Auto merge of #53778 - petrochenkov:shadrelax2, r=nikomatsakis

resolve: Relax shadowing restrictions on macro-expanded macros

Previously any macro-expanded macros weren't allowed to shadow macros from outer scopes.
Now only "more macro-expanded" macros cannot shadow "less macro-expanded" macros.
See comments to `fn may_appear_after` and added tests for more details and examples.

The functional changes are a21f6f588fc28c97533130ae44a6957b579ab58c and 46dd365ce9ca0a6b8653849b80267763c542842a, other commits are refactorings.

src/librustc_resolve/build_reduced_graph.rs

@@ -946,7 +946,7 @@ fn legacy_macro_imports(&mut self, attrs: &[ast::Attribute]) -> LegacyMacroImpor
 
 pub struct BuildReducedGraphVisitor<'a, 'b: 'a, 'c: 'b> {
     pub resolver: &'a mut Resolver<'b, 'c>,
-    pub legacy_scope: LegacyScope<'b>,
+    pub current_legacy_scope: LegacyScope<'b>,
     pub expansion: Mark,
 }
 
@@ -956,7 +956,8 @@ fn visit_invoc(&mut self, id: ast::NodeId) -> &'b InvocationData<'b> {
         self.resolver.current_module.unresolved_invocations.borrow_mut().insert(mark);
         let invocation = self.resolver.invocations[&mark];
         invocation.module.set(self.resolver.current_module);
-        invocation.legacy_scope.set(self.legacy_scope);
+        invocation.parent_legacy_scope.set(self.current_legacy_scope);
+        invocation.output_legacy_scope.set(self.current_legacy_scope);
         invocation
     }
 }
@@ -982,29 +983,30 @@ impl<'a, 'b, 'cl> Visitor<'a> for BuildReducedGraphVisitor<'a, 'b, 'cl> {
     fn visit_item(&mut self, item: &'a Item) {
         let macro_use = match item.node {
             ItemKind::MacroDef(..) => {
-                self.resolver.define_macro(item, self.expansion, &mut self.legacy_scope);
+                self.resolver.define_macro(item, self.expansion, &mut self.current_legacy_scope);
                 return
             }
             ItemKind::Mac(..) => {
-                self.legacy_scope = LegacyScope::Expansion(self.visit_invoc(item.id));
+                self.current_legacy_scope = LegacyScope::Invocation(self.visit_invoc(item.id));
                 return
             }
             ItemKind::Mod(..) => self.resolver.contains_macro_use(&item.attrs),
             _ => false,
         };
 
-        let (parent, legacy_scope) = (self.resolver.current_module, self.legacy_scope);
+        let orig_current_module = self.resolver.current_module;
+        let orig_current_legacy_scope = self.current_legacy_scope;
         self.resolver.build_reduced_graph_for_item(item, self.expansion);
         visit::walk_item(self, item);
-        self.resolver.current_module = parent;
+        self.resolver.current_module = orig_current_module;
         if !macro_use {
-            self.legacy_scope = legacy_scope;
+            self.current_legacy_scope = orig_current_legacy_scope;
         }
     }
 
     fn visit_stmt(&mut self, stmt: &'a ast::Stmt) {
         if let ast::StmtKind::Mac(..) = stmt.node {
-            self.legacy_scope = LegacyScope::Expansion(self.visit_invoc(stmt.id));
+            self.current_legacy_scope = LegacyScope::Invocation(self.visit_invoc(stmt.id));
         } else {
             visit::walk_stmt(self, stmt);
         }
@@ -1021,11 +1023,12 @@ fn visit_foreign_item(&mut self, foreign_item: &'a ForeignItem) {
     }
 
     fn visit_block(&mut self, block: &'a Block) {
-        let (parent, legacy_scope) = (self.resolver.current_module, self.legacy_scope);
+        let orig_current_module = self.resolver.current_module;
+        let orig_current_legacy_scope = self.current_legacy_scope;
         self.resolver.build_reduced_graph_for_block(block, self.expansion);
         visit::walk_block(self, block);
-        self.resolver.current_module = parent;
-        self.legacy_scope = legacy_scope;
+        self.resolver.current_module = orig_current_module;
+        self.current_legacy_scope = orig_current_legacy_scope;
     }
 
     fn visit_trait_item(&mut self, item: &'a TraitItem) {

src/librustc_resolve/lib.rs

@@ -1177,9 +1177,7 @@ struct UseError<'a> {
 }
 
 struct AmbiguityError<'a> {
-    span: Span,
-    name: Name,
-    lexical: bool,
+    ident: Ident,
     b1: &'a NameBinding<'a>,
     b2: &'a NameBinding<'a>,
 }
@@ -1283,6 +1281,26 @@ fn is_macro_def(&self) -> bool {
     fn descr(&self) -> &'static str {
         if self.is_extern_crate() { "extern crate" } else { self.def().kind_name() }
     }
+
+    // Suppose that we resolved macro invocation with `invoc_id` to binding `binding` at some
+    // expansion round `max(invoc_id, binding)` when they both emerged from macros.
+    // Then this function returns `true` if `self` may emerge from a macro *after* that
+    // in some later round and screw up our previously found resolution.
+    // See more detailed explanation in
+    // https://github.com/rust-lang/rust/pull/53778#issuecomment-419224049
+    fn may_appear_after(&self, invoc_id: Mark, binding: &NameBinding) -> bool {
+        // self > max(invoc_id, binding) => !(self <= invoc_id || self <= binding)
+        // Expansions are partially ordered, so "may appear after" is an inversion of
+        // "certainly appears before or simultaneously" and includes unordered cases.
+        let self_parent_expansion = self.expansion;
+        let other_parent_expansion = binding.expansion;
+        let invoc_parent_expansion = invoc_id.parent();
+        let certainly_before_other_or_simultaneously =
+            other_parent_expansion.is_descendant_of(self_parent_expansion);
+        let certainly_before_invoc_or_simultaneously =
+            invoc_parent_expansion.is_descendant_of(self_parent_expansion);
+        !(certainly_before_other_or_simultaneously || certainly_before_invoc_or_simultaneously)
+    }
 }
 
 /// Interns the names of the primitive types.
@@ -1416,8 +1434,6 @@ pub struct Resolver<'a, 'b: 'a> {
     proc_mac_errors: Vec<macros::ProcMacError>,
     /// crate-local macro expanded `macro_export` referred to by a module-relative path
     macro_expanded_macro_export_errors: BTreeSet<(Span, Span)>,
-    /// macro-expanded `macro_rules` shadowing existing macros
-    disallowed_shadowing: Vec<&'a LegacyBinding<'a>>,
 
     arenas: &'a ResolverArenas<'a>,
     dummy_binding: &'a NameBinding<'a>,
@@ -1729,7 +1745,6 @@ pub fn new(session: &'a Session,
             ambiguity_errors: Vec::new(),
             use_injections: Vec::new(),
             proc_mac_errors: Vec::new(),
-            disallowed_shadowing: Vec::new(),
             macro_expanded_macro_export_errors: BTreeSet::new(),
 
             arenas,
@@ -1815,7 +1830,7 @@ fn new_module(
         self.arenas.alloc_module(module)
     }
 
-    fn record_use(&mut self, ident: Ident, ns: Namespace, binding: &'a NameBinding<'a>, span: Span)
+    fn record_use(&mut self, ident: Ident, ns: Namespace, binding: &'a NameBinding<'a>)
                   -> bool /* true if an error was reported */ {
         match binding.kind {
             NameBindingKind::Import { directive, binding, ref used }
@@ -1824,13 +1839,11 @@ fn record_use(&mut self, ident: Ident, ns: Namespace, binding: &'a NameBinding<'
                 directive.used.set(true);
                 self.used_imports.insert((directive.id, ns));
                 self.add_to_glob_map(directive.id, ident);
-                self.record_use(ident, ns, binding, span)
+                self.record_use(ident, ns, binding)
             }
             NameBindingKind::Import { .. } => false,
             NameBindingKind::Ambiguity { b1, b2 } => {
-                self.ambiguity_errors.push(AmbiguityError {
-                    span, name: ident.name, lexical: false, b1, b2,
-                });
+                self.ambiguity_errors.push(AmbiguityError { ident, b1, b2 });
                 true
             }
             _ => false
@@ -2850,7 +2863,7 @@ fn resolve_pattern(&mut self,
                             Def::Const(..) if is_syntactic_ambiguity => {
                                 // Disambiguate in favor of a unit struct/variant
                                 // or constant pattern.
-                                self.record_use(ident, ValueNS, binding.unwrap(), ident.span);
+                                self.record_use(ident, ValueNS, binding.unwrap());
                                 Some(PathResolution::new(def))
                             }
                             Def::StructCtor(..) | Def::VariantCtor(..) |
@@ -3483,6 +3496,20 @@ fn resolve_path(
         record_used: bool,
         path_span: Span,
         crate_lint: CrateLint,
+    ) -> PathResult<'a> {
+        self.resolve_path_with_invoc_id(base_module, path, opt_ns, Mark::root(),
+                                        record_used, path_span, crate_lint)
+    }
+
+    fn resolve_path_with_invoc_id(
+        &mut self,
+        base_module: Option<ModuleOrUniformRoot<'a>>,
+        path: &[Ident],
+        opt_ns: Option<Namespace>, // `None` indicates a module path
+        invoc_id: Mark,
+        record_used: bool,
+        path_span: Span,
+        crate_lint: CrateLint,
     ) -> PathResult<'a> {
         let mut module = base_module;
         let mut allow_super = true;
@@ -3572,8 +3599,9 @@ fn resolve_path(
                 self.resolve_ident_in_module(module, ident, ns, record_used, path_span)
             } else if opt_ns == Some(MacroNS) {
                 assert!(ns == TypeNS);
-                self.resolve_lexical_macro_path_segment(ident, ns, record_used, record_used,
-                                                        false, path_span).map(|(b, _)| b)
+                self.resolve_lexical_macro_path_segment(ident, ns, invoc_id, record_used,
+                                                        record_used, false, path_span)
+                                                        .map(|(binding, _)| binding)
             } else {
                 let record_used_id =
                     if record_used { crate_lint.node_id().or(Some(CRATE_NODE_ID)) } else { None };
@@ -4514,35 +4542,33 @@ fn is_accessible_from(&self, vis: ty::Visibility, module: Module<'a>) -> bool {
         vis.is_accessible_from(module.normal_ancestor_id, self)
     }
 
-    fn report_ambiguity_error(
-        &self, name: Name, span: Span, _lexical: bool,
-        def1: Def, is_import1: bool, is_glob1: bool, from_expansion1: bool, span1: Span,
-        def2: Def, is_import2: bool, _is_glob2: bool, _from_expansion2: bool, span2: Span,
-    ) {
+    fn report_ambiguity_error(&self, ident: Ident, b1: &NameBinding, b2: &NameBinding) {
         let participle = |is_import: bool| if is_import { "imported" } else { "defined" };
-        let msg1 = format!("`{}` could refer to the name {} here", name, participle(is_import1));
+        let msg1 =
+            format!("`{}` could refer to the name {} here", ident, participle(b1.is_import()));
         let msg2 =
-            format!("`{}` could also refer to the name {} here", name, participle(is_import2));
-        let note = if from_expansion1 {
-            Some(if let Def::Macro(..) = def1 {
+            format!("`{}` could also refer to the name {} here", ident, participle(b2.is_import()));
+        let note = if b1.expansion != Mark::root() {
+            Some(if let Def::Macro(..) = b1.def() {
                 format!("macro-expanded {} do not shadow",
-                        if is_import1 { "macro imports" } else { "macros" })
+                        if b1.is_import() { "macro imports" } else { "macros" })
             } else {
                 format!("macro-expanded {} do not shadow when used in a macro invocation path",
-                        if is_import1 { "imports" } else { "items" })
+                        if b1.is_import() { "imports" } else { "items" })
             })
-        } else if is_glob1 {
-            Some(format!("consider adding an explicit import of `{}` to disambiguate", name))
+        } else if b1.is_glob_import() {
+            Some(format!("consider adding an explicit import of `{}` to disambiguate", ident))
         } else {
             None
         };
 
-        let mut err = struct_span_err!(self.session, span, E0659, "`{}` is ambiguous", name);
-        err.span_note(span1, &msg1);
-        match def2 {
-            Def::Macro(..) if span2.is_dummy() =>
-                err.note(&format!("`{}` is also a builtin macro", name)),
-            _ => err.span_note(span2, &msg2),
+        let mut err = struct_span_err!(self.session, ident.span, E0659, "`{}` is ambiguous", ident);
+        err.span_label(ident.span, "ambiguous name");
+        err.span_note(b1.span, &msg1);
+        match b2.def() {
+            Def::Macro(..) if b2.span.is_dummy() =>
+                err.note(&format!("`{}` is also a builtin macro", ident)),
+            _ => err.span_note(b2.span, &msg2),
         };
         if let Some(note) = note {
             err.note(&note);
@@ -4551,7 +4577,6 @@ fn report_ambiguity_error(
     }
 
     fn report_errors(&mut self, krate: &Crate) {
-        self.report_shadowing_errors();
         self.report_with_use_injections(krate);
         self.report_proc_macro_import(krate);
         let mut reported_spans = FxHashSet();
@@ -4567,15 +4592,9 @@ fn report_errors(&mut self, krate: &Crate) {
             );
         }
 
-        for &AmbiguityError { span, name, b1, b2, lexical } in &self.ambiguity_errors {
-            if reported_spans.insert(span) {
-                self.report_ambiguity_error(
-                    name, span, lexical,
-                    b1.def(), b1.is_import(), b1.is_glob_import(),
-                    b1.expansion != Mark::root(), b1.span,
-                    b2.def(), b2.is_import(), b2.is_glob_import(),
-                    b2.expansion != Mark::root(), b2.span,
-                );
+        for &AmbiguityError { ident, b1, b2 } in &self.ambiguity_errors {
+            if reported_spans.insert(ident.span) {
+                self.report_ambiguity_error(ident, b1, b2);
             }
         }
 
@@ -4595,20 +4614,6 @@ fn report_with_use_injections(&mut self, krate: &Crate) {
         }
     }
 
-    fn report_shadowing_errors(&mut self) {
-        let mut reported_errors = FxHashSet();
-        for binding in replace(&mut self.disallowed_shadowing, Vec::new()) {
-            if self.resolve_legacy_scope(&binding.parent, binding.ident, false).is_some() &&
-               reported_errors.insert((binding.ident, binding.span)) {
-                let msg = format!("`{}` is already in scope", binding.ident);
-                self.session.struct_span_err(binding.span, &msg)
-                    .note("macro-expanded `macro_rules!`s may not shadow \
-                           existing macros (see RFC 1560)")
-                    .emit();
-            }
-        }
-    }
-
     fn report_conflict<'b>(&mut self,
                        parent: Module,
                        ident: Ident,

src/librustc_resolve/resolve_imports.rs

@@ -242,22 +242,19 @@ pub fn resolve_ident_in_module_unadjusted(&mut self,
         if record_used {
             if let Some(binding) = resolution.binding {
                 if let Some(shadowed_glob) = resolution.shadowed_glob {
-                    let name = ident.name;
                     // Forbid expanded shadowing to avoid time travel.
                     if restricted_shadowing &&
                        binding.expansion != Mark::root() &&
                        ns != MacroNS && // In MacroNS, `try_define` always forbids this shadowing
                        binding.def() != shadowed_glob.def() {
                         self.ambiguity_errors.push(AmbiguityError {
-                            span: path_span,
-                            name,
-                            lexical: false,
+                            ident,
                             b1: binding,
                             b2: shadowed_glob,
                         });
                     }
                 }
-                if self.record_use(ident, ns, binding, path_span) {
+                if self.record_use(ident, ns, binding) {
                     return Ok(self.dummy_binding);
                 }
                 if !self.is_accessible(binding.vis) {
@@ -937,7 +934,7 @@ fn finalize_import(&mut self, directive: &'b ImportDirective<'b>) -> Option<(Spa
         self.per_ns(|this, ns| if !type_ns_only || ns == TypeNS {
             if let Ok(binding) = result[ns].get() {
                 all_ns_err = false;
-                if this.record_use(ident, ns, binding, directive.span) {
+                if this.record_use(ident, ns, binding) {
                     if let ModuleOrUniformRoot::Module(module) = module {
                         this.resolution(module, ident, ns).borrow_mut().binding =
                             Some(this.dummy_binding);

src/libsyntax/feature_gate.rs

@@ -966,6 +966,10 @@ pub fn is_builtin_attr(attr: &ast::Attribute) -> bool {
                                      "the `#[rustc_test_marker]` attribute \
                                       is used internally to track tests",
                                      cfg_fn!(rustc_attrs))),
+    ("rustc_transparent_macro", Whitelisted, Gated(Stability::Unstable,
+                                                   "rustc_attrs",
+                                                   "used internally for testing macro hygiene",
+                                                    cfg_fn!(rustc_attrs))),
 
     // RFC #2094
     ("nll", Whitelisted, Gated(Stability::Unstable,

src/libsyntax_pos/hygiene.rs

@@ -100,6 +100,11 @@ pub fn from_u32(raw: u32) -> Mark {
         Mark(raw)
     }
 
+    #[inline]
+    pub fn parent(self) -> Mark {
+        HygieneData::with(|data| data.marks[self.0 as usize].parent)
+    }
+
     #[inline]
     pub fn expn_info(self) -> Option<ExpnInfo> {
         HygieneData::with(|data| data.marks[self.0 as usize].expn_info.clone())

src/test/ui/error-codes/E0659.stderr

 error[E0659]: `foo` is ambiguous
-  --> $DIR/E0659.rs:25:5
+  --> $DIR/E0659.rs:25:15
    |
 LL |     collider::foo(); //~ ERROR E0659
-   |     ^^^^^^^^^^^^^
+   |               ^^^ ambiguous name
    |
 note: `foo` could refer to the name imported here
   --> $DIR/E0659.rs:20:13

src/test/ui/imports/duplicate.stderr

@@ -13,10 +13,10 @@ LL |     use a::foo as other_foo; //~ ERROR the name `foo` is defined multiple t
    |         ^^^^^^^^^^^^^^^^^^^
 
 error[E0659]: `foo` is ambiguous
-  --> $DIR/duplicate.rs:56:9
+  --> $DIR/duplicate.rs:56:15
    |
 LL |     use self::foo::bar; //~ ERROR `foo` is ambiguous
-   |         ^^^^^^^^^^^^^^
+   |               ^^^ ambiguous name
    |
 note: `foo` could refer to the name imported here
   --> $DIR/duplicate.rs:53:9
@@ -31,10 +31,10 @@ LL |     use self::m2::*;
    = note: consider adding an explicit import of `foo` to disambiguate
 
 error[E0659]: `foo` is ambiguous
-  --> $DIR/duplicate.rs:45:5
+  --> $DIR/duplicate.rs:45:8
    |
 LL |     f::foo(); //~ ERROR `foo` is ambiguous
-   |     ^^^^^^
+   |        ^^^ ambiguous name
    |
 note: `foo` could refer to the name imported here
   --> $DIR/duplicate.rs:34:13
@@ -49,10 +49,10 @@ LL |     pub use b::*;
    = note: consider adding an explicit import of `foo` to disambiguate
 
 error[E0659]: `foo` is ambiguous
-  --> $DIR/duplicate.rs:46:5
+  --> $DIR/duplicate.rs:46:8
    |
 LL |     g::foo(); //~ ERROR `foo` is ambiguous
-   |     ^^^^^^
+   |        ^^^ ambiguous name
    |
 note: `foo` could refer to the name imported here
   --> $DIR/duplicate.rs:39:13
@@ -70,7 +70,7 @@ error[E0659]: `foo` is ambiguous
   --> $DIR/duplicate.rs:59:9
    |
 LL |         foo::bar(); //~ ERROR `foo` is ambiguous
-   |         ^^^^^^^^
+   |         ^^^ ambiguous name
    |
 note: `foo` could refer to the name imported here
   --> $DIR/duplicate.rs:53:9

src/test/ui/imports/glob-shadowing.stderr

@@ -2,7 +2,7 @@ error[E0659]: `env` is ambiguous
   --> $DIR/glob-shadowing.rs:21:17
    |
 LL |         let x = env!("PATH"); //~ ERROR `env` is ambiguous
-   |                 ^^^
+   |                 ^^^ ambiguous name
    |
 note: `env` could refer to the name imported here
   --> $DIR/glob-shadowing.rs:19:9
@@ -16,7 +16,7 @@ error[E0659]: `env` is ambiguous
   --> $DIR/glob-shadowing.rs:29:21
    |
 LL |             let x = env!("PATH"); //~ ERROR `env` is ambiguous
-   |                     ^^^
+   |                     ^^^ ambiguous name
    |
 note: `env` could refer to the name imported here
   --> $DIR/glob-shadowing.rs:27:13
@@ -30,7 +30,7 @@ error[E0659]: `fenv` is ambiguous
   --> $DIR/glob-shadowing.rs:39:21
    |
 LL |             let x = fenv!(); //~ ERROR `fenv` is ambiguous
-   |                     ^^^^
+   |                     ^^^^ ambiguous name
    |
 note: `fenv` could refer to the name imported here
   --> $DIR/glob-shadowing.rs:37:13

src/test/ui/imports/issue-53269.stderr

@@ -8,7 +8,7 @@ error[E0659]: `mac` is ambiguous
   --> $DIR/issue-53269.rs:18:5
    |
 LL |     mac!(); //~ ERROR `mac` is ambiguous
-   |     ^^^
+   |     ^^^ ambiguous name
    |
 note: `mac` could refer to the name defined here
   --> $DIR/issue-53269.rs:13:1

src/test/ui/imports/local-modularized-tricky-fail-1.rs

@@ -43,7 +43,6 @@ mod inner2 {
 
 fn main() {
     panic!(); //~ ERROR `panic` is ambiguous
-              //~^ ERROR `panic` is ambiguous
 }
 
 mod inner3 {

src/test/ui/imports/local-modularized-tricky-fail-1.stderr

@@ -2,7 +2,7 @@ error[E0659]: `exported` is ambiguous
   --> $DIR/local-modularized-tricky-fail-1.rs:38:1
    |
 LL | exported!(); //~ ERROR `exported` is ambiguous
-   | ^^^^^^^^
+   | ^^^^^^^^ ambiguous name
    |
 note: `exported` could refer to the name defined here
   --> $DIR/local-modularized-tricky-fail-1.rs:15:5
@@ -22,10 +22,10 @@ LL | use inner1::*;
    = note: macro-expanded macros do not shadow
 
 error[E0659]: `include` is ambiguous
-  --> $DIR/local-modularized-tricky-fail-1.rs:57:1
+  --> $DIR/local-modularized-tricky-fail-1.rs:56:1
    |
 LL | include!(); //~ ERROR `include` is ambiguous
-   | ^^^^^^^
+   | ^^^^^^^ ambiguous name
    |
 note: `include` could refer to the name defined here
   --> $DIR/local-modularized-tricky-fail-1.rs:27:5
@@ -44,7 +44,7 @@ error[E0659]: `panic` is ambiguous
   --> $DIR/local-modularized-tricky-fail-1.rs:45:5
    |
 LL |     panic!(); //~ ERROR `panic` is ambiguous
-   |     ^^^^^
+   |     ^^^^^ ambiguous name
    |
 note: `panic` could refer to the name defined here
   --> $DIR/local-modularized-tricky-fail-1.rs:21:5
@@ -60,10 +60,10 @@ LL |       define_panic!();
    = note: macro-expanded macros do not shadow
 
 error[E0659]: `panic` is ambiguous
-  --> $DIR/local-modularized-tricky-fail-1.rs:45:5
+  --> <panic macros>:1:13
    |
-LL |     panic!(); //~ ERROR `panic` is ambiguous
-   |     ^^^^^^^^^
+LL | (  ) => ( { panic ! ( "explicit panic" ) } ) ; ( $ msg : expr ) => (
+   |             ^^^^^ ambiguous name
    |
 note: `panic` could refer to the name defined here
   --> $DIR/local-modularized-tricky-fail-1.rs:21:5
@@ -77,7 +77,6 @@ LL |       define_panic!();
    |       ---------------- in this macro invocation
    = note: `panic` is also a builtin macro
    = note: macro-expanded macros do not shadow
-   = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
 
 error: aborting due to 4 previous errors
 

src/test/ui/imports/macro-paths.stderr

@@ -2,7 +2,7 @@ error[E0659]: `bar` is ambiguous
   --> $DIR/macro-paths.rs:23:5
    |
 LL |     bar::m! { //~ ERROR ambiguous
-   |     ^^^^^^
+   |     ^^^ ambiguous name
    |
 note: `bar` could refer to the name defined here
   --> $DIR/macro-paths.rs:24:9
@@ -20,7 +20,7 @@ error[E0659]: `baz` is ambiguous
   --> $DIR/macro-paths.rs:33:5
    |
 LL |     baz::m! { //~ ERROR ambiguous
-   |     ^^^^^^
+   |     ^^^ ambiguous name
    |
 note: `baz` could refer to the name defined here
   --> $DIR/macro-paths.rs:34:9

src/test/ui/imports/macros.stderr

@@ -2,7 +2,7 @@ error[E0659]: `m` is ambiguous
   --> $DIR/macros.rs:48:5
    |
 LL |     m!(); //~ ERROR ambiguous
-   |     ^
+   |     ^ ambiguous name
    |
 note: `m` could refer to the name defined here
   --> $DIR/macros.rs:46:5
@@ -19,7 +19,7 @@ error[E0659]: `m` is ambiguous
   --> $DIR/macros.rs:26:5
    |
 LL |     m! { //~ ERROR ambiguous
-   |     ^
+   |     ^ ambiguous name
    |
 note: `m` could refer to the name imported here
   --> $DIR/macros.rs:27:13
@@ -37,7 +37,7 @@ error[E0659]: `m` is ambiguous
   --> $DIR/macros.rs:39:9
    |
 LL |         m! { //~ ERROR ambiguous
-   |         ^
+   |         ^ ambiguous name
    |
 note: `m` could refer to the name imported here
   --> $DIR/macros.rs:40:17

src/test/ui/imports/rfc-1560-warning-cycle.stderr

@@ -2,7 +2,7 @@ error[E0659]: `Foo` is ambiguous
   --> $DIR/rfc-1560-warning-cycle.rs:19:17
    |
 LL |         fn f(_: Foo) {} //~ ERROR `Foo` is ambiguous
-   |                 ^^^
+   |                 ^^^ ambiguous name
    |
 note: `Foo` could refer to the name imported here
   --> $DIR/rfc-1560-warning-cycle.rs:17:13

src/test/ui/imports/shadow_builtin_macros.stderr

@@ -2,7 +2,7 @@ error[E0659]: `panic` is ambiguous
   --> $DIR/shadow_builtin_macros.rs:43:5
    |
 LL |     panic!(); //~ ERROR `panic` is ambiguous
-   |     ^^^^^
+   |     ^^^^^ ambiguous name
    |
 note: `panic` could refer to the name defined here
   --> $DIR/shadow_builtin_macros.rs:40:9
@@ -19,7 +19,7 @@ error[E0659]: `panic` is ambiguous
   --> $DIR/shadow_builtin_macros.rs:25:14
    |
 LL |     fn f() { panic!(); } //~ ERROR ambiguous
-   |              ^^^^^
+   |              ^^^^^ ambiguous name
    |
 note: `panic` could refer to the name imported here
   --> $DIR/shadow_builtin_macros.rs:24:9
@@ -33,7 +33,7 @@ error[E0659]: `panic` is ambiguous
   --> $DIR/shadow_builtin_macros.rs:30:14
    |
 LL |     fn f() { panic!(); } //~ ERROR ambiguous
-   |              ^^^^^
+   |              ^^^^^ ambiguous name
    |
 note: `panic` could refer to the name imported here
   --> $DIR/shadow_builtin_macros.rs:29:26
@@ -47,7 +47,7 @@ error[E0659]: `n` is ambiguous
   --> $DIR/shadow_builtin_macros.rs:59:5
    |
 LL |     n!(); //~ ERROR ambiguous
-   |     ^
+   |     ^ ambiguous name
    |
 note: `n` could refer to the name imported here
   --> $DIR/shadow_builtin_macros.rs:58:9

src/test/ui/macros/auxiliary/macro-in-other-crate.rs

@@ -17,3 +17,8 @@
 macro_rules! inline {
     () => ()
 }
+
+#[macro_export]
+macro_rules! from_prelude {
+    () => ()
+}

src/test/ui/macros/macro-path-prelude-shadowing.stderr

@@ -2,7 +2,7 @@ error[E0659]: `std` is ambiguous
   --> $DIR/macro-path-prelude-shadowing.rs:39:9
    |
 LL |         std::panic!(); //~ ERROR `std` is ambiguous
-   |         ^^^^^^^^^^
+   |         ^^^ ambiguous name
    |
 note: `std` could refer to the name imported here
   --> $DIR/macro-path-prelude-shadowing.rs:37:9

src/test/ui/macros/macro-shadowing-relaxed.rs

+// Copyright 2016 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// compile-pass
+// aux-build:macro-in-other-crate.rs
+
+#![feature(decl_macro)]
+
+macro_rules! my_include {() => {
+    // Outer
+    macro m() {}
+    #[macro_use(from_prelude)] extern crate macro_in_other_crate;
+
+    fn inner() {
+        // Inner
+        macro m() {}
+        macro_rules! from_prelude { () => {} }
+
+        // OK, both `m` and `from_prelude` are macro-expanded,
+        // but no more macro-expanded than their counterpart from outer scope.
+        m!();
+        from_prelude!();
+    }
+}}
+
+my_include!();
+
+fn main() {}

src/test/ui/macros/macro-shadowing.rs

@@ -17,14 +17,14 @@
 #[macro_use(macro_two)] extern crate two_macros;
 
 macro_rules! m1 { () => {
-    macro_rules! foo { () => {} } //~ ERROR `foo` is already in scope
+    macro_rules! foo { () => {} }
 
     #[macro_use] //~ ERROR `macro_two` is already in scope
     extern crate two_macros as __;
 }}
 m1!();
 
-foo!();
+foo!(); //~ ERROR `foo` is ambiguous
 
 macro_rules! m2 { () => {
     macro_rules! foo { () => {} }

src/test/ui/macros/macro-shadowing.stderr

@@ -9,16 +9,27 @@ LL | m1!();
    |
    = note: macro-expanded `#[macro_use]`s may not shadow existing macros (see RFC 1560)
 
-error: `foo` is already in scope
+error[E0659]: `foo` is ambiguous
+  --> $DIR/macro-shadowing.rs:27:1
+   |
+LL | foo!(); //~ ERROR `foo` is ambiguous
+   | ^^^ ambiguous name
+   |
+note: `foo` could refer to the name defined here
   --> $DIR/macro-shadowing.rs:20:5
    |
-LL |     macro_rules! foo { () => {} } //~ ERROR `foo` is already in scope
+LL |     macro_rules! foo { () => {} }
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 ...
 LL | m1!();
    | ------ in this macro invocation
+note: `foo` could also refer to the name defined here
+  --> $DIR/macro-shadowing.rs:15:1
    |
-   = note: macro-expanded `macro_rules!`s may not shadow existing macros (see RFC 1560)
+LL | macro_rules! foo { () => {} }
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   = note: macro-expanded macros do not shadow
 
 error: aborting due to 2 previous errors
 
+For more information about this error, try `rustc --explain E0659`.

src/test/ui/macros/restricted-shadowing-legacy.rs

+// Legend:
+// `N` - number of combination, from 0 to 4*4*4=64
+// `Outer < Invoc` means that expansion that produced macro definition `Outer`
+// is a strict ancestor of expansion that produced macro definition `Inner`.
+// `>`, `=` and `Unordered` mean "strict descendant", "same" and
+// "not in ordering relation" for parent expansions.
+// `+` - possible configuration
+// `-` - configuration impossible due to properties of partial ordering
+// `-?` - configuration impossible due to block/scope syntax
+// `+?` - configuration possible only with legacy scoping
+
+//  N | Outer ~ Invoc | Invoc ~ Inner | Outer ~ Inner | Possible |
+//  1 |       <       |       <       |       <       |    +     |
+//  2 |       <       |       <       |       =       |    -     |
+//  3 |       <       |       <       |       >       |    -     |
+//  4 |       <       |       <       |   Unordered   |    -     |
+//  5 |       <       |       =       |       <       |    +     |
+//  6 |       <       |       =       |       =       |    -     |
+//  7 |       <       |       =       |       >       |    -     |
+//  8 |       <       |       =       |   Unordered   |    -     |
+//  9 |       <       |       >       |       <       |    +     |
+// 10 |       <       |       >       |       =       |    +     |
+// 11 |       <       |       >       |       >       |    -?    |
+// 12 |       <       |       >       |   Unordered   |    -?    |
+// 13 |       <       |   Unordered   |       <       |    +     |
+// 14 |       <       |   Unordered   |       =       |    -     |
+// 15 |       <       |   Unordered   |       >       |    -     |
+// 16 |       <       |   Unordered   |   Unordered   |    -?    |
+// 17 |       =       |       <       |       <       |    +     |
+// 18 |       =       |       <       |       =       |    -     |
+// 19 |       =       |       <       |       >       |    -     |
+// 20 |       =       |       <       |   Unordered   |    -     |
+// 21 |       =       |       =       |       <       |    -     |
+// 22 |       =       |       =       |       =       |    +     |
+// 23 |       =       |       =       |       >       |    -     |
+// 24 |       =       |       =       |   Unordered   |    -     |
+// 25 |       =       |       >       |       <       |    -     |
+// 26 |       =       |       >       |       =       |    -     |
+// 27 |       =       |       >       |       >       |    -?    |
+// 28 |       =       |       >       |   Unordered   |    -     |
+// 29 |       =       |   Unordered   |       <       |    -     |
+// 30 |       =       |   Unordered   |       =       |    -     |
+// 31 |       =       |   Unordered   |       >       |    -     |
+// 32 |       =       |   Unordered   |   Unordered   |    -?    |
+// 33 |       >       |       <       |       <       |    +?    |
+// 34 |       >       |       <       |       =       |    +?    |
+// 35 |       >       |       <       |       >       |    +?    |
+// 36 |       >       |       <       |   Unordered   |    +     |
+// 37 |       >       |       =       |       <       |    -     |
+// 38 |       >       |       =       |       =       |    -     |
+// 39 |       >       |       =       |       >       |    +     |
+// 40 |       >       |       =       |   Unordered   |    -     |
+// 41 |       >       |       >       |       <       |    -     |
+// 42 |       >       |       >       |       =       |    -     |
+// 43 |       >       |       >       |       >       |    -?    |
+// 44 |       >       |       >       |   Unordered   |    -     |
+// 45 |       >       |   Unordered   |       <       |    -     |
+// 46 |       >       |   Unordered   |       =       |    -     |
+// 47 |       >       |   Unordered   |       >       |    -?    |
+// 48 |       >       |   Unordered   |   Unordered   |    -?    |
+// 49 |   Unordered   |       <       |       <       |    -?    |
+// 50 |   Unordered   |       <       |       =       |    -     |
+// 51 |   Unordered   |       <       |       >       |    -     |
+// 52 |   Unordered   |       <       |   Unordered   |    +     |
+// 53 |   Unordered   |       =       |       <       |    -     |
+// 54 |   Unordered   |       =       |       =       |    -     |
+// 55 |   Unordered   |       =       |       >       |    -     |
+// 56 |   Unordered   |       =       |   Unordered   |    +     |
+// 57 |   Unordered   |       >       |       <       |    -     |
+// 58 |   Unordered   |       >       |       =       |    -     |
+// 59 |   Unordered   |       >       |       >       |    +     |
+// 60 |   Unordered   |       >       |   Unordered   |    +     |
+// 61 |   Unordered   |   Unordered   |       <       |    +?    |
+// 62 |   Unordered   |   Unordered   |       =       |    +?    |
+// 63 |   Unordered   |   Unordered   |       >       |    +?    |
+// 64 |   Unordered   |   Unordered   |   Unordered   |    +     |
+
+#![feature(decl_macro, rustc_attrs)]
+
+struct Right;
+// struct Wrong; // not defined
+
+macro_rules! include { () => {
+    macro_rules! gen_outer { () => {
+        macro_rules! m { () => { Wrong } }
+    }}
+    macro_rules! gen_inner { () => {
+        macro_rules! m { () => { Right } }
+    }}
+    macro_rules! gen_invoc { () => {
+        m!()
+    }}
+
+    // -----------------------------------------------------------
+
+    fn check1() {
+        macro_rules! m { () => {} }
+
+        macro_rules! gen_gen_inner_invoc { () => {
+            gen_inner!();
+            m!(); //~ ERROR `m` is ambiguous
+        }}
+        gen_gen_inner_invoc!();
+    }
+
+    fn check5() {
+        macro_rules! m { () => { Wrong } }
+
+        macro_rules! gen_inner_invoc { () => {
+            macro_rules! m { () => { Right } }
+            m!(); // OK
+        }}
+        gen_inner_invoc!();
+    }
+
+    fn check9() {
+        macro_rules! m { () => { Wrong } }
+
+        macro_rules! gen_inner_gen_invoc { () => {
+            macro_rules! m { () => { Right } }
+            gen_invoc!(); // OK
+        }}
+        gen_inner_gen_invoc!();
+    }
+
+    fn check10() {
+        macro_rules! m { () => { Wrong } }
+
+        macro_rules! m { () => { Right } }
+
+        gen_invoc!(); // OK
+    }
+
+    fn check13() {
+        macro_rules! m { () => {} }
+
+        gen_inner!();
+
+        macro_rules! gen_invoc { () => { m!() } } //~ ERROR `m` is ambiguous
+        gen_invoc!();
+    }
+
+    fn check17() {
+        macro_rules! m { () => {} }
+
+        gen_inner!();
+
+        m!(); //~ ERROR `m` is ambiguous
+    }
+
+    fn check22() {
+        macro_rules! m { () => { Wrong } }
+
+        macro_rules! m { () => { Right } }
+
+        m!(); // OK
+    }
+
+    fn check36() {
+        gen_outer!();
+
+        gen_inner!();
+
+        m!(); //~ ERROR `m` is ambiguous
+    }
+
+    fn check39() {
+        gen_outer!();
+
+        macro_rules! m { () => { Right } }
+
+        m!(); // OK
+    }
+
+    fn check52() {
+        gen_outer!();
+
+        macro_rules! gen_gen_inner_invoc { () => {
+            gen_inner!();
+            m!(); //~ ERROR `m` is ambiguous
+        }}
+        gen_gen_inner_invoc!();
+    }
+
+    fn check56() {
+        gen_outer!();
+
+        macro_rules! gen_inner_invoc { () => {
+            macro_rules! m { () => { Right } }
+            m!(); // OK
+        }}
+        gen_inner_invoc!();
+    }
+
+    fn check59() {
+        gen_outer!();
+
+        macro_rules! m { () => { Right } }
+
+        gen_invoc!(); // OK
+    }
+
+    fn check60() {
+        gen_outer!();
+
+        macro_rules! gen_inner_gen_invoc { () => {
+            macro_rules! m { () => { Right } }
+            gen_invoc!(); // OK
+        }}
+        gen_inner_gen_invoc!();
+    }
+
+    fn check64() {
+        gen_outer!();
+
+        gen_inner!();
+
+        macro_rules! gen_invoc { () => { m!() } } //~ ERROR `m` is ambiguous
+        gen_invoc!();
+    }
+
+    // -----------------------------------------------------------
+    // These configurations are only possible with legacy macro scoping
+
+    fn check33() {
+        macro_rules! gen_outer_gen_inner { () => {
+            macro_rules! m { () => {} }
+            gen_inner!();
+        }}
+        gen_outer_gen_inner!();
+
+        m!(); //~ ERROR `m` is ambiguous
+    }
+
+    fn check34() {
+        macro_rules! gen_outer_inner { () => {
+            macro_rules! m { () => { Wrong } }
+            macro_rules! m { () => { Right } }
+        }}
+        gen_outer_inner!();
+
+        m!(); // OK
+    }
+
+    fn check35() {
+        macro_rules! gen_gen_outer_inner { () => {
+            gen_outer!();
+            macro_rules! m { () => { Right } }
+        }}
+        gen_gen_outer_inner!();
+
+        m!(); // OK
+    }
+
+    fn check61() {
+        macro_rules! gen_outer_gen_inner { () => {
+            macro_rules! m { () => {} }
+            gen_inner!();
+        }}
+        gen_outer_gen_inner!();
+
+        macro_rules! gen_invoc { () => { m!() } } //~ ERROR `m` is ambiguous
+        gen_invoc!();
+    }
+
+    fn check62() {
+        macro_rules! gen_outer_inner { () => {
+            macro_rules! m { () => { Wrong } }
+            macro_rules! m { () => { Right } }
+        }}
+        gen_outer_inner!();
+
+        gen_invoc!(); // OK
+    }
+
+    fn check63() {
+        macro_rules! gen_gen_outer_inner { () => {
+            gen_outer!();
+            macro_rules! m { () => { Right } }
+        }}
+        gen_gen_outer_inner!();
+
+        gen_invoc!(); // OK
+    }
+}}
+
+include!();
+
+fn main() {}

src/test/ui/macros/restricted-shadowing-legacy.stderr

+error[E0659]: `m` is ambiguous
+  --> $DIR/restricted-shadowing-legacy.rs:101:13
+   |
+LL |             m!(); //~ ERROR `m` is ambiguous
+   |             ^ ambiguous name
+   |
+note: `m` could refer to the name defined here
+  --> $DIR/restricted-shadowing-legacy.rs:88:9
+   |
+LL |         macro_rules! m { () => { Right } }
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+...
+LL | include!();
+   | ----------- in this macro invocation
+note: `m` could also refer to the name defined here
+  --> $DIR/restricted-shadowing-legacy.rs:97:9
+   |
+LL |         macro_rules! m { () => {} }
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+...
+LL | include!();
+   | ----------- in this macro invocation
+   = note: macro-expanded macros do not shadow
+
+error[E0659]: `m` is ambiguous
+  --> $DIR/restricted-shadowing-legacy.rs:139:42
+   |
+LL |         macro_rules! gen_invoc { () => { m!() } } //~ ERROR `m` is ambiguous
+   |                                          ^ ambiguous name
+   |
+note: `m` could refer to the name defined here
+  --> $DIR/restricted-shadowing-legacy.rs:88:9
+   |
+LL |         macro_rules! m { () => { Right } }
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+...
+LL | include!();
+   | ----------- in this macro invocation
+note: `m` could also refer to the name defined here
+  --> $DIR/restricted-shadowing-legacy.rs:135:9
+   |
+LL |         macro_rules! m { () => {} }
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+...
+LL | include!();
+   | ----------- in this macro invocation
+   = note: macro-expanded macros do not shadow
+
+error[E0659]: `m` is ambiguous
+  --> $DIR/restricted-shadowing-legacy.rs:148:9
+   |
+LL |         m!(); //~ ERROR `m` is ambiguous
+   |         ^ ambiguous name
+   |
+note: `m` could refer to the name defined here
+  --> $DIR/restricted-shadowing-legacy.rs:88:9
+   |
+LL |         macro_rules! m { () => { Right } }
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+...
+LL | include!();
+   | ----------- in this macro invocation
+note: `m` could also refer to the name defined here
+  --> $DIR/restricted-shadowing-legacy.rs:144:9
+   |
+LL |         macro_rules! m { () => {} }
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+...
+LL | include!();
+   | ----------- in this macro invocation
+   = note: macro-expanded macros do not shadow
+
+error[E0659]: `m` is ambiguous
+  --> $DIR/restricted-shadowing-legacy.rs:164:9
+   |
+LL |         m!(); //~ ERROR `m` is ambiguous
+   |         ^ ambiguous name
+   |
+note: `m` could refer to the name defined here
+  --> $DIR/restricted-shadowing-legacy.rs:88:9
+   |
+LL |         macro_rules! m { () => { Right } }
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+...
+LL | include!();
+   | ----------- in this macro invocation
+note: `m` could also refer to the name defined here
+  --> $DIR/restricted-shadowing-legacy.rs:85:9
+   |
+LL |         macro_rules! m { () => { Wrong } }
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+...
+LL | include!();
+   | ----------- in this macro invocation
+   = note: macro-expanded macros do not shadow
+
+error[E0659]: `m` is ambiguous
+  --> $DIR/restricted-shadowing-legacy.rs:180:13
+   |
+LL |             m!(); //~ ERROR `m` is ambiguous
+   |             ^ ambiguous name
+   |
+note: `m` could refer to the name defined here
+  --> $DIR/restricted-shadowing-legacy.rs:88:9
+   |
+LL |         macro_rules! m { () => { Right } }
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+...
+LL | include!();
+   | ----------- in this macro invocation
+note: `m` could also refer to the name defined here
+  --> $DIR/restricted-shadowing-legacy.rs:85:9
+   |
+LL |         macro_rules! m { () => { Wrong } }
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+...
+LL | include!();
+   | ----------- in this macro invocation
+   = note: macro-expanded macros do not shadow
+
+error[E0659]: `m` is ambiguous
+  --> $DIR/restricted-shadowing-legacy.rs:218:42
+   |
+LL |         macro_rules! gen_invoc { () => { m!() } } //~ ERROR `m` is ambiguous
+   |                                          ^ ambiguous name
+   |
+note: `m` could refer to the name defined here
+  --> $DIR/restricted-shadowing-legacy.rs:88:9
+   |
+LL |         macro_rules! m { () => { Right } }
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+...
+LL | include!();
+   | ----------- in this macro invocation
+note: `m` could also refer to the name defined here
+  --> $DIR/restricted-shadowing-legacy.rs:85:9
+   |
+LL |         macro_rules! m { () => { Wrong } }
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+...
+LL | include!();
+   | ----------- in this macro invocation
+   = note: macro-expanded macros do not shadow
+
+error[E0659]: `m` is ambiguous
+  --> $DIR/restricted-shadowing-legacy.rs:232:9
+   |
+LL |         m!(); //~ ERROR `m` is ambiguous
+   |         ^ ambiguous name
+   |
+note: `m` could refer to the name defined here
+  --> $DIR/restricted-shadowing-legacy.rs:88:9
+   |
+LL |         macro_rules! m { () => { Right } }
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+...
+LL | include!();
+   | ----------- in this macro invocation
+note: `m` could also refer to the name defined here
+  --> $DIR/restricted-shadowing-legacy.rs:227:13
+   |
+LL |             macro_rules! m { () => {} }
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+...
+LL | include!();
+   | ----------- in this macro invocation
+   = note: macro-expanded macros do not shadow
+
+error[E0659]: `m` is ambiguous
+  --> $DIR/restricted-shadowing-legacy.rs:262:42
+   |
+LL |         macro_rules! gen_invoc { () => { m!() } } //~ ERROR `m` is ambiguous
+   |                                          ^ ambiguous name
+   |
+note: `m` could refer to the name defined here
+  --> $DIR/restricted-shadowing-legacy.rs:88:9
+   |
+LL |         macro_rules! m { () => { Right } }
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+...
+LL | include!();
+   | ----------- in this macro invocation
+note: `m` could also refer to the name defined here
+  --> $DIR/restricted-shadowing-legacy.rs:257:13
+   |
+LL |             macro_rules! m { () => {} }
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+...
+LL | include!();
+   | ----------- in this macro invocation
+   = note: macro-expanded macros do not shadow
+
+error: aborting due to 8 previous errors
+
+For more information about this error, try `rustc --explain E0659`.

src/test/ui/macros/restricted-shadowing-modern.rs

+// Legend:
+// `N` - number of combination, from 0 to 4*4*4=64
+// `Outer < Invoc` means that expansion that produced macro definition `Outer`
+// is a strict ancestor of expansion that produced macro definition `Inner`.
+// `>`, `=` and `Unordered` mean "strict descendant", "same" and
+// "not in ordering relation" for parent expansions.
+// `+` - possible configuration
+// `-` - configuration impossible due to properties of partial ordering
+// `-?` - configuration impossible due to block/scope syntax
+// `+?` - configuration possible only with legacy scoping
+
+//  N | Outer ~ Invoc | Invoc ~ Inner | Outer ~ Inner | Possible |
+//  1 |       <       |       <       |       <       |    +     |
+//  2 |       <       |       <       |       =       |    -     |
+//  3 |       <       |       <       |       >       |    -     |
+//  4 |       <       |       <       |   Unordered   |    -     |
+//  5 |       <       |       =       |       <       |    +     |
+//  6 |       <       |       =       |       =       |    -     |
+//  7 |       <       |       =       |       >       |    -     |
+//  8 |       <       |       =       |   Unordered   |    -     |
+//  9 |       <       |       >       |       <       |    +     |
+// 10 |       <       |       >       |       =       |    +     |
+// 11 |       <       |       >       |       >       |    -?    |
+// 12 |       <       |       >       |   Unordered   |    -?    |
+// 13 |       <       |   Unordered   |       <       |    +     |
+// 14 |       <       |   Unordered   |       =       |    -     |
+// 15 |       <       |   Unordered   |       >       |    -     |
+// 16 |       <       |   Unordered   |   Unordered   |    -?    |
+// 17 |       =       |       <       |       <       |    +     |
+// 18 |       =       |       <       |       =       |    -     |
+// 19 |       =       |       <       |       >       |    -     |
+// 20 |       =       |       <       |   Unordered   |    -     |
+// 21 |       =       |       =       |       <       |    -     |
+// 22 |       =       |       =       |       =       |    +     |
+// 23 |       =       |       =       |       >       |    -     |
+// 24 |       =       |       =       |   Unordered   |    -     |
+// 25 |       =       |       >       |       <       |    -     |
+// 26 |       =       |       >       |       =       |    -     |
+// 27 |       =       |       >       |       >       |    -?    |
+// 28 |       =       |       >       |   Unordered   |    -     |
+// 29 |       =       |   Unordered   |       <       |    -     |
+// 30 |       =       |   Unordered   |       =       |    -     |
+// 31 |       =       |   Unordered   |       >       |    -     |
+// 32 |       =       |   Unordered   |   Unordered   |    -?    |
+// 33 |       >       |       <       |       <       |    -?    |
+// 34 |       >       |       <       |       =       |    -?    |
+// 35 |       >       |       <       |       >       |    -?    |
+// 36 |       >       |       <       |   Unordered   |    +     |
+// 37 |       >       |       =       |       <       |    -     |
+// 38 |       >       |       =       |       =       |    -     |
+// 39 |       >       |       =       |       >       |    +     |
+// 40 |       >       |       =       |   Unordered   |    -     |
+// 41 |       >       |       >       |       <       |    -     |
+// 42 |       >       |       >       |       =       |    -     |
+// 43 |       >       |       >       |       >       |    -?    |
+// 44 |       >       |       >       |   Unordered   |    -     |
+// 45 |       >       |   Unordered   |       <       |    -     |
+// 46 |       >       |   Unordered   |       =       |    -     |
+// 47 |       >       |   Unordered   |       >       |    -?    |
+// 48 |       >       |   Unordered   |   Unordered   |    -?    |
+// 49 |   Unordered   |       <       |       <       |    -?    |
+// 50 |   Unordered   |       <       |       =       |    -     |
+// 51 |   Unordered   |       <       |       >       |    -     |
+// 52 |   Unordered   |       <       |   Unordered   |    +     |
+// 53 |   Unordered   |       =       |       <       |    -     |
+// 54 |   Unordered   |       =       |       =       |    -     |
+// 55 |   Unordered   |       =       |       >       |    -     |
+// 56 |   Unordered   |       =       |   Unordered   |    +     |
+// 57 |   Unordered   |       >       |       <       |    -     |
+// 58 |   Unordered   |       >       |       =       |    -     |
+// 59 |   Unordered   |       >       |       >       |    +     |
+// 60 |   Unordered   |       >       |   Unordered   |    +     |
+// 61 |   Unordered   |   Unordered   |       <       |    -?    |
+// 62 |   Unordered   |   Unordered   |       =       |    -?    |
+// 63 |   Unordered   |   Unordered   |       >       |    -?    |
+// 64 |   Unordered   |   Unordered   |   Unordered   |    +     |
+
+#![feature(decl_macro, rustc_attrs)]
+
+struct Right;
+// struct Wrong; // not defined
+
+#[rustc_transparent_macro]
+macro include() {
+    #[rustc_transparent_macro]
+    macro gen_outer() {
+        macro m() { Wrong }
+    }
+    #[rustc_transparent_macro]
+    macro gen_inner() {
+        macro m() { Right }
+    }
+    #[rustc_transparent_macro]
+    macro gen_invoc() {
+        m!()
+    }
+
+    // -----------------------------------------------------------
+
+    fn check1() {
+        macro m() {}
+        {
+            #[rustc_transparent_macro]
+            macro gen_gen_inner_invoc() {
+                gen_inner!();
+                m!(); //~ ERROR `m` is ambiguous
+            }
+            gen_gen_inner_invoc!();
+        }
+    }
+
+    fn check5() {
+        macro m() { Wrong }
+        {
+            #[rustc_transparent_macro]
+            macro gen_inner_invoc() {
+                macro m() { Right }
+                m!(); // OK
+            }
+            gen_inner_invoc!();
+        }
+    }
+
+    fn check9() {
+        macro m() { Wrong }
+        {
+            #[rustc_transparent_macro]
+            macro gen_inner_gen_invoc() {
+                macro m() { Right }
+                gen_invoc!(); // OK
+            }
+            gen_inner_gen_invoc!();
+        }
+    }
+
+    fn check10() {
+        macro m() { Wrong }
+        {
+            macro m() { Right }
+            gen_invoc!(); // OK
+        }
+    }
+
+    fn check13() {
+        macro m() {}
+        {
+            gen_inner!();
+            #[rustc_transparent_macro]
+            macro gen_invoc() { m!() } //~ ERROR `m` is ambiguous
+            gen_invoc!();
+        }
+    }
+
+    fn check17() {
+        macro m() {}
+        {
+            gen_inner!();
+            m!(); //~ ERROR `m` is ambiguous
+        }
+    }
+
+    fn check22() {
+        macro m() { Wrong }
+        {
+            macro m() { Right }
+            m!(); // OK
+        }
+    }
+
+    fn check36() {
+        gen_outer!();
+        {
+            gen_inner!();
+            m!(); //~ ERROR `m` is ambiguous
+        }
+    }
+
+    fn check39() {
+        gen_outer!();
+        {
+            macro m() { Right }
+            m!(); // OK
+        }
+    }
+
+    fn check52() {
+        gen_outer!();
+        {
+            #[rustc_transparent_macro]
+            macro gen_gen_inner_invoc() {
+                gen_inner!();
+                m!(); //~ ERROR `m` is ambiguous
+            }
+            gen_gen_inner_invoc!();
+        }
+    }
+
+    fn check56() {
+        gen_outer!();
+        {
+            #[rustc_transparent_macro]
+            macro gen_inner_invoc() {
+                macro m() { Right }
+                m!(); // OK
+            }
+            gen_inner_invoc!();
+        }
+    }
+
+    fn check59() {
+        gen_outer!();
+        {
+            macro m() { Right }
+            gen_invoc!(); // OK
+        }
+    }
+
+    fn check60() {
+        gen_outer!();
+        {
+            #[rustc_transparent_macro]
+            macro gen_inner_gen_invoc() {
+                macro m() { Right }
+                gen_invoc!(); // OK
+            }
+            gen_inner_gen_invoc!();
+        }
+    }
+
+    fn check64() {
+        gen_outer!();
+        {
+            gen_inner!();
+            #[rustc_transparent_macro]
+            macro gen_invoc() { m!() } //~ ERROR `m` is ambiguous
+            gen_invoc!();
+        }
+    }
+}
+
+include!();
+
+fn main() {}

src/test/ui/macros/restricted-shadowing-modern.stderr

+error[E0659]: `m` is ambiguous
+  --> $DIR/restricted-shadowing-modern.rs:106:17
+   |
+LL |                 m!(); //~ ERROR `m` is ambiguous
+   |                 ^ ambiguous name
+   |
+note: `m` could refer to the name defined here
+  --> $DIR/restricted-shadowing-modern.rs:91:9
+   |
+LL |         macro m() { Right }
+   |         ^^^^^^^^^^^^^^^^^^^
+...
+LL | include!();
+   | ----------- in this macro invocation
+note: `m` could also refer to the name defined here
+  --> $DIR/restricted-shadowing-modern.rs:101:9
+   |
+LL |         macro m() {}
+   |         ^^^^^^^^^^^^
+...
+LL | include!();
+   | ----------- in this macro invocation
+   = note: macro-expanded macros do not shadow
+
+error[E0659]: `m` is ambiguous
+  --> $DIR/restricted-shadowing-modern.rs:149:33
+   |
+LL |             macro gen_invoc() { m!() } //~ ERROR `m` is ambiguous
+   |                                 ^ ambiguous name
+   |
+note: `m` could refer to the name defined here
+  --> $DIR/restricted-shadowing-modern.rs:91:9
+   |
+LL |         macro m() { Right }
+   |         ^^^^^^^^^^^^^^^^^^^
+...
+LL | include!();
+   | ----------- in this macro invocation
+note: `m` could also refer to the name defined here
+  --> $DIR/restricted-shadowing-modern.rs:145:9
+   |
+LL |         macro m() {}
+   |         ^^^^^^^^^^^^
+...
+LL | include!();
+   | ----------- in this macro invocation
+   = note: macro-expanded macros do not shadow
+
+error[E0659]: `m` is ambiguous
+  --> $DIR/restricted-shadowing-modern.rs:158:13
+   |
+LL |             m!(); //~ ERROR `m` is ambiguous
+   |             ^ ambiguous name
+   |
+note: `m` could refer to the name defined here
+  --> $DIR/restricted-shadowing-modern.rs:91:9
+   |
+LL |         macro m() { Right }
+   |         ^^^^^^^^^^^^^^^^^^^
+...
+LL | include!();
+   | ----------- in this macro invocation
+note: `m` could also refer to the name defined here
+  --> $DIR/restricted-shadowing-modern.rs:155:9
+   |
+LL |         macro m() {}
+   |         ^^^^^^^^^^^^
+...
+LL | include!();
+   | ----------- in this macro invocation
+   = note: macro-expanded macros do not shadow
+
+error[E0659]: `m` is ambiguous
+  --> $DIR/restricted-shadowing-modern.rs:174:13
+   |
+LL |             m!(); //~ ERROR `m` is ambiguous
+   |             ^ ambiguous name
+   |
+note: `m` could refer to the name defined here
+  --> $DIR/restricted-shadowing-modern.rs:91:9
+   |
+LL |         macro m() { Right }
+   |         ^^^^^^^^^^^^^^^^^^^
+...
+LL | include!();
+   | ----------- in this macro invocation
+note: `m` could also refer to the name defined here
+  --> $DIR/restricted-shadowing-modern.rs:87:9
+   |
+LL |         macro m() { Wrong }
+   |         ^^^^^^^^^^^^^^^^^^^
+...
+LL | include!();
+   | ----------- in this macro invocation
+   = note: macro-expanded macros do not shadow
+
+error[E0659]: `m` is ambiguous
+  --> $DIR/restricted-shadowing-modern.rs:192:17
+   |
+LL |                 m!(); //~ ERROR `m` is ambiguous
+   |                 ^ ambiguous name
+   |
+note: `m` could refer to the name defined here
+  --> $DIR/restricted-shadowing-modern.rs:91:9
+   |
+LL |         macro m() { Right }
+   |         ^^^^^^^^^^^^^^^^^^^
+...
+LL | include!();
+   | ----------- in this macro invocation
+note: `m` could also refer to the name defined here
+  --> $DIR/restricted-shadowing-modern.rs:87:9
+   |
+LL |         macro m() { Wrong }
+   |         ^^^^^^^^^^^^^^^^^^^
+...
+LL | include!();
+   | ----------- in this macro invocation
+   = note: macro-expanded macros do not shadow
+
+error[E0659]: `m` is ambiguous
+  --> $DIR/restricted-shadowing-modern.rs:235:33
+   |
+LL |             macro gen_invoc() { m!() } //~ ERROR `m` is ambiguous
+   |                                 ^ ambiguous name
+   |
+note: `m` could refer to the name defined here
+  --> $DIR/restricted-shadowing-modern.rs:91:9
+   |
+LL |         macro m() { Right }
+   |         ^^^^^^^^^^^^^^^^^^^
+...
+LL | include!();
+   | ----------- in this macro invocation
+note: `m` could also refer to the name defined here
+  --> $DIR/restricted-shadowing-modern.rs:87:9
+   |
+LL |         macro m() { Wrong }
+   |         ^^^^^^^^^^^^^^^^^^^
+...
+LL | include!();
+   | ----------- in this macro invocation
+   = note: macro-expanded macros do not shadow
+
+error: aborting due to 6 previous errors
+
+For more information about this error, try `rustc --explain E0659`.

src/test/ui/out-of-order-shadowing.rs

@@ -9,11 +9,10 @@
 // except according to those terms.
 
 // aux-build:define_macro.rs
-// error-pattern: `bar` is already in scope
 
 macro_rules! bar { () => {} }
 define_macro!(bar);
-bar!();
+bar!(); //~ ERROR `bar` is ambiguous
 
 macro_rules! m { () => { #[macro_use] extern crate define_macro; } }
 m!();

src/test/ui/out-of-order-shadowing.stderr

-error: `bar` is already in scope
+error[E0659]: `bar` is ambiguous
   --> $DIR/out-of-order-shadowing.rs:15:1
    |
+LL | bar!(); //~ ERROR `bar` is ambiguous
+   | ^^^ ambiguous name
+   |
+note: `bar` could refer to the name defined here
+  --> $DIR/out-of-order-shadowing.rs:14:1
+   |
 LL | define_macro!(bar);
    | ^^^^^^^^^^^^^^^^^^^
+note: `bar` could also refer to the name defined here
+  --> $DIR/out-of-order-shadowing.rs:13:1
    |
-   = note: macro-expanded `macro_rules!`s may not shadow existing macros (see RFC 1560)
+LL | macro_rules! bar { () => {} }
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   = note: macro-expanded macros do not shadow
    = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0659`.