Prohibit duplicated macro_exports

src/librustc_resolve/resolve_imports.rs

@@ -887,14 +887,24 @@ impl<'a, 'b:'a> ImportResolver<'a, 'b> {
         // Since import resolution is finished, globs will not define any more names.
         *module.globs.borrow_mut() = Vec::new();
 
+        let report_already_exported = |this: &mut Self, ident, span, prev_span| {
+            let msg = format!("a macro named `{}` has already been exported", ident);
+            this.session.struct_span_err(span, &msg)
+                .span_label(span, format!("`{}` already exported", ident))
+                .span_note(prev_span, "previous macro export here")
+                .emit();
+        };
+
         let mut reexports = Vec::new();
         let mut exported_macro_names = FxHashMap();
         if module as *const _ == self.graph_root as *const _ {
             let macro_exports = mem::replace(&mut self.macro_exports, Vec::new());
-            for export in macro_exports.into_iter().rev() {
-                if exported_macro_names.insert(export.ident.modern(), export.span).is_none() {
-                    reexports.push(export);
+            for export in macro_exports.into_iter() {
+                if let Some(prev_span) = exported_macro_names.insert(export.ident.modern(),
+                                                                     export.span) {
+                    report_already_exported(self, export.ident, export.span, prev_span);
                 }
+                reexports.push(export);
             }
         }
 
@@ -912,13 +922,8 @@ impl<'a, 'b:'a> ImportResolver<'a, 'b> {
                         self.cstore.export_macros_untracked(def.def_id().krate);
                     }
                     if let Def::Macro(..) = def {
-                        if let Some(&span) = exported_macro_names.get(&ident.modern()) {
-                            let msg =
-                                format!("a macro named `{}` has already been exported", ident);
-                            self.session.struct_span_err(span, &msg)
-                                .span_label(span, format!("`{}` already exported", ident))
-                                .span_note(binding.span, "previous macro export here")
-                                .emit();
+                        if let Some(legacy_span) = exported_macro_names.get(&ident.modern()) {
+                            report_already_exported(self, ident, *legacy_span, binding.span);
                         }
                     }
                     reexports.push(Export {

src/test/run-pass/issue-38715.rs → src/test/run-pass/auxiliary/two_macros_2.rs

@@ -1,4 +1,4 @@
-// Copyright 2016 The Rust Project Developers. See the COPYRIGHT
+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
 // file at the top-level directory of this distribution and at
 // http://rust-lang.org/COPYRIGHT.
 //
@@ -8,13 +8,6 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-// aux-build:issue_38715.rs
+macro_rules! macro_one { ($($t:tt)*) => ($($t)*) }
 
-// Test that `#[macro_export] macro_rules!` shadow earlier `#[macro_export] macro_rules!`
-
-#[macro_use]
-extern crate issue_38715;
-
-fn main() {
-    foo!();
-}
+macro_rules! macro_two { ($($t:tt)*) => ($($t)*) }

src/test/run-pass/mod_dir_path.rs

@@ -20,12 +20,12 @@ pub fn main() {
 
     #[path = "auxiliary"]
     mod foo {
-        mod two_macros;
+        mod two_macros_2;
     }
 
     #[path = "auxiliary"]
     mod bar {
-        macro_rules! m { () => { mod two_macros; } }
+        macro_rules! m { () => { mod two_macros_2; } }
         m!();
     }
 }

src/test/run-pass/auxiliary/issue_38715.rs → src/test/ui/issue-38715.rs

@@ -12,4 +12,4 @@
 macro_rules! foo { ($i:ident) => {} }
 
 #[macro_export]
-macro_rules! foo { () => {} }
+macro_rules! foo { () => {} } //~ ERROR a macro named `foo` has already been exported

src/test/ui/issue-38715.stderr

@@ -0,0 +1,19 @@
+error: a macro named `foo` has already been exported
+  --> $DIR/issue-38715.rs:15:1
+   |
+LL | macro_rules! foo { () => {} } //~ ERROR a macro named `foo` has already been exported
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `foo` already exported
+   |
+note: previous macro export here
+  --> $DIR/issue-38715.rs:12:1
+   |
+LL | macro_rules! foo { ($i:ident) => {} }
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error[E0601]: `main` function not found in crate `issue_38715`
+   |
+   = note: consider adding a `main` function to `$DIR/issue-38715.rs`
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0601`.