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, BUILTIN_MACROS_CRATE, CRATE_DEF_INDEX, DefIndex,
  18                          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 pub struct ProcMacError {
 105     crate_name: Symbol,
 106     name: Symbol,
 107     module: ast::NodeId,
 108     use_span: Span,
 109     warn_msg: &'static str,
 110 }
 111
 112 // For compatibility bang macros are skipped when resolving potentially built-in attributes.
 113 fn macro_kind_mismatch(name: Name, requirement: Option<MacroKind>, candidate: Option<MacroKind>)
 114                        -> bool {
 115     requirement == Some(MacroKind::Attr) && candidate == Some(MacroKind::Bang) &&
 116     (name == "test" || name == "bench" || is_builtin_attr_name(name))
 117 }
 118
 119 impl<'a, 'crateloader: 'a> base::Resolver for Resolver<'a, 'crateloader> {
 120     fn next_node_id(&mut self) -> ast::NodeId {
 121         self.session.next_node_id()
 122     }
 123
 124     fn get_module_scope(&mut self, id: ast::NodeId) -> Mark {
 125         let mark = Mark::fresh(Mark::root());
 126         let module = self.module_map[&self.definitions.local_def_id(id)];
 127         self.invocations.insert(mark, self.arenas.alloc_invocation_data(InvocationData {
 128             module: Cell::new(module),
 129             def_index: module.def_id().unwrap().index,
 130             parent_legacy_scope: Cell::new(LegacyScope::Empty),
 131             output_legacy_scope: Cell::new(LegacyScope::Empty),
 132         }));
 133         mark
 134     }
 135
 136     fn eliminate_crate_var(&mut self, item: P<ast::Item>) -> P<ast::Item> {
 137         struct EliminateCrateVar<'b, 'a: 'b, 'crateloader: 'a>(
 138             &'b mut Resolver<'a, 'crateloader>, Span
 139         );
 140
 141         impl<'a, 'b, 'crateloader> Folder for EliminateCrateVar<'a, 'b, 'crateloader> {
 142             fn fold_path(&mut self, path: ast::Path) -> ast::Path {
 143                 match self.fold_qpath(None, path) {
 144                     (None, path) => path,
 145                     _ => unreachable!(),
 146                 }
 147             }
 148
 149             fn fold_qpath(&mut self, mut qself: Option<ast::QSelf>, mut path: ast::Path)
 150                           -> (Option<ast::QSelf>, ast::Path) {
 151                 qself = qself.map(|ast::QSelf { ty, path_span, position }| {
 152                     ast::QSelf {
 153                         ty: self.fold_ty(ty),
 154                         path_span: self.new_span(path_span),
 155                         position,
 156                     }
 157                 });
 158
 159                 if path.segments[0].ident.name == keywords::DollarCrate.name() {
 160                     let module = self.0.resolve_crate_root(path.segments[0].ident);
 161                     path.segments[0].ident.name = keywords::CrateRoot.name();
 162                     if !module.is_local() {
 163                         let span = path.segments[0].ident.span;
 164                         path.segments.insert(1, match module.kind {
 165                             ModuleKind::Def(_, name) => ast::PathSegment::from_ident(
 166                                 ast::Ident::with_empty_ctxt(name).with_span_pos(span)
 167                             ),
 168                             _ => unreachable!(),
 169                         });
 170                         if let Some(qself) = &mut qself {
 171                             qself.position += 1;
 172                         }
 173                     }
 174                 }
 175                 (qself, path)
 176             }
 177
 178             fn fold_mac(&mut self, mac: ast::Mac) -> ast::Mac {
 179                 fold::noop_fold_mac(mac, self)
 180             }
 181         }
 182
 183         EliminateCrateVar(self, item.span).fold_item(item).expect_one("")
 184     }
 185
 186     fn is_whitelisted_legacy_custom_derive(&self, name: Name) -> bool {
 187         self.whitelisted_legacy_custom_derives.contains(&name)
 188     }
 189
 190     fn visit_ast_fragment_with_placeholders(&mut self, mark: Mark, fragment: &AstFragment,
 191                                             derives: &[Mark]) {
 192         let invocation = self.invocations[&mark];
 193         self.collect_def_ids(mark, invocation, fragment);
 194
 195         self.current_module = invocation.module.get();
 196         self.current_module.unresolved_invocations.borrow_mut().remove(&mark);
 197         self.current_module.unresolved_invocations.borrow_mut().extend(derives);
 198         for &derive in derives {
 199             self.invocations.insert(derive, invocation);
 200         }
 201         let mut visitor = BuildReducedGraphVisitor {
 202             resolver: self,
 203             current_legacy_scope: invocation.parent_legacy_scope.get(),
 204             expansion: mark,
 205         };
 206         fragment.visit_with(&mut visitor);
 207         invocation.output_legacy_scope.set(visitor.current_legacy_scope);
 208     }
 209
 210     fn add_builtin(&mut self, ident: ast::Ident, ext: Lrc<SyntaxExtension>) {
 211         let def_id = DefId {
 212             krate: BUILTIN_MACROS_CRATE,
 213             index: DefIndex::from_array_index(self.macro_map.len(),
 214                                               DefIndexAddressSpace::Low),
 215         };
 216         let kind = ext.kind();
 217         self.macro_map.insert(def_id, ext);
 218         let binding = self.arenas.alloc_name_binding(NameBinding {
 219             kind: NameBindingKind::Def(Def::Macro(def_id, kind), false),
 220             span: DUMMY_SP,
 221             vis: ty::Visibility::Invisible,
 222             expansion: Mark::root(),
 223         });
 224         if self.builtin_macros.insert(ident.name, binding).is_some() {
 225             self.session.span_err(ident.span,
 226                                   &format!("built-in macro `{}` was already defined", ident));
 227         }
 228     }
 229
 230     fn resolve_imports(&mut self) {
 231         ImportResolver { resolver: self }.resolve_imports()
 232     }
 233
 234     // Resolves attribute and derive legacy macros from `#![plugin(..)]`.
 235     fn find_legacy_attr_invoc(&mut self, attrs: &mut Vec<ast::Attribute>, allow_derive: bool)
 236                               -> Option<ast::Attribute> {
 237         for i in 0..attrs.len() {
 238             let name = attrs[i].name();
 239
 240             if self.session.plugin_attributes.borrow().iter()
 241                     .any(|&(ref attr_nm, _)| name == &**attr_nm) {
 242                 attr::mark_known(&attrs[i]);
 243             }
 244
 245             match self.builtin_macros.get(&name).cloned() {
 246                 Some(binding) => match *binding.get_macro(self) {
 247                     MultiModifier(..) | MultiDecorator(..) | SyntaxExtension::AttrProcMacro(..) => {
 248                         return Some(attrs.remove(i))
 249                     }
 250                     _ => {}
 251                 },
 252                 None => {}
 253             }
 254         }
 255
 256         if !allow_derive { return None }
 257
 258         // Check for legacy derives
 259         for i in 0..attrs.len() {
 260             let name = attrs[i].name();
 261
 262             if name == "derive" {
 263                 let result = attrs[i].parse_list(&self.session.parse_sess, |parser| {
 264                     parser.parse_path_allowing_meta(PathStyle::Mod)
 265                 });
 266
 267                 let mut traits = match result {
 268                     Ok(traits) => traits,
 269                     Err(mut e) => {
 270                         e.cancel();
 271                         continue
 272                     }
 273                 };
 274
 275                 for j in 0..traits.len() {
 276                     if traits[j].segments.len() > 1 {
 277                         continue
 278                     }
 279                     let trait_name = traits[j].segments[0].ident.name;
 280                     let legacy_name = Symbol::intern(&format!("derive_{}", trait_name));
 281                     if !self.builtin_macros.contains_key(&legacy_name) {
 282                         continue
 283                     }
 284                     let span = traits.remove(j).span;
 285                     self.gate_legacy_custom_derive(legacy_name, span);
 286                     if traits.is_empty() {
 287                         attrs.remove(i);
 288                     } else {
 289                         let mut tokens = Vec::new();
 290                         for (j, path) in traits.iter().enumerate() {
 291                             if j > 0 {
 292                                 tokens.push(TokenTree::Token(attrs[i].span, Token::Comma).into());
 293                             }
 294                             for (k, segment) in path.segments.iter().enumerate() {
 295                                 if k > 0 {
 296                                     tokens.push(TokenTree::Token(path.span, Token::ModSep).into());
 297                                 }
 298                                 let tok = Token::from_ast_ident(segment.ident);
 299                                 tokens.push(TokenTree::Token(path.span, tok).into());
 300                             }
 301                         }
 302                         let delim_span = DelimSpan::from_single(attrs[i].span);
 303                         attrs[i].tokens = TokenTree::Delimited(delim_span, Delimited {
 304                             delim: token::Paren,
 305                             tts: TokenStream::concat(tokens).into(),
 306                         }).into();
 307                     }
 308                     return Some(ast::Attribute {
 309                         path: ast::Path::from_ident(Ident::new(legacy_name, span)),
 310                         tokens: TokenStream::empty(),
 311                         id: attr::mk_attr_id(),
 312                         style: ast::AttrStyle::Outer,
 313                         is_sugared_doc: false,
 314                         span,
 315                     });
 316                 }
 317             }
 318         }
 319
 320         None
 321     }
 322
 323     fn resolve_macro_invocation(&mut self, invoc: &Invocation, invoc_id: Mark, force: bool)
 324                                 -> Result<Option<Lrc<SyntaxExtension>>, Determinacy> {
 325         let (path, kind, derives_in_scope) = match invoc.kind {
 326             InvocationKind::Attr { attr: None, .. } =>
 327                 return Ok(None),
 328             InvocationKind::Attr { attr: Some(ref attr), ref traits, .. } =>
 329                 (&attr.path, MacroKind::Attr, &traits[..]),
 330             InvocationKind::Bang { ref mac, .. } =>
 331                 (&mac.node.path, MacroKind::Bang, &[][..]),
 332             InvocationKind::Derive { ref path, .. } =>
 333                 (path, MacroKind::Derive, &[][..]),
 334         };
 335
 336         let (def, ext) = self.resolve_macro_to_def(path, kind, invoc_id, derives_in_scope, force)?;
 337
 338         if let Def::Macro(def_id, _) = def {
 339             self.macro_defs.insert(invoc.expansion_data.mark, def_id);
 340             let normal_module_def_id =
 341                 self.macro_def_scope(invoc.expansion_data.mark).normal_ancestor_id;
 342             self.definitions.add_parent_module_of_macro_def(invoc.expansion_data.mark,
 343                                                             normal_module_def_id);
 344             invoc.expansion_data.mark.set_default_transparency(ext.default_transparency());
 345             invoc.expansion_data.mark.set_is_builtin(def_id.krate == BUILTIN_MACROS_CRATE);
 346         }
 347
 348         Ok(Some(ext))
 349     }
 350
 351     fn resolve_macro_path(&mut self, path: &ast::Path, kind: MacroKind, invoc_id: Mark,
 352                           derives_in_scope: &[ast::Path], force: bool)
 353                           -> Result<Lrc<SyntaxExtension>, Determinacy> {
 354         Ok(self.resolve_macro_to_def(path, kind, invoc_id, derives_in_scope, force)?.1)
 355     }
 356
 357     fn check_unused_macros(&self) {
 358         for did in self.unused_macros.iter() {
 359             let id_span = match *self.macro_map[did] {
 360                 SyntaxExtension::NormalTT { def_info, .. } |
 361                 SyntaxExtension::DeclMacro { def_info, .. } => def_info,
 362                 _ => None,
 363             };
 364             if let Some((id, span)) = id_span {
 365                 let lint = lint::builtin::UNUSED_MACROS;
 366                 let msg = "unused macro definition";
 367                 self.session.buffer_lint(lint, id, span, msg);
 368             } else {
 369                 bug!("attempted to create unused macro error, but span not available");
 370             }
 371         }
 372     }
 373 }
 374
 375 impl<'a, 'cl> Resolver<'a, 'cl> {
 376     fn resolve_macro_to_def(&mut self, path: &ast::Path, kind: MacroKind, invoc_id: Mark,
 377                             derives_in_scope: &[ast::Path], force: bool)
 378                             -> Result<(Def, Lrc<SyntaxExtension>), Determinacy> {
 379         let def = self.resolve_macro_to_def_inner(path, kind, invoc_id, derives_in_scope, force);
 380
 381         // Report errors and enforce feature gates for the resolved macro.
 382         if def != Err(Determinacy::Undetermined) {
 383             // Do not report duplicated errors on every undetermined resolution.
 384             for segment in &path.segments {
 385                 if let Some(args) = &segment.args {
 386                     self.session.span_err(args.span(), "generic arguments in macro path");
 387                 }
 388             }
 389         }
 390
 391         let def = def?;
 392
 393         match def {
 394             Def::Macro(def_id, macro_kind) => {
 395                 self.unused_macros.remove(&def_id);
 396                 if macro_kind == MacroKind::ProcMacroStub {
 397                     let msg = "can't use a procedural macro from the same crate that defines it";
 398                     self.session.span_err(path.span, msg);
 399                     return Err(Determinacy::Determined);
 400                 }
 401             }
 402             Def::NonMacroAttr(attr_kind) => {
 403                 if kind == MacroKind::Attr {
 404                     let features = self.session.features_untracked();
 405                     if attr_kind == NonMacroAttrKind::Custom {
 406                         assert!(path.segments.len() == 1);
 407                         let name = path.segments[0].ident.name.as_str();
 408                         if name.starts_with("rustc_") {
 409                             if !features.rustc_attrs {
 410                                 let msg = "unless otherwise specified, attributes with the prefix \
 411                                            `rustc_` are reserved for internal compiler diagnostics";
 412                                 feature_err(&self.session.parse_sess, "rustc_attrs", path.span,
 413                                             GateIssue::Language, &msg).emit();
 414                             }
 415                         } else if name.starts_with("derive_") {
 416                             if !features.custom_derive {
 417                                 feature_err(&self.session.parse_sess, "custom_derive", path.span,
 418                                             GateIssue::Language, EXPLAIN_DERIVE_UNDERSCORE).emit();
 419                             }
 420                         } else if !features.custom_attribute {
 421                             let msg = format!("The attribute `{}` is currently unknown to the \
 422                                                compiler and may have meaning added to it in the \
 423                                                future", path);
 424                             feature_err(&self.session.parse_sess, "custom_attribute", path.span,
 425                                         GateIssue::Language, &msg).emit();
 426                         }
 427                     }
 428                 } else {
 429                     // Not only attributes, but anything in macro namespace can result in
 430                     // `Def::NonMacroAttr` definition (e.g. `inline!()`), so we must report
 431                     // an error for those cases.
 432                     let msg = format!("expected a macro, found {}", def.kind_name());
 433                     self.session.span_err(path.span, &msg);
 434                     return Err(Determinacy::Determined);
 435                 }
 436             }
 437             _ => panic!("expected `Def::Macro` or `Def::NonMacroAttr`"),
 438         }
 439
 440         Ok((def, self.get_macro(def)))
 441     }
 442
 443     pub fn resolve_macro_to_def_inner(&mut self, path: &ast::Path, kind: MacroKind, invoc_id: Mark,
 444                                       derives_in_scope: &[ast::Path], force: bool)
 445                                       -> Result<Def, Determinacy> {
 446         let ast::Path { ref segments, span } = *path;
 447         let mut path: Vec<_> = segments.iter().map(|seg| seg.ident).collect();
 448         let invocation = self.invocations[&invoc_id];
 449         let parent_expansion = invoc_id.parent();
 450         let parent_legacy_scope = invocation.parent_legacy_scope.get();
 451         self.current_module = invocation.module.get().nearest_item_scope();
 452
 453         // Possibly apply the macro helper hack
 454         if kind == MacroKind::Bang && path.len() == 1 &&
 455            path[0].span.ctxt().outer().expn_info().map_or(false, |info| info.local_inner_macros) {
 456             let root = Ident::new(keywords::DollarCrate.name(), path[0].span);
 457             path.insert(0, root);
 458         }
 459
 460         if path.len() > 1 {
 461             let def = match self.resolve_path_with_parent_expansion(None, &path, Some(MacroNS),
 462                                                                     parent_expansion, false, span,
 463                                                                     CrateLint::No) {
 464                 PathResult::NonModule(path_res) => match path_res.base_def() {
 465                     Def::Err => Err(Determinacy::Determined),
 466                     def @ _ => {
 467                         if path_res.unresolved_segments() > 0 {
 468                             self.found_unresolved_macro = true;
 469                             self.session.span_err(span, "fail to resolve non-ident macro path");
 470                             Err(Determinacy::Determined)
 471                         } else {
 472                             Ok(def)
 473                         }
 474                     }
 475                 },
 476                 PathResult::Module(..) => unreachable!(),
 477                 PathResult::Indeterminate if !force => return Err(Determinacy::Undetermined),
 478                 _ => {
 479                     self.found_unresolved_macro = true;
 480                     Err(Determinacy::Determined)
 481                 },
 482             };
 483             self.current_module.macro_resolutions.borrow_mut()
 484                 .push((path.into_boxed_slice(), span));
 485             return def;
 486         }
 487
 488         let legacy_resolution = self.resolve_legacy_scope(
 489             path[0], Some(kind), parent_expansion, parent_legacy_scope, false
 490         );
 491         let result = if let Some(legacy_binding) = legacy_resolution {
 492             Ok(legacy_binding.def())
 493         } else {
 494             match self.resolve_lexical_macro_path_segment(path[0], MacroNS, Some(kind),
 495                                                           parent_expansion, false, force, span) {
 496                 Ok((binding, _)) => Ok(binding.def_ignoring_ambiguity()),
 497                 Err(Determinacy::Undetermined) => return Err(Determinacy::Undetermined),
 498                 Err(Determinacy::Determined) => {
 499                     self.found_unresolved_macro = true;
 500                     Err(Determinacy::Determined)
 501                 }
 502             }
 503         };
 504
 505         self.current_module.legacy_macro_resolutions.borrow_mut()
 506             .push((path[0], kind, parent_expansion, parent_legacy_scope, result.ok()));
 507
 508         if let Ok(Def::NonMacroAttr(NonMacroAttrKind::Custom)) = result {} else {
 509             return result;
 510         }
 511
 512         // At this point we've found that the `attr` is determinately unresolved and thus can be
 513         // interpreted as a custom attribute. Normally custom attributes are feature gated, but
 514         // it may be a custom attribute whitelisted by a derive macro and they do not require
 515         // a feature gate.
 516         //
 517         // So here we look through all of the derive annotations in scope and try to resolve them.
 518         // If they themselves successfully resolve *and* one of the resolved derive macros
 519         // whitelists this attribute's name, then this is a registered attribute and we can convert
 520         // it from a "generic custom attrite" into a "known derive helper attribute".
 521         assert!(kind == MacroKind::Attr);
 522         enum ConvertToDeriveHelper { Yes, No, DontKnow }
 523         let mut convert_to_derive_helper = ConvertToDeriveHelper::No;
 524         for derive in derives_in_scope {
 525             match self.resolve_macro_path(derive, MacroKind::Derive, invoc_id, &[], force) {
 526                 Ok(ext) => if let SyntaxExtension::ProcMacroDerive(_, ref inert_attrs, _) = *ext {
 527                     if inert_attrs.contains(&path[0].name) {
 528                         convert_to_derive_helper = ConvertToDeriveHelper::Yes;
 529                         break
 530                     }
 531                 },
 532                 Err(Determinacy::Undetermined) =>
 533                     convert_to_derive_helper = ConvertToDeriveHelper::DontKnow,
 534                 Err(Determinacy::Determined) => {}
 535             }
 536         }
 537
 538         match convert_to_derive_helper {
 539             ConvertToDeriveHelper::Yes => Ok(Def::NonMacroAttr(NonMacroAttrKind::DeriveHelper)),
 540             ConvertToDeriveHelper::No => result,
 541             ConvertToDeriveHelper::DontKnow => Err(Determinacy::determined(force)),
 542         }
 543     }
 544
 545     // Resolve the initial segment of a non-global macro path
 546     // (e.g. `foo` in `foo::bar!(); or `foo!();`).
 547     // This is a variation of `fn resolve_ident_in_lexical_scope` that can be run during
 548     // expansion and import resolution (perhaps they can be merged in the future).
 549     crate fn resolve_lexical_macro_path_segment(
 550         &mut self,
 551         mut ident: Ident,
 552         ns: Namespace,
 553         kind: Option<MacroKind>,
 554         parent_expansion: Mark,
 555         record_used: bool,
 556         force: bool,
 557         path_span: Span,
 558     ) -> Result<(&'a NameBinding<'a>, FromPrelude), Determinacy> {
 559         // General principles:
 560         // 1. Not controlled (user-defined) names should have higher priority than controlled names
 561         //    built into the language or standard library. This way we can add new names into the
 562         //    language or standard library without breaking user code.
 563         // 2. "Closed set" below means new names can appear after the current resolution attempt.
 564         // Places to search (in order of decreasing priority):
 565         // (Type NS)
 566         // 1. FIXME: Ribs (type parameters), there's no necessary infrastructure yet
 567         //    (open set, not controlled).
 568         // 2. Names in modules (both normal `mod`ules and blocks), loop through hygienic parents
 569         //    (open, not controlled).
 570         // 3. Extern prelude (closed, not controlled).
 571         // 4. Tool modules (closed, controlled right now, but not in the future).
 572         // 5. Standard library prelude (de-facto closed, controlled).
 573         // 6. Language prelude (closed, controlled).
 574         // (Macro NS)
 575         // 1. Names in modules (both normal `mod`ules and blocks), loop through hygienic parents
 576         //    (open, not controlled).
 577         // 2. `macro_use` prelude (open, the open part is from macro expansions, not controlled).
 578         // 2a. User-defined prelude from macro-use
 579         //    (open, the open part is from macro expansions, not controlled).
 580         // 2b. Standard library prelude is currently implemented as `macro-use` (closed, controlled)
 581         // 3. Language prelude: builtin macros (closed, controlled, except for legacy plugins).
 582         // 4. Language prelude: builtin attributes (closed, controlled).
 583
 584         assert!(ns == TypeNS  || ns == MacroNS);
 585         assert!(force || !record_used); // `record_used` implies `force`
 586         ident = ident.modern();
 587
 588         // This is *the* result, resolution from the scope closest to the resolved identifier.
 589         // However, sometimes this result is "weak" because it comes from a glob import or
 590         // a macro expansion, and in this case it cannot shadow names from outer scopes, e.g.
 591         // mod m { ... } // solution in outer scope
 592         // {
 593         //     use prefix::*; // imports another `m` - innermost solution
 594         //                    // weak, cannot shadow the outer `m`, need to report ambiguity error
 595         //     m::mac!();
 596         // }
 597         // So we have to save the innermost solution and continue searching in outer scopes
 598         // to detect potential ambiguities.
 599         let mut innermost_result: Option<(&NameBinding, FromPrelude)> = None;
 600
 601         enum WhereToResolve<'a> {
 602             Module(Module<'a>),
 603             MacroUsePrelude,
 604             BuiltinMacros,
 605             BuiltinAttrs,
 606             ExternPrelude,
 607             ToolPrelude,
 608             StdLibPrelude,
 609             BuiltinTypes,
 610         }
 611
 612         // Go through all the scopes and try to resolve the name.
 613         let mut where_to_resolve = WhereToResolve::Module(self.current_module);
 614         let mut use_prelude = !self.current_module.no_implicit_prelude;
 615         loop {
 616             let result = match where_to_resolve {
 617                 WhereToResolve::Module(module) => {
 618                     let orig_current_module = mem::replace(&mut self.current_module, module);
 619                     let binding = self.resolve_ident_in_module_unadjusted(
 620                         ModuleOrUniformRoot::Module(module),
 621                         ident,
 622                         ns,
 623                         true,
 624                         record_used,
 625                         path_span,
 626                     );
 627                     self.current_module = orig_current_module;
 628                     binding.map(|binding| (binding, FromPrelude(false)))
 629                 }
 630                 WhereToResolve::MacroUsePrelude => {
 631                     match self.macro_use_prelude.get(&ident.name).cloned() {
 632                         Some(binding) => Ok((binding, FromPrelude(true))),
 633                         None => Err(Determinacy::Determined),
 634                     }
 635                 }
 636                 WhereToResolve::BuiltinMacros => {
 637                     match self.builtin_macros.get(&ident.name).cloned() {
 638                         Some(binding) => Ok((binding, FromPrelude(true))),
 639                         None => Err(Determinacy::Determined),
 640                     }
 641                 }
 642                 WhereToResolve::BuiltinAttrs => {
 643                     // FIXME: Only built-in attributes are not considered as candidates for
 644                     // non-attributes to fight off regressions on stable channel (#53205).
 645                     // We need to come up with some more principled approach instead.
 646                     if kind == Some(MacroKind::Attr) && is_builtin_attr_name(ident.name) {
 647                         let binding = (Def::NonMacroAttr(NonMacroAttrKind::Builtin),
 648                                        ty::Visibility::Public, ident.span, Mark::root())
 649                                        .to_name_binding(self.arenas);
 650                         Ok((binding, FromPrelude(true)))
 651                     } else {
 652                         Err(Determinacy::Determined)
 653                     }
 654                 }
 655                 WhereToResolve::ExternPrelude => {
 656                     if use_prelude && self.extern_prelude.contains(&ident.name) {
 657                         if !self.session.features_untracked().extern_prelude &&
 658                            !self.ignore_extern_prelude_feature {
 659                             feature_err(&self.session.parse_sess, "extern_prelude",
 660                                         ident.span, GateIssue::Language,
 661                                         "access to extern crates through prelude is experimental")
 662                                         .emit();
 663                         }
 664
 665                         let crate_id =
 666                             self.crate_loader.process_path_extern(ident.name, ident.span);
 667                         let crate_root =
 668                             self.get_module(DefId { krate: crate_id, index: CRATE_DEF_INDEX });
 669                         self.populate_module_if_necessary(crate_root);
 670
 671                         let binding = (crate_root, ty::Visibility::Public,
 672                                        ident.span, Mark::root()).to_name_binding(self.arenas);
 673                         Ok((binding, FromPrelude(true)))
 674                     } else {
 675                         Err(Determinacy::Determined)
 676                     }
 677                 }
 678                 WhereToResolve::ToolPrelude => {
 679                     if use_prelude && is_known_tool(ident.name) {
 680                         let binding = (Def::ToolMod, ty::Visibility::Public,
 681                                        ident.span, Mark::root()).to_name_binding(self.arenas);
 682                         Ok((binding, FromPrelude(true)))
 683                     } else {
 684                         Err(Determinacy::Determined)
 685                     }
 686                 }
 687                 WhereToResolve::StdLibPrelude => {
 688                     let mut result = Err(Determinacy::Determined);
 689                     if use_prelude {
 690                         if let Some(prelude) = self.prelude {
 691                             if let Ok(binding) = self.resolve_ident_in_module_unadjusted(
 692                                 ModuleOrUniformRoot::Module(prelude),
 693                                 ident,
 694                                 ns,
 695                                 false,
 696                                 false,
 697                                 path_span,
 698                             ) {
 699                                 result = Ok((binding, FromPrelude(true)));
 700                             }
 701                         }
 702                     }
 703                     result
 704                 }
 705                 WhereToResolve::BuiltinTypes => {
 706                     if let Some(prim_ty) =
 707                             self.primitive_type_table.primitive_types.get(&ident.name).cloned() {
 708                         let binding = (Def::PrimTy(prim_ty), 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             };
 716
 717             macro_rules! continue_search { () => {
 718                 where_to_resolve = match where_to_resolve {
 719                     WhereToResolve::Module(module) => {
 720                         match self.hygienic_lexical_parent(module, &mut ident.span) {
 721                             Some(parent_module) => WhereToResolve::Module(parent_module),
 722                             None => {
 723                                 use_prelude = !module.no_implicit_prelude;
 724                                 if ns == MacroNS {
 725                                     WhereToResolve::MacroUsePrelude
 726                                 } else {
 727                                     WhereToResolve::ExternPrelude
 728                                 }
 729                             }
 730                         }
 731                     }
 732                     WhereToResolve::MacroUsePrelude => WhereToResolve::BuiltinMacros,
 733                     WhereToResolve::BuiltinMacros => WhereToResolve::BuiltinAttrs,
 734                     WhereToResolve::BuiltinAttrs => break, // nowhere else to search
 735                     WhereToResolve::ExternPrelude => WhereToResolve::ToolPrelude,
 736                     WhereToResolve::ToolPrelude => WhereToResolve::StdLibPrelude,
 737                     WhereToResolve::StdLibPrelude => WhereToResolve::BuiltinTypes,
 738                     WhereToResolve::BuiltinTypes => break, // nowhere else to search
 739                 };
 740
 741                 continue;
 742             }}
 743
 744             match result {
 745                 Ok(result) => {
 746                     if macro_kind_mismatch(ident.name, kind, result.0.macro_kind()) {
 747                         continue_search!();
 748                     }
 749
 750                     if !record_used {
 751                         return Ok(result);
 752                     }
 753
 754                     if let Some(innermost_result) = innermost_result {
 755                         // Found another solution, if the first one was "weak", report an error.
 756                         if result.0.def() != innermost_result.0.def() &&
 757                            (innermost_result.0.is_glob_import() ||
 758                             innermost_result.0.may_appear_after(parent_expansion, result.0)) {
 759                             self.ambiguity_errors.push(AmbiguityError {
 760                                 ident,
 761                                 b1: innermost_result.0,
 762                                 b2: result.0,
 763                             });
 764                             return Ok(innermost_result);
 765                         }
 766                     } else {
 767                         // Found the first solution.
 768                         innermost_result = Some(result);
 769                     }
 770
 771                     continue_search!();
 772                 },
 773                 Err(Determinacy::Determined) => {
 774                     continue_search!();
 775                 }
 776                 Err(Determinacy::Undetermined) => return Err(Determinacy::determined(force)),
 777             }
 778         }
 779
 780         // The first found solution was the only one, return it.
 781         if let Some(innermost_result) = innermost_result {
 782             return Ok(innermost_result);
 783         }
 784
 785         let determinacy = Determinacy::determined(force);
 786         if determinacy == Determinacy::Determined && kind == Some(MacroKind::Attr) {
 787             // For single-segment attributes interpret determinate "no resolution" as a custom
 788             // attribute. (Lexical resolution implies the first segment and attr kind should imply
 789             // the last segment, so we are certainly working with a single-segment attribute here.)
 790             assert!(ns == MacroNS);
 791             let binding = (Def::NonMacroAttr(NonMacroAttrKind::Custom),
 792                            ty::Visibility::Public, ident.span, Mark::root())
 793                            .to_name_binding(self.arenas);
 794             Ok((binding, FromPrelude(true)))
 795         } else {
 796             Err(determinacy)
 797         }
 798     }
 799
 800     fn resolve_legacy_scope(&mut self,
 801                             ident: Ident,
 802                             kind: Option<MacroKind>,
 803                             parent_expansion: Mark,
 804                             parent_legacy_scope: LegacyScope<'a>,
 805                             record_used: bool)
 806                             -> Option<&'a NameBinding<'a>> {
 807         if macro_kind_mismatch(ident.name, kind, Some(MacroKind::Bang)) {
 808             return None;
 809         }
 810
 811         let ident = ident.modern();
 812
 813         // This is *the* result, resolution from the scope closest to the resolved identifier.
 814         // However, sometimes this result is "weak" because it comes from a macro expansion,
 815         // and in this case it cannot shadow names from outer scopes, e.g.
 816         // macro_rules! m { ... } // solution in outer scope
 817         // {
 818         //     define_m!(); // generates another `macro_rules! m` - innermost solution
 819         //                  // weak, cannot shadow the outer `m`, need to report ambiguity error
 820         //     m!();
 821         // }
 822         // So we have to save the innermost solution and continue searching in outer scopes
 823         // to detect potential ambiguities.
 824         let mut innermost_result: Option<&NameBinding> = None;
 825
 826         // Go through all the scopes and try to resolve the name.
 827         let mut where_to_resolve = parent_legacy_scope;
 828         loop {
 829             let result = match where_to_resolve {
 830                 LegacyScope::Binding(legacy_binding) if ident == legacy_binding.ident =>
 831                     Some(legacy_binding.binding),
 832                 _ => None,
 833             };
 834
 835             macro_rules! continue_search { () => {
 836                 where_to_resolve = match where_to_resolve {
 837                     LegacyScope::Empty => break, // nowhere else to search
 838                     LegacyScope::Binding(binding) => binding.parent_legacy_scope,
 839                     LegacyScope::Invocation(invocation) => invocation.output_legacy_scope.get(),
 840                     LegacyScope::Uninitialized => unreachable!(),
 841                 };
 842
 843                 continue;
 844             }}
 845
 846             match result {
 847                 Some(result) => {
 848                     if !record_used {
 849                         return Some(result);
 850                     }
 851
 852                     if let Some(innermost_result) = innermost_result {
 853                         // Found another solution, if the first one was "weak", report an error.
 854                         if result.def() != innermost_result.def() &&
 855                            innermost_result.may_appear_after(parent_expansion, result) {
 856                             self.ambiguity_errors.push(AmbiguityError {
 857                                 ident,
 858                                 b1: innermost_result,
 859                                 b2: result,
 860                             });
 861                             return Some(innermost_result);
 862                         }
 863                     } else {
 864                         // Found the first solution.
 865                         innermost_result = Some(result);
 866                     }
 867
 868                     continue_search!();
 869                 }
 870                 None => {
 871                     continue_search!();
 872                 }
 873             }
 874         }
 875
 876         // The first found solution was the only one (or there was no solution at all), return it.
 877         innermost_result
 878     }
 879
 880     pub fn finalize_current_module_macro_resolutions(&mut self) {
 881         let module = self.current_module;
 882         for &(ref path, span) in module.macro_resolutions.borrow().iter() {
 883             match self.resolve_path(None, &path, Some(MacroNS), true, span, CrateLint::No) {
 884                 PathResult::NonModule(_) => {},
 885                 PathResult::Failed(span, msg, _) => {
 886                     resolve_error(self, span, ResolutionError::FailedToResolve(&msg));
 887                 }
 888                 _ => unreachable!(),
 889             }
 890         }
 891
 892         for &(ident, kind, parent_expansion, parent_legacy_scope, def)
 893                 in module.legacy_macro_resolutions.borrow().iter() {
 894             let span = ident.span;
 895             let legacy_resolution = self.resolve_legacy_scope(
 896                 ident, Some(kind), parent_expansion, parent_legacy_scope, true
 897             );
 898             let resolution = self.resolve_lexical_macro_path_segment(
 899                 ident, MacroNS, Some(kind), parent_expansion, true, true, span
 900             );
 901
 902             let check_consistency = |this: &Self, new_def: Def| {
 903                 if let Some(def) = def {
 904                     if this.ambiguity_errors.is_empty() && new_def != def && new_def != Def::Err {
 905                         // Make sure compilation does not succeed if preferred macro resolution
 906                         // has changed after the macro had been expanded. In theory all such
 907                         // situations should be reported as ambiguity errors, so this is span-bug.
 908                         span_bug!(span, "inconsistent resolution for a macro");
 909                     }
 910                 } else {
 911                     // It's possible that the macro was unresolved (indeterminate) and silently
 912                     // expanded into a dummy fragment for recovery during expansion.
 913                     // Now, post-expansion, the resolution may succeed, but we can't change the
 914                     // past and need to report an error.
 915                     let msg =
 916                         format!("cannot determine resolution for the {} `{}`", kind.descr(), ident);
 917                     let msg_note = "import resolution is stuck, try simplifying macro imports";
 918                     this.session.struct_span_err(span, &msg).note(msg_note).emit();
 919                 }
 920             };
 921
 922             match (legacy_resolution, resolution) {
 923                 (None, Err(_)) => {
 924                     assert!(def.is_none());
 925                     let bang = if kind == MacroKind::Bang { "!" } else { "" };
 926                     let msg =
 927                         format!("cannot find {} `{}{}` in this scope", kind.descr(), ident, bang);
 928                     let mut err = self.session.struct_span_err(span, &msg);
 929                     self.suggest_macro_name(&ident.as_str(), kind, &mut err, span);
 930                     err.emit();
 931                 },
 932                 (Some(legacy_binding), Ok((binding, FromPrelude(from_prelude))))
 933                         if legacy_binding.def() != binding.def_ignoring_ambiguity() &&
 934                            (!from_prelude ||
 935                             legacy_binding.may_appear_after(parent_expansion, binding)) => {
 936                     self.report_ambiguity_error(ident, legacy_binding, binding);
 937                 },
 938                 // OK, non-macro-expanded legacy wins over prelude even if defs are different
 939                 // Also, legacy and modern can co-exist if their defs are same
 940                 (Some(legacy_binding), Ok(_)) |
 941                 // OK, unambiguous resolution
 942                 (Some(legacy_binding), Err(_)) => {
 943                     check_consistency(self, legacy_binding.def());
 944                 }
 945                 // OK, unambiguous resolution
 946                 (None, Ok((binding, FromPrelude(from_prelude)))) => {
 947                     check_consistency(self, binding.def_ignoring_ambiguity());
 948                     if from_prelude {
 949                         self.record_use(ident, MacroNS, binding);
 950                         self.err_if_macro_use_proc_macro(ident.name, span, binding);
 951                     }
 952                 }
 953             };
 954         }
 955
 956         for &(ident, parent_expansion, parent_legacy_scope)
 957                 in module.builtin_attrs.borrow().iter() {
 958             let resolve_legacy = |this: &mut Self| this.resolve_legacy_scope(
 959                 ident, Some(MacroKind::Attr), parent_expansion, parent_legacy_scope, true
 960             );
 961             let resolve_modern = |this: &mut Self| this.resolve_lexical_macro_path_segment(
 962                 ident, MacroNS, Some(MacroKind::Attr), parent_expansion, true, true, ident.span
 963             ).map(|(binding, _)| binding).ok();
 964
 965             if let Some(binding) = resolve_legacy(self).or_else(|| resolve_modern(self)) {
 966                 if binding.def_ignoring_ambiguity() !=
 967                         Def::NonMacroAttr(NonMacroAttrKind::Builtin) {
 968                     let builtin_binding = (Def::NonMacroAttr(NonMacroAttrKind::Builtin),
 969                                            ty::Visibility::Public, ident.span, Mark::root())
 970                                            .to_name_binding(self.arenas);
 971                     self.report_ambiguity_error(ident, binding, builtin_binding);
 972                 }
 973             }
 974         }
 975     }
 976
 977     fn suggest_macro_name(&mut self, name: &str, kind: MacroKind,
 978                           err: &mut DiagnosticBuilder<'a>, span: Span) {
 979         // First check if this is a locally-defined bang macro.
 980         let suggestion = if let MacroKind::Bang = kind {
 981             find_best_match_for_name(self.macro_names.iter().map(|ident| &ident.name), name, None)
 982         } else {
 983             None
 984         // Then check global macros.
 985         }.or_else(|| {
 986             let names = self.builtin_macros.iter().chain(self.macro_use_prelude.iter())
 987                                                   .filter_map(|(name, binding)| {
 988                 if binding.macro_kind() == Some(kind) { Some(name) } else { None }
 989             });
 990             find_best_match_for_name(names, name, None)
 991         // Then check modules.
 992         }).or_else(|| {
 993             let is_macro = |def| {
 994                 if let Def::Macro(_, def_kind) = def {
 995                     def_kind == kind
 996                 } else {
 997                     false
 998                 }
 999             };
1000             let ident = Ident::new(Symbol::intern(name), span);
1001             self.lookup_typo_candidate(&[ident], MacroNS, is_macro, span)
1002         });
1003
1004         if let Some(suggestion) = suggestion {
1005             if suggestion != name {
1006                 if let MacroKind::Bang = kind {
1007                     err.span_suggestion_with_applicability(
1008                         span,
1009                         "you could try the macro",
1010                         suggestion.to_string(),
1011                         Applicability::MaybeIncorrect
1012                     );
1013                 } else {
1014                     err.span_suggestion_with_applicability(
1015                         span,
1016                         "try",
1017                         suggestion.to_string(),
1018                         Applicability::MaybeIncorrect
1019                     );
1020                 }
1021             } else {
1022                 err.help("have you added the `#[macro_use]` on the module/import?");
1023             }
1024         }
1025     }
1026
1027     fn collect_def_ids(&mut self,
1028                        mark: Mark,
1029                        invocation: &'a InvocationData<'a>,
1030                        fragment: &AstFragment) {
1031         let Resolver { ref mut invocations, arenas, graph_root, .. } = *self;
1032         let InvocationData { def_index, .. } = *invocation;
1033
1034         let visit_macro_invoc = &mut |invoc: map::MacroInvocationData| {
1035             invocations.entry(invoc.mark).or_insert_with(|| {
1036                 arenas.alloc_invocation_data(InvocationData {
1037                     def_index: invoc.def_index,
1038                     module: Cell::new(graph_root),
1039                     parent_legacy_scope: Cell::new(LegacyScope::Uninitialized),
1040                     output_legacy_scope: Cell::new(LegacyScope::Uninitialized),
1041                 })
1042             });
1043         };
1044
1045         let mut def_collector = DefCollector::new(&mut self.definitions, mark);
1046         def_collector.visit_macro_invoc = Some(visit_macro_invoc);
1047         def_collector.with_parent(def_index, |def_collector| {
1048             fragment.visit_with(def_collector)
1049         });
1050     }
1051
1052     pub fn define_macro(&mut self,
1053                         item: &ast::Item,
1054                         expansion: Mark,
1055                         current_legacy_scope: &mut LegacyScope<'a>) {
1056         self.local_macro_def_scopes.insert(item.id, self.current_module);
1057         let ident = item.ident;
1058         if ident.name == "macro_rules" {
1059             self.session.span_err(item.span, "user-defined macros may not be named `macro_rules`");
1060         }
1061
1062         let def_id = self.definitions.local_def_id(item.id);
1063         let ext = Lrc::new(macro_rules::compile(&self.session.parse_sess,
1064                                                &self.session.features_untracked(),
1065                                                item, hygiene::default_edition()));
1066         self.macro_map.insert(def_id, ext);
1067
1068         let def = match item.node { ast::ItemKind::MacroDef(ref def) => def, _ => unreachable!() };
1069         if def.legacy {
1070             let ident = ident.modern();
1071             self.macro_names.insert(ident);
1072             let def = Def::Macro(def_id, MacroKind::Bang);
1073             let vis = ty::Visibility::Invisible; // Doesn't matter for legacy bindings
1074             let binding = (def, vis, item.span, expansion).to_name_binding(self.arenas);
1075             let legacy_binding = self.arenas.alloc_legacy_binding(LegacyBinding {
1076                 parent_legacy_scope: *current_legacy_scope, binding, ident
1077             });
1078             *current_legacy_scope = LegacyScope::Binding(legacy_binding);
1079             self.all_macros.insert(ident.name, def);
1080             if attr::contains_name(&item.attrs, "macro_export") {
1081                 let module = self.graph_root;
1082                 let vis = ty::Visibility::Public;
1083                 self.define(module, ident, MacroNS,
1084                             (def, vis, item.span, expansion, IsMacroExport));
1085             } else {
1086                 if !attr::contains_name(&item.attrs, "rustc_doc_only_macro") {
1087                     self.check_reserved_macro_name(ident, MacroNS);
1088                 }
1089                 self.unused_macros.insert(def_id);
1090             }
1091         } else {
1092             let module = self.current_module;
1093             let def = Def::Macro(def_id, MacroKind::Bang);
1094             let vis = self.resolve_visibility(&item.vis);
1095             if vis != ty::Visibility::Public {
1096                 self.unused_macros.insert(def_id);
1097             }
1098             self.define(module, ident, MacroNS, (def, vis, item.span, expansion));
1099         }
1100     }
1101
1102     /// Error if `ext` is a Macros 1.1 procedural macro being imported by `#[macro_use]`
1103     fn err_if_macro_use_proc_macro(&mut self, name: Name, use_span: Span,
1104                                    binding: &NameBinding<'a>) {
1105         let krate = match binding.def() {
1106             Def::NonMacroAttr(..) | Def::Err => return,
1107             Def::Macro(def_id, _) => def_id.krate,
1108             _ => unreachable!(),
1109         };
1110
1111         // Plugin-based syntax extensions are exempt from this check
1112         if krate == BUILTIN_MACROS_CRATE { return; }
1113
1114         let ext = binding.get_macro(self);
1115
1116         match *ext {
1117             // If `ext` is a procedural macro, check if we've already warned about it
1118             SyntaxExtension::AttrProcMacro(..) | SyntaxExtension::ProcMacro { .. } =>
1119                 if !self.warned_proc_macros.insert(name) { return; },
1120             _ => return,
1121         }
1122
1123         let warn_msg = match *ext {
1124             SyntaxExtension::AttrProcMacro(..) =>
1125                 "attribute procedural macros cannot be imported with `#[macro_use]`",
1126             SyntaxExtension::ProcMacro { .. } =>
1127                 "procedural macros cannot be imported with `#[macro_use]`",
1128             _ => return,
1129         };
1130
1131         let def_id = self.current_module.normal_ancestor_id;
1132         let node_id = self.definitions.as_local_node_id(def_id).unwrap();
1133
1134         self.proc_mac_errors.push(ProcMacError {
1135             crate_name: self.cstore.crate_name_untracked(krate),
1136             name,
1137             module: node_id,
1138             use_span,
1139             warn_msg,
1140         });
1141     }
1142
1143     pub fn report_proc_macro_import(&mut self, krate: &ast::Crate) {
1144         for err in self.proc_mac_errors.drain(..) {
1145             let (span, found_use) = ::UsePlacementFinder::check(krate, err.module);
1146
1147             if let Some(span) = span {
1148                 let found_use = if found_use { "" } else { "\n" };
1149                 self.session.struct_span_err(err.use_span, err.warn_msg)
1150                     .span_suggestion_with_applicability(
1151                         span,
1152                         "instead, import the procedural macro like any other item",
1153                         format!("use {}::{};{}", err.crate_name, err.name, found_use),
1154                         Applicability::MachineApplicable
1155                     ).emit();
1156             } else {
1157                 self.session.struct_span_err(err.use_span, err.warn_msg)
1158                     .help(&format!("instead, import the procedural macro like any other item: \
1159                                     `use {}::{};`", err.crate_name, err.name))
1160                     .emit();
1161             }
1162         }
1163     }
1164
1165     fn gate_legacy_custom_derive(&mut self, name: Symbol, span: Span) {
1166         if !self.session.features_untracked().custom_derive {
1167             let sess = &self.session.parse_sess;
1168             let explain = feature_gate::EXPLAIN_CUSTOM_DERIVE;
1169             emit_feature_err(sess, "custom_derive", span, GateIssue::Language, explain);
1170         } else if !self.is_whitelisted_legacy_custom_derive(name) {
1171             self.session.span_warn(span, feature_gate::EXPLAIN_DEPR_CUSTOM_DERIVE);
1172         }
1173     }
1174 }