resolve: Future proof resolutions for potentially built-in attributes

src/librustc_resolve/build_reduced_graph.rs

@@ -39,6 +39,7 @@ use syntax::ext::base::{MacroKind, SyntaxExtension};
 use syntax::ext::base::Determinacy::Undetermined;
 use syntax::ext::hygiene::Mark;
 use syntax::ext::tt::macro_rules;
+use syntax::feature_gate::is_builtin_attr;
 use syntax::parse::token::{self, Token};
 use syntax::std_inject::injected_crate_name;
 use syntax::symbol::keywords;
@@ -1060,4 +1061,13 @@ impl<'a, 'b, 'cl> Visitor<'a> for BuildReducedGraphVisitor<'a, 'b, 'cl> {
             }
         }
     }
+
+    fn visit_attribute(&mut self, attr: &'a ast::Attribute) {
+        if !attr.is_sugared_doc && is_builtin_attr(attr) {
+            self.resolver.current_module.builtin_attrs.borrow_mut().push((
+                attr.path.segments[0].ident, self.expansion, self.current_legacy_scope
+            ));
+        }
+        visit::walk_attribute(self, attr);
+    }
 }

src/librustc_resolve/lib.rs

@@ -1012,6 +1012,7 @@ pub struct ModuleData<'a> {
     resolutions: RefCell<FxHashMap<(Ident, Namespace), &'a RefCell<NameResolution<'a>>>>,
     legacy_macro_resolutions: RefCell<Vec<(Ident, MacroKind, Mark, LegacyScope<'a>, Option<Def>)>>,
     macro_resolutions: RefCell<Vec<(Box<[Ident]>, Span)>>,
+    builtin_attrs: RefCell<Vec<(Ident, Mark, LegacyScope<'a>)>>,
 
     // Macro invocations that can expand into items in this module.
     unresolved_invocations: RefCell<FxHashSet<Mark>>,
@@ -1050,6 +1051,7 @@ impl<'a> ModuleData<'a> {
             resolutions: RefCell::new(FxHashMap()),
             legacy_macro_resolutions: RefCell::new(Vec::new()),
             macro_resolutions: RefCell::new(Vec::new()),
+            builtin_attrs: RefCell::new(Vec::new()),
             unresolved_invocations: RefCell::new(FxHashSet()),
             no_implicit_prelude: false,
             glob_importers: RefCell::new(Vec::new()),

src/librustc_resolve/macros.rs

@@ -619,7 +619,19 @@ impl<'a, 'cl> Resolver<'a, 'cl> {
                 }
                 WhereToResolve::MacroPrelude => {
                     match self.macro_prelude.get(&ident.name).cloned() {
-                        Some(binding) => Ok((binding, FromPrelude(true))),
+                        Some(binding) => {
+                            let mut result = Ok((binding, FromPrelude(true)));
+                            // HACK: Keep some built-in attributes working even if they are
+                            // shadowed by other built-in or standard library macros.
+                            // We need to come up with some more principled approach instead.
+                            if is_attr && (ident.name == "cfg" || ident.name == "thread_local") {
+                                if let Def::Macro(_, MacroKind::Bang) =
+                                        binding.def_ignoring_ambiguity() {
+                                    result = Err(Determinacy::Determined);
+                                }
+                            }
+                            result
+                        }
                         None => Err(Determinacy::Determined),
                     }
                 }
@@ -928,6 +940,32 @@ impl<'a, 'cl> Resolver<'a, 'cl> {
                 }
             };
         }
+
+        for &(ident, parent_expansion, parent_legacy_scope)
+                in module.builtin_attrs.borrow().iter() {
+            let resolution = if ident.name == "doc" {
+                // HACK: Some sugared doc comments in macros lose their memory about being
+                // sugared doc comments and become shadowed by other macros.
+                // We need to come up with some more principled approach instead.
+                None
+            } else {
+                self.resolve_legacy_scope(ident, parent_expansion, parent_legacy_scope, true)
+            }.or_else(|| {
+                self.resolve_lexical_macro_path_segment(ident, MacroNS, parent_expansion, true,
+                                                        true, true, ident.span)
+                                                        .map(|(binding, _)| binding).ok()
+            });
+
+            if let Some(binding) = resolution {
+                if binding.def_ignoring_ambiguity() !=
+                        Def::NonMacroAttr(NonMacroAttrKind::Builtin) {
+                    let builtin_binding = (Def::NonMacroAttr(NonMacroAttrKind::Builtin),
+                                           ty::Visibility::Public, ident.span, Mark::root())
+                                           .to_name_binding(self.arenas);
+                    self.report_ambiguity_error(ident.name, ident.span, binding, builtin_binding);
+                }
+            }
+        }
     }
 
     fn suggest_macro_name(&mut self, name: &str, kind: MacroKind,

src/test/ui/macros/ambiguous-builtin-attrs-test.rs

@@ -0,0 +1,17 @@
+// compile-flags:--test
+
+#![feature(decl_macro, test)]
+
+extern crate test;
+
+macro test() {}
+
+#[test] //~ ERROR `test` is ambiguous
+fn test() {}
+
+macro bench() {}
+
+#[bench] //~ ERROR `bench` is ambiguous
+fn bench(b: &mut test::Bencher) {}
+
+fn main() {}

src/test/ui/macros/ambiguous-builtin-attrs-test.stderr

@@ -0,0 +1,37 @@
+error[E0659]: `test` is ambiguous
+  --> $DIR/ambiguous-builtin-attrs-test.rs:9:3
+   |
+LL | #[test] //~ ERROR `test` is ambiguous
+   |   ^^^^
+   |
+note: `test` could refer to the name defined here
+  --> $DIR/ambiguous-builtin-attrs-test.rs:7:1
+   |
+LL | macro test() {}
+   | ^^^^^^^^^^^^^^^
+note: `test` could also refer to the name defined here
+  --> $DIR/ambiguous-builtin-attrs-test.rs:9:3
+   |
+LL | #[test] //~ ERROR `test` is ambiguous
+   |   ^^^^
+
+error[E0659]: `bench` is ambiguous
+  --> $DIR/ambiguous-builtin-attrs-test.rs:14:3
+   |
+LL | #[bench] //~ ERROR `bench` is ambiguous
+   |   ^^^^^
+   |
+note: `bench` could refer to the name defined here
+  --> $DIR/ambiguous-builtin-attrs-test.rs:12:1
+   |
+LL | macro bench() {}
+   | ^^^^^^^^^^^^^^^^
+note: `bench` could also refer to the name defined here
+  --> $DIR/ambiguous-builtin-attrs-test.rs:14:3
+   |
+LL | #[bench] //~ ERROR `bench` is ambiguous
+   |   ^^^^^
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0659`.

src/test/ui/macros/ambiguous-builtin-attrs.rs

@@ -0,0 +1,46 @@
+#![feature(decl_macro)]
+
+macro repr() {}
+
+#[repr(C)] //~ ERROR `repr` is ambiguous
+struct S;
+#[cfg_attr(all(), repr(C))] //~ ERROR `repr` is ambiguous
+struct SCond;
+
+macro cfg() {}
+
+#[cfg(all())] //~ ERROR `cfg` is ambiguous
+struct A;
+#[cfg(any())] // ERROR FIXME
+struct A;
+
+macro cfg_attr() {}
+
+#[cfg_attr(all(), cold)] // ERROR FIXME
+fn g() {}
+#[cfg_attr(any(), cold)] // ERROR FIXME
+fn h() {}
+
+macro derive() {}
+
+#[derive(Clone)] // ERROR FIXME
+struct B;
+
+macro test() {}
+
+#[test] // ERROR FIXME
+fn test() {}
+
+macro bench() {}
+
+#[bench] // ERROR FIXME
+fn bench() {}
+
+macro_rules! inline { () => () }
+
+#[inline] //~ ERROR `inline` is ambiguous
+fn f() {}
+#[cfg_attr(all(), inline)] //~ ERROR `inline` is ambiguous
+fn f_cond() {}
+
+fn main() {}

src/test/ui/macros/ambiguous-builtin-attrs.stderr

@@ -0,0 +1,88 @@
+error[E0659]: `repr` is ambiguous
+  --> $DIR/ambiguous-builtin-attrs.rs:5:3
+   |
+LL | #[repr(C)] //~ ERROR `repr` is ambiguous
+   |   ^^^^
+   |
+note: `repr` could refer to the name defined here
+  --> $DIR/ambiguous-builtin-attrs.rs:3:1
+   |
+LL | macro repr() {}
+   | ^^^^^^^^^^^^^^^
+note: `repr` could also refer to the name defined here
+  --> $DIR/ambiguous-builtin-attrs.rs:5:3
+   |
+LL | #[repr(C)] //~ ERROR `repr` is ambiguous
+   |   ^^^^
+
+error[E0659]: `repr` is ambiguous
+  --> $DIR/ambiguous-builtin-attrs.rs:7:19
+   |
+LL | #[cfg_attr(all(), repr(C))] //~ ERROR `repr` is ambiguous
+   |                   ^^^^
+   |
+note: `repr` could refer to the name defined here
+  --> $DIR/ambiguous-builtin-attrs.rs:3:1
+   |
+LL | macro repr() {}
+   | ^^^^^^^^^^^^^^^
+note: `repr` could also refer to the name defined here
+  --> $DIR/ambiguous-builtin-attrs.rs:7:19
+   |
+LL | #[cfg_attr(all(), repr(C))] //~ ERROR `repr` is ambiguous
+   |                   ^^^^
+
+error[E0659]: `cfg` is ambiguous
+  --> $DIR/ambiguous-builtin-attrs.rs:12:3
+   |
+LL | #[cfg(all())] //~ ERROR `cfg` is ambiguous
+   |   ^^^
+   |
+note: `cfg` could refer to the name defined here
+  --> $DIR/ambiguous-builtin-attrs.rs:10:1
+   |
+LL | macro cfg() {}
+   | ^^^^^^^^^^^^^^
+note: `cfg` could also refer to the name defined here
+  --> $DIR/ambiguous-builtin-attrs.rs:12:3
+   |
+LL | #[cfg(all())] //~ ERROR `cfg` is ambiguous
+   |   ^^^
+
+error[E0659]: `inline` is ambiguous
+  --> $DIR/ambiguous-builtin-attrs.rs:41:3
+   |
+LL | #[inline] //~ ERROR `inline` is ambiguous
+   |   ^^^^^^
+   |
+note: `inline` could refer to the name defined here
+  --> $DIR/ambiguous-builtin-attrs.rs:39:1
+   |
+LL | macro_rules! inline { () => () }
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+note: `inline` could also refer to the name defined here
+  --> $DIR/ambiguous-builtin-attrs.rs:41:3
+   |
+LL | #[inline] //~ ERROR `inline` is ambiguous
+   |   ^^^^^^
+
+error[E0659]: `inline` is ambiguous
+  --> $DIR/ambiguous-builtin-attrs.rs:43:19
+   |
+LL | #[cfg_attr(all(), inline)] //~ ERROR `inline` is ambiguous
+   |                   ^^^^^^
+   |
+note: `inline` could refer to the name defined here
+  --> $DIR/ambiguous-builtin-attrs.rs:39:1
+   |
+LL | macro_rules! inline { () => () }
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+note: `inline` could also refer to the name defined here
+  --> $DIR/ambiguous-builtin-attrs.rs:43:19
+   |
+LL | #[cfg_attr(all(), inline)] //~ ERROR `inline` is ambiguous
+   |                   ^^^^^^
+
+error: aborting due to 5 previous errors
+
+For more information about this error, try `rustc --explain E0659`.