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, TypeNS, MacroNS};
  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 rustc::middle::cstore::CrateStore;
  23 use syntax::ast::{self, Name, Ident};
  24 use syntax::attr;
  25 use syntax::errors::DiagnosticBuilder;
  26 use syntax::ext::base::{self, Determinacy, MultiModifier, MultiDecorator};
  27 use syntax::ext::base::{MacroKind, SyntaxExtension, Resolver as SyntaxResolver};
  28 use syntax::ext::expand::{AstFragment, Invocation, InvocationKind};
  29 use syntax::ext::hygiene::{self, Mark};
  30 use syntax::ext::tt::macro_rules;
  31 use syntax::feature_gate::{self, feature_err, emit_feature_err, is_builtin_attr_name, GateIssue};
  32 use syntax::feature_gate::EXPLAIN_DERIVE_UNDERSCORE;
  33 use syntax::fold::{self, Folder};
  34 use syntax::parse::parser::PathStyle;
  35 use syntax::parse::token::{self, Token};
  36 use syntax::ptr::P;
  37 use syntax::symbol::{Symbol, keywords};
  38 use syntax::tokenstream::{TokenStream, TokenTree, Delimited, DelimSpan};
  39 use syntax::util::lev_distance::find_best_match_for_name;
  40 use syntax_pos::{Span, DUMMY_SP};
  41 use errors::Applicability;
  42
  43 use std::cell::Cell;
  44 use std::mem;
  45 use rustc_data_structures::sync::Lrc;
  46 use rustc_data_structures::small_vec::ExpectOne;
  47
  48 #[derive(Clone, Copy)]
  49 crate struct FromPrelude(bool);
  50
  51 #[derive(Clone)]
  52 pub struct InvocationData<'a> {
  53     def_index: DefIndex,
  54     /// Module in which the macro was invoked.
  55     crate module: Cell<Module<'a>>,
  56     /// Legacy scope in which the macro was invoked.
  57     /// The invocation path is resolved in this scope.
  58     crate parent_legacy_scope: Cell<LegacyScope<'a>>,
  59     /// Legacy scope *produced* by expanding this macro invocation,
  60     /// includes all the macro_rules items, other invocations, etc generated by it.
  61     /// Set to the parent scope if the macro is not expanded yet (as if the macro produced nothing).
  62     crate output_legacy_scope: Cell<LegacyScope<'a>>,
  63 }
  64
  65 impl<'a> InvocationData<'a> {
  66     pub fn root(graph_root: Module<'a>) -> Self {
  67         InvocationData {
  68             module: Cell::new(graph_root),
  69             def_index: CRATE_DEF_INDEX,
  70             parent_legacy_scope: Cell::new(LegacyScope::Empty),
  71             output_legacy_scope: Cell::new(LegacyScope::Empty),
  72         }
  73     }
  74 }
  75
  76 /// Binding produced by a `macro_rules` item.
  77 /// Not modularized, can shadow previous legacy bindings, etc.
  78 pub struct LegacyBinding<'a> {
  79     binding: &'a NameBinding<'a>,
  80     /// Legacy scope into which the `macro_rules` item was planted.
  81     parent_legacy_scope: LegacyScope<'a>,
  82     ident: Ident,
  83 }
  84
  85 /// Scope introduced by a `macro_rules!` macro.
  86 /// Starts at the macro's definition and ends at the end of the macro's parent module
  87 /// (named or unnamed), or even further if it escapes with `#[macro_use]`.
  88 /// Some macro invocations need to introduce legacy scopes too because they
  89 /// potentially can expand into macro definitions.
  90 #[derive(Copy, Clone)]
  91 pub enum LegacyScope<'a> {
  92     /// Created when invocation data is allocated in the arena,
  93     /// must be replaced with a proper scope later.
  94     Uninitialized,
  95     /// Empty "root" scope at the crate start containing no names.
  96     Empty,
  97     /// Scope introduced by a `macro_rules!` macro definition.
  98     Binding(&'a LegacyBinding<'a>),
  99     /// Scope introduced by a macro invocation that can potentially
 100     /// create a `macro_rules!` macro definition.
 101     Invocation(&'a InvocationData<'a>),
 102 }
 103
 104 /// Everything you need to resolve a macro path.
 105 #[derive(Clone)]
 106 pub struct ParentScope<'a> {
 107     crate module: Module<'a>,
 108     crate expansion: Mark,
 109     crate legacy: LegacyScope<'a>,
 110     crate derives: Vec<ast::Path>,
 111 }
 112
 113 pub struct ProcMacError {
 114     crate_name: Symbol,
 115     name: Symbol,
 116     module: ast::NodeId,
 117     use_span: Span,
 118     warn_msg: &'static str,
 119 }
 120
 121 // Macro namespace is separated into two sub-namespaces, one for bang macros and
 122 // one for attribute-like macros (attributes, derives).
 123 // We ignore resolutions from one sub-namespace when searching names in scope for another.
 124 fn sub_namespace_mismatch(requirement: Option<MacroKind>, candidate: Option<MacroKind>) -> bool {
 125     #[derive(PartialEq)]
 126     enum SubNS { Bang, AttrLike }
 127     let sub_ns = |kind| match kind {
 128         MacroKind::Bang => Some(SubNS::Bang),
 129         MacroKind::Attr | MacroKind::Derive => Some(SubNS::AttrLike),
 130         MacroKind::ProcMacroStub => None,
 131     };
 132     let requirement = requirement.and_then(|kind| sub_ns(kind));
 133     let candidate = candidate.and_then(|kind| sub_ns(kind));
 134     // "No specific sub-namespace" means "matches anything" for both requirements and candidates.
 135     candidate.is_some() && requirement.is_some() && candidate != requirement
 136 }
 137
 138 impl<'a, 'crateloader: 'a> base::Resolver for Resolver<'a, 'crateloader> {
 139     fn next_node_id(&mut self) -> ast::NodeId {
 140         self.session.next_node_id()
 141     }
 142
 143     fn get_module_scope(&mut self, id: ast::NodeId) -> Mark {
 144         let mark = Mark::fresh(Mark::root());
 145         let module = self.module_map[&self.definitions.local_def_id(id)];
 146         self.invocations.insert(mark, self.arenas.alloc_invocation_data(InvocationData {
 147             module: Cell::new(module),
 148             def_index: module.def_id().unwrap().index,
 149             parent_legacy_scope: Cell::new(LegacyScope::Empty),
 150             output_legacy_scope: Cell::new(LegacyScope::Empty),
 151         }));
 152         mark
 153     }
 154
 155     fn eliminate_crate_var(&mut self, item: P<ast::Item>) -> P<ast::Item> {
 156         struct EliminateCrateVar<'b, 'a: 'b, 'crateloader: 'a>(
 157             &'b mut Resolver<'a, 'crateloader>, Span
 158         );
 159
 160         impl<'a, 'b, 'crateloader> Folder for EliminateCrateVar<'a, 'b, 'crateloader> {
 161             fn fold_path(&mut self, path: ast::Path) -> ast::Path {
 162                 match self.fold_qpath(None, path) {
 163                     (None, path) => path,
 164                     _ => unreachable!(),
 165                 }
 166             }
 167
 168             fn fold_qpath(&mut self, mut qself: Option<ast::QSelf>, mut path: ast::Path)
 169                           -> (Option<ast::QSelf>, ast::Path) {
 170                 qself = qself.map(|ast::QSelf { ty, path_span, position }| {
 171                     ast::QSelf {
 172                         ty: self.fold_ty(ty),
 173                         path_span: self.new_span(path_span),
 174                         position,
 175                     }
 176                 });
 177
 178                 if path.segments[0].ident.name == keywords::DollarCrate.name() {
 179                     let module = self.0.resolve_crate_root(path.segments[0].ident);
 180                     path.segments[0].ident.name = keywords::CrateRoot.name();
 181                     if !module.is_local() {
 182                         let span = path.segments[0].ident.span;
 183                         path.segments.insert(1, match module.kind {
 184                             ModuleKind::Def(_, name) => ast::PathSegment::from_ident(
 185                                 ast::Ident::with_empty_ctxt(name).with_span_pos(span)
 186                             ),
 187                             _ => unreachable!(),
 188                         });
 189                         if let Some(qself) = &mut qself {
 190                             qself.position += 1;
 191                         }
 192                     }
 193                 }
 194                 (qself, path)
 195             }
 196
 197             fn fold_mac(&mut self, mac: ast::Mac) -> ast::Mac {
 198                 fold::noop_fold_mac(mac, self)
 199             }
 200         }
 201
 202         EliminateCrateVar(self, item.span).fold_item(item).expect_one("")
 203     }
 204
 205     fn is_whitelisted_legacy_custom_derive(&self, name: Name) -> bool {
 206         self.whitelisted_legacy_custom_derives.contains(&name)
 207     }
 208
 209     fn visit_ast_fragment_with_placeholders(&mut self, mark: Mark, fragment: &AstFragment,
 210                                             derives: &[Mark]) {
 211         let invocation = self.invocations[&mark];
 212         self.collect_def_ids(mark, invocation, fragment);
 213
 214         self.current_module = invocation.module.get();
 215         self.current_module.unresolved_invocations.borrow_mut().remove(&mark);
 216         self.current_module.unresolved_invocations.borrow_mut().extend(derives);
 217         for &derive in derives {
 218             self.invocations.insert(derive, invocation);
 219         }
 220         let mut visitor = BuildReducedGraphVisitor {
 221             resolver: self,
 222             current_legacy_scope: invocation.parent_legacy_scope.get(),
 223             expansion: mark,
 224         };
 225         fragment.visit_with(&mut visitor);
 226         invocation.output_legacy_scope.set(visitor.current_legacy_scope);
 227     }
 228
 229     fn add_builtin(&mut self, ident: ast::Ident, ext: Lrc<SyntaxExtension>) {
 230         let def_id = DefId {
 231             krate: CrateNum::BuiltinMacros,
 232             index: DefIndex::from_array_index(self.macro_map.len(),
 233                                               DefIndexAddressSpace::Low),
 234         };
 235         let kind = ext.kind();
 236         self.macro_map.insert(def_id, ext);
 237         let binding = self.arenas.alloc_name_binding(NameBinding {
 238             kind: NameBindingKind::Def(Def::Macro(def_id, kind), false),
 239             span: DUMMY_SP,
 240             vis: ty::Visibility::Invisible,
 241             expansion: Mark::root(),
 242         });
 243         if self.builtin_macros.insert(ident.name, binding).is_some() {
 244             self.session.span_err(ident.span,
 245                                   &format!("built-in macro `{}` was already defined", ident));
 246         }
 247     }
 248
 249     fn resolve_imports(&mut self) {
 250         ImportResolver { resolver: self }.resolve_imports()
 251     }
 252
 253     // Resolves attribute and derive legacy macros from `#![plugin(..)]`.
 254     fn find_legacy_attr_invoc(&mut self, attrs: &mut Vec<ast::Attribute>, allow_derive: bool)
 255                               -> Option<ast::Attribute> {
 256         for i in 0..attrs.len() {
 257             let name = attrs[i].name();
 258
 259             if self.session.plugin_attributes.borrow().iter()
 260                     .any(|&(ref attr_nm, _)| name == &**attr_nm) {
 261                 attr::mark_known(&attrs[i]);
 262             }
 263
 264             match self.builtin_macros.get(&name).cloned() {
 265                 Some(binding) => match *binding.get_macro(self) {
 266                     MultiModifier(..) | MultiDecorator(..) | SyntaxExtension::AttrProcMacro(..) => {
 267                         return Some(attrs.remove(i))
 268                     }
 269                     _ => {}
 270                 },
 271                 None => {}
 272             }
 273         }
 274
 275         if !allow_derive { return None }
 276
 277         // Check for legacy derives
 278         for i in 0..attrs.len() {
 279             let name = attrs[i].name();
 280
 281             if name == "derive" {
 282                 let result = attrs[i].parse_list(&self.session.parse_sess, |parser| {
 283                     parser.parse_path_allowing_meta(PathStyle::Mod)
 284                 });
 285
 286                 let mut traits = match result {
 287                     Ok(traits) => traits,
 288                     Err(mut e) => {
 289                         e.cancel();
 290                         continue
 291                     }
 292                 };
 293
 294                 for j in 0..traits.len() {
 295                     if traits[j].segments.len() > 1 {
 296                         continue
 297                     }
 298                     let trait_name = traits[j].segments[0].ident.name;
 299                     let legacy_name = Symbol::intern(&format!("derive_{}", trait_name));
 300                     if !self.builtin_macros.contains_key(&legacy_name) {
 301                         continue
 302                     }
 303                     let span = traits.remove(j).span;
 304                     self.gate_legacy_custom_derive(legacy_name, span);
 305                     if traits.is_empty() {
 306                         attrs.remove(i);
 307                     } else {
 308                         let mut tokens = Vec::new();
 309                         for (j, path) in traits.iter().enumerate() {
 310                             if j > 0 {
 311                                 tokens.push(TokenTree::Token(attrs[i].span, Token::Comma).into());
 312                             }
 313                             for (k, segment) in path.segments.iter().enumerate() {
 314                                 if k > 0 {
 315                                     tokens.push(TokenTree::Token(path.span, Token::ModSep).into());
 316                                 }
 317                                 let tok = Token::from_ast_ident(segment.ident);
 318                                 tokens.push(TokenTree::Token(path.span, tok).into());
 319                             }
 320                         }
 321                         let delim_span = DelimSpan::from_single(attrs[i].span);
 322                         attrs[i].tokens = TokenTree::Delimited(delim_span, Delimited {
 323                             delim: token::Paren,
 324                             tts: TokenStream::concat(tokens).into(),
 325                         }).into();
 326                     }
 327                     return Some(ast::Attribute {
 328                         path: ast::Path::from_ident(Ident::new(legacy_name, span)),
 329                         tokens: TokenStream::empty(),
 330                         id: attr::mk_attr_id(),
 331                         style: ast::AttrStyle::Outer,
 332                         is_sugared_doc: false,
 333                         span,
 334                     });
 335                 }
 336             }
 337         }
 338
 339         None
 340     }
 341
 342     fn resolve_macro_invocation(&mut self, invoc: &Invocation, invoc_id: Mark, force: bool)
 343                                 -> Result<Option<Lrc<SyntaxExtension>>, Determinacy> {
 344         let (path, kind, derives_in_scope) = match invoc.kind {
 345             InvocationKind::Attr { attr: None, .. } =>
 346                 return Ok(None),
 347             InvocationKind::Attr { attr: Some(ref attr), ref traits, .. } =>
 348                 (&attr.path, MacroKind::Attr, traits.clone()),
 349             InvocationKind::Bang { ref mac, .. } =>
 350                 (&mac.node.path, MacroKind::Bang, Vec::new()),
 351             InvocationKind::Derive { ref path, .. } =>
 352                 (path, MacroKind::Derive, Vec::new()),
 353         };
 354
 355         let parent_scope = self.invoc_parent_scope(invoc_id, derives_in_scope);
 356         let (def, ext) = self.resolve_macro_to_def(path, kind, &parent_scope, force)?;
 357
 358         if let Def::Macro(def_id, _) = def {
 359             self.macro_defs.insert(invoc.expansion_data.mark, def_id);
 360             let normal_module_def_id =
 361                 self.macro_def_scope(invoc.expansion_data.mark).normal_ancestor_id;
 362             self.definitions.add_parent_module_of_macro_def(invoc.expansion_data.mark,
 363                                                             normal_module_def_id);
 364             invoc.expansion_data.mark.set_default_transparency(ext.default_transparency());
 365             invoc.expansion_data.mark.set_is_builtin(def_id.krate == CrateNum::BuiltinMacros);
 366         }
 367
 368         Ok(Some(ext))
 369     }
 370
 371     fn resolve_macro_path(&mut self, path: &ast::Path, kind: MacroKind, invoc_id: Mark,
 372                           derives_in_scope: Vec<ast::Path>, force: bool)
 373                           -> Result<Lrc<SyntaxExtension>, Determinacy> {
 374         let parent_scope = self.invoc_parent_scope(invoc_id, derives_in_scope);
 375         Ok(self.resolve_macro_to_def(path, kind, &parent_scope, force)?.1)
 376     }
 377
 378     fn check_unused_macros(&self) {
 379         for did in self.unused_macros.iter() {
 380             let id_span = match *self.macro_map[did] {
 381                 SyntaxExtension::NormalTT { def_info, .. } |
 382                 SyntaxExtension::DeclMacro { def_info, .. } => def_info,
 383                 _ => None,
 384             };
 385             if let Some((id, span)) = id_span {
 386                 let lint = lint::builtin::UNUSED_MACROS;
 387                 let msg = "unused macro definition";
 388                 self.session.buffer_lint(lint, id, span, msg);
 389             } else {
 390                 bug!("attempted to create unused macro error, but span not available");
 391             }
 392         }
 393     }
 394 }
 395
 396 impl<'a, 'cl> Resolver<'a, 'cl> {
 397     pub fn dummy_parent_scope(&mut self) -> ParentScope<'a> {
 398         self.invoc_parent_scope(Mark::root(), Vec::new())
 399     }
 400
 401     fn invoc_parent_scope(&mut self, invoc_id: Mark, derives: Vec<ast::Path>) -> ParentScope<'a> {
 402         let invoc = self.invocations[&invoc_id];
 403         ParentScope {
 404             module: invoc.module.get().nearest_item_scope(),
 405             expansion: invoc_id.parent(),
 406             legacy: invoc.parent_legacy_scope.get(),
 407             derives,
 408         }
 409     }
 410
 411     fn resolve_macro_to_def(
 412         &mut self,
 413         path: &ast::Path,
 414         kind: MacroKind,
 415         parent_scope: &ParentScope<'a>,
 416         force: bool,
 417     ) -> Result<(Def, Lrc<SyntaxExtension>), Determinacy> {
 418         let def = self.resolve_macro_to_def_inner(path, kind, parent_scope, force);
 419
 420         // Report errors and enforce feature gates for the resolved macro.
 421         if def != Err(Determinacy::Undetermined) {
 422             // Do not report duplicated errors on every undetermined resolution.
 423             for segment in &path.segments {
 424                 if let Some(args) = &segment.args {
 425                     self.session.span_err(args.span(), "generic arguments in macro path");
 426                 }
 427             }
 428         }
 429
 430         let def = def?;
 431
 432         match def {
 433             Def::Macro(def_id, macro_kind) => {
 434                 self.unused_macros.remove(&def_id);
 435                 if macro_kind == MacroKind::ProcMacroStub {
 436                     let msg = "can't use a procedural macro from the same crate that defines it";
 437                     self.session.span_err(path.span, msg);
 438                     return Err(Determinacy::Determined);
 439                 }
 440             }
 441             Def::NonMacroAttr(attr_kind) => {
 442                 if kind == MacroKind::Attr {
 443                     let features = self.session.features_untracked();
 444                     if attr_kind == NonMacroAttrKind::Custom {
 445                         assert!(path.segments.len() == 1);
 446                         let name = path.segments[0].ident.name.as_str();
 447                         if name.starts_with("rustc_") {
 448                             if !features.rustc_attrs {
 449                                 let msg = "unless otherwise specified, attributes with the prefix \
 450                                            `rustc_` are reserved for internal compiler diagnostics";
 451                                 feature_err(&self.session.parse_sess, "rustc_attrs", path.span,
 452                                             GateIssue::Language, &msg).emit();
 453                             }
 454                         } else if name.starts_with("derive_") {
 455                             if !features.custom_derive {
 456                                 feature_err(&self.session.parse_sess, "custom_derive", path.span,
 457                                             GateIssue::Language, EXPLAIN_DERIVE_UNDERSCORE).emit();
 458                             }
 459                         } else if !features.custom_attribute {
 460                             let msg = format!("The attribute `{}` is currently unknown to the \
 461                                                compiler and may have meaning added to it in the \
 462                                                future", path);
 463                             feature_err(&self.session.parse_sess, "custom_attribute", path.span,
 464                                         GateIssue::Language, &msg).emit();
 465                         }
 466                     }
 467                 } else {
 468                     // Not only attributes, but anything in macro namespace can result in
 469                     // `Def::NonMacroAttr` definition (e.g. `inline!()`), so we must report
 470                     // an error for those cases.
 471                     let msg = format!("expected a macro, found {}", def.kind_name());
 472                     self.session.span_err(path.span, &msg);
 473                     return Err(Determinacy::Determined);
 474                 }
 475             }
 476             _ => panic!("expected `Def::Macro` or `Def::NonMacroAttr`"),
 477         }
 478
 479         Ok((def, self.get_macro(def)))
 480     }
 481
 482     pub fn resolve_macro_to_def_inner(
 483         &mut self,
 484         path: &ast::Path,
 485         kind: MacroKind,
 486         parent_scope: &ParentScope<'a>,
 487         force: bool,
 488     ) -> Result<Def, Determinacy> {
 489         let ast::Path { ref segments, span } = *path;
 490         let mut path: Vec<_> = segments.iter().map(|seg| seg.ident).collect();
 491
 492         // Possibly apply the macro helper hack
 493         if kind == MacroKind::Bang && path.len() == 1 &&
 494            path[0].span.ctxt().outer().expn_info().map_or(false, |info| info.local_inner_macros) {
 495             let root = Ident::new(keywords::DollarCrate.name(), path[0].span);
 496             path.insert(0, root);
 497         }
 498
 499         if path.len() > 1 {
 500             let def = match self.resolve_path_with_parent_scope(None, &path, Some(MacroNS),
 501                                                                 parent_scope, false, span,
 502                                                                 CrateLint::No) {
 503                 PathResult::NonModule(path_res) => match path_res.base_def() {
 504                     Def::Err => Err(Determinacy::Determined),
 505                     def @ _ => {
 506                         if path_res.unresolved_segments() > 0 {
 507                             self.found_unresolved_macro = true;
 508                             self.session.span_err(span, "fail to resolve non-ident macro path");
 509                             Err(Determinacy::Determined)
 510                         } else {
 511                             Ok(def)
 512                         }
 513                     }
 514                 },
 515                 PathResult::Module(..) => unreachable!(),
 516                 PathResult::Indeterminate if !force => return Err(Determinacy::Undetermined),
 517                 _ => {
 518                     self.found_unresolved_macro = true;
 519                     Err(Determinacy::Determined)
 520                 },
 521             };
 522             parent_scope.module.macro_resolutions.borrow_mut()
 523                 .push((path.into_boxed_slice(), span));
 524             return def;
 525         }
 526
 527         let result = if let Some(legacy_binding) = self.resolve_legacy_scope(path[0], Some(kind),
 528                                                                              parent_scope, false) {
 529             Ok(legacy_binding.def())
 530         } else {
 531             match self.resolve_lexical_macro_path_segment(path[0], MacroNS, Some(kind),
 532                                                           parent_scope, false, force, span) {
 533                 Ok((binding, _)) => Ok(binding.def_ignoring_ambiguity()),
 534                 Err(Determinacy::Undetermined) => return Err(Determinacy::Undetermined),
 535                 Err(Determinacy::Determined) => {
 536                     self.found_unresolved_macro = true;
 537                     Err(Determinacy::Determined)
 538                 }
 539             }
 540         };
 541
 542         parent_scope.module.legacy_macro_resolutions.borrow_mut()
 543             .push((path[0], kind, parent_scope.clone(), result.ok()));
 544
 545         result
 546     }
 547
 548     // Resolve the initial segment of a non-global macro path
 549     // (e.g. `foo` in `foo::bar!(); or `foo!();`).
 550     // This is a variation of `fn resolve_ident_in_lexical_scope` that can be run during
 551     // expansion and import resolution (perhaps they can be merged in the future).
 552     crate fn resolve_lexical_macro_path_segment(
 553         &mut self,
 554         mut ident: Ident,
 555         ns: Namespace,
 556         kind: Option<MacroKind>,
 557         parent_scope: &ParentScope<'a>,
 558         record_used: bool,
 559         force: bool,
 560         path_span: Span,
 561     ) -> Result<(&'a NameBinding<'a>, FromPrelude), Determinacy> {
 562         // General principles:
 563         // 1. Not controlled (user-defined) names should have higher priority than controlled names
 564         //    built into the language or standard library. This way we can add new names into the
 565         //    language or standard library without breaking user code.
 566         // 2. "Closed set" below means new names can appear after the current resolution attempt.
 567         // Places to search (in order of decreasing priority):
 568         // (Type NS)
 569         // 1. FIXME: Ribs (type parameters), there's no necessary infrastructure yet
 570         //    (open set, not controlled).
 571         // 2. Names in modules (both normal `mod`ules and blocks), loop through hygienic parents
 572         //    (open, not controlled).
 573         // 3. Extern prelude (closed, not controlled).
 574         // 4. Tool modules (closed, controlled right now, but not in the future).
 575         // 5. Standard library prelude (de-facto closed, controlled).
 576         // 6. Language prelude (closed, controlled).
 577         // (Macro NS)
 578         // 1. Names in modules (both normal `mod`ules and blocks), loop through hygienic parents
 579         //    (open, not controlled).
 580         // 2. `macro_use` prelude (open, the open part is from macro expansions, not controlled).
 581         // 2a. User-defined prelude from macro-use
 582         //    (open, the open part is from macro expansions, not controlled).
 583         // 2b. Standard library prelude is currently implemented as `macro-use` (closed, controlled)
 584         // 3. Language prelude: builtin macros (closed, controlled, except for legacy plugins).
 585         // 4. Language prelude: builtin attributes (closed, controlled).
 586         // N (unordered). Derive helpers (open, not controlled). All ambiguities with other names
 587         //    are currently reported as errors. They should be higher in priority than preludes
 588         //    and maybe even names in modules according to the "general principles" above. They
 589         //    also should be subject to restricted shadowing because are effectively produced by
 590         //    derives (you need to resolve the derive first to add helpers into scope), but they
 591         //    should be available before the derive is expanded for compatibility.
 592         //    It's mess in general, so we are being conservative for now.
 593
 594         assert!(ns == TypeNS  || ns == MacroNS);
 595         assert!(force || !record_used); // `record_used` implies `force`
 596         ident = ident.modern();
 597
 598         // This is *the* result, resolution from the scope closest to the resolved identifier.
 599         // However, sometimes this result is "weak" because it comes from a glob import or
 600         // a macro expansion, and in this case it cannot shadow names from outer scopes, e.g.
 601         // mod m { ... } // solution in outer scope
 602         // {
 603         //     use prefix::*; // imports another `m` - innermost solution
 604         //                    // weak, cannot shadow the outer `m`, need to report ambiguity error
 605         //     m::mac!();
 606         // }
 607         // So we have to save the innermost solution and continue searching in outer scopes
 608         // to detect potential ambiguities.
 609         let mut innermost_result: Option<(&NameBinding, FromPrelude)> = None;
 610
 611         enum WhereToResolve<'a> {
 612             Module(Module<'a>),
 613             MacroUsePrelude,
 614             BuiltinMacros,
 615             BuiltinAttrs,
 616             DeriveHelpers,
 617             ExternPrelude,
 618             ToolPrelude,
 619             StdLibPrelude,
 620             BuiltinTypes,
 621         }
 622
 623         // Go through all the scopes and try to resolve the name.
 624         let mut where_to_resolve = WhereToResolve::Module(parent_scope.module);
 625         let mut use_prelude = !parent_scope.module.no_implicit_prelude;
 626         loop {
 627             let result = match where_to_resolve {
 628                 WhereToResolve::Module(module) => {
 629                     let orig_current_module = mem::replace(&mut self.current_module, module);
 630                     let binding = self.resolve_ident_in_module_unadjusted(
 631                         ModuleOrUniformRoot::Module(module),
 632                         ident,
 633                         ns,
 634                         true,
 635                         record_used,
 636                         path_span,
 637                     );
 638                     self.current_module = orig_current_module;
 639                     binding.map(|binding| (binding, FromPrelude(false)))
 640                 }
 641                 WhereToResolve::MacroUsePrelude => {
 642                     match self.macro_use_prelude.get(&ident.name).cloned() {
 643                         Some(binding) => Ok((binding, FromPrelude(true))),
 644                         None => Err(Determinacy::Determined),
 645                     }
 646                 }
 647                 WhereToResolve::BuiltinMacros => {
 648                     match self.builtin_macros.get(&ident.name).cloned() {
 649                         Some(binding) => Ok((binding, FromPrelude(true))),
 650                         None => Err(Determinacy::Determined),
 651                     }
 652                 }
 653                 WhereToResolve::BuiltinAttrs => {
 654                     if is_builtin_attr_name(ident.name) {
 655                         let binding = (Def::NonMacroAttr(NonMacroAttrKind::Builtin),
 656                                        ty::Visibility::Public, ident.span, Mark::root())
 657                                        .to_name_binding(self.arenas);
 658                         Ok((binding, FromPrelude(true)))
 659                     } else {
 660                         Err(Determinacy::Determined)
 661                     }
 662                 }
 663                 WhereToResolve::DeriveHelpers => {
 664                     let mut result = Err(Determinacy::Determined);
 665                     for derive in &parent_scope.derives {
 666                         let parent_scope = ParentScope { derives: Vec::new(), ..*parent_scope };
 667                         if let Ok((_, ext)) = self.resolve_macro_to_def(derive, MacroKind::Derive,
 668                                                                         &parent_scope, force) {
 669                             if let SyntaxExtension::ProcMacroDerive(_, helper_attrs, _) = &*ext {
 670                                 if helper_attrs.contains(&ident.name) {
 671                                     let binding =
 672                                         (Def::NonMacroAttr(NonMacroAttrKind::DeriveHelper),
 673                                         ty::Visibility::Public, derive.span, Mark::root())
 674                                         .to_name_binding(self.arenas);
 675                                     result = Ok((binding, FromPrelude(false)));
 676                                     break;
 677                                 }
 678                             }
 679                         }
 680                     }
 681                     result
 682                 }
 683                 WhereToResolve::ExternPrelude => {
 684                     if use_prelude && self.extern_prelude.contains(&ident.name) {
 685                         if !self.session.features_untracked().extern_prelude &&
 686                            !self.ignore_extern_prelude_feature {
 687                             feature_err(&self.session.parse_sess, "extern_prelude",
 688                                         ident.span, GateIssue::Language,
 689                                         "access to extern crates through prelude is experimental")
 690                                         .emit();
 691                         }
 692
 693                         let crate_id =
 694                             self.crate_loader.process_path_extern(ident.name, ident.span);
 695                         let crate_root =
 696                             self.get_module(DefId { krate: crate_id, index: CRATE_DEF_INDEX });
 697                         self.populate_module_if_necessary(crate_root);
 698
 699                         let binding = (crate_root, ty::Visibility::Public,
 700                                        ident.span, Mark::root()).to_name_binding(self.arenas);
 701                         Ok((binding, FromPrelude(true)))
 702                     } else {
 703                         Err(Determinacy::Determined)
 704                     }
 705                 }
 706                 WhereToResolve::ToolPrelude => {
 707                     if use_prelude && is_known_tool(ident.name) {
 708                         let binding = (Def::ToolMod, ty::Visibility::Public,
 709                                        ident.span, Mark::root()).to_name_binding(self.arenas);
 710                         Ok((binding, FromPrelude(true)))
 711                     } else {
 712                         Err(Determinacy::Determined)
 713                     }
 714                 }
 715                 WhereToResolve::StdLibPrelude => {
 716                     let mut result = Err(Determinacy::Determined);
 717                     if use_prelude {
 718                         if let Some(prelude) = self.prelude {
 719                             if let Ok(binding) = self.resolve_ident_in_module_unadjusted(
 720                                 ModuleOrUniformRoot::Module(prelude),
 721                                 ident,
 722                                 ns,
 723                                 false,
 724                                 false,
 725                                 path_span,
 726                             ) {
 727                                 result = Ok((binding, FromPrelude(true)));
 728                             }
 729                         }
 730                     }
 731                     result
 732                 }
 733                 WhereToResolve::BuiltinTypes => {
 734                     if let Some(prim_ty) =
 735                             self.primitive_type_table.primitive_types.get(&ident.name).cloned() {
 736                         let binding = (Def::PrimTy(prim_ty), ty::Visibility::Public,
 737                                        ident.span, Mark::root()).to_name_binding(self.arenas);
 738                         Ok((binding, FromPrelude(true)))
 739                     } else {
 740                         Err(Determinacy::Determined)
 741                     }
 742                 }
 743             };
 744
 745             macro_rules! continue_search { () => {
 746                 where_to_resolve = match where_to_resolve {
 747                     WhereToResolve::Module(module) => {
 748                         match self.hygienic_lexical_parent(module, &mut ident.span) {
 749                             Some(parent_module) => WhereToResolve::Module(parent_module),
 750                             None => {
 751                                 use_prelude = !module.no_implicit_prelude;
 752                                 if ns == MacroNS {
 753                                     WhereToResolve::MacroUsePrelude
 754                                 } else {
 755                                     WhereToResolve::ExternPrelude
 756                                 }
 757                             }
 758                         }
 759                     }
 760                     WhereToResolve::MacroUsePrelude => WhereToResolve::BuiltinMacros,
 761                     WhereToResolve::BuiltinMacros => WhereToResolve::BuiltinAttrs,
 762                     WhereToResolve::BuiltinAttrs => WhereToResolve::DeriveHelpers,
 763                     WhereToResolve::DeriveHelpers => break, // nowhere else to search
 764                     WhereToResolve::ExternPrelude => WhereToResolve::ToolPrelude,
 765                     WhereToResolve::ToolPrelude => WhereToResolve::StdLibPrelude,
 766                     WhereToResolve::StdLibPrelude => WhereToResolve::BuiltinTypes,
 767                     WhereToResolve::BuiltinTypes => break, // nowhere else to search
 768                 };
 769
 770                 continue;
 771             }}
 772
 773             match result {
 774                 Ok(result) => {
 775                     if sub_namespace_mismatch(kind, result.0.macro_kind()) {
 776                         continue_search!();
 777                     }
 778
 779                     if !record_used {
 780                         return Ok(result);
 781                     }
 782
 783                     if let Some(innermost_result) = innermost_result {
 784                         // Found another solution, if the first one was "weak", report an error.
 785                         let (def, innermost_def) = (result.0.def(), innermost_result.0.def());
 786                         if def != innermost_def &&
 787                            (innermost_result.0.is_glob_import() ||
 788                             innermost_result.0.may_appear_after(parent_scope.expansion, result.0) ||
 789                             innermost_def == Def::NonMacroAttr(NonMacroAttrKind::DeriveHelper) ||
 790                             def == Def::NonMacroAttr(NonMacroAttrKind::DeriveHelper)) {
 791                             self.ambiguity_errors.push(AmbiguityError {
 792                                 ident,
 793                                 b1: innermost_result.0,
 794                                 b2: result.0,
 795                             });
 796                             return Ok(innermost_result);
 797                         }
 798                     } else {
 799                         // Found the first solution.
 800                         innermost_result = Some(result);
 801                     }
 802
 803                     continue_search!();
 804                 },
 805                 Err(Determinacy::Determined) => {
 806                     continue_search!();
 807                 }
 808                 Err(Determinacy::Undetermined) => return Err(Determinacy::determined(force)),
 809             }
 810         }
 811
 812         // The first found solution was the only one, return it.
 813         if let Some(innermost_result) = innermost_result {
 814             return Ok(innermost_result);
 815         }
 816
 817         let determinacy = Determinacy::determined(force);
 818         if determinacy == Determinacy::Determined && kind == Some(MacroKind::Attr) {
 819             // For single-segment attributes interpret determinate "no resolution" as a custom
 820             // attribute. (Lexical resolution implies the first segment and attr kind should imply
 821             // the last segment, so we are certainly working with a single-segment attribute here.)
 822             assert!(ns == MacroNS);
 823             let binding = (Def::NonMacroAttr(NonMacroAttrKind::Custom),
 824                            ty::Visibility::Public, ident.span, Mark::root())
 825                            .to_name_binding(self.arenas);
 826             Ok((binding, FromPrelude(true)))
 827         } else {
 828             Err(determinacy)
 829         }
 830     }
 831
 832     fn resolve_legacy_scope(
 833         &mut self,
 834         ident: Ident,
 835         kind: Option<MacroKind>,
 836         parent_scope: &ParentScope<'a>,
 837         record_used: bool,
 838     ) -> Option<&'a NameBinding<'a>> {
 839         if sub_namespace_mismatch(kind, Some(MacroKind::Bang)) {
 840             return None;
 841         }
 842
 843         let ident = ident.modern();
 844
 845         // This is *the* result, resolution from the scope closest to the resolved identifier.
 846         // However, sometimes this result is "weak" because it comes from a macro expansion,
 847         // and in this case it cannot shadow names from outer scopes, e.g.
 848         // macro_rules! m { ... } // solution in outer scope
 849         // {
 850         //     define_m!(); // generates another `macro_rules! m` - innermost solution
 851         //                  // weak, cannot shadow the outer `m`, need to report ambiguity error
 852         //     m!();
 853         // }
 854         // So we have to save the innermost solution and continue searching in outer scopes
 855         // to detect potential ambiguities.
 856         let mut innermost_result: Option<&NameBinding> = None;
 857
 858         // Go through all the scopes and try to resolve the name.
 859         let mut where_to_resolve = parent_scope.legacy;
 860         loop {
 861             let result = match where_to_resolve {
 862                 LegacyScope::Binding(legacy_binding) if ident == legacy_binding.ident =>
 863                     Some(legacy_binding.binding),
 864                 _ => None,
 865             };
 866
 867             macro_rules! continue_search { () => {
 868                 where_to_resolve = match where_to_resolve {
 869                     LegacyScope::Empty => break, // nowhere else to search
 870                     LegacyScope::Binding(binding) => binding.parent_legacy_scope,
 871                     LegacyScope::Invocation(invocation) => invocation.output_legacy_scope.get(),
 872                     LegacyScope::Uninitialized => unreachable!(),
 873                 };
 874
 875                 continue;
 876             }}
 877
 878             match result {
 879                 Some(result) => {
 880                     if !record_used {
 881                         return Some(result);
 882                     }
 883
 884                     if let Some(innermost_result) = innermost_result {
 885                         // Found another solution, if the first one was "weak", report an error.
 886                         if result.def() != innermost_result.def() &&
 887                            innermost_result.may_appear_after(parent_scope.expansion, result) {
 888                             self.ambiguity_errors.push(AmbiguityError {
 889                                 ident,
 890                                 b1: innermost_result,
 891                                 b2: result,
 892                             });
 893                             return Some(innermost_result);
 894                         }
 895                     } else {
 896                         // Found the first solution.
 897                         innermost_result = Some(result);
 898                     }
 899
 900                     continue_search!();
 901                 }
 902                 None => {
 903                     continue_search!();
 904                 }
 905             }
 906         }
 907
 908         // The first found solution was the only one (or there was no solution at all), return it.
 909         innermost_result
 910     }
 911
 912     pub fn finalize_current_module_macro_resolutions(&mut self) {
 913         let module = self.current_module;
 914         for &(ref path, span) in module.macro_resolutions.borrow().iter() {
 915             match self.resolve_path(None, &path, Some(MacroNS), true, span, CrateLint::No) {
 916                 PathResult::NonModule(_) => {},
 917                 PathResult::Failed(span, msg, _) => {
 918                     resolve_error(self, span, ResolutionError::FailedToResolve(&msg));
 919                 }
 920                 _ => unreachable!(),
 921             }
 922         }
 923
 924         let legacy_macro_resolutions =
 925             mem::replace(&mut *module.legacy_macro_resolutions.borrow_mut(), Vec::new());
 926         for (ident, kind, parent_scope, def) in legacy_macro_resolutions {
 927             let span = ident.span;
 928             let legacy_resolution = self.resolve_legacy_scope(
 929                 ident, Some(kind), &parent_scope, true
 930             );
 931             let resolution = self.resolve_lexical_macro_path_segment(
 932                 ident, MacroNS, Some(kind), &parent_scope, true, true, span
 933             );
 934
 935             let check_consistency = |this: &Self, new_def: Def| {
 936                 if let Some(def) = def {
 937                     if this.ambiguity_errors.is_empty() && new_def != def && new_def != Def::Err {
 938                         // Make sure compilation does not succeed if preferred macro resolution
 939                         // has changed after the macro had been expanded. In theory all such
 940                         // situations should be reported as ambiguity errors, so this is span-bug.
 941                         span_bug!(span, "inconsistent resolution for a macro");
 942                     }
 943                 } else {
 944                     // It's possible that the macro was unresolved (indeterminate) and silently
 945                     // expanded into a dummy fragment for recovery during expansion.
 946                     // Now, post-expansion, the resolution may succeed, but we can't change the
 947                     // past and need to report an error.
 948                     let msg =
 949                         format!("cannot determine resolution for the {} `{}`", kind.descr(), ident);
 950                     let msg_note = "import resolution is stuck, try simplifying macro imports";
 951                     this.session.struct_span_err(span, &msg).note(msg_note).emit();
 952                 }
 953             };
 954
 955             match (legacy_resolution, resolution) {
 956                 (None, Err(_)) => {
 957                     assert!(def.is_none());
 958                     let bang = if kind == MacroKind::Bang { "!" } else { "" };
 959                     let msg =
 960                         format!("cannot find {} `{}{}` in this scope", kind.descr(), ident, bang);
 961                     let mut err = self.session.struct_span_err(span, &msg);
 962                     self.suggest_macro_name(&ident.as_str(), kind, &mut err, span);
 963                     err.emit();
 964                 },
 965                 (Some(legacy_binding), Ok((binding, FromPrelude(from_prelude))))
 966                         if legacy_binding.def() != binding.def_ignoring_ambiguity() &&
 967                            (!from_prelude ||
 968                             legacy_binding.may_appear_after(parent_scope.expansion, binding)) => {
 969                     self.report_ambiguity_error(ident, legacy_binding, binding);
 970                 },
 971                 // OK, non-macro-expanded legacy wins over prelude even if defs are different
 972                 // Also, legacy and modern can co-exist if their defs are same
 973                 (Some(legacy_binding), Ok(_)) |
 974                 // OK, unambiguous resolution
 975                 (Some(legacy_binding), Err(_)) => {
 976                     check_consistency(self, legacy_binding.def());
 977                 }
 978                 // OK, unambiguous resolution
 979                 (None, Ok((binding, FromPrelude(from_prelude)))) => {
 980                     check_consistency(self, binding.def_ignoring_ambiguity());
 981                     if from_prelude {
 982                         self.record_use(ident, MacroNS, binding);
 983                         self.err_if_macro_use_proc_macro(ident.name, span, binding);
 984                     }
 985                 }
 986             };
 987         }
 988
 989         let builtin_attrs = mem::replace(&mut *module.builtin_attrs.borrow_mut(), Vec::new());
 990         for (ident, parent_scope) in builtin_attrs {
 991             let resolve_legacy = |this: &mut Self| this.resolve_legacy_scope(
 992                 ident, Some(MacroKind::Attr), &parent_scope, true
 993             );
 994             let resolve_modern = |this: &mut Self| this.resolve_lexical_macro_path_segment(
 995                 ident, MacroNS, Some(MacroKind::Attr), &parent_scope, true, true, ident.span
 996             ).map(|(binding, _)| binding).ok();
 997
 998             if let Some(binding) = resolve_legacy(self).or_else(|| resolve_modern(self)) {
 999                 if binding.def_ignoring_ambiguity() !=
1000                         Def::NonMacroAttr(NonMacroAttrKind::Builtin) {
1001                     let builtin_binding = (Def::NonMacroAttr(NonMacroAttrKind::Builtin),
1002                                            ty::Visibility::Public, ident.span, Mark::root())
1003                                            .to_name_binding(self.arenas);
1004                     self.report_ambiguity_error(ident, binding, builtin_binding);
1005                 }
1006             }
1007         }
1008     }
1009
1010     fn suggest_macro_name(&mut self, name: &str, kind: MacroKind,
1011                           err: &mut DiagnosticBuilder<'a>, span: Span) {
1012         // First check if this is a locally-defined bang macro.
1013         let suggestion = if let MacroKind::Bang = kind {
1014             find_best_match_for_name(self.macro_names.iter().map(|ident| &ident.name), name, None)
1015         } else {
1016             None
1017         // Then check global macros.
1018         }.or_else(|| {
1019             let names = self.builtin_macros.iter().chain(self.macro_use_prelude.iter())
1020                                                   .filter_map(|(name, binding)| {
1021                 if binding.macro_kind() == Some(kind) { Some(name) } else { None }
1022             });
1023             find_best_match_for_name(names, name, None)
1024         // Then check modules.
1025         }).or_else(|| {
1026             let is_macro = |def| {
1027                 if let Def::Macro(_, def_kind) = def {
1028                     def_kind == kind
1029                 } else {
1030                     false
1031                 }
1032             };
1033             let ident = Ident::new(Symbol::intern(name), span);
1034             self.lookup_typo_candidate(&[ident], MacroNS, is_macro, span)
1035         });
1036
1037         if let Some(suggestion) = suggestion {
1038             if suggestion != name {
1039                 if let MacroKind::Bang = kind {
1040                     err.span_suggestion_with_applicability(
1041                         span,
1042                         "you could try the macro",
1043                         suggestion.to_string(),
1044                         Applicability::MaybeIncorrect
1045                     );
1046                 } else {
1047                     err.span_suggestion_with_applicability(
1048                         span,
1049                         "try",
1050                         suggestion.to_string(),
1051                         Applicability::MaybeIncorrect
1052                     );
1053                 }
1054             } else {
1055                 err.help("have you added the `#[macro_use]` on the module/import?");
1056             }
1057         }
1058     }
1059
1060     fn collect_def_ids(&mut self,
1061                        mark: Mark,
1062                        invocation: &'a InvocationData<'a>,
1063                        fragment: &AstFragment) {
1064         let Resolver { ref mut invocations, arenas, graph_root, .. } = *self;
1065         let InvocationData { def_index, .. } = *invocation;
1066
1067         let visit_macro_invoc = &mut |invoc: map::MacroInvocationData| {
1068             invocations.entry(invoc.mark).or_insert_with(|| {
1069                 arenas.alloc_invocation_data(InvocationData {
1070                     def_index: invoc.def_index,
1071                     module: Cell::new(graph_root),
1072                     parent_legacy_scope: Cell::new(LegacyScope::Uninitialized),
1073                     output_legacy_scope: Cell::new(LegacyScope::Uninitialized),
1074                 })
1075             });
1076         };
1077
1078         let mut def_collector = DefCollector::new(&mut self.definitions, mark);
1079         def_collector.visit_macro_invoc = Some(visit_macro_invoc);
1080         def_collector.with_parent(def_index, |def_collector| {
1081             fragment.visit_with(def_collector)
1082         });
1083     }
1084
1085     pub fn define_macro(&mut self,
1086                         item: &ast::Item,
1087                         expansion: Mark,
1088                         current_legacy_scope: &mut LegacyScope<'a>) {
1089         self.local_macro_def_scopes.insert(item.id, self.current_module);
1090         let ident = item.ident;
1091         if ident.name == "macro_rules" {
1092             self.session.span_err(item.span, "user-defined macros may not be named `macro_rules`");
1093         }
1094
1095         let def_id = self.definitions.local_def_id(item.id);
1096         let ext = Lrc::new(macro_rules::compile(&self.session.parse_sess,
1097                                                &self.session.features_untracked(),
1098                                                item, hygiene::default_edition()));
1099         self.macro_map.insert(def_id, ext);
1100
1101         let def = match item.node { ast::ItemKind::MacroDef(ref def) => def, _ => unreachable!() };
1102         if def.legacy {
1103             let ident = ident.modern();
1104             self.macro_names.insert(ident);
1105             let def = Def::Macro(def_id, MacroKind::Bang);
1106             let vis = ty::Visibility::Invisible; // Doesn't matter for legacy bindings
1107             let binding = (def, vis, item.span, expansion).to_name_binding(self.arenas);
1108             let legacy_binding = self.arenas.alloc_legacy_binding(LegacyBinding {
1109                 parent_legacy_scope: *current_legacy_scope, binding, ident
1110             });
1111             *current_legacy_scope = LegacyScope::Binding(legacy_binding);
1112             self.all_macros.insert(ident.name, def);
1113             if attr::contains_name(&item.attrs, "macro_export") {
1114                 let module = self.graph_root;
1115                 let vis = ty::Visibility::Public;
1116                 self.define(module, ident, MacroNS,
1117                             (def, vis, item.span, expansion, IsMacroExport));
1118             } else {
1119                 if !attr::contains_name(&item.attrs, "rustc_doc_only_macro") {
1120                     self.check_reserved_macro_name(ident, MacroNS);
1121                 }
1122                 self.unused_macros.insert(def_id);
1123             }
1124         } else {
1125             let module = self.current_module;
1126             let def = Def::Macro(def_id, MacroKind::Bang);
1127             let vis = self.resolve_visibility(&item.vis);
1128             if vis != ty::Visibility::Public {
1129                 self.unused_macros.insert(def_id);
1130             }
1131             self.define(module, ident, MacroNS, (def, vis, item.span, expansion));
1132         }
1133     }
1134
1135     /// Error if `ext` is a Macros 1.1 procedural macro being imported by `#[macro_use]`
1136     fn err_if_macro_use_proc_macro(&mut self, name: Name, use_span: Span,
1137                                    binding: &NameBinding<'a>) {
1138         let krate = match binding.def() {
1139             Def::NonMacroAttr(..) | Def::Err => return,
1140             Def::Macro(def_id, _) => def_id.krate,
1141             _ => unreachable!(),
1142         };
1143
1144         // Plugin-based syntax extensions are exempt from this check
1145         if krate == CrateNum::BuiltinMacros { return; }
1146
1147         let ext = binding.get_macro(self);
1148
1149         match *ext {
1150             // If `ext` is a procedural macro, check if we've already warned about it
1151             SyntaxExtension::AttrProcMacro(..) | SyntaxExtension::ProcMacro { .. } =>
1152                 if !self.warned_proc_macros.insert(name) { return; },
1153             _ => return,
1154         }
1155
1156         let warn_msg = match *ext {
1157             SyntaxExtension::AttrProcMacro(..) =>
1158                 "attribute procedural macros cannot be imported with `#[macro_use]`",
1159             SyntaxExtension::ProcMacro { .. } =>
1160                 "procedural macros cannot be imported with `#[macro_use]`",
1161             _ => return,
1162         };
1163
1164         let def_id = self.current_module.normal_ancestor_id;
1165         let node_id = self.definitions.as_local_node_id(def_id).unwrap();
1166
1167         self.proc_mac_errors.push(ProcMacError {
1168             crate_name: self.cstore.crate_name_untracked(krate),
1169             name,
1170             module: node_id,
1171             use_span,
1172             warn_msg,
1173         });
1174     }
1175
1176     pub fn report_proc_macro_import(&mut self, krate: &ast::Crate) {
1177         for err in self.proc_mac_errors.drain(..) {
1178             let (span, found_use) = ::UsePlacementFinder::check(krate, err.module);
1179
1180             if let Some(span) = span {
1181                 let found_use = if found_use { "" } else { "\n" };
1182                 self.session.struct_span_err(err.use_span, err.warn_msg)
1183                     .span_suggestion_with_applicability(
1184                         span,
1185                         "instead, import the procedural macro like any other item",
1186                         format!("use {}::{};{}", err.crate_name, err.name, found_use),
1187                         Applicability::MachineApplicable
1188                     ).emit();
1189             } else {
1190                 self.session.struct_span_err(err.use_span, err.warn_msg)
1191                     .help(&format!("instead, import the procedural macro like any other item: \
1192                                     `use {}::{};`", err.crate_name, err.name))
1193                     .emit();
1194             }
1195         }
1196     }
1197
1198     fn gate_legacy_custom_derive(&mut self, name: Symbol, span: Span) {
1199         if !self.session.features_untracked().custom_derive {
1200             let sess = &self.session.parse_sess;
1201             let explain = feature_gate::EXPLAIN_CUSTOM_DERIVE;
1202             emit_feature_err(sess, "custom_derive", span, GateIssue::Language, explain);
1203         } else if !self.is_whitelisted_legacy_custom_derive(name) {
1204             self.session.span_warn(span, feature_gate::EXPLAIN_DEPR_CUSTOM_DERIVE);
1205         }
1206     }
1207 }