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};
  39 use syntax::util::lev_distance::find_best_match_for_name;
  40 use syntax_pos::{Span, DUMMY_SP};
  41
  42 use std::cell::Cell;
  43 use std::mem;
  44 use rustc_data_structures::sync::Lrc;
  45
  46 #[derive(Clone)]
  47 pub struct InvocationData<'a> {
  48     pub module: Cell<Module<'a>>,
  49     pub def_index: DefIndex,
  50     // The scope in which the invocation path is resolved.
  51     pub legacy_scope: Cell<LegacyScope<'a>>,
  52     // The smallest scope that includes this invocation's expansion,
  53     // or `Empty` if this invocation has not been expanded yet.
  54     pub expansion: Cell<LegacyScope<'a>>,
  55 }
  56
  57 impl<'a> InvocationData<'a> {
  58     pub fn root(graph_root: Module<'a>) -> Self {
  59         InvocationData {
  60             module: Cell::new(graph_root),
  61             def_index: CRATE_DEF_INDEX,
  62             legacy_scope: Cell::new(LegacyScope::Empty),
  63             expansion: Cell::new(LegacyScope::Empty),
  64         }
  65     }
  66 }
  67
  68 #[derive(Copy, Clone)]
  69 pub enum LegacyScope<'a> {
  70     Empty,
  71     Invocation(&'a InvocationData<'a>), // The scope of the invocation, not including its expansion
  72     Expansion(&'a InvocationData<'a>), // The scope of the invocation, including its expansion
  73     Binding(&'a LegacyBinding<'a>),
  74 }
  75
  76 pub struct LegacyBinding<'a> {
  77     pub parent: Cell<LegacyScope<'a>>,
  78     pub ident: Ident,
  79     def_id: DefId,
  80     pub span: Span,
  81 }
  82
  83 pub struct ProcMacError {
  84     crate_name: Symbol,
  85     name: Symbol,
  86     module: ast::NodeId,
  87     use_span: Span,
  88     warn_msg: &'static str,
  89 }
  90
  91 #[derive(Copy, Clone)]
  92 pub enum MacroBinding<'a> {
  93     Legacy(&'a LegacyBinding<'a>),
  94     Global(&'a NameBinding<'a>),
  95     Modern(&'a NameBinding<'a>),
  96 }
  97
  98 impl<'a> MacroBinding<'a> {
  99     pub fn span(self) -> Span {
 100         match self {
 101             MacroBinding::Legacy(binding) => binding.span,
 102             MacroBinding::Global(binding) | MacroBinding::Modern(binding) => binding.span,
 103         }
 104     }
 105
 106     pub fn binding(self) -> &'a NameBinding<'a> {
 107         match self {
 108             MacroBinding::Global(binding) | MacroBinding::Modern(binding) => binding,
 109             MacroBinding::Legacy(_) => panic!("unexpected MacroBinding::Legacy"),
 110         }
 111     }
 112
 113     pub fn def_ignoring_ambiguity(self) -> Def {
 114         match self {
 115             MacroBinding::Legacy(binding) => Def::Macro(binding.def_id, MacroKind::Bang),
 116             MacroBinding::Global(binding) | MacroBinding::Modern(binding) =>
 117                 binding.def_ignoring_ambiguity(),
 118         }
 119     }
 120 }
 121
 122 impl<'a, 'crateloader: 'a> base::Resolver for Resolver<'a, 'crateloader> {
 123     fn next_node_id(&mut self) -> ast::NodeId {
 124         self.session.next_node_id()
 125     }
 126
 127     fn get_module_scope(&mut self, id: ast::NodeId) -> Mark {
 128         let mark = Mark::fresh(Mark::root());
 129         let module = self.module_map[&self.definitions.local_def_id(id)];
 130         self.invocations.insert(mark, self.arenas.alloc_invocation_data(InvocationData {
 131             module: Cell::new(module),
 132             def_index: module.def_id().unwrap().index,
 133             legacy_scope: Cell::new(LegacyScope::Empty),
 134             expansion: Cell::new(LegacyScope::Empty),
 135         }));
 136         mark
 137     }
 138
 139     fn eliminate_crate_var(&mut self, item: P<ast::Item>) -> P<ast::Item> {
 140         struct EliminateCrateVar<'b, 'a: 'b, 'crateloader: 'a>(
 141             &'b mut Resolver<'a, 'crateloader>, Span
 142         );
 143
 144         impl<'a, 'b, 'crateloader> Folder for EliminateCrateVar<'a, 'b, 'crateloader> {
 145             fn fold_path(&mut self, path: ast::Path) -> ast::Path {
 146                 match self.fold_qpath(None, path) {
 147                     (None, path) => path,
 148                     _ => unreachable!(),
 149                 }
 150             }
 151
 152             fn fold_qpath(&mut self, mut qself: Option<ast::QSelf>, mut path: ast::Path)
 153                           -> (Option<ast::QSelf>, ast::Path) {
 154                 qself = qself.map(|ast::QSelf { ty, path_span, position }| {
 155                     ast::QSelf {
 156                         ty: self.fold_ty(ty),
 157                         path_span: self.new_span(path_span),
 158                         position,
 159                     }
 160                 });
 161
 162                 if path.segments[0].ident.name == keywords::DollarCrate.name() {
 163                     let module = self.0.resolve_crate_root(path.segments[0].ident);
 164                     path.segments[0].ident.name = keywords::CrateRoot.name();
 165                     if !module.is_local() {
 166                         let span = path.segments[0].ident.span;
 167                         path.segments.insert(1, match module.kind {
 168                             ModuleKind::Def(_, name) => ast::PathSegment::from_ident(
 169                                 ast::Ident::with_empty_ctxt(name).with_span_pos(span)
 170                             ),
 171                             _ => unreachable!(),
 172                         });
 173                         if let Some(qself) = &mut qself {
 174                             qself.position += 1;
 175                         }
 176                     }
 177                 }
 178                 (qself, path)
 179             }
 180
 181             fn fold_mac(&mut self, mac: ast::Mac) -> ast::Mac {
 182                 fold::noop_fold_mac(mac, self)
 183             }
 184         }
 185
 186         EliminateCrateVar(self, item.span).fold_item(item).expect_one("")
 187     }
 188
 189     fn is_whitelisted_legacy_custom_derive(&self, name: Name) -> bool {
 190         self.whitelisted_legacy_custom_derives.contains(&name)
 191     }
 192
 193     fn visit_ast_fragment_with_placeholders(&mut self, mark: Mark, fragment: &AstFragment,
 194                                             derives: &[Mark]) {
 195         let invocation = self.invocations[&mark];
 196         self.collect_def_ids(mark, invocation, fragment);
 197
 198         self.current_module = invocation.module.get();
 199         self.current_module.unresolved_invocations.borrow_mut().remove(&mark);
 200         self.current_module.unresolved_invocations.borrow_mut().extend(derives);
 201         for &derive in derives {
 202             self.invocations.insert(derive, invocation);
 203         }
 204         let mut visitor = BuildReducedGraphVisitor {
 205             resolver: self,
 206             legacy_scope: LegacyScope::Invocation(invocation),
 207             expansion: mark,
 208         };
 209         fragment.visit_with(&mut visitor);
 210         invocation.expansion.set(visitor.legacy_scope);
 211     }
 212
 213     fn add_builtin(&mut self, ident: ast::Ident, ext: Lrc<SyntaxExtension>) {
 214         let def_id = DefId {
 215             krate: BUILTIN_MACROS_CRATE,
 216             index: DefIndex::from_array_index(self.macro_map.len(),
 217                                               DefIndexAddressSpace::Low),
 218         };
 219         let kind = ext.kind();
 220         self.macro_map.insert(def_id, ext);
 221         let binding = self.arenas.alloc_name_binding(NameBinding {
 222             kind: NameBindingKind::Def(Def::Macro(def_id, kind), false),
 223             span: DUMMY_SP,
 224             vis: ty::Visibility::Invisible,
 225             expansion: Mark::root(),
 226         });
 227         self.macro_prelude.insert(ident.name, binding);
 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.macro_prelude.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.macro_prelude.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                         attrs[i].tokens = TokenTree::Delimited(attrs[i].span, Delimited {
 303                             delim: token::Paren,
 304                             tts: TokenStream::concat(tokens).into(),
 305                         }).into();
 306                     }
 307                     return Some(ast::Attribute {
 308                         path: ast::Path::from_ident(Ident::new(legacy_name, span)),
 309                         tokens: TokenStream::empty(),
 310                         id: attr::mk_attr_id(),
 311                         style: ast::AttrStyle::Outer,
 312                         is_sugared_doc: false,
 313                         span,
 314                     });
 315                 }
 316             }
 317         }
 318
 319         None
 320     }
 321
 322     fn resolve_invoc(&mut self, invoc: &Invocation, scope: Mark, force: bool)
 323                      -> Result<Option<Lrc<SyntaxExtension>>, Determinacy> {
 324         let def = match invoc.kind {
 325             InvocationKind::Attr { attr: None, .. } => return Ok(None),
 326             _ => self.resolve_invoc_to_def(invoc, scope, force)?,
 327         };
 328         if let Def::Macro(_, MacroKind::ProcMacroStub) = def {
 329             self.report_proc_macro_stub(invoc.span());
 330             return Err(Determinacy::Determined);
 331         } else if let Def::NonMacroAttr(attr_kind) = def {
 332             // Note that not only attributes, but anything in macro namespace can result in a
 333             // `Def::NonMacroAttr` definition (e.g. `inline!()`), so we must report the error
 334             // below for these cases.
 335             let is_attr_invoc =
 336                 if let InvocationKind::Attr { .. } = invoc.kind { true } else { false };
 337             let path = invoc.path().expect("no path for non-macro attr");
 338             match attr_kind {
 339                 NonMacroAttrKind::Tool | NonMacroAttrKind::DeriveHelper |
 340                 NonMacroAttrKind::Custom if is_attr_invoc => {
 341                     let features = self.session.features_untracked();
 342                     if attr_kind == NonMacroAttrKind::Tool &&
 343                        !features.tool_attributes {
 344                         feature_err(&self.session.parse_sess, "tool_attributes",
 345                                     invoc.span(), GateIssue::Language,
 346                                     "tool attributes are unstable").emit();
 347                     }
 348                     if attr_kind == NonMacroAttrKind::Custom {
 349                         assert!(path.segments.len() == 1);
 350                         let name = path.segments[0].ident.name.as_str();
 351                         if name.starts_with("rustc_") {
 352                             if !features.rustc_attrs {
 353                                 let msg = "unless otherwise specified, attributes with the prefix \
 354                                         `rustc_` are reserved for internal compiler diagnostics";
 355                                 feature_err(&self.session.parse_sess, "rustc_attrs", invoc.span(),
 356                                             GateIssue::Language, &msg).emit();
 357                             }
 358                         } else if name.starts_with("derive_") {
 359                             if !features.custom_derive {
 360                                 feature_err(&self.session.parse_sess, "custom_derive", invoc.span(),
 361                                             GateIssue::Language, EXPLAIN_DERIVE_UNDERSCORE).emit();
 362                             }
 363                         } else if !features.custom_attribute {
 364                             let msg = format!("The attribute `{}` is currently unknown to the \
 365                                                compiler and may have meaning added to it in the \
 366                                                future", path);
 367                             feature_err(&self.session.parse_sess, "custom_attribute", invoc.span(),
 368                                         GateIssue::Language, &msg).emit();
 369                         }
 370                     }
 371
 372                     return Ok(Some(Lrc::new(SyntaxExtension::NonMacroAttr {
 373                         mark_used: attr_kind == NonMacroAttrKind::Tool,
 374                     })));
 375                 }
 376                 _ => {
 377                     self.report_non_macro_attr(path.span, def);
 378                     return Err(Determinacy::Determined);
 379                 }
 380             }
 381         }
 382         let def_id = def.def_id();
 383
 384         self.macro_defs.insert(invoc.expansion_data.mark, def_id);
 385         let normal_module_def_id =
 386             self.macro_def_scope(invoc.expansion_data.mark).normal_ancestor_id;
 387         self.definitions.add_parent_module_of_macro_def(invoc.expansion_data.mark,
 388                                                         normal_module_def_id);
 389
 390         self.unused_macros.remove(&def_id);
 391         let ext = self.get_macro(def);
 392         invoc.expansion_data.mark.set_default_transparency(ext.default_transparency());
 393         invoc.expansion_data.mark.set_is_builtin(def_id.krate == BUILTIN_MACROS_CRATE);
 394         Ok(Some(ext))
 395     }
 396
 397     fn resolve_macro(&mut self, scope: Mark, path: &ast::Path, kind: MacroKind, force: bool)
 398                      -> Result<Lrc<SyntaxExtension>, Determinacy> {
 399         self.resolve_macro_to_def(scope, path, kind, force).and_then(|def| {
 400             if let Def::Macro(_, MacroKind::ProcMacroStub) = def {
 401                 self.report_proc_macro_stub(path.span);
 402                 return Err(Determinacy::Determined);
 403             } else if let Def::NonMacroAttr(..) = def {
 404                 self.report_non_macro_attr(path.span, def);
 405                 return Err(Determinacy::Determined);
 406             }
 407             self.unused_macros.remove(&def.def_id());
 408             Ok(self.get_macro(def))
 409         })
 410     }
 411
 412     fn check_unused_macros(&self) {
 413         for did in self.unused_macros.iter() {
 414             let id_span = match *self.macro_map[did] {
 415                 SyntaxExtension::NormalTT { def_info, .. } |
 416                 SyntaxExtension::DeclMacro { def_info, .. } => def_info,
 417                 _ => None,
 418             };
 419             if let Some((id, span)) = id_span {
 420                 let lint = lint::builtin::UNUSED_MACROS;
 421                 let msg = "unused macro definition";
 422                 self.session.buffer_lint(lint, id, span, msg);
 423             } else {
 424                 bug!("attempted to create unused macro error, but span not available");
 425             }
 426         }
 427     }
 428 }
 429
 430 impl<'a, 'cl> Resolver<'a, 'cl> {
 431     fn report_proc_macro_stub(&self, span: Span) {
 432         self.session.span_err(span,
 433                               "can't use a procedural macro from the same crate that defines it");
 434     }
 435
 436     fn report_non_macro_attr(&self, span: Span, def: Def) {
 437         self.session.span_err(span, &format!("expected a macro, found {}", def.kind_name()));
 438     }
 439
 440     fn resolve_invoc_to_def(&mut self, invoc: &Invocation, scope: Mark, force: bool)
 441                             -> Result<Def, Determinacy> {
 442         let (attr, traits) = match invoc.kind {
 443             InvocationKind::Attr { ref attr, ref traits, .. } => (attr, traits),
 444             InvocationKind::Bang { ref mac, .. } => {
 445                 return self.resolve_macro_to_def(scope, &mac.node.path, MacroKind::Bang, force);
 446             }
 447             InvocationKind::Derive { ref path, .. } => {
 448                 return self.resolve_macro_to_def(scope, path, MacroKind::Derive, force);
 449             }
 450         };
 451
 452         let path = attr.as_ref().unwrap().path.clone();
 453         let def = self.resolve_macro_to_def(scope, &path, MacroKind::Attr, force);
 454         if let Ok(Def::NonMacroAttr(NonMacroAttrKind::Custom)) = def {} else {
 455             return def;
 456         }
 457
 458         // At this point we've found that the `attr` is determinately unresolved and thus can be
 459         // interpreted as a custom attribute. Normally custom attributes are feature gated, but
 460         // it may be a custom attribute whitelisted by a derive macro and they do not require
 461         // a feature gate.
 462         //
 463         // So here we look through all of the derive annotations in scope and try to resolve them.
 464         // If they themselves successfully resolve *and* one of the resolved derive macros
 465         // whitelists this attribute's name, then this is a registered attribute and we can convert
 466         // it from a "generic custom attrite" into a "known derive helper attribute".
 467         enum ConvertToDeriveHelper { Yes, No, DontKnow }
 468         let mut convert_to_derive_helper = ConvertToDeriveHelper::No;
 469         let attr_name = path.segments[0].ident.name;
 470         for path in traits {
 471             match self.resolve_macro(scope, path, MacroKind::Derive, force) {
 472                 Ok(ext) => if let SyntaxExtension::ProcMacroDerive(_, ref inert_attrs, _) = *ext {
 473                     if inert_attrs.contains(&attr_name) {
 474                         convert_to_derive_helper = ConvertToDeriveHelper::Yes;
 475                         break
 476                     }
 477                 },
 478                 Err(Determinacy::Undetermined) =>
 479                     convert_to_derive_helper = ConvertToDeriveHelper::DontKnow,
 480                 Err(Determinacy::Determined) => {}
 481             }
 482         }
 483
 484         match convert_to_derive_helper {
 485             ConvertToDeriveHelper::Yes => Ok(Def::NonMacroAttr(NonMacroAttrKind::DeriveHelper)),
 486             ConvertToDeriveHelper::No => def,
 487             ConvertToDeriveHelper::DontKnow => Err(Determinacy::determined(force)),
 488         }
 489     }
 490
 491     fn resolve_macro_to_def(&mut self, scope: Mark, path: &ast::Path, kind: MacroKind, force: bool)
 492                             -> Result<Def, Determinacy> {
 493         let def = self.resolve_macro_to_def_inner(scope, path, kind, force);
 494         if def != Err(Determinacy::Undetermined) {
 495             // Do not report duplicated errors on every undetermined resolution.
 496             path.segments.iter().find(|segment| segment.args.is_some()).map(|segment| {
 497                 self.session.span_err(segment.args.as_ref().unwrap().span(),
 498                                       "generic arguments in macro path");
 499             });
 500         }
 501         if kind != MacroKind::Bang && path.segments.len() > 1 &&
 502            def != Ok(Def::NonMacroAttr(NonMacroAttrKind::Tool)) {
 503             if !self.session.features_untracked().proc_macro_path_invoc {
 504                 emit_feature_err(
 505                     &self.session.parse_sess,
 506                     "proc_macro_path_invoc",
 507                     path.span,
 508                     GateIssue::Language,
 509                     "paths of length greater than one in macro invocations are \
 510                      currently unstable",
 511                 );
 512             }
 513         }
 514         def
 515     }
 516
 517     pub fn resolve_macro_to_def_inner(&mut self, scope: Mark, path: &ast::Path,
 518                                   kind: MacroKind, force: bool)
 519                                   -> Result<Def, Determinacy> {
 520         let ast::Path { ref segments, span } = *path;
 521         let mut path: Vec<_> = segments.iter().map(|seg| seg.ident).collect();
 522         let invocation = self.invocations[&scope];
 523         let module = invocation.module.get();
 524         self.current_module = if module.is_trait() { module.parent.unwrap() } else { module };
 525
 526         // Possibly apply the macro helper hack
 527         if kind == MacroKind::Bang && path.len() == 1 &&
 528            path[0].span.ctxt().outer().expn_info().map_or(false, |info| info.local_inner_macros) {
 529             let root = Ident::new(keywords::DollarCrate.name(), path[0].span);
 530             path.insert(0, root);
 531         }
 532
 533         if path.len() > 1 {
 534             let res = self.resolve_path(None, &path, Some(MacroNS), false, span, CrateLint::No);
 535             let def = match res {
 536                 PathResult::NonModule(path_res) => match path_res.base_def() {
 537                     Def::Err => Err(Determinacy::Determined),
 538                     def @ _ => {
 539                         if path_res.unresolved_segments() > 0 {
 540                             self.found_unresolved_macro = true;
 541                             self.session.span_err(span, "fail to resolve non-ident macro path");
 542                             Err(Determinacy::Determined)
 543                         } else {
 544                             Ok(def)
 545                         }
 546                     }
 547                 },
 548                 PathResult::Module(..) => unreachable!(),
 549                 PathResult::Indeterminate if !force => return Err(Determinacy::Undetermined),
 550                 _ => {
 551                     self.found_unresolved_macro = true;
 552                     Err(Determinacy::Determined)
 553                 },
 554             };
 555             self.current_module.nearest_item_scope().macro_resolutions.borrow_mut()
 556                 .push((path.into_boxed_slice(), span));
 557             return def;
 558         }
 559
 560         let legacy_resolution = self.resolve_legacy_scope(&invocation.legacy_scope, path[0], false);
 561         let result = if let Some(MacroBinding::Legacy(binding)) = legacy_resolution {
 562             Ok(Def::Macro(binding.def_id, MacroKind::Bang))
 563         } else {
 564             match self.resolve_lexical_macro_path_segment(path[0], MacroNS, false, force,
 565                                                           kind == MacroKind::Attr, span) {
 566                 Ok(binding) => Ok(binding.binding().def_ignoring_ambiguity()),
 567                 Err(Determinacy::Undetermined) => return Err(Determinacy::Undetermined),
 568                 Err(Determinacy::Determined) => {
 569                     self.found_unresolved_macro = true;
 570                     Err(Determinacy::Determined)
 571                 }
 572             }
 573         };
 574
 575         self.current_module.nearest_item_scope().legacy_macro_resolutions.borrow_mut()
 576             .push((scope, path[0], kind, result.ok()));
 577
 578         result
 579     }
 580
 581     // Resolve the initial segment of a non-global macro path
 582     // (e.g. `foo` in `foo::bar!(); or `foo!();`).
 583     // This is a variation of `fn resolve_ident_in_lexical_scope` that can be run during
 584     // expansion and import resolution (perhaps they can be merged in the future).
 585     pub fn resolve_lexical_macro_path_segment(&mut self,
 586                                               mut ident: Ident,
 587                                               ns: Namespace,
 588                                               record_used: bool,
 589                                               force: bool,
 590                                               is_attr: bool,
 591                                               path_span: Span)
 592                                               -> Result<MacroBinding<'a>, Determinacy> {
 593         // General principles:
 594         // 1. Not controlled (user-defined) names should have higher priority than controlled names
 595         //    built into the language or standard library. This way we can add new names into the
 596         //    language or standard library without breaking user code.
 597         // 2. "Closed set" below means new names can appear after the current resolution attempt.
 598         // Places to search (in order of decreasing priority):
 599         // (Type NS)
 600         // 1. FIXME: Ribs (type parameters), there's no necessary infrastructure yet
 601         //    (open set, not controlled).
 602         // 2. Names in modules (both normal `mod`ules and blocks), loop through hygienic parents
 603         //    (open, not controlled).
 604         // 3. Extern prelude (closed, not controlled).
 605         // 4. Tool modules (closed, controlled right now, but not in the future).
 606         // 5. Standard library prelude (de-facto closed, controlled).
 607         // 6. Language prelude (closed, controlled).
 608         // (Macro NS)
 609         // 1. Names in modules (both normal `mod`ules and blocks), loop through hygienic parents
 610         //    (open, not controlled).
 611         // 2. Macro prelude (language, standard library, user-defined legacy plugins lumped into
 612         //    one set) (open, the open part is from macro expansions, not controlled).
 613         // 2a. User-defined prelude from macro-use
 614         //    (open, the open part is from macro expansions, not controlled).
 615         // 2b. Standard library prelude, currently just a macro-use (closed, controlled)
 616         // 2c. Language prelude, perhaps including builtin attributes
 617         //    (closed, controlled, except for legacy plugins).
 618         // 3. Builtin attributes (closed, controlled).
 619
 620         assert!(ns == TypeNS  || ns == MacroNS);
 621         assert!(force || !record_used); // `record_used` implies `force`
 622         ident = ident.modern();
 623
 624         // Names from inner scope that can't shadow names from outer scopes, e.g.
 625         // mod m { ... }
 626         // {
 627         //     use prefix::*; // if this imports another `m`, then it can't shadow the outer `m`
 628         //                    // and we have and ambiguity error
 629         //     m::mac!();
 630         // }
 631         // This includes names from globs and from macro expansions.
 632         let mut potentially_ambiguous_result: Option<MacroBinding> = None;
 633
 634         enum WhereToResolve<'a> {
 635             Module(Module<'a>),
 636             MacroPrelude,
 637             BuiltinAttrs,
 638             ExternPrelude,
 639             ToolPrelude,
 640             StdLibPrelude,
 641             PrimitiveTypes,
 642         }
 643
 644         // Go through all the scopes and try to resolve the name.
 645         let mut where_to_resolve = WhereToResolve::Module(self.current_module);
 646         let mut use_prelude = !self.current_module.no_implicit_prelude;
 647         loop {
 648             let result = match where_to_resolve {
 649                 WhereToResolve::Module(module) => {
 650                     let orig_current_module = mem::replace(&mut self.current_module, module);
 651                     let binding = self.resolve_ident_in_module_unadjusted(
 652                         ModuleOrUniformRoot::Module(module),
 653                         ident,
 654                         ns,
 655                         true,
 656                         record_used,
 657                         path_span,
 658                     );
 659                     self.current_module = orig_current_module;
 660                     binding.map(MacroBinding::Modern)
 661                 }
 662                 WhereToResolve::MacroPrelude => {
 663                     match self.macro_prelude.get(&ident.name).cloned() {
 664                         Some(binding) => Ok(MacroBinding::Global(binding)),
 665                         None => Err(Determinacy::Determined),
 666                     }
 667                 }
 668                 WhereToResolve::BuiltinAttrs => {
 669                     // FIXME: Only built-in attributes are not considered as candidates for
 670                     // non-attributes to fight off regressions on stable channel (#53205).
 671                     // We need to come up with some more principled approach instead.
 672                     if is_attr && is_builtin_attr_name(ident.name) {
 673                         let binding = (Def::NonMacroAttr(NonMacroAttrKind::Builtin),
 674                                        ty::Visibility::Public, ident.span, Mark::root())
 675                                        .to_name_binding(self.arenas);
 676                         Ok(MacroBinding::Global(binding))
 677                     } else {
 678                         Err(Determinacy::Determined)
 679                     }
 680                 }
 681                 WhereToResolve::ExternPrelude => {
 682                     if use_prelude && self.extern_prelude.contains(&ident.name) {
 683                         if !self.session.features_untracked().extern_prelude &&
 684                            !self.ignore_extern_prelude_feature {
 685                             feature_err(&self.session.parse_sess, "extern_prelude",
 686                                         ident.span, GateIssue::Language,
 687                                         "access to extern crates through prelude is experimental")
 688                                         .emit();
 689                         }
 690
 691                         let crate_id =
 692                             self.crate_loader.process_path_extern(ident.name, ident.span);
 693                         let crate_root =
 694                             self.get_module(DefId { krate: crate_id, index: CRATE_DEF_INDEX });
 695                         self.populate_module_if_necessary(crate_root);
 696
 697                         let binding = (crate_root, ty::Visibility::Public,
 698                                        ident.span, Mark::root()).to_name_binding(self.arenas);
 699                         Ok(MacroBinding::Global(binding))
 700                     } else {
 701                         Err(Determinacy::Determined)
 702                     }
 703                 }
 704                 WhereToResolve::ToolPrelude => {
 705                     if use_prelude && is_known_tool(ident.name) {
 706                         let binding = (Def::ToolMod, ty::Visibility::Public,
 707                                        ident.span, Mark::root()).to_name_binding(self.arenas);
 708                         Ok(MacroBinding::Global(binding))
 709                     } else {
 710                         Err(Determinacy::Determined)
 711                     }
 712                 }
 713                 WhereToResolve::StdLibPrelude => {
 714                     let mut result = Err(Determinacy::Determined);
 715                     if use_prelude {
 716                         if let Some(prelude) = self.prelude {
 717                             if let Ok(binding) = self.resolve_ident_in_module_unadjusted(
 718                                 ModuleOrUniformRoot::Module(prelude),
 719                                 ident,
 720                                 ns,
 721                                 false,
 722                                 false,
 723                                 path_span,
 724                             ) {
 725                                 result = Ok(MacroBinding::Global(binding));
 726                             }
 727                         }
 728                     }
 729                     result
 730                 }
 731                 WhereToResolve::PrimitiveTypes => {
 732                     if let Some(prim_ty) =
 733                             self.primitive_type_table.primitive_types.get(&ident.name).cloned() {
 734                         let binding = (Def::PrimTy(prim_ty), ty::Visibility::Public,
 735                                        ident.span, Mark::root()).to_name_binding(self.arenas);
 736                         Ok(MacroBinding::Global(binding))
 737                     } else {
 738                         Err(Determinacy::Determined)
 739                     }
 740                 }
 741             };
 742
 743             macro_rules! continue_search { () => {
 744                 where_to_resolve = match where_to_resolve {
 745                     WhereToResolve::Module(module) => {
 746                         match self.hygienic_lexical_parent(module, &mut ident.span) {
 747                             Some(parent_module) => WhereToResolve::Module(parent_module),
 748                             None => {
 749                                 use_prelude = !module.no_implicit_prelude;
 750                                 if ns == MacroNS {
 751                                     WhereToResolve::MacroPrelude
 752                                 } else {
 753                                     WhereToResolve::ExternPrelude
 754                                 }
 755                             }
 756                         }
 757                     }
 758                     WhereToResolve::MacroPrelude => WhereToResolve::BuiltinAttrs,
 759                     WhereToResolve::BuiltinAttrs => break, // nowhere else to search
 760                     WhereToResolve::ExternPrelude => WhereToResolve::ToolPrelude,
 761                     WhereToResolve::ToolPrelude => WhereToResolve::StdLibPrelude,
 762                     WhereToResolve::StdLibPrelude => WhereToResolve::PrimitiveTypes,
 763                     WhereToResolve::PrimitiveTypes => break, // nowhere else to search
 764                 };
 765
 766                 continue;
 767             }}
 768
 769             match result {
 770                 Ok(result) => {
 771                     if !record_used {
 772                         return Ok(result);
 773                     }
 774
 775                     let binding = result.binding();
 776
 777                     // Found a solution that is ambiguous with a previously found solution.
 778                     // Push an ambiguity error for later reporting and
 779                     // return something for better recovery.
 780                     if let Some(previous_result) = potentially_ambiguous_result {
 781                         if binding.def() != previous_result.binding().def() {
 782                             self.ambiguity_errors.push(AmbiguityError {
 783                                 span: path_span,
 784                                 name: ident.name,
 785                                 b1: previous_result.binding(),
 786                                 b2: binding,
 787                                 lexical: true,
 788                             });
 789                             return Ok(previous_result);
 790                         }
 791                     }
 792
 793                     // Found a solution that's not an ambiguity yet, but is "suspicious" and
 794                     // can participate in ambiguities later on.
 795                     // Remember it and go search for other solutions in outer scopes.
 796                     if binding.is_glob_import() || binding.expansion != Mark::root() {
 797                         potentially_ambiguous_result = Some(result);
 798
 799                         continue_search!();
 800                     }
 801
 802                     // Found a solution that can't be ambiguous, great success.
 803                     return Ok(result);
 804                 },
 805                 Err(Determinacy::Determined) => {
 806                     continue_search!();
 807                 }
 808                 Err(Determinacy::Undetermined) => return Err(Determinacy::determined(force)),
 809             }
 810         }
 811
 812         // Previously found potentially ambiguous result turned out to not be ambiguous after all.
 813         if let Some(previous_result) = potentially_ambiguous_result {
 814             return Ok(previous_result);
 815         }
 816
 817         let determinacy = Determinacy::determined(force);
 818         if determinacy == Determinacy::Determined && is_attr {
 819             // For single-segment attributes interpret determinate "no resolution" as a custom
 820             // attribute. (Lexical resolution implies the first segment and is_attr 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(MacroBinding::Global(binding))
 827         } else {
 828             Err(determinacy)
 829         }
 830     }
 831
 832     pub fn resolve_legacy_scope(&mut self,
 833                                 mut scope: &'a Cell<LegacyScope<'a>>,
 834                                 ident: Ident,
 835                                 record_used: bool)
 836                                 -> Option<MacroBinding<'a>> {
 837         let ident = ident.modern();
 838         let mut relative_depth: u32 = 0;
 839         let mut binding = None;
 840         loop {
 841             match scope.get() {
 842                 LegacyScope::Empty => break,
 843                 LegacyScope::Expansion(invocation) => {
 844                     match invocation.expansion.get() {
 845                         LegacyScope::Invocation(_) => scope.set(invocation.legacy_scope.get()),
 846                         LegacyScope::Empty => {
 847                             scope = &invocation.legacy_scope;
 848                         }
 849                         _ => {
 850                             relative_depth += 1;
 851                             scope = &invocation.expansion;
 852                         }
 853                     }
 854                 }
 855                 LegacyScope::Invocation(invocation) => {
 856                     relative_depth = relative_depth.saturating_sub(1);
 857                     scope = &invocation.legacy_scope;
 858                 }
 859                 LegacyScope::Binding(potential_binding) => {
 860                     if potential_binding.ident == ident {
 861                         if record_used && relative_depth > 0 {
 862                             self.disallowed_shadowing.push(potential_binding);
 863                         }
 864                         binding = Some(potential_binding);
 865                         break
 866                     }
 867                     scope = &potential_binding.parent;
 868                 }
 869             };
 870         }
 871
 872         let binding = if let Some(binding) = binding {
 873             MacroBinding::Legacy(binding)
 874         } else if let Some(binding) = self.macro_prelude.get(&ident.name).cloned() {
 875             MacroBinding::Global(binding)
 876         } else {
 877             return None;
 878         };
 879
 880         Some(binding)
 881     }
 882
 883     pub fn finalize_current_module_macro_resolutions(&mut self) {
 884         let module = self.current_module;
 885         for &(ref path, span) in module.macro_resolutions.borrow().iter() {
 886             match self.resolve_path(None, &path, Some(MacroNS), true, span, CrateLint::No) {
 887                 PathResult::NonModule(_) => {},
 888                 PathResult::Failed(span, msg, _) => {
 889                     resolve_error(self, span, ResolutionError::FailedToResolve(&msg));
 890                 }
 891                 _ => unreachable!(),
 892             }
 893         }
 894
 895         for &(mark, ident, kind, def) in module.legacy_macro_resolutions.borrow().iter() {
 896             let span = ident.span;
 897             let legacy_scope = &self.invocations[&mark].legacy_scope;
 898             let legacy_resolution = self.resolve_legacy_scope(legacy_scope, ident, true);
 899             let resolution = self.resolve_lexical_macro_path_segment(ident, MacroNS, true, true,
 900                                                                      kind == MacroKind::Attr, span);
 901
 902             let check_consistency = |this: &Self, binding: MacroBinding| {
 903                 if let Some(def) = def {
 904                     if this.ambiguity_errors.is_empty() && this.disallowed_shadowing.is_empty() &&
 905                        binding.def_ignoring_ambiguity() != def {
 906                         // Make sure compilation does not succeed if preferred macro resolution
 907                         // has changed after the macro had been expanded. In theory all such
 908                         // situations should be reported as ambiguity errors, so this is span-bug.
 909                         span_bug!(span, "inconsistent resolution for a macro");
 910                     }
 911                 } else {
 912                     // It's possible that the macro was unresolved (indeterminate) and silently
 913                     // expanded into a dummy fragment for recovery during expansion.
 914                     // Now, post-expansion, the resolution may succeed, but we can't change the
 915                     // past and need to report an error.
 916                     let msg =
 917                         format!("cannot determine resolution for the {} `{}`", kind.descr(), ident);
 918                     let msg_note = "import resolution is stuck, try simplifying macro imports";
 919                     this.session.struct_span_err(span, &msg).note(msg_note).emit();
 920                 }
 921             };
 922
 923             match (legacy_resolution, resolution) {
 924                 (Some(MacroBinding::Legacy(legacy_binding)), Ok(MacroBinding::Modern(binding))) => {
 925                     if legacy_binding.def_id != binding.def_ignoring_ambiguity().def_id() {
 926                         let msg1 = format!("`{}` could refer to the macro defined here", ident);
 927                         let msg2 =
 928                             format!("`{}` could also refer to the macro imported here", ident);
 929                         self.session.struct_span_err(span, &format!("`{}` is ambiguous", ident))
 930                             .span_note(legacy_binding.span, &msg1)
 931                             .span_note(binding.span, &msg2)
 932                             .emit();
 933                     }
 934                 },
 935                 (None, Err(_)) => {
 936                     assert!(def.is_none());
 937                     let bang = if kind == MacroKind::Bang { "!" } else { "" };
 938                     let msg =
 939                         format!("cannot find {} `{}{}` in this scope", kind.descr(), ident, bang);
 940                     let mut err = self.session.struct_span_err(span, &msg);
 941                     self.suggest_macro_name(&ident.as_str(), kind, &mut err, span);
 942                     err.emit();
 943                 },
 944                 (Some(MacroBinding::Modern(_)), _) | (_, Ok(MacroBinding::Legacy(_))) => {
 945                     span_bug!(span, "impossible macro resolution result");
 946                 }
 947                 // OK, unambiguous resolution
 948                 (Some(binding), Err(_)) | (None, Ok(binding)) |
 949                 // OK, legacy wins over global even if their definitions are different
 950                 (Some(binding @ MacroBinding::Legacy(_)), Ok(MacroBinding::Global(_))) |
 951                 // OK, modern wins over global even if their definitions are different
 952                 (Some(MacroBinding::Global(_)), Ok(binding @ MacroBinding::Modern(_))) => {
 953                     check_consistency(self, binding);
 954                 }
 955                 (Some(MacroBinding::Global(binding1)), Ok(MacroBinding::Global(binding2))) => {
 956                     if binding1.def() != binding2.def() {
 957                         span_bug!(span, "mismatch between same global macro resolutions");
 958                     }
 959                     check_consistency(self, MacroBinding::Global(binding1));
 960
 961                     self.record_use(ident, MacroNS, binding1, span);
 962                     self.err_if_macro_use_proc_macro(ident.name, span, binding1);
 963                 },
 964             };
 965         }
 966     }
 967
 968     fn suggest_macro_name(&mut self, name: &str, kind: MacroKind,
 969                           err: &mut DiagnosticBuilder<'a>, span: Span) {
 970         // First check if this is a locally-defined bang macro.
 971         let suggestion = if let MacroKind::Bang = kind {
 972             find_best_match_for_name(self.macro_names.iter().map(|ident| &ident.name), name, None)
 973         } else {
 974             None
 975         // Then check global macros.
 976         }.or_else(|| {
 977             // FIXME: get_macro needs an &mut Resolver, can we do it without cloning?
 978             let macro_prelude = self.macro_prelude.clone();
 979             let names = macro_prelude.iter().filter_map(|(name, binding)| {
 980                 if binding.get_macro(self).kind() == kind {
 981                     Some(name)
 982                 } else {
 983                     None
 984                 }
 985             });
 986             find_best_match_for_name(names, name, None)
 987         // Then check modules.
 988         }).or_else(|| {
 989             let is_macro = |def| {
 990                 if let Def::Macro(_, def_kind) = def {
 991                     def_kind == kind
 992                 } else {
 993                     false
 994                 }
 995             };
 996             let ident = Ident::new(Symbol::intern(name), span);
 997             self.lookup_typo_candidate(&[ident], MacroNS, is_macro, span)
 998         });
 999
1000         if let Some(suggestion) = suggestion {
1001             if suggestion != name {
1002                 if let MacroKind::Bang = kind {
1003                     err.span_suggestion(span, "you could try the macro", suggestion.to_string());
1004                 } else {
1005                     err.span_suggestion(span, "try", suggestion.to_string());
1006                 }
1007             } else {
1008                 err.help("have you added the `#[macro_use]` on the module/import?");
1009             }
1010         }
1011     }
1012
1013     fn collect_def_ids(&mut self,
1014                        mark: Mark,
1015                        invocation: &'a InvocationData<'a>,
1016                        fragment: &AstFragment) {
1017         let Resolver { ref mut invocations, arenas, graph_root, .. } = *self;
1018         let InvocationData { def_index, .. } = *invocation;
1019
1020         let visit_macro_invoc = &mut |invoc: map::MacroInvocationData| {
1021             invocations.entry(invoc.mark).or_insert_with(|| {
1022                 arenas.alloc_invocation_data(InvocationData {
1023                     def_index: invoc.def_index,
1024                     module: Cell::new(graph_root),
1025                     expansion: Cell::new(LegacyScope::Empty),
1026                     legacy_scope: Cell::new(LegacyScope::Empty),
1027                 })
1028             });
1029         };
1030
1031         let mut def_collector = DefCollector::new(&mut self.definitions, mark);
1032         def_collector.visit_macro_invoc = Some(visit_macro_invoc);
1033         def_collector.with_parent(def_index, |def_collector| {
1034             fragment.visit_with(def_collector)
1035         });
1036     }
1037
1038     pub fn define_macro(&mut self,
1039                         item: &ast::Item,
1040                         expansion: Mark,
1041                         legacy_scope: &mut LegacyScope<'a>) {
1042         self.local_macro_def_scopes.insert(item.id, self.current_module);
1043         let ident = item.ident;
1044         if ident.name == "macro_rules" {
1045             self.session.span_err(item.span, "user-defined macros may not be named `macro_rules`");
1046         }
1047
1048         let def_id = self.definitions.local_def_id(item.id);
1049         let ext = Lrc::new(macro_rules::compile(&self.session.parse_sess,
1050                                                &self.session.features_untracked(),
1051                                                item, hygiene::default_edition()));
1052         self.macro_map.insert(def_id, ext);
1053
1054         let def = match item.node { ast::ItemKind::MacroDef(ref def) => def, _ => unreachable!() };
1055         if def.legacy {
1056             let ident = ident.modern();
1057             self.macro_names.insert(ident);
1058             *legacy_scope = LegacyScope::Binding(self.arenas.alloc_legacy_binding(LegacyBinding {
1059                 parent: Cell::new(*legacy_scope), ident: ident, def_id: def_id, span: item.span,
1060             }));
1061             let def = Def::Macro(def_id, MacroKind::Bang);
1062             self.all_macros.insert(ident.name, def);
1063             if attr::contains_name(&item.attrs, "macro_export") {
1064                 let module = self.graph_root;
1065                 let vis = ty::Visibility::Public;
1066                 self.define(module, ident, MacroNS,
1067                             (def, vis, item.span, expansion, IsMacroExport));
1068             } else {
1069                 self.unused_macros.insert(def_id);
1070             }
1071         } else {
1072             let module = self.current_module;
1073             let def = Def::Macro(def_id, MacroKind::Bang);
1074             let vis = self.resolve_visibility(&item.vis);
1075             if vis != ty::Visibility::Public {
1076                 self.unused_macros.insert(def_id);
1077             }
1078             self.define(module, ident, MacroNS, (def, vis, item.span, expansion));
1079         }
1080     }
1081
1082     /// Error if `ext` is a Macros 1.1 procedural macro being imported by `#[macro_use]`
1083     fn err_if_macro_use_proc_macro(&mut self, name: Name, use_span: Span,
1084                                    binding: &NameBinding<'a>) {
1085         let krate = binding.def().def_id().krate;
1086
1087         // Plugin-based syntax extensions are exempt from this check
1088         if krate == BUILTIN_MACROS_CRATE { return; }
1089
1090         let ext = binding.get_macro(self);
1091
1092         match *ext {
1093             // If `ext` is a procedural macro, check if we've already warned about it
1094             SyntaxExtension::AttrProcMacro(..) | SyntaxExtension::ProcMacro { .. } =>
1095                 if !self.warned_proc_macros.insert(name) { return; },
1096             _ => return,
1097         }
1098
1099         let warn_msg = match *ext {
1100             SyntaxExtension::AttrProcMacro(..) =>
1101                 "attribute procedural macros cannot be imported with `#[macro_use]`",
1102             SyntaxExtension::ProcMacro { .. } =>
1103                 "procedural macros cannot be imported with `#[macro_use]`",
1104             _ => return,
1105         };
1106
1107         let def_id = self.current_module.normal_ancestor_id;
1108         let node_id = self.definitions.as_local_node_id(def_id).unwrap();
1109
1110         self.proc_mac_errors.push(ProcMacError {
1111             crate_name: self.cstore.crate_name_untracked(krate),
1112             name,
1113             module: node_id,
1114             use_span,
1115             warn_msg,
1116         });
1117     }
1118
1119     pub fn report_proc_macro_import(&mut self, krate: &ast::Crate) {
1120         for err in self.proc_mac_errors.drain(..) {
1121             let (span, found_use) = ::UsePlacementFinder::check(krate, err.module);
1122
1123             if let Some(span) = span {
1124                 let found_use = if found_use { "" } else { "\n" };
1125                 self.session.struct_span_err(err.use_span, err.warn_msg)
1126                     .span_suggestion(
1127                         span,
1128                         "instead, import the procedural macro like any other item",
1129                         format!("use {}::{};{}", err.crate_name, err.name, found_use),
1130                     ).emit();
1131             } else {
1132                 self.session.struct_span_err(err.use_span, err.warn_msg)
1133                     .help(&format!("instead, import the procedural macro like any other item: \
1134                                     `use {}::{};`", err.crate_name, err.name))
1135                     .emit();
1136             }
1137         }
1138     }
1139
1140     fn gate_legacy_custom_derive(&mut self, name: Symbol, span: Span) {
1141         if !self.session.features_untracked().custom_derive {
1142             let sess = &self.session.parse_sess;
1143             let explain = feature_gate::EXPLAIN_CUSTOM_DERIVE;
1144             emit_feature_err(sess, "custom_derive", span, GateIssue::Language, explain);
1145         } else if !self.is_whitelisted_legacy_custom_derive(name) {
1146             self.session.span_warn(span, feature_gate::EXPLAIN_DEPR_CUSTOM_DERIVE);
1147         }
1148     }
1149 }