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