Add target to produce API proto

This change should help users who want to use the API exporter, which was previously unused.

Closes bazelbuild#15220.

PiperOrigin-RevId: 441183743

src/main/java/com/google/devtools/build/lib/BUILD

@@ -521,3 +521,21 @@ genrule(
  "popd && mv $(@D)/gen_docs/tmp.zip $@",
  visibility = ["//scripts/docs:__pkg__"],
 )
+
+genrule(
+ name = "gen_api_proto",
+ srcs = [
+ "//src/main/java/com/google/devtools/build/docgen:bazel_link_map",
+ ],
+ outs = ["builtin.pb"],
+ cmd = (
+ "$(location //src/main/java/com/google/devtools/build/docgen:api_exporter)" +
+ " --output_file=$@" +
+ " --link_map_path=$(location //src/main/java/com/google/devtools/build/docgen:bazel_link_map) " +
+ " --provider=com.google.devtools.build.lib.bazel.rules.BazelRuleClassProvider" +
+ " --input_dir=$$PWD/src/main/java/com/google/devtools/build/lib"
+ ),
+ tools = [
+ "//src/main/java/com/google/devtools/build/docgen:api_exporter",
+ ],
+)