add enable_ddc attribute to dart_library (#60)

dart/build_rules/core.bzl

@@ -26,6 +26,7 @@ dart_library = rule(
             allow_files = True,
             cfg = "data",
         ),
+        "enable_ddc": attr.bool(default = True),
         "pub_pkg_name": attr.string(default = ""),
         "deps": attr.label_list(providers = ["dart"]),
         "force_ddc_compile": attr.bool(default = False),

dart/build_rules/internal/dart_library.bzl

@@ -14,8 +14,8 @@ def dart_library_impl(ctx):
   """Implements the dart_library() rule."""
   assert_third_party_licenses(ctx)
 
-  ddc_output = ctx.outputs.ddc_output
-  source_map_output = ctx.outputs.ddc_sourcemap
+  ddc_output = ctx.outputs.ddc_output if ctx.attr.enable_ddc else None
+  source_map_output = ctx.outputs.ddc_sourcemap if ctx.attr.enable_ddc else None
   strong_summary = ctx.outputs.strong_summary
   _has_dart_sources = has_dart_sources(ctx.files.srcs)
 
@@ -34,42 +34,48 @@ def dart_library_impl(ctx):
   else:
     summary_action(ctx, dart_ctx)
 
-  if not _has_dart_sources:
-    ctx.file_action(
-        output=ddc_output,
-        content=("// intentionally empty: package %s has no dart sources" %
-                 ctx.label.name))
-    ctx.file_action(
-        output=source_map_output,
-        content=("// intentionally empty: package %s has no dart sources" %
-                 ctx.label.name))
-  else:
-    ddc_action(ctx, dart_ctx, ddc_output, source_map_output)
+  if ctx.attr.enable_ddc:
+    if not _has_dart_sources:
+      ctx.file_action(
+          output=ddc_output,
+          content=("// intentionally empty: package %s has no dart sources" %
+                   ctx.label.name))
+      ctx.file_action(
+          output=source_map_output,
+          content=("// intentionally empty: package %s has no dart sources" %
+                   ctx.label.name))
+    else:
+      ddc_action(ctx, dart_ctx, ddc_output, source_map_output)
 
   return struct(
       dart=dart_ctx,
       ddc=struct(
+        enabled=ctx.attr.enable_ddc,
         output=ddc_output,
         sourcemap=source_map_output,
       ),
   )
 
-def dart_library_outputs():
+def dart_library_outputs(enable_ddc):
   """Returns the outputs of a Dart library rule.
 
   Dart library targets emit the following outputs:
 
   * name.api.ds: the strong-mode summary from dart analyzer (API only), if specified.
-  * name.js:     the js generated by DDC
-  * name.js.map: the source map generated by DDC
+  * name.js:     the js generated by DDC if enabled
+  * name.js.map: the source map generated by DDC if enabled
 
   Returns:
     a dict of types of outputs to their respective file suffixes
   """
   outs = {
-    "ddc_output": "%{name}.js",
-    "ddc_sourcemap": "%{name}.js.map",
     "strong_summary": "%{name}." + api_summary_extension,
   }
 
+  if enable_ddc:
+    outs += {
+      "ddc_output": "%{name}.js",
+      "ddc_sourcemap": "%{name}.js.map",
+    }
+
   return outs

dart/build_rules/internal/ddc.bzl

@@ -29,6 +29,9 @@ def ddc_action(ctx, dart_ctx, ddc_output, source_map_output):
 
   # Specify all input summaries on the command line args
   for dep in dart_ctx.transitive_deps.values():
+    if not dep.ddc.enabled:
+      continue
+
     strict_transitive_srcs += dep.dart.srcs
     if has_dart_sources(dep.dart.srcs):
       if dep.ddc.output and dep.dart.strong_summary:
@@ -135,7 +138,7 @@ def dart_ddc_bundle_impl(ctx):
     dart_srcs_to_pkgs = {}
 
   for dep in dart_ctx.transitive_deps.values():
-    if has_dart_sources(dep.dart.srcs):
+    if dep.ddc.enabled and has_dart_sources(dep.dart.srcs):
       # Collect dict of dart srcs to packages, if checking duplicate srcs
       # Note that we skip angular2 which is an exception to this rule for now.
       if (ctx.attr.check_duplicate_srcs and