add support to custom main branch name

Summary: This diff adds support to customize main branch name when generating GitHub Actions.

Differential Revision: D30679305

fbshipit-source-id: 0fc7eb1c97c27e2b42e60cc1ab69a48ab93b93fa

build/fbcode_builder/getdeps.py

@@ -772,13 +772,6 @@ class TestCmd(ProjectCmdBase):
 @cmd("generate-github-actions", "generate a GitHub actions configuration")
 class GenerateGitHubActionsCmd(ProjectCmdBase):
     RUN_ON_ALL = """ [push, pull_request]"""
-    RUN_ON_DEFAULT = """
-  push:
-    branches:
-    - master
-  pull_request:
-    branches:
-    - master"""
 
     def run_project_cmd(self, args, loader, manifest):
         platforms = [
@@ -790,6 +783,17 @@ class GenerateGitHubActionsCmd(ProjectCmdBase):
         for p in platforms:
             self.write_job_for_platform(p, args)
 
+    def get_run_on(self, args):
+        if args.run_on_all_branches:
+            return self.RUN_ON_ALL
+        return f"""
+  push:
+    branches:
+    - {args.main_branch}
+  pull_request:
+    branches:
+    - {args.main_branch}"""
+
     # TODO: Break up complex function
     def write_job_for_platform(self, platform, args):  # noqa: C901
         build_opts = setup_build_options(args, platform)
@@ -797,7 +801,7 @@ class GenerateGitHubActionsCmd(ProjectCmdBase):
         loader = ManifestLoader(build_opts, ctx_gen)
         manifest = loader.load_manifest(args.project)
         manifest_ctx = loader.ctx_gen.get_context(manifest.name)
-        run_on = self.RUN_ON_ALL if args.run_on_all_branches else self.RUN_ON_DEFAULT
+        run_on = self.get_run_on(args)
 
         # Some projects don't do anything "useful" as a leaf project, only
         # as a dep for a leaf project. Check for those here; we don't want
@@ -945,6 +949,11 @@ jobs:
         parser.add_argument(
             "--ubuntu-version", default="18.04", help="Version of Ubuntu to use"
         )
+        parser.add_argument(
+            "--main-branch",
+            default="master",
+            help="Main branch to trigger GitHub Action on",
+        )
 
 
 def get_arg_var_name(args):