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::{span_bug, ty};
  11 use rustc_ast::ast::{self, Ident, NodeId};
  12 use rustc_ast_pretty::pprust;
  13 use rustc_attr::{self as attr, StabilityLevel};
  14 use rustc_data_structures::fx::FxHashSet;
  15 use rustc_expand::base::SyntaxExtension;
  16 use rustc_expand::base::{self, Indeterminate, InvocationRes};
  17 use rustc_expand::compile_declarative_macro;
  18 use rustc_expand::expand::{AstFragment, AstFragmentKind, Invocation, InvocationKind};
  19 use rustc_feature::is_builtin_attr_name;
  20 use rustc_hir::def::{self, DefKind, NonMacroAttrKind};
  21 use rustc_hir::def_id;
  22 use rustc_session::lint::builtin::UNUSED_MACROS;
  23 use rustc_session::parse::feature_err;
  24 use rustc_session::Session;
  25 use rustc_span::edition::Edition;
  26 use rustc_span::hygiene::{self, ExpnData, ExpnId, ExpnKind};
  27 use rustc_span::symbol::{kw, sym, Symbol};
  28 use rustc_span::{Span, DUMMY_SP};
  29
  30 use rustc_data_structures::sync::Lrc;
  31 use rustc_span::hygiene::{AstPass, MacroKind};
  32 use std::{mem, ptr};
  33
  34 type Res = def::Res<NodeId>;
  35
  36 /// Binding produced by a `macro_rules` item.
  37 /// Not modularized, can shadow previous `macro_rules` bindings, etc.
  38 #[derive(Debug)]
  39 pub struct MacroRulesBinding<'a> {
  40     crate binding: &'a NameBinding<'a>,
  41     /// `macro_rules` scope into which the `macro_rules` item was planted.
  42     crate parent_macro_rules_scope: MacroRulesScope<'a>,
  43     crate ident: Ident,
  44 }
  45
  46 /// The scope introduced by a `macro_rules!` macro.
  47 /// This starts at the macro's definition and ends at the end of the macro's parent
  48 /// module (named or unnamed), or even further if it escapes with `#[macro_use]`.
  49 /// Some macro invocations need to introduce `macro_rules` scopes too because they
  50 /// can potentially expand into macro definitions.
  51 #[derive(Copy, Clone, Debug)]
  52 pub enum MacroRulesScope<'a> {
  53     /// Empty "root" scope at the crate start containing no names.
  54     Empty,
  55     /// The scope introduced by a `macro_rules!` macro definition.
  56     Binding(&'a MacroRulesBinding<'a>),
  57     /// The scope introduced by a macro invocation that can potentially
  58     /// create a `macro_rules!` macro definition.
  59     Invocation(ExpnId),
  60 }
  61
  62 // Macro namespace is separated into two sub-namespaces, one for bang macros and
  63 // one for attribute-like macros (attributes, derives).
  64 // We ignore resolutions from one sub-namespace when searching names in scope for another.
  65 fn sub_namespace_match(candidate: Option<MacroKind>, requirement: Option<MacroKind>) -> bool {
  66     #[derive(PartialEq)]
  67     enum SubNS {
  68         Bang,
  69         AttrLike,
  70     }
  71     let sub_ns = |kind| match kind {
  72         MacroKind::Bang => SubNS::Bang,
  73         MacroKind::Attr | MacroKind::Derive => SubNS::AttrLike,
  74     };
  75     let candidate = candidate.map(sub_ns);
  76     let requirement = requirement.map(sub_ns);
  77     // "No specific sub-namespace" means "matches anything" for both requirements and candidates.
  78     candidate.is_none() || requirement.is_none() || candidate == requirement
  79 }
  80
  81 // We don't want to format a path using pretty-printing,
  82 // `format!("{}", path)`, because that tries to insert
  83 // line-breaks and is slow.
  84 fn fast_print_path(path: &ast::Path) -> Symbol {
  85     if path.segments.len() == 1 {
  86         return path.segments[0].ident.name;
  87     } else {
  88         let mut path_str = String::with_capacity(64);
  89         for (i, segment) in path.segments.iter().enumerate() {
  90             if i != 0 {
  91                 path_str.push_str("::");
  92             }
  93             if segment.ident.name != kw::PathRoot {
  94                 path_str.push_str(&segment.ident.as_str())
  95             }
  96         }
  97         Symbol::intern(&path_str)
  98     }
  99 }
 100
 101 /// The code common between processing `#![register_tool]` and `#![register_attr]`.
 102 fn registered_idents(
 103     sess: &Session,
 104     attrs: &[ast::Attribute],
 105     attr_name: Symbol,
 106     descr: &str,
 107 ) -> FxHashSet<Ident> {
 108     let mut registered = FxHashSet::default();
 109     for attr in attr::filter_by_name(attrs, attr_name) {
 110         for nested_meta in attr.meta_item_list().unwrap_or_default() {
 111             match nested_meta.ident() {
 112                 Some(ident) => {
 113                     if let Some(old_ident) = registered.replace(ident) {
 114                         let msg = format!("{} `{}` was already registered", descr, ident);
 115                         sess.struct_span_err(ident.span, &msg)
 116                             .span_label(old_ident.span, "already registered here")
 117                             .emit();
 118                     }
 119                 }
 120                 None => {
 121                     let msg = format!("`{}` only accepts identifiers", attr_name);
 122                     let span = nested_meta.span();
 123                     sess.struct_span_err(span, &msg).span_label(span, "not an identifier").emit();
 124                 }
 125             }
 126         }
 127     }
 128     registered
 129 }
 130
 131 crate fn registered_attrs_and_tools(
 132     sess: &Session,
 133     attrs: &[ast::Attribute],
 134 ) -> (FxHashSet<Ident>, FxHashSet<Ident>) {
 135     let registered_attrs = registered_idents(sess, attrs, sym::register_attr, "attribute");
 136     let mut registered_tools = registered_idents(sess, attrs, sym::register_tool, "tool");
 137     // We implicitly add `rustfmt` and `clippy` to known tools,
 138     // but it's not an error to register them explicitly.
 139     let predefined_tools = [sym::clippy, sym::rustfmt];
 140     registered_tools.extend(predefined_tools.iter().cloned().map(Ident::with_dummy_span));
 141     (registered_attrs, registered_tools)
 142 }
 143
 144 impl<'a> base::Resolver for Resolver<'a> {
 145     fn next_node_id(&mut self) -> NodeId {
 146         self.next_node_id()
 147     }
 148
 149     fn resolve_dollar_crates(&mut self) {
 150         hygiene::update_dollar_crate_names(|ctxt| {
 151             let ident = Ident::new(kw::DollarCrate, DUMMY_SP.with_ctxt(ctxt));
 152             match self.resolve_crate_root(ident).kind {
 153                 ModuleKind::Def(.., name) if name != kw::Invalid => name,
 154                 _ => kw::Crate,
 155             }
 156         });
 157     }
 158
 159     fn visit_ast_fragment_with_placeholders(&mut self, expansion: ExpnId, fragment: &AstFragment) {
 160         // Integrate the new AST fragment into all the definition and module structures.
 161         // We are inside the `expansion` now, but other parent scope components are still the same.
 162         let parent_scope = ParentScope { expansion, ..self.invocation_parent_scopes[&expansion] };
 163         let output_macro_rules_scope = self.build_reduced_graph(fragment, parent_scope);
 164         self.output_macro_rules_scopes.insert(expansion, output_macro_rules_scope);
 165
 166         parent_scope.module.unexpanded_invocations.borrow_mut().remove(&expansion);
 167     }
 168
 169     fn register_builtin_macro(&mut self, ident: ast::Ident, ext: SyntaxExtension) {
 170         if self.builtin_macros.insert(ident.name, ext).is_some() {
 171             self.session
 172                 .span_err(ident.span, &format!("built-in macro `{}` was already defined", ident));
 173         }
 174     }
 175
 176     // Create a new Expansion with a definition site of the provided module, or
 177     // a fake empty `#[no_implicit_prelude]` module if no module is provided.
 178     fn expansion_for_ast_pass(
 179         &mut self,
 180         call_site: Span,
 181         pass: AstPass,
 182         features: &[Symbol],
 183         parent_module_id: Option<NodeId>,
 184     ) -> ExpnId {
 185         let expn_id = ExpnId::fresh(Some(ExpnData::allow_unstable(
 186             ExpnKind::AstPass(pass),
 187             call_site,
 188             self.session.edition(),
 189             features.into(),
 190         )));
 191
 192         let parent_scope = if let Some(module_id) = parent_module_id {
 193             let parent_def_id = self.definitions.local_def_id(module_id);
 194             self.definitions.add_parent_module_of_macro_def(expn_id, parent_def_id);
 195             self.module_map[&parent_def_id]
 196         } else {
 197             self.definitions.add_parent_module_of_macro_def(
 198                 expn_id,
 199                 def_id::DefId::local(def_id::CRATE_DEF_INDEX),
 200             );
 201             self.empty_module
 202         };
 203         self.ast_transform_scopes.insert(expn_id, parent_scope);
 204         expn_id
 205     }
 206
 207     fn resolve_imports(&mut self) {
 208         ImportResolver { r: self }.resolve_imports()
 209     }
 210
 211     fn resolve_macro_invocation(
 212         &mut self,
 213         invoc: &Invocation,
 214         eager_expansion_root: ExpnId,
 215         force: bool,
 216     ) -> Result<InvocationRes, Indeterminate> {
 217         let invoc_id = invoc.expansion_data.id;
 218         let parent_scope = match self.invocation_parent_scopes.get(&invoc_id) {
 219             Some(parent_scope) => *parent_scope,
 220             None => {
 221                 // If there's no entry in the table, then we are resolving an eagerly expanded
 222                 // macro, which should inherit its parent scope from its eager expansion root -
 223                 // the macro that requested this eager expansion.
 224                 let parent_scope = *self
 225                     .invocation_parent_scopes
 226                     .get(&eager_expansion_root)
 227                     .expect("non-eager expansion without a parent scope");
 228                 self.invocation_parent_scopes.insert(invoc_id, parent_scope);
 229                 parent_scope
 230             }
 231         };
 232
 233         let (path, kind, derives, after_derive) = match invoc.kind {
 234             InvocationKind::Attr { ref attr, ref derives, after_derive, .. } => (
 235                 &attr.get_normal_item().path,
 236                 MacroKind::Attr,
 237                 self.arenas.alloc_ast_paths(derives),
 238                 after_derive,
 239             ),
 240             InvocationKind::Bang { ref mac, .. } => (&mac.path, MacroKind::Bang, &[][..], false),
 241             InvocationKind::Derive { ref path, .. } => (path, MacroKind::Derive, &[][..], false),
 242             InvocationKind::DeriveContainer { ref derives, .. } => {
 243                 // Block expansion of the container until we resolve all derives in it.
 244                 // This is required for two reasons:
 245                 // - Derive helper attributes are in scope for the item to which the `#[derive]`
 246                 //   is applied, so they have to be produced by the container's expansion rather
 247                 //   than by individual derives.
 248                 // - Derives in the container need to know whether one of them is a built-in `Copy`.
 249                 // FIXME: Try to avoid repeated resolutions for derives here and in expansion.
 250                 let mut exts = Vec::new();
 251                 let mut helper_attrs = Vec::new();
 252                 for path in derives {
 253                     exts.push(
 254                         match self.resolve_macro_path(
 255                             path,
 256                             Some(MacroKind::Derive),
 257                             &parent_scope,
 258                             true,
 259                             force,
 260                         ) {
 261                             Ok((Some(ext), _)) => {
 262                                 let span = path
 263                                     .segments
 264                                     .last()
 265                                     .unwrap()
 266                                     .ident
 267                                     .span
 268                                     .normalize_to_macros_2_0();
 269                                 helper_attrs.extend(
 270                                     ext.helper_attrs.iter().map(|name| Ident::new(*name, span)),
 271                                 );
 272                                 if ext.is_derive_copy {
 273                                     self.add_derive_copy(invoc_id);
 274                                 }
 275                                 ext
 276                             }
 277                             Ok(_) | Err(Determinacy::Determined) => {
 278                                 self.dummy_ext(MacroKind::Derive)
 279                             }
 280                             Err(Determinacy::Undetermined) => return Err(Indeterminate),
 281                         },
 282                     )
 283                 }
 284                 self.helper_attrs.insert(invoc_id, helper_attrs);
 285                 return Ok(InvocationRes::DeriveContainer(exts));
 286             }
 287         };
 288
 289         // Derives are not included when `invocations` are collected, so we have to add them here.
 290         let parent_scope = &ParentScope { derives, ..parent_scope };
 291         let (ext, res) = self.smart_resolve_macro_path(path, kind, parent_scope, force)?;
 292
 293         let span = invoc.span();
 294         invoc_id.set_expn_data(ext.expn_data(parent_scope.expansion, span, fast_print_path(path)));
 295
 296         if let Res::Def(_, def_id) = res {
 297             if after_derive {
 298                 self.session.span_err(span, "macro attributes must be placed before `#[derive]`");
 299             }
 300             self.macro_defs.insert(invoc_id, def_id);
 301             let normal_module_def_id = self.macro_def_scope(invoc_id).normal_ancestor_id;
 302             self.definitions.add_parent_module_of_macro_def(invoc_id, normal_module_def_id);
 303         }
 304
 305         match invoc.fragment_kind {
 306             AstFragmentKind::Arms
 307             | AstFragmentKind::Fields
 308             | AstFragmentKind::FieldPats
 309             | AstFragmentKind::GenericParams
 310             | AstFragmentKind::Params
 311             | AstFragmentKind::StructFields
 312             | AstFragmentKind::Variants => {
 313                 if let Res::Def(..) = res {
 314                     self.session.span_err(
 315                         span,
 316                         &format!(
 317                             "expected an inert attribute, found {} {}",
 318                             res.article(),
 319                             res.descr()
 320                         ),
 321                     );
 322                     return Ok(InvocationRes::Single(self.dummy_ext(kind)));
 323                 }
 324             }
 325             _ => {}
 326         }
 327
 328         Ok(InvocationRes::Single(ext))
 329     }
 330
 331     fn check_unused_macros(&mut self) {
 332         for (&node_id, &span) in self.unused_macros.iter() {
 333             self.lint_buffer.buffer_lint(UNUSED_MACROS, node_id, span, "unused macro definition");
 334         }
 335     }
 336
 337     fn has_derive_copy(&self, expn_id: ExpnId) -> bool {
 338         self.containers_deriving_copy.contains(&expn_id)
 339     }
 340
 341     fn add_derive_copy(&mut self, expn_id: ExpnId) {
 342         self.containers_deriving_copy.insert(expn_id);
 343     }
 344
 345     // The function that implements the resolution logic of `#[cfg_accessible(path)]`.
 346     // Returns true if the path can certainly be resolved in one of three namespaces,
 347     // returns false if the path certainly cannot be resolved in any of the three namespaces.
 348     // Returns `Indeterminate` if we cannot give a certain answer yet.
 349     fn cfg_accessible(&mut self, expn_id: ExpnId, path: &ast::Path) -> Result<bool, Indeterminate> {
 350         let span = path.span;
 351         let path = &Segment::from_path(path);
 352         let parent_scope = self.invocation_parent_scopes[&expn_id];
 353
 354         let mut indeterminate = false;
 355         for ns in [TypeNS, ValueNS, MacroNS].iter().copied() {
 356             match self.resolve_path(path, Some(ns), &parent_scope, false, span, CrateLint::No) {
 357                 PathResult::Module(ModuleOrUniformRoot::Module(_)) => return Ok(true),
 358                 PathResult::NonModule(partial_res) if partial_res.unresolved_segments() == 0 => {
 359                     return Ok(true);
 360                 }
 361                 PathResult::Indeterminate => indeterminate = true,
 362                 // FIXME: `resolve_path` is not ready to report partially resolved paths
 363                 // correctly, so we just report an error if the path was reported as unresolved.
 364                 // This needs to be fixed for `cfg_accessible` to be useful.
 365                 PathResult::NonModule(..) | PathResult::Failed { .. } => {}
 366                 PathResult::Module(_) => panic!("unexpected path resolution"),
 367             }
 368         }
 369
 370         if indeterminate {
 371             return Err(Indeterminate);
 372         }
 373
 374         self.session
 375             .struct_span_err(span, "not sure whether the path is accessible or not")
 376             .span_note(span, "`cfg_accessible` is not fully implemented")
 377             .emit();
 378         Ok(false)
 379     }
 380 }
 381
 382 impl<'a> Resolver<'a> {
 383     /// Resolve macro path with error reporting and recovery.
 384     fn smart_resolve_macro_path(
 385         &mut self,
 386         path: &ast::Path,
 387         kind: MacroKind,
 388         parent_scope: &ParentScope<'a>,
 389         force: bool,
 390     ) -> Result<(Lrc<SyntaxExtension>, Res), Indeterminate> {
 391         let (ext, res) = match self.resolve_macro_path(path, Some(kind), parent_scope, true, force)
 392         {
 393             Ok((Some(ext), res)) => (ext, res),
 394             // Use dummy syntax extensions for unresolved macros for better recovery.
 395             Ok((None, res)) => (self.dummy_ext(kind), res),
 396             Err(Determinacy::Determined) => (self.dummy_ext(kind), Res::Err),
 397             Err(Determinacy::Undetermined) => return Err(Indeterminate),
 398         };
 399
 400         // Report errors and enforce feature gates for the resolved macro.
 401         let features = self.session.features_untracked();
 402         for segment in &path.segments {
 403             if let Some(args) = &segment.args {
 404                 self.session.span_err(args.span(), "generic arguments in macro path");
 405             }
 406             if kind == MacroKind::Attr
 407                 && !features.rustc_attrs
 408                 && segment.ident.as_str().starts_with("rustc")
 409             {
 410                 let msg =
 411                     "attributes starting with `rustc` are reserved for use by the `rustc` compiler";
 412                 feature_err(&self.session.parse_sess, sym::rustc_attrs, segment.ident.span, msg)
 413                     .emit();
 414             }
 415         }
 416
 417         match res {
 418             Res::Def(DefKind::Macro(_), def_id) => {
 419                 if let Some(node_id) = self.definitions.as_local_node_id(def_id) {
 420                     self.unused_macros.remove(&node_id);
 421                     if self.proc_macro_stubs.contains(&node_id) {
 422                         self.session.span_err(
 423                             path.span,
 424                             "can't use a procedural macro from the same crate that defines it",
 425                         );
 426                     }
 427                 }
 428             }
 429             Res::NonMacroAttr(..) | Res::Err => {}
 430             _ => panic!("expected `DefKind::Macro` or `Res::NonMacroAttr`"),
 431         };
 432
 433         self.check_stability_and_deprecation(&ext, path);
 434
 435         Ok(if ext.macro_kind() != kind {
 436             let expected = kind.descr_expected();
 437             let path_str = pprust::path_to_string(path);
 438             let msg = format!("expected {}, found {} `{}`", expected, res.descr(), path_str);
 439             self.session
 440                 .struct_span_err(path.span, &msg)
 441                 .span_label(path.span, format!("not {} {}", kind.article(), expected))
 442                 .emit();
 443             // Use dummy syntax extensions for unexpected macro kinds for better recovery.
 444             (self.dummy_ext(kind), Res::Err)
 445         } else {
 446             (ext, res)
 447         })
 448     }
 449
 450     pub fn resolve_macro_path(
 451         &mut self,
 452         path: &ast::Path,
 453         kind: Option<MacroKind>,
 454         parent_scope: &ParentScope<'a>,
 455         trace: bool,
 456         force: bool,
 457     ) -> Result<(Option<Lrc<SyntaxExtension>>, Res), Determinacy> {
 458         let path_span = path.span;
 459         let mut path = Segment::from_path(path);
 460
 461         // Possibly apply the macro helper hack
 462         if kind == Some(MacroKind::Bang)
 463             && path.len() == 1
 464             && path[0].ident.span.ctxt().outer_expn_data().local_inner_macros
 465         {
 466             let root = Ident::new(kw::DollarCrate, path[0].ident.span);
 467             path.insert(0, Segment::from_ident(root));
 468         }
 469
 470         let res = if path.len() > 1 {
 471             let res = match self.resolve_path(
 472                 &path,
 473                 Some(MacroNS),
 474                 parent_scope,
 475                 false,
 476                 path_span,
 477                 CrateLint::No,
 478             ) {
 479                 PathResult::NonModule(path_res) if path_res.unresolved_segments() == 0 => {
 480                     Ok(path_res.base_res())
 481                 }
 482                 PathResult::Indeterminate if !force => return Err(Determinacy::Undetermined),
 483                 PathResult::NonModule(..)
 484                 | PathResult::Indeterminate
 485                 | PathResult::Failed { .. } => Err(Determinacy::Determined),
 486                 PathResult::Module(..) => unreachable!(),
 487             };
 488
 489             if trace {
 490                 let kind = kind.expect("macro kind must be specified if tracing is enabled");
 491                 self.multi_segment_macro_resolutions.push((
 492                     path,
 493                     path_span,
 494                     kind,
 495                     *parent_scope,
 496                     res.ok(),
 497                 ));
 498             }
 499
 500             self.prohibit_imported_non_macro_attrs(None, res.ok(), path_span);
 501             res
 502         } else {
 503             let scope_set = kind.map_or(ScopeSet::All(MacroNS, false), ScopeSet::Macro);
 504             let binding = self.early_resolve_ident_in_lexical_scope(
 505                 path[0].ident,
 506                 scope_set,
 507                 parent_scope,
 508                 false,
 509                 force,
 510                 path_span,
 511             );
 512             if let Err(Determinacy::Undetermined) = binding {
 513                 return Err(Determinacy::Undetermined);
 514             }
 515
 516             if trace {
 517                 let kind = kind.expect("macro kind must be specified if tracing is enabled");
 518                 self.single_segment_macro_resolutions.push((
 519                     path[0].ident,
 520                     kind,
 521                     *parent_scope,
 522                     binding.ok(),
 523                 ));
 524             }
 525
 526             let res = binding.map(|binding| binding.res());
 527             self.prohibit_imported_non_macro_attrs(binding.ok(), res.ok(), path_span);
 528             res
 529         };
 530
 531         res.map(|res| (self.get_macro(res), res))
 532     }
 533
 534     // Resolve an identifier in lexical scope.
 535     // This is a variation of `fn resolve_ident_in_lexical_scope` that can be run during
 536     // expansion and import resolution (perhaps they can be merged in the future).
 537     // The function is used for resolving initial segments of macro paths (e.g., `foo` in
 538     // `foo::bar!(); or `foo!();`) and also for import paths on 2018 edition.
 539     crate fn early_resolve_ident_in_lexical_scope(
 540         &mut self,
 541         orig_ident: Ident,
 542         scope_set: ScopeSet,
 543         parent_scope: &ParentScope<'a>,
 544         record_used: bool,
 545         force: bool,
 546         path_span: Span,
 547     ) -> Result<&'a NameBinding<'a>, Determinacy> {
 548         bitflags::bitflags! {
 549             struct Flags: u8 {
 550                 const MACRO_RULES          = 1 << 0;
 551                 const MODULE               = 1 << 1;
 552                 const DERIVE_HELPER_COMPAT = 1 << 2;
 553                 const MISC_SUGGEST_CRATE   = 1 << 3;
 554                 const MISC_SUGGEST_SELF    = 1 << 4;
 555                 const MISC_FROM_PRELUDE    = 1 << 5;
 556             }
 557         }
 558
 559         assert!(force || !record_used); // `record_used` implies `force`
 560
 561         // Make sure `self`, `super` etc produce an error when passed to here.
 562         if orig_ident.is_path_segment_keyword() {
 563             return Err(Determinacy::Determined);
 564         }
 565
 566         let (ns, macro_kind, is_import) = match scope_set {
 567             ScopeSet::All(ns, is_import) => (ns, None, is_import),
 568             ScopeSet::AbsolutePath(ns) => (ns, None, false),
 569             ScopeSet::Macro(macro_kind) => (MacroNS, Some(macro_kind), false),
 570         };
 571
 572         // This is *the* result, resolution from the scope closest to the resolved identifier.
 573         // However, sometimes this result is "weak" because it comes from a glob import or
 574         // a macro expansion, and in this case it cannot shadow names from outer scopes, e.g.
 575         // mod m { ... } // solution in outer scope
 576         // {
 577         //     use prefix::*; // imports another `m` - innermost solution
 578         //                    // weak, cannot shadow the outer `m`, need to report ambiguity error
 579         //     m::mac!();
 580         // }
 581         // So we have to save the innermost solution and continue searching in outer scopes
 582         // to detect potential ambiguities.
 583         let mut innermost_result: Option<(&NameBinding<'_>, Flags)> = None;
 584         let mut determinacy = Determinacy::Determined;
 585
 586         // Go through all the scopes and try to resolve the name.
 587         let break_result = self.visit_scopes(
 588             scope_set,
 589             parent_scope,
 590             orig_ident,
 591             |this, scope, use_prelude, ident| {
 592                 let ok = |res, span, arenas| {
 593                     Ok((
 594                         (res, ty::Visibility::Public, span, ExpnId::root()).to_name_binding(arenas),
 595                         Flags::empty(),
 596                     ))
 597                 };
 598                 let result = match scope {
 599                     Scope::DeriveHelpers(expn_id) => {
 600                         if let Some(attr) = this
 601                             .helper_attrs
 602                             .get(&expn_id)
 603                             .and_then(|attrs| attrs.iter().rfind(|i| ident == **i))
 604                         {
 605                             let binding = (
 606                                 Res::NonMacroAttr(NonMacroAttrKind::DeriveHelper),
 607                                 ty::Visibility::Public,
 608                                 attr.span,
 609                                 expn_id,
 610                             )
 611                                 .to_name_binding(this.arenas);
 612                             Ok((binding, Flags::empty()))
 613                         } else {
 614                             Err(Determinacy::Determined)
 615                         }
 616                     }
 617                     Scope::DeriveHelpersCompat => {
 618                         let mut result = Err(Determinacy::Determined);
 619                         for derive in parent_scope.derives {
 620                             let parent_scope = &ParentScope { derives: &[], ..*parent_scope };
 621                             match this.resolve_macro_path(
 622                                 derive,
 623                                 Some(MacroKind::Derive),
 624                                 parent_scope,
 625                                 true,
 626                                 force,
 627                             ) {
 628                                 Ok((Some(ext), _)) => {
 629                                     if ext.helper_attrs.contains(&ident.name) {
 630                                         let binding = (
 631                                             Res::NonMacroAttr(NonMacroAttrKind::DeriveHelper),
 632                                             ty::Visibility::Public,
 633                                             derive.span,
 634                                             ExpnId::root(),
 635                                         )
 636                                             .to_name_binding(this.arenas);
 637                                         result = Ok((binding, Flags::DERIVE_HELPER_COMPAT));
 638                                         break;
 639                                     }
 640                                 }
 641                                 Ok(_) | Err(Determinacy::Determined) => {}
 642                                 Err(Determinacy::Undetermined) => {
 643                                     result = Err(Determinacy::Undetermined)
 644                                 }
 645                             }
 646                         }
 647                         result
 648                     }
 649                     Scope::MacroRules(macro_rules_scope) => match macro_rules_scope {
 650                         MacroRulesScope::Binding(macro_rules_binding)
 651                             if ident == macro_rules_binding.ident =>
 652                         {
 653                             Ok((macro_rules_binding.binding, Flags::MACRO_RULES))
 654                         }
 655                         MacroRulesScope::Invocation(invoc_id)
 656                             if !this.output_macro_rules_scopes.contains_key(&invoc_id) =>
 657                         {
 658                             Err(Determinacy::Undetermined)
 659                         }
 660                         _ => Err(Determinacy::Determined),
 661                     },
 662                     Scope::CrateRoot => {
 663                         let root_ident = Ident::new(kw::PathRoot, ident.span);
 664                         let root_module = this.resolve_crate_root(root_ident);
 665                         let binding = this.resolve_ident_in_module_ext(
 666                             ModuleOrUniformRoot::Module(root_module),
 667                             ident,
 668                             ns,
 669                             parent_scope,
 670                             record_used,
 671                             path_span,
 672                         );
 673                         match binding {
 674                             Ok(binding) => Ok((binding, Flags::MODULE | Flags::MISC_SUGGEST_CRATE)),
 675                             Err((Determinacy::Undetermined, Weak::No)) => {
 676                                 return Some(Err(Determinacy::determined(force)));
 677                             }
 678                             Err((Determinacy::Undetermined, Weak::Yes)) => {
 679                                 Err(Determinacy::Undetermined)
 680                             }
 681                             Err((Determinacy::Determined, _)) => Err(Determinacy::Determined),
 682                         }
 683                     }
 684                     Scope::Module(module) => {
 685                         let adjusted_parent_scope = &ParentScope { module, ..*parent_scope };
 686                         let binding = this.resolve_ident_in_module_unadjusted_ext(
 687                             ModuleOrUniformRoot::Module(module),
 688                             ident,
 689                             ns,
 690                             adjusted_parent_scope,
 691                             true,
 692                             record_used,
 693                             path_span,
 694                         );
 695                         match binding {
 696                             Ok(binding) => {
 697                                 let misc_flags = if ptr::eq(module, this.graph_root) {
 698                                     Flags::MISC_SUGGEST_CRATE
 699                                 } else if module.is_normal() {
 700                                     Flags::MISC_SUGGEST_SELF
 701                                 } else {
 702                                     Flags::empty()
 703                                 };
 704                                 Ok((binding, Flags::MODULE | misc_flags))
 705                             }
 706                             Err((Determinacy::Undetermined, Weak::No)) => {
 707                                 return Some(Err(Determinacy::determined(force)));
 708                             }
 709                             Err((Determinacy::Undetermined, Weak::Yes)) => {
 710                                 Err(Determinacy::Undetermined)
 711                             }
 712                             Err((Determinacy::Determined, _)) => Err(Determinacy::Determined),
 713                         }
 714                     }
 715                     Scope::RegisteredAttrs => match this.registered_attrs.get(&ident).cloned() {
 716                         Some(ident) => ok(
 717                             Res::NonMacroAttr(NonMacroAttrKind::Registered),
 718                             ident.span,
 719                             this.arenas,
 720                         ),
 721                         None => Err(Determinacy::Determined),
 722                     },
 723                     Scope::MacroUsePrelude => {
 724                         match this.macro_use_prelude.get(&ident.name).cloned() {
 725                             Some(binding) => Ok((binding, Flags::MISC_FROM_PRELUDE)),
 726                             None => Err(Determinacy::determined(
 727                                 this.graph_root.unexpanded_invocations.borrow().is_empty(),
 728                             )),
 729                         }
 730                     }
 731                     Scope::BuiltinAttrs => {
 732                         if is_builtin_attr_name(ident.name) {
 733                             ok(Res::NonMacroAttr(NonMacroAttrKind::Builtin), DUMMY_SP, this.arenas)
 734                         } else {
 735                             Err(Determinacy::Determined)
 736                         }
 737                     }
 738                     Scope::ExternPrelude => match this.extern_prelude_get(ident, !record_used) {
 739                         Some(binding) => Ok((binding, Flags::empty())),
 740                         None => Err(Determinacy::determined(
 741                             this.graph_root.unexpanded_invocations.borrow().is_empty(),
 742                         )),
 743                     },
 744                     Scope::ToolPrelude => match this.registered_tools.get(&ident).cloned() {
 745                         Some(ident) => ok(Res::ToolMod, ident.span, this.arenas),
 746                         None => Err(Determinacy::Determined),
 747                     },
 748                     Scope::StdLibPrelude => {
 749                         let mut result = Err(Determinacy::Determined);
 750                         if let Some(prelude) = this.prelude {
 751                             if let Ok(binding) = this.resolve_ident_in_module_unadjusted(
 752                                 ModuleOrUniformRoot::Module(prelude),
 753                                 ident,
 754                                 ns,
 755                                 parent_scope,
 756                                 false,
 757                                 path_span,
 758                             ) {
 759                                 if use_prelude || this.is_builtin_macro(binding.res()) {
 760                                     result = Ok((binding, Flags::MISC_FROM_PRELUDE));
 761                                 }
 762                             }
 763                         }
 764                         result
 765                     }
 766                     Scope::BuiltinTypes => {
 767                         match this.primitive_type_table.primitive_types.get(&ident.name).cloned() {
 768                             Some(prim_ty) => ok(Res::PrimTy(prim_ty), DUMMY_SP, this.arenas),
 769                             None => Err(Determinacy::Determined),
 770                         }
 771                     }
 772                 };
 773
 774                 match result {
 775                     Ok((binding, flags))
 776                         if sub_namespace_match(binding.macro_kind(), macro_kind) =>
 777                     {
 778                         if !record_used {
 779                             return Some(Ok(binding));
 780                         }
 781
 782                         if let Some((innermost_binding, innermost_flags)) = innermost_result {
 783                             // Found another solution, if the first one was "weak", report an error.
 784                             let (res, innermost_res) = (binding.res(), innermost_binding.res());
 785                             if res != innermost_res {
 786                                 let builtin = Res::NonMacroAttr(NonMacroAttrKind::Builtin);
 787                                 let is_derive_helper_compat = |res, flags: Flags| {
 788                                     res == Res::NonMacroAttr(NonMacroAttrKind::DeriveHelper)
 789                                         && flags.contains(Flags::DERIVE_HELPER_COMPAT)
 790                                 };
 791
 792                                 let ambiguity_error_kind = if is_import {
 793                                     Some(AmbiguityKind::Import)
 794                                 } else if innermost_res == builtin || res == builtin {
 795                                     Some(AmbiguityKind::BuiltinAttr)
 796                                 } else if is_derive_helper_compat(innermost_res, innermost_flags)
 797                                     || is_derive_helper_compat(res, flags)
 798                                 {
 799                                     Some(AmbiguityKind::DeriveHelper)
 800                                 } else if innermost_flags.contains(Flags::MACRO_RULES)
 801                                     && flags.contains(Flags::MODULE)
 802                                     && !this.disambiguate_macro_rules_vs_modularized(
 803                                         innermost_binding,
 804                                         binding,
 805                                     )
 806                                     || flags.contains(Flags::MACRO_RULES)
 807                                         && innermost_flags.contains(Flags::MODULE)
 808                                         && !this.disambiguate_macro_rules_vs_modularized(
 809                                             binding,
 810                                             innermost_binding,
 811                                         )
 812                                 {
 813                                     Some(AmbiguityKind::MacroRulesVsModularized)
 814                                 } else if innermost_binding.is_glob_import() {
 815                                     Some(AmbiguityKind::GlobVsOuter)
 816                                 } else if innermost_binding
 817                                     .may_appear_after(parent_scope.expansion, binding)
 818                                 {
 819                                     Some(AmbiguityKind::MoreExpandedVsOuter)
 820                                 } else {
 821                                     None
 822                                 };
 823                                 if let Some(kind) = ambiguity_error_kind {
 824                                     let misc = |f: Flags| {
 825                                         if f.contains(Flags::MISC_SUGGEST_CRATE) {
 826                                             AmbiguityErrorMisc::SuggestCrate
 827                                         } else if f.contains(Flags::MISC_SUGGEST_SELF) {
 828                                             AmbiguityErrorMisc::SuggestSelf
 829                                         } else if f.contains(Flags::MISC_FROM_PRELUDE) {
 830                                             AmbiguityErrorMisc::FromPrelude
 831                                         } else {
 832                                             AmbiguityErrorMisc::None
 833                                         }
 834                                     };
 835                                     this.ambiguity_errors.push(AmbiguityError {
 836                                         kind,
 837                                         ident: orig_ident,
 838                                         b1: innermost_binding,
 839                                         b2: binding,
 840                                         misc1: misc(innermost_flags),
 841                                         misc2: misc(flags),
 842                                     });
 843                                     return Some(Ok(innermost_binding));
 844                                 }
 845                             }
 846                         } else {
 847                             // Found the first solution.
 848                             innermost_result = Some((binding, flags));
 849                         }
 850                     }
 851                     Ok(..) | Err(Determinacy::Determined) => {}
 852                     Err(Determinacy::Undetermined) => determinacy = Determinacy::Undetermined,
 853                 }
 854
 855                 None
 856             },
 857         );
 858
 859         if let Some(break_result) = break_result {
 860             return break_result;
 861         }
 862
 863         // The first found solution was the only one, return it.
 864         if let Some((binding, _)) = innermost_result {
 865             return Ok(binding);
 866         }
 867
 868         Err(Determinacy::determined(determinacy == Determinacy::Determined || force))
 869     }
 870
 871     crate fn finalize_macro_resolutions(&mut self) {
 872         let check_consistency = |this: &mut Self,
 873                                  path: &[Segment],
 874                                  span,
 875                                  kind: MacroKind,
 876                                  initial_res: Option<Res>,
 877                                  res: Res| {
 878             if let Some(initial_res) = initial_res {
 879                 if res != initial_res && res != Res::Err && this.ambiguity_errors.is_empty() {
 880                     // Make sure compilation does not succeed if preferred macro resolution
 881                     // has changed after the macro had been expanded. In theory all such
 882                     // situations should be reported as ambiguity errors, so this is a bug.
 883                     span_bug!(span, "inconsistent resolution for a macro");
 884                 }
 885             } else {
 886                 // It's possible that the macro was unresolved (indeterminate) and silently
 887                 // expanded into a dummy fragment for recovery during expansion.
 888                 // Now, post-expansion, the resolution may succeed, but we can't change the
 889                 // past and need to report an error.
 890                 // However, non-speculative `resolve_path` can successfully return private items
 891                 // even if speculative `resolve_path` returned nothing previously, so we skip this
 892                 // less informative error if the privacy error is reported elsewhere.
 893                 if this.privacy_errors.is_empty() {
 894                     let msg = format!(
 895                         "cannot determine resolution for the {} `{}`",
 896                         kind.descr(),
 897                         Segment::names_to_string(path)
 898                     );
 899                     let msg_note = "import resolution is stuck, try simplifying macro imports";
 900                     this.session.struct_span_err(span, &msg).note(msg_note).emit();
 901                 }
 902             }
 903         };
 904
 905         let macro_resolutions = mem::take(&mut self.multi_segment_macro_resolutions);
 906         for (mut path, path_span, kind, parent_scope, initial_res) in macro_resolutions {
 907             // FIXME: Path resolution will ICE if segment IDs present.
 908             for seg in &mut path {
 909                 seg.id = None;
 910             }
 911             match self.resolve_path(
 912                 &path,
 913                 Some(MacroNS),
 914                 &parent_scope,
 915                 true,
 916                 path_span,
 917                 CrateLint::No,
 918             ) {
 919                 PathResult::NonModule(path_res) if path_res.unresolved_segments() == 0 => {
 920                     let res = path_res.base_res();
 921                     check_consistency(self, &path, path_span, kind, initial_res, res);
 922                 }
 923                 path_res @ PathResult::NonModule(..) | path_res @ PathResult::Failed { .. } => {
 924                     let (span, label) = if let PathResult::Failed { span, label, .. } = path_res {
 925                         (span, label)
 926                     } else {
 927                         (
 928                             path_span,
 929                             format!(
 930                                 "partially resolved path in {} {}",
 931                                 kind.article(),
 932                                 kind.descr()
 933                             ),
 934                         )
 935                     };
 936                     self.report_error(
 937                         span,
 938                         ResolutionError::FailedToResolve { label, suggestion: None },
 939                     );
 940                 }
 941                 PathResult::Module(..) | PathResult::Indeterminate => unreachable!(),
 942             }
 943         }
 944
 945         let macro_resolutions = mem::take(&mut self.single_segment_macro_resolutions);
 946         for (ident, kind, parent_scope, initial_binding) in macro_resolutions {
 947             match self.early_resolve_ident_in_lexical_scope(
 948                 ident,
 949                 ScopeSet::Macro(kind),
 950                 &parent_scope,
 951                 true,
 952                 true,
 953                 ident.span,
 954             ) {
 955                 Ok(binding) => {
 956                     let initial_res = initial_binding.map(|initial_binding| {
 957                         self.record_use(ident, MacroNS, initial_binding, false);
 958                         initial_binding.res()
 959                     });
 960                     let res = binding.res();
 961                     let seg = Segment::from_ident(ident);
 962                     check_consistency(self, &[seg], ident.span, kind, initial_res, res);
 963                 }
 964                 Err(..) => {
 965                     let expected = kind.descr_expected();
 966                     let msg = format!("cannot find {} `{}` in this scope", expected, ident);
 967                     let mut err = self.session.struct_span_err(ident.span, &msg);
 968                     self.unresolved_macro_suggestions(&mut err, kind, &parent_scope, ident);
 969                     err.emit();
 970                 }
 971             }
 972         }
 973
 974         let builtin_attrs = mem::take(&mut self.builtin_attrs);
 975         for (ident, parent_scope) in builtin_attrs {
 976             let _ = self.early_resolve_ident_in_lexical_scope(
 977                 ident,
 978                 ScopeSet::Macro(MacroKind::Attr),
 979                 &parent_scope,
 980                 true,
 981                 true,
 982                 ident.span,
 983             );
 984         }
 985     }
 986
 987     fn check_stability_and_deprecation(&mut self, ext: &SyntaxExtension, path: &ast::Path) {
 988         let span = path.span;
 989         if let Some(stability) = &ext.stability {
 990             if let StabilityLevel::Unstable { reason, issue, is_soft } = stability.level {
 991                 let feature = stability.feature;
 992                 if !self.active_features.contains(&feature) && !span.allows_unstable(feature) {
 993                     let node_id = ast::CRATE_NODE_ID;
 994                     let lint_buffer = &mut self.lint_buffer;
 995                     let soft_handler =
 996                         |lint, span, msg: &_| lint_buffer.buffer_lint(lint, node_id, span, msg);
 997                     stability::report_unstable(
 998                         self.session,
 999                         feature,
1000                         reason,
1001                         issue,
1002                         is_soft,
1003                         span,
1004                         soft_handler,
1005                     );
1006                 }
1007             }
1008             if let Some(depr) = &stability.rustc_depr {
1009                 let path = pprust::path_to_string(path);
1010                 let (message, lint) = stability::rustc_deprecation_message(depr, &path);
1011                 stability::early_report_deprecation(
1012                     &mut self.lint_buffer,
1013                     &message,
1014                     depr.suggestion,
1015                     lint,
1016                     span,
1017                 );
1018             }
1019         }
1020         if let Some(depr) = &ext.deprecation {
1021             let path = pprust::path_to_string(&path);
1022             let (message, lint) = stability::deprecation_message(depr, &path);
1023             stability::early_report_deprecation(&mut self.lint_buffer, &message, None, lint, span);
1024         }
1025     }
1026
1027     fn prohibit_imported_non_macro_attrs(
1028         &self,
1029         binding: Option<&'a NameBinding<'a>>,
1030         res: Option<Res>,
1031         span: Span,
1032     ) {
1033         if let Some(Res::NonMacroAttr(kind)) = res {
1034             if kind != NonMacroAttrKind::Tool && binding.map_or(true, |b| b.is_import()) {
1035                 let msg =
1036                     format!("cannot use {} {} through an import", kind.article(), kind.descr());
1037                 let mut err = self.session.struct_span_err(span, &msg);
1038                 if let Some(binding) = binding {
1039                     err.span_note(binding.span, &format!("the {} imported here", kind.descr()));
1040                 }
1041                 err.emit();
1042             }
1043         }
1044     }
1045
1046     crate fn check_reserved_macro_name(&mut self, ident: Ident, res: Res) {
1047         // Reserve some names that are not quite covered by the general check
1048         // performed on `Resolver::builtin_attrs`.
1049         if ident.name == sym::cfg || ident.name == sym::cfg_attr || ident.name == sym::derive {
1050             let macro_kind = self.get_macro(res).map(|ext| ext.macro_kind());
1051             if macro_kind.is_some() && sub_namespace_match(macro_kind, Some(MacroKind::Attr)) {
1052                 self.session.span_err(
1053                     ident.span,
1054                     &format!("name `{}` is reserved in attribute namespace", ident),
1055                 );
1056             }
1057         }
1058     }
1059
1060     /// Compile the macro into a `SyntaxExtension` and possibly replace
1061     /// its expander to a pre-defined one for built-in macros.
1062     crate fn compile_macro(&mut self, item: &ast::Item, edition: Edition) -> SyntaxExtension {
1063         let mut result = compile_declarative_macro(
1064             &self.session.parse_sess,
1065             self.session.features_untracked(),
1066             item,
1067             edition,
1068         );
1069
1070         if result.is_builtin {
1071             // The macro was marked with `#[rustc_builtin_macro]`.
1072             if let Some(ext) = self.builtin_macros.remove(&item.ident.name) {
1073                 // The macro is a built-in, replace its expander function
1074                 // while still taking everything else from the source code.
1075                 result.kind = ext.kind;
1076             } else {
1077                 let msg = format!("cannot find a built-in macro with name `{}`", item.ident);
1078                 self.session.span_err(item.span, &msg);
1079             }
1080         }
1081
1082         result
1083     }
1084 }