[build] Fix Rust static library dependecies

Depending on a static_library from Rust fails because the correct
link directory path is not passed to build_rustc_target.py. This
fix adds link paths from every one of the dependecies found in
non_rust_deps.

This is not ideal since it doesn't work with source_set or any
shared library that has transitive dependencies.

TEST=Build, CQ, and Rust crate that tests scenario.
     fx run-test static_library_tests

Change-Id: I42c2d07e68d5f7a3d76c0edacbcd0d81f50c4993

build/rust/rustc_artifact.gni

@@ -448,6 +448,15 @@ template("rustc_artifact") {
       args += [ "--with-unit-tests" ]
     }
 
+    if (defined(invoker.non_rust_deps)) {
+      foreach(dep, invoker.non_rust_deps) {
+        args += [
+          "--lib-dir",
+          rebase_path(get_label_info(dep, "target_out_dir")),
+        ]
+      }
+    }
+
     args += dep_info_paths
     outputs = [
       output_file,

examples/BUILD.gn

@@ -17,5 +17,6 @@ group("tests") {
   testonly = true
   deps = [
     "hello_world:tests",
+    "rust_static_linking:static_linking_tests",
   ]
 }

examples/rust_static_linking/BUILD.gn

+# Copyright 2019 The Fuchsia Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+import("//build/package.gni")
+import("//build/rust/rustc_library.gni")
+
+rustc_library("static_linking") {
+  name = "static_linking"
+  with_unit_tests = true
+  version = "0.1.0"
+  edition = "2018"
+  non_rust_deps = [
+    ":static",
+  ]
+}
+
+static_library("static") {
+  sources = [
+    "static.c",
+  ]
+}
+
+package("static_linking_tests") {
+  testonly = true
+  deps = [
+    ":static_linking",
+  ]
+  tests = [
+    {
+      name = "static_linking_lib_test"
+    },
+  ]
+}

examples/rust_static_linking/src/lib.rs

+// Copyright 2019 The Fuchsia Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#[link(name = "static", kind = "static")]
+extern "C" {
+    pub fn returns_two() -> u32;
+}
+
+#[cfg(test)]
+mod tests {
+    use super::returns_two;
+
+    #[test]
+    fn linking_works() {
+        assert_eq!(unsafe { returns_two() }, 2);
+    }
+}

examples/rust_static_linking/static.c

+// Copyright 2019 The Fuchsia Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include <stdint.h>
+
+uint32_t returns_two() {
+  return 2;
+}