resolve: Reserve a few very special names in macro namespace

src/librustc_resolve/macros.rs

@@ -1083,6 +1083,9 @@ pub fn define_macro(&mut self,
                 self.define(module, ident, MacroNS,
                             (def, vis, item.span, expansion, IsMacroExport));
             } else {
+                if !attr::contains_name(&item.attrs, "rustc_doc_only_macro") {
+                    self.check_reserved_macro_name(ident, MacroNS);
+                }
                 self.unused_macros.insert(def_id);
             }
         } else {

src/librustc_resolve/resolve_imports.rs

@@ -452,6 +452,16 @@ pub fn import(&self, binding: &'a NameBinding<'a>, directive: &'a ImportDirectiv
         })
     }
 
+    crate fn check_reserved_macro_name(&self, ident: Ident, ns: Namespace) {
+        // Reserve some names that are not quite covered by the general check
+        // performed on `Resolver::builtin_attrs`.
+        if ns == MacroNS &&
+           (ident.name == "cfg" || ident.name == "cfg_attr" || ident.name == "derive") {
+            self.session.span_err(ident.span,
+                                  &format!("name `{}` is reserved in macro namespace", ident));
+        }
+    }
+
     // Define the name or return the existing binding if there is a collision.
     pub fn try_define(&mut self,
                       module: Module<'a>,
@@ -459,6 +469,7 @@ pub fn try_define(&mut self,
                       ns: Namespace,
                       binding: &'a NameBinding<'a>)
                       -> Result<(), &'a NameBinding<'a>> {
+        self.check_reserved_macro_name(ident, ns);
         self.update_resolution(module, ident, ns, |this, resolution| {
             if let Some(old_binding) = resolution.binding {
                 if binding.is_glob_import() {

src/test/ui-fulldeps/proc-macro/ambiguous-builtin-attrs.rs

@@ -11,19 +11,6 @@
 #[cfg_attr(all(), repr(C))] //~ ERROR `repr` is ambiguous
 struct SCond;
 
-#[cfg(all())] //~ ERROR `cfg` is ambiguous
-struct A;
-#[cfg(any())] // ERROR FIXME
-struct A;
-
-#[cfg_attr(all(), cold)] // ERROR FIXME
-fn g() {}
-#[cfg_attr(any(), cold)] // ERROR FIXME
-fn h() {}
-
-#[derive(Clone)] // ERROR FIXME
-struct B;
-
 #[test] // OK, shadowed
 fn test() {}
 

src/test/ui-fulldeps/proc-macro/ambiguous-builtin-attrs.stderr

@@ -34,26 +34,8 @@ LL | #[cfg_attr(all(), repr(C))] //~ ERROR `repr` is ambiguous
    |                   ^^^^
    = note: consider adding an explicit import of `repr` to disambiguate
 
-error[E0659]: `cfg` is ambiguous
-  --> $DIR/ambiguous-builtin-attrs.rs:14:3
-   |
-LL | #[cfg(all())] //~ ERROR `cfg` is ambiguous
-   |   ^^^ ambiguous name
-   |
-note: `cfg` could refer to the name imported here
-  --> $DIR/ambiguous-builtin-attrs.rs:7:5
-   |
-LL | use builtin_attrs::*;
-   |     ^^^^^^^^^^^^^^^^
-note: `cfg` could also refer to the name defined here
-  --> $DIR/ambiguous-builtin-attrs.rs:14:3
-   |
-LL | #[cfg(all())] //~ ERROR `cfg` is ambiguous
-   |   ^^^
-   = note: consider adding an explicit import of `cfg` to disambiguate
-
 error[E0659]: `repr` is ambiguous
-  --> $DIR/ambiguous-builtin-attrs.rs:33:34
+  --> $DIR/ambiguous-builtin-attrs.rs:20:34
    |
 LL | fn non_macro_expanded_location<#[repr(C)] T>() { //~ ERROR `repr` is ambiguous
    |                                  ^^^^ ambiguous name
@@ -64,14 +46,14 @@ note: `repr` could refer to the name imported here
 LL | use builtin_attrs::*;
    |     ^^^^^^^^^^^^^^^^
 note: `repr` could also refer to the name defined here
-  --> $DIR/ambiguous-builtin-attrs.rs:33:34
+  --> $DIR/ambiguous-builtin-attrs.rs:20:34
    |
 LL | fn non_macro_expanded_location<#[repr(C)] T>() { //~ ERROR `repr` is ambiguous
    |                                  ^^^^
    = note: consider adding an explicit import of `repr` to disambiguate
 
 error[E0659]: `repr` is ambiguous
-  --> $DIR/ambiguous-builtin-attrs.rs:35:11
+  --> $DIR/ambiguous-builtin-attrs.rs:22:11
    |
 LL |         #[repr(C)] //~ ERROR `repr` is ambiguous
    |           ^^^^ ambiguous name
@@ -82,7 +64,7 @@ note: `repr` could refer to the name imported here
 LL | use builtin_attrs::*;
    |     ^^^^^^^^^^^^^^^^
 note: `repr` could also refer to the name defined here
-  --> $DIR/ambiguous-builtin-attrs.rs:35:11
+  --> $DIR/ambiguous-builtin-attrs.rs:22:11
    |
 LL |         #[repr(C)] //~ ERROR `repr` is ambiguous
    |           ^^^^
@@ -107,12 +89,12 @@ LL | #![feature(decl_macro)] //~ ERROR `feature` is ambiguous
    = note: consider adding an explicit import of `feature` to disambiguate
 
 error[E0425]: cannot find value `NonExistent` in this scope
-  --> $DIR/ambiguous-builtin-attrs.rs:43:5
+  --> $DIR/ambiguous-builtin-attrs.rs:30:5
    |
 LL |     NonExistent; //~ ERROR cannot find value `NonExistent` in this scope
    |     ^^^^^^^^^^^ not found in this scope
 
-error: aborting due to 7 previous errors
+error: aborting due to 6 previous errors
 
 Some errors occurred: E0425, E0659.
 For more information about an error, try `rustc --explain E0425`.

src/test/ui-fulldeps/proc-macro/auxiliary/builtin-attrs.rs

@@ -25,21 +25,6 @@ pub fn repr(_: TokenStream, input: TokenStream) -> TokenStream {
     input
 }
 
-#[proc_macro_attribute]
-pub fn cfg(_: TokenStream, input: TokenStream) -> TokenStream {
-    input
-}
-
-#[proc_macro_attribute]
-pub fn cfg_attr(_: TokenStream, input: TokenStream) -> TokenStream {
-    input
-}
-
-#[proc_macro_attribute]
-pub fn derive(_: TokenStream, input: TokenStream) -> TokenStream {
-    input
-}
-
 #[proc_macro_attribute]
 pub fn test(_: TokenStream, input: TokenStream) -> TokenStream {
     "struct Test;".parse().unwrap()

src/test/ui-fulldeps/proc-macro/reserved-macro-names.rs

@@ -0,0 +1,22 @@
+#![crate_type = "proc-macro"]
+
+extern crate proc_macro;
+use proc_macro::*;
+
+#[proc_macro_attribute]
+pub fn cfg(_: TokenStream, input: TokenStream) -> TokenStream {
+    //~^ ERROR name `cfg` is reserved in macro namespace
+    input
+}
+
+#[proc_macro_attribute]
+pub fn cfg_attr(_: TokenStream, input: TokenStream) -> TokenStream {
+    //~^ ERROR name `cfg_attr` is reserved in macro namespace
+    input
+}
+
+#[proc_macro_attribute]
+pub fn derive(_: TokenStream, input: TokenStream) -> TokenStream {
+    //~^ ERROR name `derive` is reserved in macro namespace
+    input
+}

src/test/ui-fulldeps/proc-macro/reserved-macro-names.stderr

@@ -0,0 +1,20 @@
+error: name `cfg` is reserved in macro namespace
+  --> $DIR/reserved-macro-names.rs:7:8
+   |
+LL | pub fn cfg(_: TokenStream, input: TokenStream) -> TokenStream {
+   |        ^^^
+
+error: name `cfg_attr` is reserved in macro namespace
+  --> $DIR/reserved-macro-names.rs:13:8
+   |
+LL | pub fn cfg_attr(_: TokenStream, input: TokenStream) -> TokenStream {
+   |        ^^^^^^^^
+
+error: name `derive` is reserved in macro namespace
+  --> $DIR/reserved-macro-names.rs:19:8
+   |
+LL | pub fn derive(_: TokenStream, input: TokenStream) -> TokenStream {
+   |        ^^^^^^
+
+error: aborting due to 3 previous errors
+