 474
 475         if path.len() > 1 {
 476             let def = match self.resolve_path_with_parent_scope(None, &path, Some(MacroNS),
 477                                                                 parent_scope, false, span,
 478                                                                 CrateLint::No) {
 479                 PathResult::NonModule(path_res) => match path_res.base_def() {
 480                     Def::Err => Err(Determinacy::Determined),
 481                     def @ _ => {
 482                         if path_res.unresolved_segments() > 0 {
 483                             self.found_unresolved_macro = true;
 484                             self.session.span_err(span, "fail to resolve non-ident macro path");
 485                             Err(Determinacy::Determined)
 486                         } else {
 487                             Ok(def)
 488                         }
 489                     }
 490                 },
 491                 PathResult::Module(..) => unreachable!(),
 492                 PathResult::Indeterminate if !force => return Err(Determinacy::Undetermined),
 493                 _ => {
 494                     self.found_unresolved_macro = true;
 495                     Err(Determinacy::Determined)
 496                 },
 497             };
 498
 499             parent_scope.module.macro_resolutions.borrow_mut()
 500                 .push((path.into_boxed_slice(), span));
 501
 502             def
 503         } else {
 504             let binding = self.early_resolve_ident_in_lexical_scope(
 505                 path[0], MacroNS, Some(kind), parent_scope, false, force, span
 506             );
 507             match binding {
 508                 Ok(..) => {}
 509                 Err(Determinacy::Determined) => self.found_unresolved_macro = true,
 510                 Err(Determinacy::Undetermined) => return Err(Determinacy::Undetermined),
 511             }
 512
 513             parent_scope.module.legacy_macro_resolutions.borrow_mut()
 514                 .push((path[0], kind, parent_scope.clone(), binding.ok()));
 515
 516             binding.map(|binding| binding.def_ignoring_ambiguity())
 517         }
 518     }
 519
 520     // Resolve an identifier in lexical scope.
 521     // This is a variation of `fn resolve_ident_in_lexical_scope` that can be run during
 522     // expansion and import resolution (perhaps they can be merged in the future).
 523     // The function is used for resolving initial segments of macro paths (e.g. `foo` in
 524     // `foo::bar!(); or `foo!();`) and can be used for "uniform path" imports in the future.
 525     crate fn early_resolve_ident_in_lexical_scope(
 526         &mut self,
 527         mut ident: Ident,
 528         ns: Namespace,
 529         kind: Option<MacroKind>,
 530         parent_scope: &ParentScope<'a>,
 531         record_used: bool,
 532         force: bool,
 533         path_span: Span,
 534     ) -> Result<&'a NameBinding<'a>, Determinacy> {
 535         // General principles:
 536         // 1. Not controlled (user-defined) names should have higher priority than controlled names
 537         //    built into the language or standard library. This way we can add new names into the
 538         //    language or standard library without breaking user code.
 539         // 2. "Closed set" below means new names cannot appear after the current resolution attempt.
 540         // Places to search (in order of decreasing priority):
 541         // (Type NS)
 542         // 1. FIXME: Ribs (type parameters), there's no necessary infrastructure yet
 543         //    (open set, not controlled).
 544         // 2. Names in modules (both normal `mod`ules and blocks), loop through hygienic parents
 545         //    (open, not controlled).
 546         // 3. Extern prelude (closed, not controlled).
 547         // 4. Tool modules (closed, controlled right now, but not in the future).
 548         // 5. Standard library prelude (de-facto closed, controlled).
 549         // 6. Language prelude (closed, controlled).
 550         // (Value NS)
 551         // 1. FIXME: Ribs (local variables), there's no necessary infrastructure yet
 552         //    (open set, not controlled).
 553         // 2. Names in modules (both normal `mod`ules and blocks), loop through hygienic parents
 554         //    (open, not controlled).
 555         // 3. Standard library prelude (de-facto closed, controlled).
 556         // (Macro NS)
 557         // 1-3. Derive helpers (open, not controlled). All ambiguities with other names
 558         //    are currently reported as errors. They should be higher in priority than preludes
 559         //    and probably even names in modules according to the "general principles" above. They
 560         //    also should be subject to restricted shadowing because are effectively produced by
 561         //    derives (you need to resolve the derive first to add helpers into scope), but they
 562         //    should be available before the derive is expanded for compatibility.
 563         //    It's mess in general, so we are being conservative for now.
 564         // 1-3. `macro_rules` (open, not controlled), loop through legacy scopes. Have higher
 565         //    priority than prelude macros, but create ambiguities with macros in modules.
 566         // 1-3. Names in modules (both normal `mod`ules and blocks), loop through hygienic parents
 567         //    (open, not controlled). Have higher priority than prelude macros, but create
 568         //    ambiguities with `macro_rules`.
 569         // 4. `macro_use` prelude (open, the open part is from macro expansions, not controlled).
 570         // 4a. User-defined prelude from macro-use
 571         //    (open, the open part is from macro expansions, not controlled).
 572         // 4b. Standard library prelude is currently implemented as `macro-use` (closed, controlled)
 573         // 5. Language prelude: builtin macros (closed, controlled, except for legacy plugins).
 574         // 6. Language prelude: builtin attributes (closed, controlled).
 575         // 4-6. Legacy plugin helpers (open, not controlled). Similar to derive helpers,
 576         //    but introduced by legacy plugins using `register_attribute`. Priority is somewhere
 577         //    in prelude, not sure where exactly (creates ambiguities with any other prelude names).
 578
 579         enum WhereToResolve<'a> {
 580             DeriveHelpers,
 581             MacroRules(LegacyScope<'a>),
 582             Module(Module<'a>),
 583             MacroUsePrelude,
 584             BuiltinMacros,
 585             BuiltinAttrs,
 586             LegacyPluginHelpers,
 587             ExternPrelude,
 588             ToolPrelude,
 589             StdLibPrelude,
 590             BuiltinTypes,
 591         }
 592
 593         bitflags! {
 594             struct Flags: u8 {
 595                 const DERIVE_HELPERS = 1 << 0;
 596                 const MACRO_RULES    = 1 << 1;
 597                 const MODULE         = 1 << 2;
 598                 const PRELUDE        = 1 << 3;
 599             }
 600         }
 601
 602         assert!(force || !record_used); // `record_used` implies `force`
 603         ident = ident.modern();
 604
 605         // This is *the* result, resolution from the scope closest to the resolved identifier.
 606         // However, sometimes this result is "weak" because it comes from a glob import or
 607         // a macro expansion, and in this case it cannot shadow names from outer scopes, e.g.
 608         // mod m { ... } // solution in outer scope
 609         // {
 610         //     use prefix::*; // imports another `m` - innermost solution
 611         //                    // weak, cannot shadow the outer `m`, need to report ambiguity error
 612         //     m::mac!();
 613         // }
 614         // So we have to save the innermost solution and continue searching in outer scopes
 615         // to detect potential ambiguities.
 616         let mut innermost_result: Option<(&NameBinding, Flags, /* conflicts with */ Flags)> = None;
 617
 618         // Go through all the scopes and try to resolve the name.
 619         let mut where_to_resolve = WhereToResolve::DeriveHelpers;
 620         let mut use_prelude = !parent_scope.module.no_implicit_prelude;
 621         loop {
 622             let result = match where_to_resolve {
 623                 WhereToResolve::DeriveHelpers => {
 624                     let mut result = Err(Determinacy::Determined);
 625                     for derive in &parent_scope.derives {
 626                         let parent_scope = ParentScope { derives: Vec::new(), ..*parent_scope };
 627                         if let Ok((_, ext)) = self.resolve_macro_to_def(derive, MacroKind::Derive,
 628                                                                         &parent_scope, force) {
 629                             if let SyntaxExtension::ProcMacroDerive(_, helper_attrs, _) = &*ext {
 630                                 if helper_attrs.contains(&ident.name) {
 631                                     let binding =
 632                                         (Def::NonMacroAttr(NonMacroAttrKind::DeriveHelper),
 633                                         ty::Visibility::Public, derive.span, Mark::root())
 634                                         .to_name_binding(self.arenas);
 635                                     result = Ok((binding, Flags::DERIVE_HELPERS, Flags::all()));
 636                                     break;
 637                                 }
 638                             }
 639                         }
 640                     }
 641                     result
 642                 }
 643                 WhereToResolve::MacroRules(legacy_scope) => match legacy_scope {
 644                     LegacyScope::Binding(legacy_binding) if ident == legacy_binding.ident =>
 645                         Ok((legacy_binding.binding, Flags::MACRO_RULES, Flags::MODULE)),
 646                     _ => Err(Determinacy::Determined),
 647                 }
 648                 WhereToResolve::Module(module) => {
 649                     let orig_current_module = mem::replace(&mut self.current_module, module);
 650                     let binding = self.resolve_ident_in_module_unadjusted(
 651                         ModuleOrUniformRoot::Module(module),
 652                         ident,
 653                         ns,
 654                         true,
 655                         record_used,
 656                         path_span,
 657                     );
 658                     self.current_module = orig_current_module;
 659                     binding.map(|binding| (binding, Flags::MODULE, Flags::empty()))
 660                 }
 661                 WhereToResolve::MacroUsePrelude => {
 662                     match self.macro_use_prelude.get(&ident.name).cloned() {
 663                         Some(binding) => Ok((binding, Flags::PRELUDE, Flags::empty())),
 664                         None => Err(Determinacy::Determined),
 665                     }
 666                 }
 667                 WhereToResolve::BuiltinMacros => {
 668                     match self.builtin_macros.get(&ident.name).cloned() {
 669                         Some(binding) => Ok((binding, Flags::PRELUDE, Flags::empty())),
 670                         None => Err(Determinacy::Determined),
 671                     }
 672                 }
 673                 WhereToResolve::BuiltinAttrs => {
 674                     if is_builtin_attr_name(ident.name) {
 675                         let binding = (Def::NonMacroAttr(NonMacroAttrKind::Builtin),
 676                                        ty::Visibility::Public, ident.span, Mark::root())
 677                                        .to_name_binding(self.arenas);
 678                         Ok((binding, Flags::PRELUDE, Flags::empty()))
 679                     } else {
 680                         Err(Determinacy::Determined)
 681                     }
 682                 }
 683                 WhereToResolve::LegacyPluginHelpers => {
 684                     if self.session.plugin_attributes.borrow().iter()
 685                                                      .any(|(name, _)| ident.name == &**name) {
 686                         let binding = (Def::NonMacroAttr(NonMacroAttrKind::LegacyPluginHelper),
 687                                        ty::Visibility::Public, ident.span, Mark::root())
 688                                        .to_name_binding(self.arenas);
 689                         Ok((binding, Flags::PRELUDE, Flags::PRELUDE))
 690                     } else {
 691                         Err(Determinacy::Determined)
 692                     }
 693                 }
 694                 WhereToResolve::ExternPrelude => {
 695                     if use_prelude && self.session.extern_prelude.contains(&ident.name) {
 696                         let crate_id =
 697                             self.crate_loader.process_path_extern(ident.name, ident.span);
 698                         let crate_root =
 699                             self.get_module(DefId { krate: crate_id, index: CRATE_DEF_INDEX });
 700                         self.populate_module_if_necessary(crate_root);
 701
 702                         let binding = (crate_root, ty::Visibility::Public,
 703                                        ident.span, Mark::root()).to_name_binding(self.arenas);
 704                         Ok((binding, Flags::PRELUDE, Flags::empty()))
 705                     } else {
 706                         Err(Determinacy::Determined)
 707                     }
 708                 }
 709                 WhereToResolve::ToolPrelude => {
 710                     if use_prelude && is_known_tool(ident.name) {
 711                         let binding = (Def::ToolMod, ty::Visibility::Public,
 712                                        ident.span, Mark::root()).to_name_binding(self.arenas);
 713                         Ok((binding, Flags::PRELUDE, Flags::empty()))
 714                     } else {
 715                         Err(Determinacy::Determined)
 716                     }
 717                 }
 718                 WhereToResolve::StdLibPrelude => {
 719                     let mut result = Err(Determinacy::Determined);
 720                     if use_prelude {
 721                         if let Some(prelude) = self.prelude {
 722                             if let Ok(binding) = self.resolve_ident_in_module_unadjusted(
 723                                 ModuleOrUniformRoot::Module(prelude),
 724                                 ident,
 725                                 ns,
 726                                 false,
 727                                 false,
 728                                 path_span,
 729                             ) {
 730                                 result = Ok((binding, Flags::PRELUDE, Flags::empty()));
 731                             }
 732                         }
 733                     }
 734                     result
 735                 }
 736                 WhereToResolve::BuiltinTypes => {
 737                     match self.primitive_type_table.primitive_types.get(&ident.name).cloned() {
 738                         Some(prim_ty) => {
 739                             let binding = (Def::PrimTy(prim_ty), ty::Visibility::Public,
 740                                            ident.span, Mark::root()).to_name_binding(self.arenas);
 741                             Ok((binding, Flags::PRELUDE, Flags::empty()))
 742                         }
 743                         None => Err(Determinacy::Determined)
 744                     }
 745                 }
 746             };
 747
 748             macro_rules! continue_search { () => {
 749                 where_to_resolve = match where_to_resolve {
 750                     WhereToResolve::DeriveHelpers =>
 751                         WhereToResolve::MacroRules(parent_scope.legacy),
 752                     WhereToResolve::MacroRules(legacy_scope) => match legacy_scope {
 753                         LegacyScope::Binding(binding) =>
 754                             WhereToResolve::MacroRules(binding.parent_legacy_scope),
 755                         LegacyScope::Invocation(invocation) =>
 756                             WhereToResolve::MacroRules(invocation.output_legacy_scope.get()),
 757                         LegacyScope::Empty => WhereToResolve::Module(parent_scope.module),
 758                         LegacyScope::Uninitialized => unreachable!(),
 759                     }
 760                     WhereToResolve::Module(module) => {
 761                         match self.hygienic_lexical_parent(module, &mut ident.span) {
 762                             Some(parent_module) => WhereToResolve::Module(parent_module),
 763                             None => {
 764                                 use_prelude = !module.no_implicit_prelude;
 765                                 match ns {
 766                                     TypeNS => WhereToResolve::ExternPrelude,
 767                                     ValueNS => WhereToResolve::StdLibPrelude,
 768                                     MacroNS => WhereToResolve::MacroUsePrelude,
 769                                 }
 770                             }
 771                         }
 772                     }
 773                     WhereToResolve::MacroUsePrelude => WhereToResolve::BuiltinMacros,
 774                     WhereToResolve::BuiltinMacros => WhereToResolve::BuiltinAttrs,
 775                     WhereToResolve::BuiltinAttrs => WhereToResolve::LegacyPluginHelpers,
 776                     WhereToResolve::LegacyPluginHelpers => break, // nowhere else to search
 777                     WhereToResolve::ExternPrelude => WhereToResolve::ToolPrelude,
 778                     WhereToResolve::ToolPrelude => WhereToResolve::StdLibPrelude,
 779                     WhereToResolve::StdLibPrelude => match ns {
 780                         TypeNS => WhereToResolve::BuiltinTypes,
 781                         ValueNS => break, // nowhere else to search
 782                         MacroNS => unreachable!(),
 783                     }
 784                     WhereToResolve::BuiltinTypes => break, // nowhere else to search
 785                 };
 786
 787                 continue;
 788             }}
 789
 790             match result {
 791                 Ok((binding, flags, ambig_flags)) => {
 792                     if sub_namespace_mismatch(kind, binding.macro_kind()) {
 793                         continue_search!();
 794                     }
 795
 796                     if !record_used {
 797                         return Ok(binding);
 798                     }
 799
 800                     if let Some((innermost_binding, innermost_flags, innermost_ambig_flags))
 801                             = innermost_result {
 802                         // Found another solution, if the first one was "weak", report an error.
 803                         if binding.def() != innermost_binding.def() &&
 804                            (innermost_binding.is_glob_import() ||
 805                             innermost_binding.may_appear_after(parent_scope.expansion, binding) ||
 806                             innermost_flags.intersects(ambig_flags) ||
 807                             flags.intersects(innermost_ambig_flags)) {
 808                             self.ambiguity_errors.push(AmbiguityError {
 809                                 ident,
 810                                 b1: innermost_binding,
 811                                 b2: binding,
 812                             });
 813                             return Ok(innermost_binding);
 814                         }
 815                     } else {
 816                         // Found the first solution.
 817                         innermost_result = Some((binding, flags, ambig_flags));
 818                     }
 819
 820                     continue_search!();
 821                 },
 822                 Err(Determinacy::Determined) => {
 823                     continue_search!();
 824                 }
 825                 Err(Determinacy::Undetermined) => return Err(Determinacy::determined(force)),
 826             }
 827         }
 828
 829         // The first found solution was the only one, return it.
 830         if let Some((binding, ..)) = innermost_result {
 831             return Ok(binding);
 832         }
 833
 834         let determinacy = Determinacy::determined(force);
 835         if determinacy == Determinacy::Determined && kind == Some(MacroKind::Attr) {
 836             // For single-segment attributes interpret determinate "no resolution" as a custom
 837             // attribute. (Lexical resolution implies the first segment and attr kind should imply
 838             // the last segment, so we are certainly working with a single-segment attribute here.)
 839             assert!(ns == MacroNS);
 840             let binding = (Def::NonMacroAttr(NonMacroAttrKind::Custom),
 841                            ty::Visibility::Public, ident.span, Mark::root())
 842                            .to_name_binding(self.arenas);
 843             Ok(binding)
 844         } else {
 845             Err(determinacy)
 846         }
 847     }
 848
 849     pub fn finalize_current_module_macro_resolutions(&mut self) {
 850         let module = self.current_module;
 851         for &(ref path, span) in module.macro_resolutions.borrow().iter() {
 852             match self.resolve_path(None, &path, Some(MacroNS), true, span, CrateLint::No) {
 853                 PathResult::NonModule(_) => {},
 854                 PathResult::Failed(span, msg, _) => {
 855                     resolve_error(self, span, ResolutionError::FailedToResolve(&msg));
 856                 }
 857                 _ => unreachable!(),
 858             }
 859         }
 860
 861         let legacy_macro_resolutions =
 862             mem::replace(&mut *module.legacy_macro_resolutions.borrow_mut(), Vec::new());
 863         for (ident, kind, parent_scope, initial_binding) in legacy_macro_resolutions {
 864             let binding = self.early_resolve_ident_in_lexical_scope(
 865                 ident, MacroNS, Some(kind), &parent_scope, true, true, ident.span
 866             );
 867             match binding {
 868                 Ok(binding) => {
 869                     let def = binding.def_ignoring_ambiguity();
 870                     if let Some(initial_binding) = initial_binding {
 871                         self.record_use(ident, MacroNS, initial_binding);
 872                         let initial_def = initial_binding.def_ignoring_ambiguity();
 873                         if self.ambiguity_errors.is_empty() &&
 874                            def != initial_def && def != Def::Err {
 875                             // Make sure compilation does not succeed if preferred macro resolution
 876                             // has changed after the macro had been expanded. In theory all such
 877                             // situations should be reported as ambiguity errors, so this is a bug.
 878                             span_bug!(ident.span, "inconsistent resolution for a macro");
 879                         }
 880                     } else {
 881                         // It's possible that the macro was unresolved (indeterminate) and silently
 882                         // expanded into a dummy fragment for recovery during expansion.
 883                         // Now, post-expansion, the resolution may succeed, but we can't change the
 884                         // past and need to report an error.
 885                         let msg = format!("cannot determine resolution for the {} `{}`",
 886                                           kind.descr(), ident);
 887                         let msg_note = "import resolution is stuck, try simplifying macro imports";
 888                         self.session.struct_span_err(ident.span, &msg).note(msg_note).emit();
 889                     }
 890                 }
 891                 Err(..) => {
 892                     assert!(initial_binding.is_none());
 893                     let bang = if kind == MacroKind::Bang { "!" } else { "" };
 894                     let msg =
 895                         format!("cannot find {} `{}{}` in this scope", kind.descr(), ident, bang);
 896                     let mut err = self.session.struct_span_err(ident.span, &msg);
 897                     self.suggest_macro_name(&ident.as_str(), kind, &mut err, ident.span);
 898                     err.emit();
 899                 }
 900             }
 901         }
 902
 903         let builtin_attrs = mem::replace(&mut *module.builtin_attrs.borrow_mut(), Vec::new());
 904         for (ident, parent_scope) in builtin_attrs {
 905             let binding = self.early_resolve_ident_in_lexical_scope(
 906                 ident, MacroNS, Some(MacroKind::Attr), &parent_scope, true, true, ident.span
 907             );
 908             if let Ok(binding) = binding {
 909                 if binding.def_ignoring_ambiguity() !=
 910                         Def::NonMacroAttr(NonMacroAttrKind::Builtin) {
 911                     let builtin_binding = (Def::NonMacroAttr(NonMacroAttrKind::Builtin),
 912                                            ty::Visibility::Public, ident.span, Mark::root())
 913                                            .to_name_binding(self.arenas);
 914                     self.report_ambiguity_error(ident, binding, builtin_binding);
 915                 }
 916             }
 917         }
 918     }
 919
 920     fn suggest_macro_name(&mut self, name: &str, kind: MacroKind,
 921                           err: &mut DiagnosticBuilder<'a>, span: Span) {
 922         // First check if this is a locally-defined bang macro.
 923         let suggestion = if let MacroKind::Bang = kind {
 924             find_best_match_for_name(self.macro_names.iter().map(|ident| &ident.name), name, None)
 925         } else {
 926             None
 927         // Then check global macros.
 928         }.or_else(|| {
 929             let names = self.builtin_macros.iter().chain(self.macro_use_prelude.iter())
 930                                                   .filter_map(|(name, binding)| {
 931                 if binding.macro_kind() == Some(kind) { Some(name) } else { None }
 932             });
 933             find_best_match_for_name(names, name, None)
 934         // Then check modules.
 935         }).or_else(|| {
 936             let is_macro = |def| {
 937                 if let Def::Macro(_, def_kind) = def {
 938                     def_kind == kind
 939                 } else {
 940                     false
 941                 }
 942             };
 943             let ident = Ident::new(Symbol::intern(name), span);
 944             self.lookup_typo_candidate(&[ident], MacroNS, is_macro, span)
 945         });
 946
 947         if let Some(suggestion) = suggestion {
 948             if suggestion != name {
 949                 if let MacroKind::Bang = kind {
 950                     err.span_suggestion_with_applicability(
 951                         span,
 952                         "you could try the macro",
 953                         suggestion.to_string(),
 954                         Applicability::MaybeIncorrect
 955                     );
 956                 } else {
 957                     err.span_suggestion_with_applicability(
 958                         span,
 959                         "try",
 960                         suggestion.to_string(),
 961                         Applicability::MaybeIncorrect
 962                     );
 963                 }
 964             } else {
 965                 err.help("have you added the `#[macro_use]` on the module/import?");
 966             }
 967         }
 968     }
 969
 970     fn collect_def_ids(&mut self,
 971                        mark: Mark,
 972                        invocation: &'a InvocationData<'a>,
 973                        fragment: &AstFragment) {
 974         let Resolver { ref mut invocations, arenas, graph_root, .. } = *self;
 975         let InvocationData { def_index, .. } = *invocation;
 976
 977         let visit_macro_invoc = &mut |invoc: map::MacroInvocationData| {
 978             invocations.entry(invoc.mark).or_insert_with(|| {
 979                 arenas.alloc_invocation_data(InvocationData {
 980                     def_index: invoc.def_index,
 981                     module: Cell::new(graph_root),
 982                     parent_legacy_scope: Cell::new(LegacyScope::Uninitialized),
 983                     output_legacy_scope: Cell::new(LegacyScope::Uninitialized),
 984                 })
 985             });
 986         };
 987
 988         let mut def_collector = DefCollector::new(&mut self.definitions, mark);
 989         def_collector.visit_macro_invoc = Some(visit_macro_invoc);
 990         def_collector.with_parent(def_index, |def_collector| {
 991             fragment.visit_with(def_collector)
 992         });
 993     }
 994
 995     pub fn define_macro(&mut self,
 996                         item: &ast::Item,
 997                         expansion: Mark,
 998                         current_legacy_scope: &mut LegacyScope<'a>) {
 999         self.local_macro_def_scopes.insert(item.id, self.current_module);
1000         let ident = item.ident;
1001         if ident.name == "macro_rules" {
1002             self.session.span_err(item.span, "user-defined macros may not be named `macro_rules`");
1003         }
1004
1005         let def_id = self.definitions.local_def_id(item.id);
1006         let ext = Lrc::new(macro_rules::compile(&self.session.parse_sess,
1007                                                &self.session.features_untracked(),
1008                                                item, hygiene::default_edition()));
1009         self.macro_map.insert(def_id, ext);
1010
1011         let def = match item.node { ast::ItemKind::MacroDef(ref def) => def, _ => unreachable!() };
1012         if def.legacy {
1013             let ident = ident.modern();
1014             self.macro_names.insert(ident);
1015             let def = Def::Macro(def_id, MacroKind::Bang);
1016             let vis = ty::Visibility::Invisible; // Doesn't matter for legacy bindings
1017             let binding = (def, vis, item.span, expansion).to_name_binding(self.arenas);
1018             self.set_binding_parent_module(binding, self.current_module);
1019             let legacy_binding = self.arenas.alloc_legacy_binding(LegacyBinding {
1020                 parent_legacy_scope: *current_legacy_scope, binding, ident
1021             });
1022             *current_legacy_scope = LegacyScope::Binding(legacy_binding);
1023             self.all_macros.insert(ident.name, def);
1024             if attr::contains_name(&item.attrs, "macro_export") {
1025                 let module = self.graph_root;
1026                 let vis = ty::Visibility::Public;
1027                 self.define(module, ident, MacroNS,
1028                             (def, vis, item.span, expansion, IsMacroExport));
1029             } else {
1030                 if !attr::contains_name(&item.attrs, "rustc_doc_only_macro") {
1031                     self.check_reserved_macro_name(ident, MacroNS);
1032                 }
1033                 self.unused_macros.insert(def_id);
1034             }
1035         } else {
1036             let module = self.current_module;
1037             let def = Def::Macro(def_id, MacroKind::Bang);
1038             let vis = self.resolve_visibility(&item.vis);
1039             if vis != ty::Visibility::Public {
1040                 self.unused_macros.insert(def_id);
1041             }
1042             self.define(module, ident, MacroNS, (def, vis, item.span, expansion));
1043         }
1044     }
1045
1046     fn gate_legacy_custom_derive(&mut self, name: Symbol, span: Span) {
1047         if !self.session.features_untracked().custom_derive {
1048             let sess = &self.session.parse_sess;
1049             let explain = feature_gate::EXPLAIN_CUSTOM_DERIVE;
1050             emit_feature_err(sess, "custom_derive", span, GateIssue::Language, explain);
1051         } else if !self.is_whitelisted_legacy_custom_derive(name) {
1052             self.session.span_warn(span, feature_gate::EXPLAIN_DEPR_CUSTOM_DERIVE);
1053         }
1054     }
1055 }