compiler/rustc_resolve/src/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::{BuiltinMacroState, Determinacy};
   7 use crate::{DeriveData, Finalize, ParentScope, ResolutionError, Resolver, ScopeSet};
   8 use crate::{ModuleKind, ModuleOrUniformRoot, NameBinding, PathResult, Segment};
   9 use rustc_ast::{self as ast, Inline, ItemKind, ModKind, NodeId};
  10 use rustc_ast_pretty::pprust;
  11 use rustc_attr::StabilityLevel;
  12 use rustc_data_structures::fx::FxHashSet;
  13 use rustc_data_structures::intern::Interned;
  14 use rustc_data_structures::sync::Lrc;
  15 use rustc_errors::struct_span_err;
  16 use rustc_expand::base::{Annotatable, DeriveResolutions, Indeterminate, ResolverExpand};
  17 use rustc_expand::base::{SyntaxExtension, SyntaxExtensionKind};
  18 use rustc_expand::compile_declarative_macro;
  19 use rustc_expand::expand::{AstFragment, Invocation, InvocationKind, SupportsMacroExpansion};
  20 use rustc_hir::def::{self, DefKind, NonMacroAttrKind};
  21 use rustc_hir::def_id::{CrateNum, LocalDefId};
  22 use rustc_middle::middle::stability;
  23 use rustc_middle::ty::RegisteredTools;
  24 use rustc_session::lint::builtin::{LEGACY_DERIVE_HELPERS, SOFT_UNSTABLE};
  25 use rustc_session::lint::builtin::{UNUSED_MACROS, UNUSED_MACRO_RULES};
  26 use rustc_session::lint::BuiltinLintDiagnostics;
  27 use rustc_session::parse::feature_err;
  28 use rustc_session::Session;
  29 use rustc_span::edition::Edition;
  30 use rustc_span::hygiene::{self, ExpnData, ExpnKind, LocalExpnId};
  31 use rustc_span::hygiene::{AstPass, MacroKind};
  32 use rustc_span::symbol::{kw, sym, Ident, Symbol};
  33 use rustc_span::{Span, DUMMY_SP};
  34 use std::cell::Cell;
  35 use std::mem;
  36
  37 type Res = def::Res<NodeId>;
  38
  39 /// Binding produced by a `macro_rules` item.
  40 /// Not modularized, can shadow previous `macro_rules` bindings, etc.
  41 #[derive(Debug)]
  42 pub struct MacroRulesBinding<'a> {
  43     pub(crate) binding: &'a NameBinding<'a>,
  44     /// `macro_rules` scope into which the `macro_rules` item was planted.
  45     pub(crate) parent_macro_rules_scope: MacroRulesScopeRef<'a>,
  46     pub(crate) ident: Ident,
  47 }
  48
  49 /// The scope introduced by a `macro_rules!` macro.
  50 /// This starts at the macro's definition and ends at the end of the macro's parent
  51 /// module (named or unnamed), or even further if it escapes with `#[macro_use]`.
  52 /// Some macro invocations need to introduce `macro_rules` scopes too because they
  53 /// can potentially expand into macro definitions.
  54 #[derive(Copy, Clone, Debug)]
  55 pub enum MacroRulesScope<'a> {
  56     /// Empty "root" scope at the crate start containing no names.
  57     Empty,
  58     /// The scope introduced by a `macro_rules!` macro definition.
  59     Binding(&'a MacroRulesBinding<'a>),
  60     /// The scope introduced by a macro invocation that can potentially
  61     /// create a `macro_rules!` macro definition.
  62     Invocation(LocalExpnId),
  63 }
  64
  65 /// `macro_rules!` scopes are always kept by reference and inside a cell.
  66 /// The reason is that we update scopes with value `MacroRulesScope::Invocation(invoc_id)`
  67 /// in-place after `invoc_id` gets expanded.
  68 /// This helps to avoid uncontrollable growth of `macro_rules!` scope chains,
  69 /// which usually grow linearly with the number of macro invocations
  70 /// in a module (including derives) and hurt performance.
  71 pub(crate) type MacroRulesScopeRef<'a> = Interned<'a, Cell<MacroRulesScope<'a>>>;
  72
  73 /// Macro namespace is separated into two sub-namespaces, one for bang macros and
  74 /// one for attribute-like macros (attributes, derives).
  75 /// We ignore resolutions from one sub-namespace when searching names in scope for another.
  76 pub(crate) fn sub_namespace_match(
  77     candidate: Option<MacroKind>,
  78     requirement: Option<MacroKind>,
  79 ) -> bool {
  80     #[derive(PartialEq)]
  81     enum SubNS {
  82         Bang,
  83         AttrLike,
  84     }
  85     let sub_ns = |kind| match kind {
  86         MacroKind::Bang => SubNS::Bang,
  87         MacroKind::Attr | MacroKind::Derive => SubNS::AttrLike,
  88     };
  89     let candidate = candidate.map(sub_ns);
  90     let requirement = requirement.map(sub_ns);
  91     // "No specific sub-namespace" means "matches anything" for both requirements and candidates.
  92     candidate.is_none() || requirement.is_none() || candidate == requirement
  93 }
  94
  95 // We don't want to format a path using pretty-printing,
  96 // `format!("{}", path)`, because that tries to insert
  97 // line-breaks and is slow.
  98 fn fast_print_path(path: &ast::Path) -> Symbol {
  99     if path.segments.len() == 1 {
 100         path.segments[0].ident.name
 101     } else {
 102         let mut path_str = String::with_capacity(64);
 103         for (i, segment) in path.segments.iter().enumerate() {
 104             if i != 0 {
 105                 path_str.push_str("::");
 106             }
 107             if segment.ident.name != kw::PathRoot {
 108                 path_str.push_str(segment.ident.as_str())
 109             }
 110         }
 111         Symbol::intern(&path_str)
 112     }
 113 }
 114
 115 /// The code common between processing `#![register_tool]` and `#![register_attr]`.
 116 fn registered_idents(
 117     sess: &Session,
 118     attrs: &[ast::Attribute],
 119     attr_name: Symbol,
 120     descr: &str,
 121 ) -> FxHashSet<Ident> {
 122     let mut registered = FxHashSet::default();
 123     for attr in sess.filter_by_name(attrs, attr_name) {
 124         for nested_meta in attr.meta_item_list().unwrap_or_default() {
 125             match nested_meta.ident() {
 126                 Some(ident) => {
 127                     if let Some(old_ident) = registered.replace(ident) {
 128                         let msg = format!("{} `{}` was already registered", descr, ident);
 129                         sess.struct_span_err(ident.span, &msg)
 130                             .span_label(old_ident.span, "already registered here")
 131                             .emit();
 132                     }
 133                 }
 134                 None => {
 135                     let msg = format!("`{}` only accepts identifiers", attr_name);
 136                     let span = nested_meta.span();
 137                     sess.struct_span_err(span, &msg).span_label(span, "not an identifier").emit();
 138                 }
 139             }
 140         }
 141     }
 142     registered
 143 }
 144
 145 pub(crate) fn registered_attrs_and_tools(
 146     sess: &Session,
 147     attrs: &[ast::Attribute],
 148 ) -> (FxHashSet<Ident>, FxHashSet<Ident>) {
 149     let registered_attrs = registered_idents(sess, attrs, sym::register_attr, "attribute");
 150     let mut registered_tools = registered_idents(sess, attrs, sym::register_tool, "tool");
 151     // We implicitly add `rustfmt` and `clippy` to known tools,
 152     // but it's not an error to register them explicitly.
 153     let predefined_tools = [sym::clippy, sym::rustfmt];
 154     registered_tools.extend(predefined_tools.iter().cloned().map(Ident::with_dummy_span));
 155     (registered_attrs, registered_tools)
 156 }
 157
 158 // Some feature gates for inner attributes are reported as lints for backward compatibility.
 159 fn soft_custom_inner_attributes_gate(path: &ast::Path, invoc: &Invocation) -> bool {
 160     match &path.segments[..] {
 161         // `#![test]`
 162         [seg] if seg.ident.name == sym::test => return true,
 163         // `#![rustfmt::skip]` on out-of-line modules
 164         [seg1, seg2] if seg1.ident.name == sym::rustfmt && seg2.ident.name == sym::skip => {
 165             if let InvocationKind::Attr { item, .. } = &invoc.kind {
 166                 if let Annotatable::Item(item) = item {
 167                     if let ItemKind::Mod(_, ModKind::Loaded(_, Inline::No, _)) = item.kind {
 168                         return true;
 169                     }
 170                 }
 171             }
 172         }
 173         _ => {}
 174     }
 175     false
 176 }
 177
 178 impl<'a> ResolverExpand for Resolver<'a> {
 179     fn next_node_id(&mut self) -> NodeId {
 180         self.next_node_id()
 181     }
 182
 183     fn invocation_parent(&self, id: LocalExpnId) -> LocalDefId {
 184         self.invocation_parents[&id].0
 185     }
 186
 187     fn resolve_dollar_crates(&mut self) {
 188         hygiene::update_dollar_crate_names(|ctxt| {
 189             let ident = Ident::new(kw::DollarCrate, DUMMY_SP.with_ctxt(ctxt));
 190             match self.resolve_crate_root(ident).kind {
 191                 ModuleKind::Def(.., name) if name != kw::Empty => name,
 192                 _ => kw::Crate,
 193             }
 194         });
 195     }
 196
 197     fn visit_ast_fragment_with_placeholders(
 198         &mut self,
 199         expansion: LocalExpnId,
 200         fragment: &AstFragment,
 201     ) {
 202         // Integrate the new AST fragment into all the definition and module structures.
 203         // We are inside the `expansion` now, but other parent scope components are still the same.
 204         let parent_scope = ParentScope { expansion, ..self.invocation_parent_scopes[&expansion] };
 205         let output_macro_rules_scope = self.build_reduced_graph(fragment, parent_scope);
 206         self.output_macro_rules_scopes.insert(expansion, output_macro_rules_scope);
 207
 208         parent_scope.module.unexpanded_invocations.borrow_mut().remove(&expansion);
 209     }
 210
 211     fn register_builtin_macro(&mut self, name: Symbol, ext: SyntaxExtensionKind) {
 212         if self.builtin_macros.insert(name, BuiltinMacroState::NotYetSeen(ext)).is_some() {
 213             self.session
 214                 .diagnostic()
 215                 .bug(&format!("built-in macro `{}` was already registered", name));
 216         }
 217     }
 218
 219     // Create a new Expansion with a definition site of the provided module, or
 220     // a fake empty `#[no_implicit_prelude]` module if no module is provided.
 221     fn expansion_for_ast_pass(
 222         &mut self,
 223         call_site: Span,
 224         pass: AstPass,
 225         features: &[Symbol],
 226         parent_module_id: Option<NodeId>,
 227     ) -> LocalExpnId {
 228         let parent_module =
 229             parent_module_id.map(|module_id| self.local_def_id(module_id).to_def_id());
 230         let expn_id = LocalExpnId::fresh(
 231             ExpnData::allow_unstable(
 232                 ExpnKind::AstPass(pass),
 233                 call_site,
 234                 self.session.edition(),
 235                 features.into(),
 236                 None,
 237                 parent_module,
 238             ),
 239             self.create_stable_hashing_context(),
 240         );
 241
 242         let parent_scope =
 243             parent_module.map_or(self.empty_module, |def_id| self.expect_module(def_id));
 244         self.ast_transform_scopes.insert(expn_id, parent_scope);
 245
 246         expn_id
 247     }
 248
 249     fn resolve_imports(&mut self) {
 250         ImportResolver { r: self }.resolve_imports()
 251     }
 252
 253     fn resolve_macro_invocation(
 254         &mut self,
 255         invoc: &Invocation,
 256         eager_expansion_root: LocalExpnId,
 257         force: bool,
 258     ) -> Result<Lrc<SyntaxExtension>, Indeterminate> {
 259         let invoc_id = invoc.expansion_data.id;
 260         let parent_scope = match self.invocation_parent_scopes.get(&invoc_id) {
 261             Some(parent_scope) => *parent_scope,
 262             None => {
 263                 // If there's no entry in the table, then we are resolving an eagerly expanded
 264                 // macro, which should inherit its parent scope from its eager expansion root -
 265                 // the macro that requested this eager expansion.
 266                 let parent_scope = *self
 267                     .invocation_parent_scopes
 268                     .get(&eager_expansion_root)
 269                     .expect("non-eager expansion without a parent scope");
 270                 self.invocation_parent_scopes.insert(invoc_id, parent_scope);
 271                 parent_scope
 272             }
 273         };
 274
 275         let (path, kind, inner_attr, derives) = match invoc.kind {
 276             InvocationKind::Attr { ref attr, ref derives, .. } => (
 277                 &attr.get_normal_item().path,
 278                 MacroKind::Attr,
 279                 attr.style == ast::AttrStyle::Inner,
 280                 self.arenas.alloc_ast_paths(derives),
 281             ),
 282             InvocationKind::Bang { ref mac, .. } => (&mac.path, MacroKind::Bang, false, &[][..]),
 283             InvocationKind::Derive { ref path, .. } => (path, MacroKind::Derive, false, &[][..]),
 284         };
 285
 286         // Derives are not included when `invocations` are collected, so we have to add them here.
 287         let parent_scope = &ParentScope { derives, ..parent_scope };
 288         let supports_macro_expansion = invoc.fragment_kind.supports_macro_expansion();
 289         let node_id = invoc.expansion_data.lint_node_id;
 290         let (ext, res) = self.smart_resolve_macro_path(
 291             path,
 292             kind,
 293             supports_macro_expansion,
 294             inner_attr,
 295             parent_scope,
 296             node_id,
 297             force,
 298             soft_custom_inner_attributes_gate(path, invoc),
 299         )?;
 300
 301         let span = invoc.span();
 302         let def_id = res.opt_def_id();
 303         invoc_id.set_expn_data(
 304             ext.expn_data(
 305                 parent_scope.expansion,
 306                 span,
 307                 fast_print_path(path),
 308                 def_id,
 309                 def_id.map(|def_id| self.macro_def_scope(def_id).nearest_parent_mod()),
 310             ),
 311             self.create_stable_hashing_context(),
 312         );
 313
 314         Ok(ext)
 315     }
 316
 317     fn record_macro_rule_usage(&mut self, id: NodeId, rule_i: usize) {
 318         let did = self.local_def_id(id);
 319         self.unused_macro_rules.remove(&(did, rule_i));
 320     }
 321
 322     fn check_unused_macros(&mut self) {
 323         for (_, &(node_id, ident)) in self.unused_macros.iter() {
 324             self.lint_buffer.buffer_lint(
 325                 UNUSED_MACROS,
 326                 node_id,
 327                 ident.span,
 328                 &format!("unused macro definition: `{}`", ident.name),
 329             );
 330         }
 331         for (&(def_id, arm_i), &(ident, rule_span)) in self.unused_macro_rules.iter() {
 332             if self.unused_macros.contains_key(&def_id) {
 333                 // We already lint the entire macro as unused
 334                 continue;
 335             }
 336             let node_id = self.def_id_to_node_id[def_id];
 337             self.lint_buffer.buffer_lint(
 338                 UNUSED_MACRO_RULES,
 339                 node_id,
 340                 rule_span,
 341                 &format!(
 342                     "{} rule of macro `{}` is never used",
 343                     crate::diagnostics::ordinalize(arm_i + 1),
 344                     ident.name
 345                 ),
 346             );
 347         }
 348     }
 349
 350     fn has_derive_copy(&self, expn_id: LocalExpnId) -> bool {
 351         self.containers_deriving_copy.contains(&expn_id)
 352     }
 353
 354     fn resolve_derives(
 355         &mut self,
 356         expn_id: LocalExpnId,
 357         force: bool,
 358         derive_paths: &dyn Fn() -> DeriveResolutions,
 359     ) -> Result<(), Indeterminate> {
 360         // Block expansion of the container until we resolve all derives in it.
 361         // This is required for two reasons:
 362         // - Derive helper attributes are in scope for the item to which the `#[derive]`
 363         //   is applied, so they have to be produced by the container's expansion rather
 364         //   than by individual derives.
 365         // - Derives in the container need to know whether one of them is a built-in `Copy`.
 366         // Temporarily take the data to avoid borrow checker conflicts.
 367         let mut derive_data = mem::take(&mut self.derive_data);
 368         let entry = derive_data.entry(expn_id).or_insert_with(|| DeriveData {
 369             resolutions: derive_paths(),
 370             helper_attrs: Vec::new(),
 371             has_derive_copy: false,
 372         });
 373         let parent_scope = self.invocation_parent_scopes[&expn_id];
 374         for (i, (path, _, opt_ext)) in entry.resolutions.iter_mut().enumerate() {
 375             if opt_ext.is_none() {
 376                 *opt_ext = Some(
 377                     match self.resolve_macro_path(
 378                         &path,
 379                         Some(MacroKind::Derive),
 380                         &parent_scope,
 381                         true,
 382                         force,
 383                     ) {
 384                         Ok((Some(ext), _)) => {
 385                             if !ext.helper_attrs.is_empty() {
 386                                 let last_seg = path.segments.last().unwrap();
 387                                 let span = last_seg.ident.span.normalize_to_macros_2_0();
 388                                 entry.helper_attrs.extend(
 389                                     ext.helper_attrs
 390                                         .iter()
 391                                         .map(|name| (i, Ident::new(*name, span))),
 392                                 );
 393                             }
 394                             entry.has_derive_copy |= ext.builtin_name == Some(sym::Copy);
 395                             ext
 396                         }
 397                         Ok(_) | Err(Determinacy::Determined) => self.dummy_ext(MacroKind::Derive),
 398                         Err(Determinacy::Undetermined) => {
 399                             assert!(self.derive_data.is_empty());
 400                             self.derive_data = derive_data;
 401                             return Err(Indeterminate);
 402                         }
 403                     },
 404                 );
 405             }
 406         }
 407         // Sort helpers in a stable way independent from the derive resolution order.
 408         entry.helper_attrs.sort_by_key(|(i, _)| *i);
 409         self.helper_attrs
 410             .insert(expn_id, entry.helper_attrs.iter().map(|(_, ident)| *ident).collect());
 411         // Mark this derive as having `Copy` either if it has `Copy` itself or if its parent derive
 412         // has `Copy`, to support cases like `#[derive(Clone, Copy)] #[derive(Debug)]`.
 413         if entry.has_derive_copy || self.has_derive_copy(parent_scope.expansion) {
 414             self.containers_deriving_copy.insert(expn_id);
 415         }
 416         assert!(self.derive_data.is_empty());
 417         self.derive_data = derive_data;
 418         Ok(())
 419     }
 420
 421     fn take_derive_resolutions(&mut self, expn_id: LocalExpnId) -> Option<DeriveResolutions> {
 422         self.derive_data.remove(&expn_id).map(|data| data.resolutions)
 423     }
 424
 425     // The function that implements the resolution logic of `#[cfg_accessible(path)]`.
 426     // Returns true if the path can certainly be resolved in one of three namespaces,
 427     // returns false if the path certainly cannot be resolved in any of the three namespaces.
 428     // Returns `Indeterminate` if we cannot give a certain answer yet.
 429     fn cfg_accessible(
 430         &mut self,
 431         expn_id: LocalExpnId,
 432         path: &ast::Path,
 433     ) -> Result<bool, Indeterminate> {
 434         let span = path.span;
 435         let path = &Segment::from_path(path);
 436         let parent_scope = self.invocation_parent_scopes[&expn_id];
 437
 438         let mut indeterminate = false;
 439         for ns in [TypeNS, ValueNS, MacroNS].iter().copied() {
 440             match self.maybe_resolve_path(path, Some(ns), &parent_scope) {
 441                 PathResult::Module(ModuleOrUniformRoot::Module(_)) => return Ok(true),
 442                 PathResult::NonModule(partial_res) if partial_res.unresolved_segments() == 0 => {
 443                     return Ok(true);
 444                 }
 445                 PathResult::NonModule(..) |
 446                 // HACK(Urgau): This shouldn't be necessary
 447                 PathResult::Failed { is_error_from_last_segment: false, .. } => {
 448                     self.session
 449                         .struct_span_err(span, "not sure whether the path is accessible or not")
 450                         .note("the type may have associated items, but we are currently not checking them")
 451                         .emit();
 452
 453                     // If we get a partially resolved NonModule in one namespace, we should get the
 454                     // same result in any other namespaces, so we can return early.
 455                     return Ok(false);
 456                 }
 457                 PathResult::Indeterminate => indeterminate = true,
 458                 // We can only be sure that a path doesn't exist after having tested all the
 459                 // posibilities, only at that time we can return false.
 460                 PathResult::Failed { .. } => {}
 461                 PathResult::Module(_) => panic!("unexpected path resolution"),
 462             }
 463         }
 464
 465         if indeterminate {
 466             return Err(Indeterminate);
 467         }
 468
 469         Ok(false)
 470     }
 471
 472     fn get_proc_macro_quoted_span(&self, krate: CrateNum, id: usize) -> Span {
 473         self.crate_loader.cstore().get_proc_macro_quoted_span_untracked(krate, id, self.session)
 474     }
 475
 476     fn declare_proc_macro(&mut self, id: NodeId) {
 477         self.proc_macros.push(id)
 478     }
 479
 480     fn registered_tools(&self) -> &RegisteredTools {
 481         &self.registered_tools
 482     }
 483 }
 484
 485 impl<'a> Resolver<'a> {
 486     /// Resolve macro path with error reporting and recovery.
 487     /// Uses dummy syntax extensions for unresolved macros or macros with unexpected resolutions
 488     /// for better error recovery.
 489     fn smart_resolve_macro_path(
 490         &mut self,
 491         path: &ast::Path,
 492         kind: MacroKind,
 493         supports_macro_expansion: SupportsMacroExpansion,
 494         inner_attr: bool,
 495         parent_scope: &ParentScope<'a>,
 496         node_id: NodeId,
 497         force: bool,
 498         soft_custom_inner_attributes_gate: bool,
 499     ) -> Result<(Lrc<SyntaxExtension>, Res), Indeterminate> {
 500         let (ext, res) = match self.resolve_macro_path(path, Some(kind), parent_scope, true, force)
 501         {
 502             Ok((Some(ext), res)) => (ext, res),
 503             Ok((None, res)) => (self.dummy_ext(kind), res),
 504             Err(Determinacy::Determined) => (self.dummy_ext(kind), Res::Err),
 505             Err(Determinacy::Undetermined) => return Err(Indeterminate),
 506         };
 507
 508         // Report errors for the resolved macro.
 509         for segment in &path.segments {
 510             if let Some(args) = &segment.args {
 511                 self.session.span_err(args.span(), "generic arguments in macro path");
 512             }
 513             if kind == MacroKind::Attr && segment.ident.as_str().starts_with("rustc") {
 514                 self.session.span_err(
 515                     segment.ident.span,
 516                     "attributes starting with `rustc` are reserved for use by the `rustc` compiler",
 517                 );
 518             }
 519         }
 520
 521         match res {
 522             Res::Def(DefKind::Macro(_), def_id) => {
 523                 if let Some(def_id) = def_id.as_local() {
 524                     self.unused_macros.remove(&def_id);
 525                     if self.proc_macro_stubs.contains(&def_id) {
 526                         self.session.span_err(
 527                             path.span,
 528                             "can't use a procedural macro from the same crate that defines it",
 529                         );
 530                     }
 531                 }
 532             }
 533             Res::NonMacroAttr(..) | Res::Err => {}
 534             _ => panic!("expected `DefKind::Macro` or `Res::NonMacroAttr`"),
 535         };
 536
 537         self.check_stability_and_deprecation(&ext, path, node_id);
 538
 539         let unexpected_res = if ext.macro_kind() != kind {
 540             Some((kind.article(), kind.descr_expected()))
 541         } else if matches!(res, Res::Def(..)) {
 542             match supports_macro_expansion {
 543                 SupportsMacroExpansion::No => Some(("a", "non-macro attribute")),
 544                 SupportsMacroExpansion::Yes { supports_inner_attrs } => {
 545                     if inner_attr && !supports_inner_attrs {
 546                         Some(("a", "non-macro inner attribute"))
 547                     } else {
 548                         None
 549                     }
 550                 }
 551             }
 552         } else {
 553             None
 554         };
 555         if let Some((article, expected)) = unexpected_res {
 556             let path_str = pprust::path_to_string(path);
 557             let msg = format!("expected {}, found {} `{}`", expected, res.descr(), path_str);
 558             self.session
 559                 .struct_span_err(path.span, &msg)
 560                 .span_label(path.span, format!("not {} {}", article, expected))
 561                 .emit();
 562             return Ok((self.dummy_ext(kind), Res::Err));
 563         }
 564
 565         // We are trying to avoid reporting this error if other related errors were reported.
 566         if res != Res::Err
 567             && inner_attr
 568             && !self.session.features_untracked().custom_inner_attributes
 569         {
 570             let msg = match res {
 571                 Res::Def(..) => "inner macro attributes are unstable",
 572                 Res::NonMacroAttr(..) => "custom inner attributes are unstable",
 573                 _ => unreachable!(),
 574             };
 575             if soft_custom_inner_attributes_gate {
 576                 self.session.parse_sess.buffer_lint(SOFT_UNSTABLE, path.span, node_id, msg);
 577             } else {
 578                 feature_err(&self.session.parse_sess, sym::custom_inner_attributes, path.span, msg)
 579                     .emit();
 580             }
 581         }
 582
 583         Ok((ext, res))
 584     }
 585
 586     pub fn resolve_macro_path(
 587         &mut self,
 588         path: &ast::Path,
 589         kind: Option<MacroKind>,
 590         parent_scope: &ParentScope<'a>,
 591         trace: bool,
 592         force: bool,
 593     ) -> Result<(Option<Lrc<SyntaxExtension>>, Res), Determinacy> {
 594         let path_span = path.span;
 595         let mut path = Segment::from_path(path);
 596
 597         // Possibly apply the macro helper hack
 598         if kind == Some(MacroKind::Bang)
 599             && path.len() == 1
 600             && path[0].ident.span.ctxt().outer_expn_data().local_inner_macros
 601         {
 602             let root = Ident::new(kw::DollarCrate, path[0].ident.span);
 603             path.insert(0, Segment::from_ident(root));
 604         }
 605
 606         let res = if path.len() > 1 {
 607             let res = match self.maybe_resolve_path(&path, Some(MacroNS), parent_scope) {
 608                 PathResult::NonModule(path_res) if path_res.unresolved_segments() == 0 => {
 609                     Ok(path_res.base_res())
 610                 }
 611                 PathResult::Indeterminate if !force => return Err(Determinacy::Undetermined),
 612                 PathResult::NonModule(..)
 613                 | PathResult::Indeterminate
 614                 | PathResult::Failed { .. } => Err(Determinacy::Determined),
 615                 PathResult::Module(..) => unreachable!(),
 616             };
 617
 618             if trace {
 619                 let kind = kind.expect("macro kind must be specified if tracing is enabled");
 620                 self.multi_segment_macro_resolutions.push((
 621                     path,
 622                     path_span,
 623                     kind,
 624                     *parent_scope,
 625                     res.ok(),
 626                 ));
 627             }
 628
 629             self.prohibit_imported_non_macro_attrs(None, res.ok(), path_span);
 630             res
 631         } else {
 632             let scope_set = kind.map_or(ScopeSet::All(MacroNS, false), ScopeSet::Macro);
 633             let binding = self.early_resolve_ident_in_lexical_scope(
 634                 path[0].ident,
 635                 scope_set,
 636                 parent_scope,
 637                 None,
 638                 force,
 639                 None,
 640             );
 641             if let Err(Determinacy::Undetermined) = binding {
 642                 return Err(Determinacy::Undetermined);
 643             }
 644
 645             if trace {
 646                 let kind = kind.expect("macro kind must be specified if tracing is enabled");
 647                 self.single_segment_macro_resolutions.push((
 648                     path[0].ident,
 649                     kind,
 650                     *parent_scope,
 651                     binding.ok(),
 652                 ));
 653             }
 654
 655             let res = binding.map(|binding| binding.res());
 656             self.prohibit_imported_non_macro_attrs(binding.ok(), res.ok(), path_span);
 657             res
 658         };
 659
 660         res.map(|res| (self.get_macro(res).map(|macro_data| macro_data.ext), res))
 661     }
 662
 663     pub(crate) fn finalize_macro_resolutions(&mut self) {
 664         let check_consistency = |this: &mut Self,
 665                                  path: &[Segment],
 666                                  span,
 667                                  kind: MacroKind,
 668                                  initial_res: Option<Res>,
 669                                  res: Res| {
 670             if let Some(initial_res) = initial_res {
 671                 if res != initial_res {
 672                     // Make sure compilation does not succeed if preferred macro resolution
 673                     // has changed after the macro had been expanded. In theory all such
 674                     // situations should be reported as errors, so this is a bug.
 675                     this.session.delay_span_bug(span, "inconsistent resolution for a macro");
 676                 }
 677             } else {
 678                 // It's possible that the macro was unresolved (indeterminate) and silently
 679                 // expanded into a dummy fragment for recovery during expansion.
 680                 // Now, post-expansion, the resolution may succeed, but we can't change the
 681                 // past and need to report an error.
 682                 // However, non-speculative `resolve_path` can successfully return private items
 683                 // even if speculative `resolve_path` returned nothing previously, so we skip this
 684                 // less informative error if the privacy error is reported elsewhere.
 685                 if this.privacy_errors.is_empty() {
 686                     let msg = format!(
 687                         "cannot determine resolution for the {} `{}`",
 688                         kind.descr(),
 689                         Segment::names_to_string(path)
 690                     );
 691                     let msg_note = "import resolution is stuck, try simplifying macro imports";
 692                     this.session.struct_span_err(span, &msg).note(msg_note).emit();
 693                 }
 694             }
 695         };
 696
 697         let macro_resolutions = mem::take(&mut self.multi_segment_macro_resolutions);
 698         for (mut path, path_span, kind, parent_scope, initial_res) in macro_resolutions {
 699             // FIXME: Path resolution will ICE if segment IDs present.
 700             for seg in &mut path {
 701                 seg.id = None;
 702             }
 703             match self.resolve_path(
 704                 &path,
 705                 Some(MacroNS),
 706                 &parent_scope,
 707                 Some(Finalize::new(ast::CRATE_NODE_ID, path_span)),
 708                 None,
 709             ) {
 710                 PathResult::NonModule(path_res) if path_res.unresolved_segments() == 0 => {
 711                     let res = path_res.base_res();
 712                     check_consistency(self, &path, path_span, kind, initial_res, res);
 713                 }
 714                 path_res @ PathResult::NonModule(..) | path_res @ PathResult::Failed { .. } => {
 715                     let (span, label) = if let PathResult::Failed { span, label, .. } = path_res {
 716                         (span, label)
 717                     } else {
 718                         (
 719                             path_span,
 720                             format!(
 721                                 "partially resolved path in {} {}",
 722                                 kind.article(),
 723                                 kind.descr()
 724                             ),
 725                         )
 726                     };
 727                     self.report_error(
 728                         span,
 729                         ResolutionError::FailedToResolve { label, suggestion: None },
 730                     );
 731                 }
 732                 PathResult::Module(..) | PathResult::Indeterminate => unreachable!(),
 733             }
 734         }
 735
 736         let macro_resolutions = mem::take(&mut self.single_segment_macro_resolutions);
 737         for (ident, kind, parent_scope, initial_binding) in macro_resolutions {
 738             match self.early_resolve_ident_in_lexical_scope(
 739                 ident,
 740                 ScopeSet::Macro(kind),
 741                 &parent_scope,
 742                 Some(Finalize::new(ast::CRATE_NODE_ID, ident.span)),
 743                 true,
 744                 None,
 745             ) {
 746                 Ok(binding) => {
 747                     let initial_res = initial_binding.map(|initial_binding| {
 748                         self.record_use(ident, initial_binding, false);
 749                         initial_binding.res()
 750                     });
 751                     let res = binding.res();
 752                     let seg = Segment::from_ident(ident);
 753                     check_consistency(self, &[seg], ident.span, kind, initial_res, res);
 754                     if res == Res::NonMacroAttr(NonMacroAttrKind::DeriveHelperCompat) {
 755                         let node_id = self
 756                             .invocation_parents
 757                             .get(&parent_scope.expansion)
 758                             .map_or(ast::CRATE_NODE_ID, |id| self.def_id_to_node_id[id.0]);
 759                         self.lint_buffer.buffer_lint_with_diagnostic(
 760                             LEGACY_DERIVE_HELPERS,
 761                             node_id,
 762                             ident.span,
 763                             "derive helper attribute is used before it is introduced",
 764                             BuiltinLintDiagnostics::LegacyDeriveHelpers(binding.span),
 765                         );
 766                     }
 767                 }
 768                 Err(..) => {
 769                     let expected = kind.descr_expected();
 770                     let msg = format!("cannot find {} `{}` in this scope", expected, ident);
 771                     let mut err = self.session.struct_span_err(ident.span, &msg);
 772                     self.unresolved_macro_suggestions(&mut err, kind, &parent_scope, ident);
 773                     err.emit();
 774                 }
 775             }
 776         }
 777
 778         let builtin_attrs = mem::take(&mut self.builtin_attrs);
 779         for (ident, parent_scope) in builtin_attrs {
 780             let _ = self.early_resolve_ident_in_lexical_scope(
 781                 ident,
 782                 ScopeSet::Macro(MacroKind::Attr),
 783                 &parent_scope,
 784                 Some(Finalize::new(ast::CRATE_NODE_ID, ident.span)),
 785                 true,
 786                 None,
 787             );
 788         }
 789     }
 790
 791     fn check_stability_and_deprecation(
 792         &mut self,
 793         ext: &SyntaxExtension,
 794         path: &ast::Path,
 795         node_id: NodeId,
 796     ) {
 797         let span = path.span;
 798         if let Some(stability) = &ext.stability {
 799             if let StabilityLevel::Unstable { reason, issue, is_soft, implied_by } = stability.level
 800             {
 801                 let feature = stability.feature;
 802
 803                 let is_allowed = |feature| {
 804                     self.active_features.contains(&feature) || span.allows_unstable(feature)
 805                 };
 806                 let allowed_by_implication =
 807                     implied_by.map(|feature| is_allowed(feature)).unwrap_or(false);
 808                 if !is_allowed(feature) && !allowed_by_implication {
 809                     let lint_buffer = &mut self.lint_buffer;
 810                     let soft_handler =
 811                         |lint, span, msg: &_| lint_buffer.buffer_lint(lint, node_id, span, msg);
 812                     stability::report_unstable(
 813                         self.session,
 814                         feature,
 815                         reason,
 816                         issue,
 817                         None,
 818                         is_soft,
 819                         span,
 820                         soft_handler,
 821                     );
 822                 }
 823             }
 824         }
 825         if let Some(depr) = &ext.deprecation {
 826             let path = pprust::path_to_string(&path);
 827             let (message, lint) = stability::deprecation_message_and_lint(depr, "macro", &path);
 828             stability::early_report_deprecation(
 829                 &mut self.lint_buffer,
 830                 &message,
 831                 depr.suggestion,
 832                 lint,
 833                 span,
 834                 node_id,
 835             );
 836         }
 837     }
 838
 839     fn prohibit_imported_non_macro_attrs(
 840         &self,
 841         binding: Option<&'a NameBinding<'a>>,
 842         res: Option<Res>,
 843         span: Span,
 844     ) {
 845         if let Some(Res::NonMacroAttr(kind)) = res {
 846             if kind != NonMacroAttrKind::Tool && binding.map_or(true, |b| b.is_import()) {
 847                 let msg =
 848                     format!("cannot use {} {} through an import", kind.article(), kind.descr());
 849                 let mut err = self.session.struct_span_err(span, &msg);
 850                 if let Some(binding) = binding {
 851                     err.span_note(binding.span, &format!("the {} imported here", kind.descr()));
 852                 }
 853                 err.emit();
 854             }
 855         }
 856     }
 857
 858     pub(crate) fn check_reserved_macro_name(&mut self, ident: Ident, res: Res) {
 859         // Reserve some names that are not quite covered by the general check
 860         // performed on `Resolver::builtin_attrs`.
 861         if ident.name == sym::cfg || ident.name == sym::cfg_attr {
 862             let macro_kind = self.get_macro(res).map(|macro_data| macro_data.ext.macro_kind());
 863             if macro_kind.is_some() && sub_namespace_match(macro_kind, Some(MacroKind::Attr)) {
 864                 self.session.span_err(
 865                     ident.span,
 866                     &format!("name `{}` is reserved in attribute namespace", ident),
 867                 );
 868             }
 869         }
 870     }
 871
 872     /// Compile the macro into a `SyntaxExtension` and its rule spans.
 873     ///
 874     /// Possibly replace its expander to a pre-defined one for built-in macros.
 875     pub(crate) fn compile_macro(
 876         &mut self,
 877         item: &ast::Item,
 878         edition: Edition,
 879     ) -> (SyntaxExtension, Vec<(usize, Span)>) {
 880         let (mut result, mut rule_spans) = compile_declarative_macro(
 881             &self.session,
 882             self.session.features_untracked(),
 883             item,
 884             edition,
 885         );
 886
 887         if let Some(builtin_name) = result.builtin_name {
 888             // The macro was marked with `#[rustc_builtin_macro]`.
 889             if let Some(builtin_macro) = self.builtin_macros.get_mut(&builtin_name) {
 890                 // The macro is a built-in, replace its expander function
 891                 // while still taking everything else from the source code.
 892                 // If we already loaded this builtin macro, give a better error message than 'no such builtin macro'.
 893                 match mem::replace(builtin_macro, BuiltinMacroState::AlreadySeen(item.span)) {
 894                     BuiltinMacroState::NotYetSeen(ext) => {
 895                         result.kind = ext;
 896                         rule_spans = Vec::new();
 897                         if item.id != ast::DUMMY_NODE_ID {
 898                             self.builtin_macro_kinds
 899                                 .insert(self.local_def_id(item.id), result.macro_kind());
 900                         }
 901                     }
 902                     BuiltinMacroState::AlreadySeen(span) => {
 903                         struct_span_err!(
 904                             self.session,
 905                             item.span,
 906                             E0773,
 907                             "attempted to define built-in macro more than once"
 908                         )
 909                         .span_note(span, "previously defined here")
 910                         .emit();
 911                     }
 912                 }
 913             } else {
 914                 let msg = format!("cannot find a built-in macro with name `{}`", item.ident);
 915                 self.session.span_err(item.span, &msg);
 916             }
 917         }
 918
 919         (result, rule_spans)
 920     }
 921 }