Don't warn about 'pub use' statements

Author: alexcrichton

src/librustc/middle/resolve.rs

@@ -5285,10 +5285,13 @@ pub impl Resolver {
         for module_.import_resolutions.each_value |&import_resolution| {
             // Ignore dummy spans for things like automatically injected
             // imports for the prelude, and also don't warn about the same
-            // import statement being unused more than once.
+            // import statement being unused more than once. Furthermore, if
+            // the import is public, then we can't be sure whether it's unused
+            // or not so don't warn about it.
             if !import_resolution.state.used &&
                     !import_resolution.state.warned &&
-                    import_resolution.span != dummy_sp() {
+                    import_resolution.span != dummy_sp() &&
+                    import_resolution.privacy != Public {
                 import_resolution.state.warned = true;
                 match self.unused_import_lint_level {
                     warn => {

src/test/compile-fail/unused-imports-warn.rs

@@ -31,6 +31,9 @@ mod foo {
 }
 
 mod bar {
+    // Don't ignore on 'pub use' because we're not sure if it's used or not
+    pub use core::cmp::Eq;
+
     pub mod c {
         use foo::Point;
         use foo::Square; //~ ERROR unused import