feat(rollup): add silent attr to rollup_bundle to support --silent fl…

…ag (#1680)

* feat(rollup): add silent attr to rollup_bundle to support --silent flag

As rollup_bundle already supports specific rollup flags with specific
attributes on the rollup_bundle rule, adding a boolean attribute for
silent makes the most sense.

This boolean determines if the --silent flag is added to the rollup command
when called.

* fixup! fix(examples): change build target label to //src:prodapp

* fixup! fix(examples): change build target label to //src:prodapp

packages/rollup/src/rollup_bundle.bzl

@@ -178,6 +178,14 @@ Otherwise, the outputs are assumed to be a single file.
         cfg = "host",
         default = "@npm//rollup/bin:rollup",
     ),
+    "silent": attr.bool(
+        doc = """Whether to execute the rollup binary with the --silent flag, defaults to False.
+
+Using --silent can cause rollup to [ignore errors/warnings](https://github.com/rollup/rollup/blob/master/docs/999-big-list-of-options.md#onwarn) 
+which are only surfaced via logging.  Since bazel expects printing nothing on success, setting silent to True
+is a more Bazel-idiomatic experience, however could cause rollup to drop important warnings.
+""",
+    ),
     "sourcemap": attr.string(
         doc = """Whether to produce sourcemaps.
 
@@ -316,6 +324,10 @@ def _rollup_bundle(ctx):
 
     args.add_all(["--format", ctx.attr.format])
 
+    if ctx.attr.silent:
+        # Run the rollup binary with the --silent flag
+        args.add("--silent")
+
     stamp = ctx.attr.node_context_data[NodeContextInfo].stamp
 
     config = ctx.actions.declare_file("_%s.rollup_config.js" % ctx.label.name)