allow #[link_args] with #[nolink]. For now, fail if two modules link same lib, and second has link_args.

I think it should undefined to have multiple modules that link in the same
library, but provide different link arguments. Unfortunately we don't track
link_args by module -- they are just appended as discovered into the crate
store -- but for now, it should be an error to provide link_args on a module
that's already been included (with or without link_args).

src/comp/metadata/creader.rs

@@ -60,23 +60,28 @@ fn visit_item(e: env, i: @ast::item) {
 
         let cstore = e.sess.get_cstore();
         let native_name = i.ident;
-        if vec::len(attr::find_attrs_by_name(i.attrs, "nolink")) > 0u {
-            ret;
+        let already_added = false;
+        if vec::len(attr::find_attrs_by_name(i.attrs, "nolink")) == 0u {
+            alt attr::get_meta_item_value_str_by_name(i.attrs, "link_name") {
+              some(nn) { native_name = nn; }
+              none. { }
+            }
+            if native_name == "" {
+                e.sess.span_fatal(i.span,
+                    "empty #[link_name] not allowed; use #[nolink].");
+            }
+            already_added = !cstore::add_used_library(cstore, native_name);
         }
-        alt attr::get_meta_item_value_str_by_name(i.attrs, "link_name") {
-          some(nn) { native_name = nn; }
-          none. { }
+        let link_args = attr::find_attrs_by_name(i.attrs, "link_args");
+        if vec::len(link_args) > 0u && already_added {
+            e.sess.span_fatal(i.span, "library '" + native_name +
+                              "' already added: can't specify link_args.");
         }
-        if native_name == "" {
-            e.sess.span_fatal(i.span,
-                "empty #[link_name] not allowed; use #[nolink].");
-        }
-        if !cstore::add_used_library(cstore, native_name) { ret; }
-        for a: ast::attribute in
-            attr::find_attrs_by_name(i.attrs, "link_args") {
-
+        for a: ast::attribute in link_args {
             alt attr::get_meta_item_value_str(attr::attr_meta(a)) {
-              some(linkarg) { cstore::add_used_link_args(cstore, linkarg); }
+              some(linkarg) {
+                cstore::add_used_link_args(cstore, linkarg);
+              }
               none. {/* fallthrough */ }
             }
         }

src/comp/metadata/cstore.rs

@@ -90,7 +90,7 @@ fn get_used_crate_files(cstore: cstore) -> [str] {
 }
 
 fn add_used_library(cstore: cstore, lib: str) -> bool {
-    if lib == "" { ret false; }
+    assert lib != "";
 
     if vec::member(lib, p(cstore).used_libraries) { ret false; }
     p(cstore).used_libraries += [lib];

src/test/compile-fail/nolink-with-link-args.rs

@@ -0,0 +1,11 @@
+// error-pattern:aFdEfSeVEE
+
+/* We're testing that link_args are indeed passed when nolink is specified.
+So we try to compile with junk link_args and make sure they are visible in
+the compiler output. */
+
+#[link_args = "aFdEfSeVEEE"]
+#[nolink]
+native mod m1 { }
+
+fn main() { }

src/test/compile-fail/redundant-link-args.rs

@@ -0,0 +1,17 @@
+// error-pattern:library 'm' already added: can't specify link_args.
+
+/* I think it should undefined to have multiple modules that link in the same
+  library, but provide different link arguments. Unfortunately we don't track
+  link_args by module -- they are just appended as discovered into the crate
+  store -- but for now, it should be an error to provide link_args on a module
+  that's already been included (with or without link_args). */
+
+#[link_name= "m"]
+#[link_args="-foo"]             // this could have been elided.
+native mod m1 {
+}
+
+#[link_name= "m"]
+#[link_args="-bar"]             // this is the actual error trigger.
+native mod m2 {
+}