rustc: Move local native libs back in link-args

src/librustc/back/link.rs

@@ -1132,8 +1132,41 @@ fn link_args(sess: Session,
         args.push(~"-Wl,--allow-multiple-definition");
     }
 
-    add_local_native_libraries(&mut args, sess);
+    // Take careful note of the ordering of the arguments we pass to the linker
+    // here. Linkers will assume that things on the left depend on things to the
+    // right. Things on the right cannot depend on things on the left. This is
+    // all formally implemented in terms of resolving symbols (libs on the right
+    // resolve unknown symbols of libs on the left, but not vice versa).
+    //
+    // For this reason, we have organized the arguments we pass to the linker as
+    // such:
+    //
+    //  1. The local object that LLVM just generated
+    //  2. Upstream rust libraries
+    //  3. Local native libraries
+    //  4. Upstream native libraries
+    //
+    // This is generally fairly natural, but some may expect 2 and 3 to be
+    // swapped. The reason that all native libraries are put last is that it's
+    // not recommended for a native library to depend on a symbol from a rust
+    // crate. If this is the case then a staticlib crate is recommended, solving
+    // the problem.
+    //
+    // Additionally, it is occasionally the case that upstream rust libraries
+    // depend on a local native library. In the case of libraries such as
+    // lua/glfw/etc the name of the library isn't the same across all platforms,
+    // so only the consumer crate of a library knows the actual name. This means
+    // that downstream crates will provide the #[link] attribute which upstream
+    // crates will depend on. Hence local native libraries are after out
+    // upstream rust crates.
+    //
+    // In theory this means that a symbol in an upstream native library will be
+    // shadowed by a local native library when it wouldn't have been before, but
+    // this kind of behavior is pretty platform specific and generally not
+    // recommended anyway, so I don't think we're shooting ourself in the foot
+    // much with that.
     add_upstream_rust_crates(&mut args, sess, dylib, tmpdir);
+    add_local_native_libraries(&mut args, sess);
     add_upstream_native_libraries(&mut args, sess);
 
     // # Telling the linker what we're doing

src/test/run-make/issue-12446/Makefile

@@ -0,0 +1,6 @@
+-include ../tools.mk
+
+all: $(call STATICLIB,foo)
+	$(RUSTC) foo.rs
+	$(RUSTC) bar.rs
+	$(call RUN,bar)

src/test/run-make/issue-12446/bar.rs

@@ -0,0 +1,18 @@
+// 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.
+
+extern crate foo;
+
+#[link(name = "foo")]
+extern {}
+
+fn main() {
+    foo::foo();
+}

src/test/run-make/issue-12446/foo.c

@@ -0,0 +1 @@
+void some_c_symbol() {}

src/test/run-make/issue-12446/foo.rs

@@ -0,0 +1,19 @@
+// 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.
+
+#[crate_type = "rlib"];
+
+extern {
+    fn some_c_symbol();
+}
+
+pub fn foo() {
+    unsafe { some_c_symbol() }
+}