Bug 1161339 - Add gtest calling rust code. r=cajbir

This is mostly to verify compilation and linkage.
The test itself just verifies the contents of an
returned string.

--HG--
extra : rebase_source : b35f41d565c6fda85ad010a328cd61b3c37681da

dom/media/gtest/TestRust.cpp

@@ -0,0 +1,8 @@
+#include <stdint.h>
+
+extern "C" uint8_t* test_rust();
+
+TEST(rust, CallFromCpp) {
+  auto greeting = test_rust();
+  EXPECT_STREQ(reinterpret_cast<char*>(greeting), "hello from rust.");
+}

dom/media/gtest/hello.rs

@@ -0,0 +1,6 @@
+#[no_mangle]
+pub extern fn test_rust() -> *const u8 {
+    // NB: rust &str aren't null terminated.
+    let greeting = "hello from rust.\0";
+    greeting.as_ptr()
+}

dom/media/gtest/moz.build

@@ -29,6 +29,11 @@ if CONFIG['MOZ_WEBM_ENCODER']:
         'TestWebMWriter.cpp',
     ]
 
+if CONFIG['MOZ_RUST']:
+    SOURCES += ['hello.rs',]
+    UNIFIED_SOURCES += ['TestRust.cpp',]
+
+
 TEST_HARNESS_FILES.gtest += [
     '../test/gizmo-frag.mp4',
     '../test/gizmo.mp4',