rustc: Don't succeed on shadowed nonexistent import

Previously resolve was checking the "import resolution" for whether an import
had succeeded or not, but this was the same structure filled in by a previous
import if a name is shadowed. Instead, this alters resolve to consult the local
resolve state (as opposed to the shared one) to test whether an import succeeded
or not.

Closes #13404

Author: alexcrichton

src/liblibc/lib.rs

@@ -146,7 +146,7 @@ pub use types::os::arch::c95::{c_ushort, clock_t, ptrdiff_t};
 pub use types::os::arch::c95::{size_t, time_t};
 pub use types::os::arch::c99::{c_longlong, c_ulonglong, intptr_t};
 pub use types::os::arch::c99::{uintptr_t};
-pub use types::os::arch::posix88::{dev_t, dirent_t, ino_t, mode_t};
+pub use types::os::arch::posix88::{dev_t, ino_t, mode_t};
 pub use types::os::arch::posix88::{off_t, pid_t, ssize_t};
 
 pub use consts::os::c95::{_IOFBF, _IOLBF, _IONBF, BUFSIZ, EOF};

src/librustc/middle/resolve.rs

@@ -144,6 +144,12 @@ impl NamespaceResult {
             _ => false
         }
     }
+    fn is_unbound(&self) -> bool {
+        match *self {
+            UnboundResult => true,
+            _ => false
+        }
+    }
 }
 
 enum NameDefinition {
@@ -2449,8 +2455,7 @@ impl<'a> Resolver<'a> {
             }
         }
 
-        if import_resolution.value_target.borrow().is_none() &&
-           import_resolution.type_target.borrow().is_none() {
+        if value_result.is_unbound() && type_result.is_unbound() {
             let msg = format!("unresolved import: there is no \
                                `{}` in `{}`",
                               token::get_ident(source),

src/test/compile-fail/issue-13404.rs

@@ -0,0 +1,21 @@
+// Copyright 2014 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.
+
+use a::f;
+use b::f;
+//~^ ERROR: unresolved import
+//~^^ ERROR: failed to resolve import
+
+mod a { pub fn f() {} }
+mod b { }
+
+fn main() {
+    f();
+}