src/librustc_resolve/macros.rs

   1 //! A bunch of methods and structures more or less related to resolving macros and
   2 //! interface provided by `Resolver` to macro expander.
   3
   4 use crate::imports::ImportResolver;
   5 use crate::Namespace::*;
   6 use crate::{AmbiguityError, AmbiguityErrorMisc, AmbiguityKind, Determinacy};
   7 use crate::{CrateLint, ParentScope, ResolutionError, Resolver, Scope, ScopeSet, Weak};
   8 use crate::{ModuleKind, ModuleOrUniformRoot, NameBinding, PathResult, Segment, ToNameBinding};
   9 use rustc::middle::stability;
  10 use rustc::session::parse::feature_err;
  11 use rustc::session::Session;
  12 use rustc::{lint, span_bug, ty};
  13 use rustc_ast::ast::{self, Ident, NodeId};
  14 use rustc_ast_pretty::pprust;
  15 use rustc_attr::{self as attr, StabilityLevel};
  16 use rustc_data_structures::fx::FxHashSet;
  17 use rustc_expand::base::SyntaxExtension;
  18 use rustc_expand::base::{self, Indeterminate, InvocationRes};
  19 use rustc_expand::compile_declarative_macro;
  20 use rustc_expand::expand::{AstFragment, AstFragmentKind, Invocation, InvocationKind};
  21 use rustc_feature::is_builtin_attr_name;
  22 use rustc_hir::def::{self, DefKind, NonMacroAttrKind};
  23 use rustc_hir::def_id;
  24 use rustc_span::edition::Edition;
  25 use rustc_span::hygiene::{self, ExpnData, ExpnId, ExpnKind};
  26 use rustc_span::symbol::{kw, sym, Symbol};
  27 use rustc_span::{Span, DUMMY_SP};
  28
  29 use rustc_data_structures::sync::Lrc;
  30 use rustc_span::hygiene::{AstPass, MacroKind};
  31 use std::{mem, ptr};
  32
  33 type Res = def::Res<NodeId>;
  34
  35 /// Binding produced by a `macro_rules` item.
  36 /// Not modularized, can shadow previous legacy bindings, etc.
  37 #[derive(Debug)]
  38 pub struct LegacyBinding<'a> {
  39     crate binding: &'a NameBinding<'a>,
  40     /// Legacy scope into which the `macro_rules` item was planted.
  41     crate parent_legacy_scope: LegacyScope<'a>,
  42     crate ident: Ident,
  43 }
  44
  45 /// The scope introduced by a `macro_rules!` macro.
  46 /// This starts at the macro's definition and ends at the end of the macro's parent
  47 /// module (named or unnamed), or even further if it escapes with `#[macro_use]`.
  48 /// Some macro invocations need to introduce legacy scopes too because they
  49 /// can potentially expand into macro definitions.
  50 #[derive(Copy, Clone, Debug)]
  51 pub enum LegacyScope<'a> {
  52     /// Empty "root" scope at the crate start containing no names.
  53     Empty,
  54     /// The scope introduced by a `macro_rules!` macro definition.
  55     Binding(&'a LegacyBinding<'a>),
  56     /// The scope introduced by a macro invocation that can potentially
  57     /// create a `macro_rules!` macro definition.
  58     Invocation(ExpnId),
  59 }
  60
  61 // Macro namespace is separated into two sub-namespaces, one for bang macros and
  62 // one for attribute-like macros (attributes, derives).
  63 // We ignore resolutions from one sub-namespace when searching names in scope for another.
  64 fn sub_namespace_match(candidate: Option<MacroKind>, requirement: Option<MacroKind>) -> bool {
  65     #[derive(PartialEq)]
  66     enum SubNS {
  67         Bang,
  68         AttrLike,
  69     }
  70     let sub_ns = |kind| match kind {
  71         MacroKind::Bang => SubNS::Bang,
  72         MacroKind::Attr | MacroKind::Derive => SubNS::AttrLike,
  73     };
  74     let candidate = candidate.map(sub_ns);
  75     let requirement = requirement.map(sub_ns);
  76     // "No specific sub-namespace" means "matches anything" for both requirements and candidates.
  77     candidate.is_none() || requirement.is_none() || candidate == requirement
  78 }
  79
  80 // We don't want to format a path using pretty-printing,
  81 // `format!("{}", path)`, because that tries to insert
  82 // line-breaks and is slow.
  83 fn fast_print_path(path: &ast::Path) -> Symbol {
  84     if path.segments.len() == 1 {
  85         return path.segments[0].ident.name;
  86     } else {
  87         let mut path_str = String::with_capacity(64);
  88         for (i, segment) in path.segments.iter().enumerate() {
  89             if i != 0 {
  90                 path_str.push_str("::");
  91             }
  92             if segment.ident.name != kw::PathRoot {
  93                 path_str.push_str(&segment.ident.as_str())
  94             }
  95         }
  96         Symbol::intern(&path_str)
  97     }
  98 }
  99
 100 /// The code common between processing `#![register_tool]` and `#![register_attr]`.
 101 fn registered_idents(
 102     sess: &Session,
 103     attrs: &[ast::Attribute],
 104     attr_name: Symbol,
 105     descr: &str,
 106 ) -> FxHashSet<Ident> {
 107     let mut registered = FxHashSet::default();
 108     for attr in attr::filter_by_name(attrs, attr_name) {
 109         for nested_meta in attr.meta_item_list().unwrap_or_default() {
 110             match nested_meta.ident() {
 111                 Some(ident) => {
 112                     if let Some(old_ident) = registered.replace(ident) {
 113                         let msg = format!("{} `{}` was already registered", descr, ident);
 114                         sess.struct_span_err(ident.span, &msg)
 115                             .span_label(old_ident.span, "already registered here")
 116                             .emit();
 117                     }
 118                 }
 119                 None => {
 120                     let msg = format!("`{}` only accepts identifiers", attr_name);
 121                     let span = nested_meta.span();
 122                     sess.struct_span_err(span, &msg).span_label(span, "not an identifier").emit();
 123                 }
 124             }
 125         }
 126     }
 127     registered
 128 }
 129
 130 crate fn registered_attrs_and_tools(
 131     sess: &Session,
 132     attrs: &[ast::Attribute],
 133 ) -> (FxHashSet<Ident>, FxHashSet<Ident>) {
 134     let registered_attrs = registered_idents(sess, attrs, sym::register_attr, "attribute");
 135     let mut registered_tools = registered_idents(sess, attrs, sym::register_tool, "tool");
 136     // We implicitly add `rustfmt` and `clippy` to known tools,
 137     // but it's not an error to register them explicitly.
 138     let predefined_tools = [sym::clippy, sym::rustfmt];
 139     registered_tools.extend(predefined_tools.iter().cloned().map(Ident::with_dummy_span));
 140     (registered_attrs, registered_tools)
 141 }
 142
 143 impl<'a> base::Resolver for Resolver<'a> {
 144     fn next_node_id(&mut self) -> NodeId {
 145         self.next_node_id()
 146     }
 147
 148     fn resolve_dollar_crates(&mut self) {
 149         hygiene::update_dollar_crate_names(|ctxt| {
 150             let ident = Ident::new(kw::DollarCrate, DUMMY_SP.with_ctxt(ctxt));
 151             match self.resolve_crate_root(ident).kind {
 152                 ModuleKind::Def(.., name) if name != kw::Invalid => name,
 153                 _ => kw::Crate,
 154             }
 155         });
 156     }
 157
 158     fn visit_ast_fragment_with_placeholders(&mut self, expansion: ExpnId, fragment: &AstFragment) {
 159         // Integrate the new AST fragment into all the definition and module structures.
 160         // We are inside the `expansion` now, but other parent scope components are still the same.
 161         let parent_scope = ParentScope { expansion, ..self.invocation_parent_scopes[&expansion] };
 162         let output_legacy_scope = self.build_reduced_graph(fragment, parent_scope);
 163         self.output_legacy_scopes.insert(expansion, output_legacy_scope);
 164
 165         parent_scope.module.unexpanded_invocations.borrow_mut().remove(&expansion);
 166     }
 167
 168     fn register_builtin_macro(&mut self, ident: ast::Ident, ext: SyntaxExtension) {
 169         if self.builtin_macros.insert(ident.name, ext).is_some() {
 170             self.session
 171                 .span_err(ident.span, &format!("built-in macro `{}` was already defined", ident));
 172         }
 173     }
 174
 175     // Create a new Expansion with a definition site of the provided module, or
 176     // a fake empty `#[no_implicit_prelude]` module if no module is provided.
 177     fn expansion_for_ast_pass(
 178         &mut self,
 179         call_site: Span,
 180         pass: AstPass,
 181         features: &[Symbol],
 182         parent_module_id: Option<NodeId>,
 183     ) -> ExpnId {
 184         let expn_id = ExpnId::fresh(Some(ExpnData::allow_unstable(
 185             ExpnKind::AstPass(pass),
 186             call_site,
 187             self.session.edition(),
 188             features.into(),
 189         )));
 190
 191         let parent_scope = if let Some(module_id) = parent_module_id {
 192             let parent_def_id = self.definitions.local_def_id(module_id);
 193             self.definitions.add_parent_module_of_macro_def(expn_id, parent_def_id);
 194             self.module_map[&parent_def_id]
 195         } else {
 196             self.definitions.add_parent_module_of_macro_def(
 197                 expn_id,
 198                 def_id::DefId::local(def_id::CRATE_DEF_INDEX),
 199             );
 200             self.empty_module
 201         };
 202         self.ast_transform_scopes.insert(expn_id, parent_scope);
 203         expn_id
 204     }
 205
 206     fn resolve_imports(&mut self) {
 207         ImportResolver { r: self }.resolve_imports()
 208     }
 209
 210     fn resolve_macro_invocation(
 211         &mut self,
 212         invoc: &Invocation,
 213         eager_expansion_root: ExpnId,
 214         force: bool,
 215     ) -> Result<InvocationRes, Indeterminate> {
 216         let invoc_id = invoc.expansion_data.id;
 217         let parent_scope = match self.invocation_parent_scopes.get(&invoc_id) {
 218             Some(parent_scope) => *parent_scope,
 219             None => {
 220                 // If there's no entry in the table, then we are resolving an eagerly expanded
 221                 // macro, which should inherit its parent scope from its eager expansion root -
 222                 // the macro that requested this eager expansion.
 223                 let parent_scope = *self
 224                     .invocation_parent_scopes
 225                     .get(&eager_expansion_root)
 226                     .expect("non-eager expansion without a parent scope");
 227                 self.invocation_parent_scopes.insert(invoc_id, parent_scope);
 228                 parent_scope
 229             }
 230         };
 231
 232         let (path, kind, derives, after_derive) = match invoc.kind {
 233             InvocationKind::Attr { ref attr, ref derives, after_derive, .. } => (
 234                 &attr.get_normal_item().path,
 235                 MacroKind::Attr,
 236                 self.arenas.alloc_ast_paths(derives),
 237                 after_derive,
 238             ),
 239             InvocationKind::Bang { ref mac, .. } => (&mac.path, MacroKind::Bang, &[][..], false),
 240             InvocationKind::Derive { ref path, .. } => (path, MacroKind::Derive, &[][..], false),
 241             InvocationKind::DeriveContainer { ref derives, .. } => {
 242                 // Block expansion of the container until we resolve all derives in it.
 243                 // This is required for two reasons:
 244                 // - Derive helper attributes are in scope for the item to which the `#[derive]`
 245                 //   is applied, so they have to be produced by the container's expansion rather
 246                 //   than by individual derives.
 247                 // - Derives in the container need to know whether one of them is a built-in `Copy`.
 248                 // FIXME: Try to avoid repeated resolutions for derives here and in expansion.
 249                 let mut exts = Vec::new();
 250                 let mut helper_attrs = Vec::new();
 251                 for path in derives {
 252                     exts.push(
 253                         match self.resolve_macro_path(
 254                             path,
 255                             Some(MacroKind::Derive),
 256                             &parent_scope,
 257                             true,
 258                             force,
 259                         ) {
 260                             Ok((Some(ext), _)) => {
 261                                 let span = path.segments.last().unwrap().ident.span.modern();
 262                                 helper_attrs.extend(
 263                                     ext.helper_attrs.iter().map(|name| Ident::new(*name, span)),
 264                                 );
 265                                 if ext.is_derive_copy {
 266                                     self.add_derive_copy(invoc_id);
 267                                 }
 268                                 ext
 269                             }
 270                             Ok(_) | Err(Determinacy::Determined) => {
 271                                 self.dummy_ext(MacroKind::Derive)
 272                             }
 273                             Err(Determinacy::Undetermined) => return Err(Indeterminate),
 274                         },
 275                     )
 276                 }
 277                 self.helper_attrs.insert(invoc_id, helper_attrs);
 278                 return Ok(InvocationRes::DeriveContainer(exts));
 279             }
 280         };
 281
 282         // Derives are not included when `invocations` are collected, so we have to add them here.
 283         let parent_scope = &ParentScope { derives, ..parent_scope };
 284         let (ext, res) = self.smart_resolve_macro_path(path, kind, parent_scope, force)?;
 285
 286         let span = invoc.span();
 287         invoc_id.set_expn_data(ext.expn_data(parent_scope.expansion, span, fast_print_path(path)));
 288
 289         if let Res::Def(_, def_id) = res {
 290             if after_derive {
 291                 self.session.span_err(span, "macro attributes must be placed before `#[derive]`");
 292             }
 293             self.macro_defs.insert(invoc_id, def_id);
 294             let normal_module_def_id = self.macro_def_scope(invoc_id).normal_ancestor_id;
 295             self.definitions.add_parent_module_of_macro_def(invoc_id, normal_module_def_id);
 296         }
 297
 298         match invoc.fragment_kind {
 299             AstFragmentKind::Arms
 300             | AstFragmentKind::Fields
 301             | AstFragmentKind::FieldPats
 302             | AstFragmentKind::GenericParams
 303             | AstFragmentKind::Params
 304             | AstFragmentKind::StructFields
 305             | AstFragmentKind::Variants => {
 306                 if let Res::Def(..) = res {
 307                     self.session.span_err(
 308                         span,
 309                         &format!(
 310                             "expected an inert attribute, found {} {}",
 311                             res.article(),
 312                             res.descr()
 313                         ),
 314                     );
 315                     return Ok(InvocationRes::Single(self.dummy_ext(kind)));
 316                 }
 317             }
 318             _ => {}
 319         }
 320
 321         Ok(InvocationRes::Single(ext))
 322     }
 323
 324     fn check_unused_macros(&mut self) {
 325         for (&node_id, &span) in self.unused_macros.iter() {
 326             self.lint_buffer.buffer_lint(
 327                 lint::builtin::UNUSED_MACROS,
 328                 node_id,
 329                 span,
 330                 "unused macro definition",
 331             );
 332         }
 333     }
 334
 335     fn has_derive_copy(&self, expn_id: ExpnId) -> bool {
 336         self.containers_deriving_copy.contains(&expn_id)
 337     }
 338
 339     fn add_derive_copy(&mut self, expn_id: ExpnId) {
 340         self.containers_deriving_copy.insert(expn_id);
 341     }
 342
 343     // The function that implements the resolution logic of `#[cfg_accessible(path)]`.
 344     // Returns true if the path can certainly be resolved in one of three namespaces,
 345     // returns false if the path certainly cannot be resolved in any of the three namespaces.
 346     // Returns `Indeterminate` if we cannot give a certain answer yet.
 347     fn cfg_accessible(&mut self, expn_id: ExpnId, path: &ast::Path) -> Result<bool, Indeterminate> {
 348         let span = path.span;
 349         let path = &Segment::from_path(path);
 350         let parent_scope = self.invocation_parent_scopes[&expn_id];
 351
 352         let mut indeterminate = false;
 353         for ns in [TypeNS, ValueNS, MacroNS].iter().copied() {
 354             match self.resolve_path(path, Some(ns), &parent_scope, false, span, CrateLint::No) {
 355                 PathResult::Module(ModuleOrUniformRoot::Module(_)) => return Ok(true),
 356                 PathResult::NonModule(partial_res) if partial_res.unresolved_segments() == 0 => {
 357                     return Ok(true);
 358                 }
 359                 PathResult::Indeterminate => indeterminate = true,
 360                 // FIXME: `resolve_path` is not ready to report partially resolved paths
 361                 // correctly, so we just report an error if the path was reported as unresolved.
 362                 // This needs to be fixed for `cfg_accessible` to be useful.
 363                 PathResult::NonModule(..) | PathResult::Failed { .. } => {}
 364                 PathResult::Module(_) => panic!("unexpected path resolution"),
 365             }
 366         }
 367
 368         if indeterminate {
 369             return Err(Indeterminate);
 370         }
 371
 372         self.session
 373             .struct_span_err(span, "not sure whether the path is accessible or not")
 374             .span_note(span, "`cfg_accessible` is not fully implemented")
 375             .emit();
 376         Ok(false)
 377     }
 378 }
 379
 380 impl<'a> Resolver<'a> {
 381     /// Resolve macro path with error reporting and recovery.
 382     fn smart_resolve_macro_path(
 383         &mut self,
 384         path: &ast::Path,
 385         kind: MacroKind,
 386         parent_scope: &ParentScope<'a>,
 387         force: bool,
 388     ) -> Result<(Lrc<SyntaxExtension>, Res), Indeterminate> {
 389         let (ext, res) = match self.resolve_macro_path(path, Some(kind), parent_scope, true, force)
 390         {
 391             Ok((Some(ext), res)) => (ext, res),
 392             // Use dummy syntax extensions for unresolved macros for better recovery.
 393             Ok((None, res)) => (self.dummy_ext(kind), res),
 394             Err(Determinacy::Determined) => (self.dummy_ext(kind), Res::Err),
 395             Err(Determinacy::Undetermined) => return Err(Indeterminate),
 396         };
 397
 398         // Report errors and enforce feature gates for the resolved macro.
 399         let features = self.session.features_untracked();
 400         for segment in &path.segments {
 401             if let Some(args) = &segment.args {
 402                 self.session.span_err(args.span(), "generic arguments in macro path");
 403             }
 404             if kind == MacroKind::Attr
 405                 && !features.rustc_attrs
 406                 && segment.ident.as_str().starts_with("rustc")
 407             {
 408                 let msg =
 409                     "attributes starting with `rustc` are reserved for use by the `rustc` compiler";
 410                 feature_err(&self.session.parse_sess, sym::rustc_attrs, segment.ident.span, msg)
 411                     .emit();
 412             }
 413         }
 414
 415         match res {
 416             Res::Def(DefKind::Macro(_), def_id) => {
 417                 if let Some(node_id) = self.definitions.as_local_node_id(def_id) {
 418                     self.unused_macros.remove(&node_id);
 419                     if self.proc_macro_stubs.contains(&node_id) {
 420                         self.session.span_err(
 421                             path.span,
 422                             "can't use a procedural macro from the same crate that defines it",
 423                         );
 424                     }
 425                 }
 426             }
 427             Res::NonMacroAttr(..) | Res::Err => {}
 428             _ => panic!("expected `DefKind::Macro` or `Res::NonMacroAttr`"),
 429         };
 430
 431         self.check_stability_and_deprecation(&ext, path);
 432
 433         Ok(if ext.macro_kind() != kind {
 434             let expected = kind.descr_expected();
 435             let path_str = pprust::path_to_string(path);
 436             let msg = format!("expected {}, found {} `{}`", expected, res.descr(), path_str);
 437             self.session
 438                 .struct_span_err(path.span, &msg)
 439                 .span_label(path.span, format!("not {} {}", kind.article(), expected))
 440                 .emit();
 441             // Use dummy syntax extensions for unexpected macro kinds for better recovery.
 442             (self.dummy_ext(kind), Res::Err)
 443         } else {
 444             (ext, res)
 445         })
 446     }
 447
 448     pub fn resolve_macro_path(
 449         &mut self,
 450         path: &ast::Path,
 451         kind: Option<MacroKind>,
 452         parent_scope: &ParentScope<'a>,
 453         trace: bool,
 454         force: bool,
 455     ) -> Result<(Option<Lrc<SyntaxExtension>>, Res), Determinacy> {
 456         let path_span = path.span;
 457         let mut path = Segment::from_path(path);
 458
 459         // Possibly apply the macro helper hack
 460         if kind == Some(MacroKind::Bang)
 461             && path.len() == 1
 462             && path[0].ident.span.ctxt().outer_expn_data().local_inner_macros
 463         {
 464             let root = Ident::new(kw::DollarCrate, path[0].ident.span);
 465             path.insert(0, Segment::from_ident(root));
 466         }
 467
 468         let res = if path.len() > 1 {
 469             let res = match self.resolve_path(
 470                 &path,
 471                 Some(MacroNS),
 472                 parent_scope,
 473                 false,
 474                 path_span,
 475                 CrateLint::No,
 476             ) {
 477                 PathResult::NonModule(path_res) if path_res.unresolved_segments() == 0 => {
 478                     Ok(path_res.base_res())
 479                 }
 480                 PathResult::Indeterminate if !force => return Err(Determinacy::Undetermined),
 481                 PathResult::NonModule(..)
 482                 | PathResult::Indeterminate
 483                 | PathResult::Failed { .. } => Err(Determinacy::Determined),
 484                 PathResult::Module(..) => unreachable!(),
 485             };
 486
 487             if trace {
 488                 let kind = kind.expect("macro kind must be specified if tracing is enabled");
 489                 self.multi_segment_macro_resolutions.push((
 490                     path,
 491                     path_span,
 492                     kind,
 493                     *parent_scope,
 494                     res.ok(),
 495                 ));
 496             }
 497
 498             self.prohibit_imported_non_macro_attrs(None, res.ok(), path_span);
 499             res
 500         } else {
 501             let scope_set = kind.map_or(ScopeSet::All(MacroNS, false), ScopeSet::Macro);
 502             let binding = self.early_resolve_ident_in_lexical_scope(
 503                 path[0].ident,
 504                 scope_set,
 505                 parent_scope,
 506                 false,
 507                 force,
 508                 path_span,
 509             );
 510             if let Err(Determinacy::Undetermined) = binding {
 511                 return Err(Determinacy::Undetermined);
 512             }
 513
 514             if trace {
 515                 let kind = kind.expect("macro kind must be specified if tracing is enabled");
 516                 self.single_segment_macro_resolutions.push((
 517                     path[0].ident,
 518                     kind,
 519                     *parent_scope,
 520                     binding.ok(),
 521                 ));
 522             }
 523
 524             let res = binding.map(|binding| binding.res());
 525             self.prohibit_imported_non_macro_attrs(binding.ok(), res.ok(), path_span);
 526             res
 527         };
 528
 529         res.map(|res| (self.get_macro(res), res))
 530     }
 531
 532     // Resolve an identifier in lexical scope.
 533     // This is a variation of `fn resolve_ident_in_lexical_scope` that can be run during
 534     // expansion and import resolution (perhaps they can be merged in the future).
 535     // The function is used for resolving initial segments of macro paths (e.g., `foo` in
 536     // `foo::bar!(); or `foo!();`) and also for import paths on 2018 edition.
 537     crate fn early_resolve_ident_in_lexical_scope(
 538         &mut self,
 539         orig_ident: Ident,
 540         scope_set: ScopeSet,
 541         parent_scope: &ParentScope<'a>,
 542         record_used: bool,
 543         force: bool,
 544         path_span: Span,
 545     ) -> Result<&'a NameBinding<'a>, Determinacy> {
 546         bitflags::bitflags! {
 547             struct Flags: u8 {
 548                 const MACRO_RULES          = 1 << 0;
 549                 const MODULE               = 1 << 1;
 550                 const DERIVE_HELPER_COMPAT = 1 << 2;
 551                 const MISC_SUGGEST_CRATE   = 1 << 3;
 552                 const MISC_SUGGEST_SELF    = 1 << 4;
 553                 const MISC_FROM_PRELUDE    = 1 << 5;
 554             }
 555         }
 556
 557         assert!(force || !record_used); // `record_used` implies `force`
 558
 559         // Make sure `self`, `super` etc produce an error when passed to here.
 560         if orig_ident.is_path_segment_keyword() {
 561             return Err(Determinacy::Determined);
 562         }
 563
 564         let (ns, macro_kind, is_import) = match scope_set {
 565             ScopeSet::All(ns, is_import) => (ns, None, is_import),
 566             ScopeSet::AbsolutePath(ns) => (ns, None, false),
 567             ScopeSet::Macro(macro_kind) => (MacroNS, Some(macro_kind), false),
 568         };
 569
 570         // This is *the* result, resolution from the scope closest to the resolved identifier.
 571         // However, sometimes this result is "weak" because it comes from a glob import or
 572         // a macro expansion, and in this case it cannot shadow names from outer scopes, e.g.
 573         // mod m { ... } // solution in outer scope
 574         // {
 575         //     use prefix::*; // imports another `m` - innermost solution
 576         //                    // weak, cannot shadow the outer `m`, need to report ambiguity error
 577         //     m::mac!();
 578         // }
 579         // So we have to save the innermost solution and continue searching in outer scopes
 580         // to detect potential ambiguities.
 581         let mut innermost_result: Option<(&NameBinding<'_>, Flags)> = None;
 582         let mut determinacy = Determinacy::Determined;
 583
 584         // Go through all the scopes and try to resolve the name.
 585         let break_result = self.visit_scopes(
 586             scope_set,
 587             parent_scope,
 588             orig_ident,
 589             |this, scope, use_prelude, ident| {
 590                 let ok = |res, span, arenas| {
 591                     Ok((
 592                         (res, ty::Visibility::Public, span, ExpnId::root()).to_name_binding(arenas),
 593                         Flags::empty(),
 594                     ))
 595                 };
 596                 let result = match scope {
 597                     Scope::DeriveHelpers(expn_id) => {
 598                         if let Some(attr) = this
 599                             .helper_attrs
 600                             .get(&expn_id)
 601                             .and_then(|attrs| attrs.iter().rfind(|i| ident == **i))
 602                         {
 603                             let binding = (
 604                                 Res::NonMacroAttr(NonMacroAttrKind::DeriveHelper),
 605                                 ty::Visibility::Public,
 606                                 attr.span,
 607                                 expn_id,
 608                             )
 609                                 .to_name_binding(this.arenas);
 610                             Ok((binding, Flags::empty()))
 611                         } else {
 612                             Err(Determinacy::Determined)
 613                         }
 614                     }
 615                     Scope::DeriveHelpersCompat => {
 616                         let mut result = Err(Determinacy::Determined);
 617                         for derive in parent_scope.derives {
 618                             let parent_scope = &ParentScope { derives: &[], ..*parent_scope };
 619                             match this.resolve_macro_path(
 620                                 derive,
 621                                 Some(MacroKind::Derive),
 622                                 parent_scope,
 623                                 true,
 624                                 force,
 625                             ) {
 626                                 Ok((Some(ext), _)) => {
 627                                     if ext.helper_attrs.contains(&ident.name) {
 628                                         let binding = (
 629                                             Res::NonMacroAttr(NonMacroAttrKind::DeriveHelper),
 630                                             ty::Visibility::Public,
 631                                             derive.span,
 632                                             ExpnId::root(),
 633                                         )
 634                                             .to_name_binding(this.arenas);
 635                                         result = Ok((binding, Flags::DERIVE_HELPER_COMPAT));
 636                                         break;
 637                                     }
 638                                 }
 639                                 Ok(_) | Err(Determinacy::Determined) => {}
 640                                 Err(Determinacy::Undetermined) => {
 641                                     result = Err(Determinacy::Undetermined)
 642                                 }
 643                             }
 644                         }
 645                         result
 646                     }
 647                     Scope::MacroRules(legacy_scope) => match legacy_scope {
 648                         LegacyScope::Binding(legacy_binding) if ident == legacy_binding.ident => {
 649                             Ok((legacy_binding.binding, Flags::MACRO_RULES))
 650                         }
 651                         LegacyScope::Invocation(invoc_id)
 652                             if !this.output_legacy_scopes.contains_key(&invoc_id) =>
 653                         {
 654                             Err(Determinacy::Undetermined)
 655                         }
 656                         _ => Err(Determinacy::Determined),
 657                     },
 658                     Scope::CrateRoot => {
 659                         let root_ident = Ident::new(kw::PathRoot, ident.span);
 660                         let root_module = this.resolve_crate_root(root_ident);
 661                         let binding = this.resolve_ident_in_module_ext(
 662                             ModuleOrUniformRoot::Module(root_module),
 663                             ident,
 664                             ns,
 665                             parent_scope,
 666                             record_used,
 667                             path_span,
 668                         );
 669                         match binding {
 670                             Ok(binding) => Ok((binding, Flags::MODULE | Flags::MISC_SUGGEST_CRATE)),
 671                             Err((Determinacy::Undetermined, Weak::No)) => {
 672                                 return Some(Err(Determinacy::determined(force)));
 673                             }
 674                             Err((Determinacy::Undetermined, Weak::Yes)) => {
 675                                 Err(Determinacy::Undetermined)
 676                             }
 677                             Err((Determinacy::Determined, _)) => Err(Determinacy::Determined),
 678                         }
 679                     }
 680                     Scope::Module(module) => {
 681                         let adjusted_parent_scope = &ParentScope { module, ..*parent_scope };
 682                         let binding = this.resolve_ident_in_module_unadjusted_ext(
 683                             ModuleOrUniformRoot::Module(module),
 684                             ident,
 685                             ns,
 686                             adjusted_parent_scope,
 687                             true,
 688                             record_used,
 689                             path_span,
 690                         );
 691                         match binding {
 692                             Ok(binding) => {
 693                                 let misc_flags = if ptr::eq(module, this.graph_root) {
 694                                     Flags::MISC_SUGGEST_CRATE
 695                                 } else if module.is_normal() {
 696                                     Flags::MISC_SUGGEST_SELF
 697                                 } else {
 698                                     Flags::empty()
 699                                 };
 700                                 Ok((binding, Flags::MODULE | misc_flags))
 701                             }
 702                             Err((Determinacy::Undetermined, Weak::No)) => {
 703                                 return Some(Err(Determinacy::determined(force)));
 704                             }
 705                             Err((Determinacy::Undetermined, Weak::Yes)) => {
 706                                 Err(Determinacy::Undetermined)
 707                             }
 708                             Err((Determinacy::Determined, _)) => Err(Determinacy::Determined),
 709                         }
 710                     }
 711                     Scope::RegisteredAttrs => match this.registered_attrs.get(&ident).cloned() {
 712                         Some(ident) => ok(
 713                             Res::NonMacroAttr(NonMacroAttrKind::Registered),
 714                             ident.span,
 715                             this.arenas,
 716                         ),
 717                         None => Err(Determinacy::Determined),
 718                     },
 719                     Scope::MacroUsePrelude => {
 720                         match this.macro_use_prelude.get(&ident.name).cloned() {
 721                             Some(binding) => Ok((binding, Flags::MISC_FROM_PRELUDE)),
 722                             None => Err(Determinacy::determined(
 723                                 this.graph_root.unexpanded_invocations.borrow().is_empty(),
 724                             )),
 725                         }
 726                     }
 727                     Scope::BuiltinAttrs => {
 728                         if is_builtin_attr_name(ident.name) {
 729                             ok(Res::NonMacroAttr(NonMacroAttrKind::Builtin), DUMMY_SP, this.arenas)
 730                         } else {
 731                             Err(Determinacy::Determined)
 732                         }
 733                     }
 734                     Scope::ExternPrelude => match this.extern_prelude_get(ident, !record_used) {
 735                         Some(binding) => Ok((binding, Flags::empty())),
 736                         None => Err(Determinacy::determined(
 737                             this.graph_root.unexpanded_invocations.borrow().is_empty(),
 738                         )),
 739                     },
 740                     Scope::ToolPrelude => match this.registered_tools.get(&ident).cloned() {
 741                         Some(ident) => ok(Res::ToolMod, ident.span, this.arenas),
 742                         None => Err(Determinacy::Determined),
 743                     },
 744                     Scope::StdLibPrelude => {
 745                         let mut result = Err(Determinacy::Determined);
 746                         if let Some(prelude) = this.prelude {
 747                             if let Ok(binding) = this.resolve_ident_in_module_unadjusted(
 748                                 ModuleOrUniformRoot::Module(prelude),
 749                                 ident,
 750                                 ns,
 751                                 parent_scope,
 752                                 false,
 753                                 path_span,
 754                             ) {
 755                                 if use_prelude || this.is_builtin_macro(binding.res()) {
 756                                     result = Ok((binding, Flags::MISC_FROM_PRELUDE));
 757                                 }
 758                             }
 759                         }
 760                         result
 761                     }
 762                     Scope::BuiltinTypes => {
 763                         match this.primitive_type_table.primitive_types.get(&ident.name).cloned() {
 764                             Some(prim_ty) => ok(Res::PrimTy(prim_ty), DUMMY_SP, this.arenas),
 765                             None => Err(Determinacy::Determined),
 766                         }
 767                     }
 768                 };
 769
 770                 match result {
 771                     Ok((binding, flags))
 772                         if sub_namespace_match(binding.macro_kind(), macro_kind) =>
 773                     {
 774                         if !record_used {
 775                             return Some(Ok(binding));
 776                         }
 777
 778                         if let Some((innermost_binding, innermost_flags)) = innermost_result {
 779                             // Found another solution, if the first one was "weak", report an error.
 780                             let (res, innermost_res) = (binding.res(), innermost_binding.res());
 781                             if res != innermost_res {
 782                                 let builtin = Res::NonMacroAttr(NonMacroAttrKind::Builtin);
 783                                 let is_derive_helper_compat = |res, flags: Flags| {
 784                                     res == Res::NonMacroAttr(NonMacroAttrKind::DeriveHelper)
 785                                         && flags.contains(Flags::DERIVE_HELPER_COMPAT)
 786                                 };
 787
 788                                 let ambiguity_error_kind = if is_import {
 789                                     Some(AmbiguityKind::Import)
 790                                 } else if innermost_res == builtin || res == builtin {
 791                                     Some(AmbiguityKind::BuiltinAttr)
 792                                 } else if is_derive_helper_compat(innermost_res, innermost_flags)
 793                                     || is_derive_helper_compat(res, flags)
 794                                 {
 795                                     Some(AmbiguityKind::DeriveHelper)
 796                                 } else if innermost_flags.contains(Flags::MACRO_RULES)
 797                                     && flags.contains(Flags::MODULE)
 798                                     && !this
 799                                         .disambiguate_legacy_vs_modern(innermost_binding, binding)
 800                                     || flags.contains(Flags::MACRO_RULES)
 801                                         && innermost_flags.contains(Flags::MODULE)
 802                                         && !this.disambiguate_legacy_vs_modern(
 803                                             binding,
 804                                             innermost_binding,
 805                                         )
 806                                 {
 807                                     Some(AmbiguityKind::LegacyVsModern)
 808                                 } else if innermost_binding.is_glob_import() {
 809                                     Some(AmbiguityKind::GlobVsOuter)
 810                                 } else if innermost_binding
 811                                     .may_appear_after(parent_scope.expansion, binding)
 812                                 {
 813                                     Some(AmbiguityKind::MoreExpandedVsOuter)
 814                                 } else {
 815                                     None
 816                                 };
 817                                 if let Some(kind) = ambiguity_error_kind {
 818                                     let misc = |f: Flags| {
 819                                         if f.contains(Flags::MISC_SUGGEST_CRATE) {
 820                                             AmbiguityErrorMisc::SuggestCrate
 821                                         } else if f.contains(Flags::MISC_SUGGEST_SELF) {
 822                                             AmbiguityErrorMisc::SuggestSelf
 823                                         } else if f.contains(Flags::MISC_FROM_PRELUDE) {
 824                                             AmbiguityErrorMisc::FromPrelude
 825                                         } else {
 826                                             AmbiguityErrorMisc::None
 827                                         }
 828                                     };
 829                                     this.ambiguity_errors.push(AmbiguityError {
 830                                         kind,
 831                                         ident: orig_ident,
 832                                         b1: innermost_binding,
 833                                         b2: binding,
 834                                         misc1: misc(innermost_flags),
 835                                         misc2: misc(flags),
 836                                     });
 837                                     return Some(Ok(innermost_binding));
 838                                 }
 839                             }
 840                         } else {
 841                             // Found the first solution.
 842                             innermost_result = Some((binding, flags));
 843                         }
 844                     }
 845                     Ok(..) | Err(Determinacy::Determined) => {}
 846                     Err(Determinacy::Undetermined) => determinacy = Determinacy::Undetermined,
 847                 }
 848
 849                 None
 850             },
 851         );
 852
 853         if let Some(break_result) = break_result {
 854             return break_result;
 855         }
 856
 857         // The first found solution was the only one, return it.
 858         if let Some((binding, _)) = innermost_result {
 859             return Ok(binding);
 860         }
 861
 862         Err(Determinacy::determined(determinacy == Determinacy::Determined || force))
 863     }
 864
 865     crate fn finalize_macro_resolutions(&mut self) {
 866         let check_consistency = |this: &mut Self,
 867                                  path: &[Segment],
 868                                  span,
 869                                  kind: MacroKind,
 870                                  initial_res: Option<Res>,
 871                                  res: Res| {
 872             if let Some(initial_res) = initial_res {
 873                 if res != initial_res && res != Res::Err && this.ambiguity_errors.is_empty() {
 874                     // Make sure compilation does not succeed if preferred macro resolution
 875                     // has changed after the macro had been expanded. In theory all such
 876                     // situations should be reported as ambiguity errors, so this is a bug.
 877                     span_bug!(span, "inconsistent resolution for a macro");
 878                 }
 879             } else {
 880                 // It's possible that the macro was unresolved (indeterminate) and silently
 881                 // expanded into a dummy fragment for recovery during expansion.
 882                 // Now, post-expansion, the resolution may succeed, but we can't change the
 883                 // past and need to report an error.
 884                 // However, non-speculative `resolve_path` can successfully return private items
 885                 // even if speculative `resolve_path` returned nothing previously, so we skip this
 886                 // less informative error if the privacy error is reported elsewhere.
 887                 if this.privacy_errors.is_empty() {
 888                     let msg = format!(
 889                         "cannot determine resolution for the {} `{}`",
 890                         kind.descr(),
 891                         Segment::names_to_string(path)
 892                     );
 893                     let msg_note = "import resolution is stuck, try simplifying macro imports";
 894                     this.session.struct_span_err(span, &msg).note(msg_note).emit();
 895                 }
 896             }
 897         };
 898
 899         let macro_resolutions = mem::take(&mut self.multi_segment_macro_resolutions);
 900         for (mut path, path_span, kind, parent_scope, initial_res) in macro_resolutions {
 901             // FIXME: Path resolution will ICE if segment IDs present.
 902             for seg in &mut path {
 903                 seg.id = None;
 904             }
 905             match self.resolve_path(
 906                 &path,
 907                 Some(MacroNS),
 908                 &parent_scope,
 909                 true,
 910                 path_span,
 911                 CrateLint::No,
 912             ) {
 913                 PathResult::NonModule(path_res) if path_res.unresolved_segments() == 0 => {
 914                     let res = path_res.base_res();
 915                     check_consistency(self, &path, path_span, kind, initial_res, res);
 916                 }
 917                 path_res @ PathResult::NonModule(..) | path_res @ PathResult::Failed { .. } => {
 918                     let (span, label) = if let PathResult::Failed { span, label, .. } = path_res {
 919                         (span, label)
 920                     } else {
 921                         (
 922                             path_span,
 923                             format!(
 924                                 "partially resolved path in {} {}",
 925                                 kind.article(),
 926                                 kind.descr()
 927                             ),
 928                         )
 929                     };
 930                     self.report_error(
 931                         span,
 932                         ResolutionError::FailedToResolve { label, suggestion: None },
 933                     );
 934                 }
 935                 PathResult::Module(..) | PathResult::Indeterminate => unreachable!(),
 936             }
 937         }
 938
 939         let macro_resolutions = mem::take(&mut self.single_segment_macro_resolutions);
 940         for (ident, kind, parent_scope, initial_binding) in macro_resolutions {
 941             match self.early_resolve_ident_in_lexical_scope(
 942                 ident,
 943                 ScopeSet::Macro(kind),
 944                 &parent_scope,
 945                 true,
 946                 true,
 947                 ident.span,
 948             ) {
 949                 Ok(binding) => {
 950                     let initial_res = initial_binding.map(|initial_binding| {
 951                         self.record_use(ident, MacroNS, initial_binding, false);
 952                         initial_binding.res()
 953                     });
 954                     let res = binding.res();
 955                     let seg = Segment::from_ident(ident);
 956                     check_consistency(self, &[seg], ident.span, kind, initial_res, res);
 957                 }
 958                 Err(..) => {
 959                     let expected = kind.descr_expected();
 960                     let msg = format!("cannot find {} `{}` in this scope", expected, ident);
 961                     let mut err = self.session.struct_span_err(ident.span, &msg);
 962                     self.unresolved_macro_suggestions(&mut err, kind, &parent_scope, ident);
 963                     err.emit();
 964                 }
 965             }
 966         }
 967
 968         let builtin_attrs = mem::take(&mut self.builtin_attrs);
 969         for (ident, parent_scope) in builtin_attrs {
 970             let _ = self.early_resolve_ident_in_lexical_scope(
 971                 ident,
 972                 ScopeSet::Macro(MacroKind::Attr),
 973                 &parent_scope,
 974                 true,
 975                 true,
 976                 ident.span,
 977             );
 978         }
 979     }
 980
 981     fn check_stability_and_deprecation(&mut self, ext: &SyntaxExtension, path: &ast::Path) {
 982         let span = path.span;
 983         if let Some(stability) = &ext.stability {
 984             if let StabilityLevel::Unstable { reason, issue, is_soft } = stability.level {
 985                 let feature = stability.feature;
 986                 if !self.active_features.contains(&feature) && !span.allows_unstable(feature) {
 987                     let node_id = ast::CRATE_NODE_ID;
 988                     let lint_buffer = &mut self.lint_buffer;
 989                     let soft_handler =
 990                         |lint, span, msg: &_| lint_buffer.buffer_lint(lint, node_id, span, msg);
 991                     stability::report_unstable(
 992                         self.session,
 993                         feature,
 994                         reason,
 995                         issue,
 996                         is_soft,
 997                         span,
 998                         soft_handler,
 999                     );
1000                 }
1001             }
1002             if let Some(depr) = &stability.rustc_depr {
1003                 let path = pprust::path_to_string(path);
1004                 let (message, lint) = stability::rustc_deprecation_message(depr, &path);
1005                 stability::early_report_deprecation(
1006                     &mut self.lint_buffer,
1007                     &message,
1008                     depr.suggestion,
1009                     lint,
1010                     span,
1011                 );
1012             }
1013         }
1014         if let Some(depr) = &ext.deprecation {
1015             let path = pprust::path_to_string(&path);
1016             let (message, lint) = stability::deprecation_message(depr, &path);
1017             stability::early_report_deprecation(&mut self.lint_buffer, &message, None, lint, span);
1018         }
1019     }
1020
1021     fn prohibit_imported_non_macro_attrs(
1022         &self,
1023         binding: Option<&'a NameBinding<'a>>,
1024         res: Option<Res>,
1025         span: Span,
1026     ) {
1027         if let Some(Res::NonMacroAttr(kind)) = res {
1028             if kind != NonMacroAttrKind::Tool && binding.map_or(true, |b| b.is_import()) {
1029                 let msg =
1030                     format!("cannot use {} {} through an import", kind.article(), kind.descr());
1031                 let mut err = self.session.struct_span_err(span, &msg);
1032                 if let Some(binding) = binding {
1033                     err.span_note(binding.span, &format!("the {} imported here", kind.descr()));
1034                 }
1035                 err.emit();
1036             }
1037         }
1038     }
1039
1040     crate fn check_reserved_macro_name(&mut self, ident: Ident, res: Res) {
1041         // Reserve some names that are not quite covered by the general check
1042         // performed on `Resolver::builtin_attrs`.
1043         if ident.name == sym::cfg || ident.name == sym::cfg_attr || ident.name == sym::derive {
1044             let macro_kind = self.get_macro(res).map(|ext| ext.macro_kind());
1045             if macro_kind.is_some() && sub_namespace_match(macro_kind, Some(MacroKind::Attr)) {
1046                 self.session.span_err(
1047                     ident.span,
1048                     &format!("name `{}` is reserved in attribute namespace", ident),
1049                 );
1050             }
1051         }
1052     }
1053
1054     /// Compile the macro into a `SyntaxExtension` and possibly replace
1055     /// its expander to a pre-defined one for built-in macros.
1056     crate fn compile_macro(&mut self, item: &ast::Item, edition: Edition) -> SyntaxExtension {
1057         let mut result = compile_declarative_macro(
1058             &self.session.parse_sess,
1059             self.session.features_untracked(),
1060             item,
1061             edition,
1062         );
1063
1064         if result.is_builtin {
1065             // The macro was marked with `#[rustc_builtin_macro]`.
1066             if let Some(ext) = self.builtin_macros.remove(&item.ident.name) {
1067                 // The macro is a built-in, replace its expander function
1068                 // while still taking everything else from the source code.
1069                 result.kind = ext.kind;
1070             } else {
1071                 let msg = format!("cannot find a built-in macro with name `{}`", item.ident);
1072                 self.session.span_err(item.span, &msg);
1073             }
1074         }
1075
1076         result
1077     }
1078 }