fuchsia: Don't define fidl js (or cpp) compile action unless necessary

Bug: 898088
Change-Id: Iaf7c0013ff0c7fa64f008023619962526bc41b81
Reviewed-on: https://chromium-review.googlesource.com/c/1298223Reviewed-by: Wez <wez@chromium.org>
Commit-Queue: Wez <wez@chromium.org>
Commit-Queue: Scott Graham <scottmg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#602394}

build/config/fuchsia/fidl_library.gni

@@ -45,6 +45,17 @@ template("fidl_library") {
     languages = [ "cpp" ]
   }
 
+  _define_cpp_action = false
+  _define_js_action = false
+
+  foreach(language, languages) {
+    if (language == "cpp") {
+      _define_cpp_action = true
+    } else if (language == "js") {
+      _define_js_action = true
+    }
+  }
+
   _response_file = "$target_gen_dir/$target_name.rsp"
   _json_representation = "$target_gen_dir/${_library_name}.fidl.json"
   _output_gen_dir = "$target_gen_dir/fidl"
@@ -139,71 +150,75 @@ template("fidl_library") {
     ]
   }
 
-  action("${target_name}_cpp_gen") {
-    visibility = [ ":${invoker.target_name}" ]
-    forward_variables_from(invoker, [ "testonly" ])
-
-    deps = [
-      ":${invoker.target_name}_compile",
-    ]
-
-    inputs = [
-      # Depend on the SDK hash, to ensure rebuild if the SDK tools change.
-      rebase_path("$fuchsia_sdk/.hash"),
-      _json_representation,
-    ]
-
-    outputs = [
-      "${_output_base}.h",
-      "${_output_base}.cc",
-    ]
-
-    script = "//build/gn_run_binary.py"
-    args = [
-      rebase_path("//third_party/fuchsia-sdk/sdk/tools/fidlgen",
-                  root_build_dir),
-      "-generators",
-      "cpp",
-      "-json",
-      rebase_path(_json_representation),
-      "-include-base",
-      rebase_path(_output_gen_dir),
-      "-output-base",
-      rebase_path("${_output_base}"),
-    ]
+  if (_define_cpp_action) {
+    action("${target_name}_cpp_gen") {
+      visibility = [ ":${invoker.target_name}" ]
+      forward_variables_from(invoker, [ "testonly" ])
+
+      deps = [
+        ":${invoker.target_name}_compile",
+      ]
+
+      inputs = [
+        # Depend on the SDK hash, to ensure rebuild if the SDK tools change.
+        rebase_path("$fuchsia_sdk/.hash"),
+        _json_representation,
+      ]
+
+      outputs = [
+        "${_output_base}.h",
+        "${_output_base}.cc",
+      ]
+
+      script = "//build/gn_run_binary.py"
+      args = [
+        rebase_path("//third_party/fuchsia-sdk/sdk/tools/fidlgen",
+                    root_build_dir),
+        "-generators",
+        "cpp",
+        "-json",
+        rebase_path(_json_representation),
+        "-include-base",
+        rebase_path(_output_gen_dir),
+        "-output-base",
+        rebase_path("${_output_base}"),
+      ]
+    }
   }
 
-  _output_js_path = "$_output_gen_dir/${_library_path}/js/fidl.js"
-  action("${target_name}_js_gen") {
-    visibility = [ ":${invoker.target_name}" ]
-    forward_variables_from(invoker, [ "testonly" ])
-
-    deps = [
-      ":${invoker.target_name}_compile",
-    ]
-
-    inputs = [
-      # Depend on the SDK hash, to ensure rebuild if the SDK tools change.
-      rebase_path("$fuchsia_sdk/.hash"),
-      _json_representation,
-      "//build/fuchsia/fidlgen_js/fidl.py",  # The schema helper file.
-    ]
-
-    outputs = [
-      _output_js_path,
-    ]
-
-    script = "//build/fuchsia/fidlgen_js/gen.py"
-
-    args = [
-      rebase_path(_json_representation),
-      "--output",
-      rebase_path("${_output_js_path}"),
-    ]
-
-    data = []
-    foreach(o, outputs) {
-      data += [ rebase_path(o) ]
+  if (_define_js_action) {
+    _output_js_path = "$_output_gen_dir/${_library_path}/js/fidl.js"
+    action("${target_name}_js_gen") {
+      visibility = [ ":${invoker.target_name}" ]
+      forward_variables_from(invoker, [ "testonly" ])
+
+      deps = [
+        ":${invoker.target_name}_compile",
+      ]
+
+      inputs = [
+        # Depend on the SDK hash, to ensure rebuild if the SDK tools change.
+        rebase_path("$fuchsia_sdk/.hash"),
+        _json_representation,
+        "//build/fuchsia/fidlgen_js/fidl.py",  # The schema helper file.
+      ]
+
+      outputs = [
+        _output_js_path,
+      ]
+
+      script = "//build/fuchsia/fidlgen_js/gen.py"
+
+      args = [
+        rebase_path(_json_representation),
+        "--output",
+        rebase_path("${_output_js_path}"),
+      ]
+
+      data = []
+      foreach(o, outputs) {
+        data += [ rebase_path(o) ]
+      }
     }
   }