Set the default branch inside the event data (#354)

* set ${{github.event.repository.default_branch}}

* change `ok == false` to `!ok`

Co-authored-by: Casey Lee <cplee@nektos.com>

pkg/runner/run_context.go

@@ -400,6 +400,13 @@ func (rc *RunContext) getGithubContext() *githubContext {
 		}
 	}
 
+	// set the branch in the event data
+	if rc.Config.DefaultBranch != "" {
+		ghc.Event = withDefaultBranch(rc.Config.DefaultBranch, ghc.Event)
+	} else {
+		ghc.Event = withDefaultBranch("master", ghc.Event)
+	}
+
 	if ghc.EventName == "pull_request" {
 		ghc.BaseRef = asString(nestedMapLookup(ghc.Event, "pull_request", "base", "ref"))
 		ghc.HeadRef = asString(nestedMapLookup(ghc.Event, "pull_request", "head", "ref"))
@@ -452,6 +459,29 @@ func nestedMapLookup(m map[string]interface{}, ks ...string) (rval interface{})
 	}
 }
 
+func withDefaultBranch(b string, event map[string]interface{}) map[string]interface{} {
+	repoI, ok := event["repository"]
+	if !ok {
+		repoI = make(map[string]interface{})
+	}
+
+	repo, ok := repoI.(map[string]interface{})
+	if !ok {
+		log.Warnf("unable to set default branch to %v", b)
+		return event
+	}
+
+	// if the branch is already there return with no changes
+	if _, ok = repo["default_branch"]; ok {
+		return event
+	}
+
+	repo["default_branch"] = b
+	event["repository"] = repo
+
+	return event
+}
+
 func (rc *RunContext) withGithubEnv(env map[string]string) map[string]string {
 	github := rc.getGithubContext()
 	env["HOME"] = "/github/home"

pkg/runner/runner.go

@@ -22,6 +22,7 @@ type Config struct {
 	BindWorkdir     bool              // bind the workdir to the job container
 	EventName       string            // name of event to run
 	EventPath       string            // path to JSON file to use for event.json in containers
+	DefaultBranch   string            // name of the main branch for this repository
 	ReuseContainers bool              // reuse containers to maintain state
 	ForcePull       bool              // force pulling of the image, if already present
 	LogOutput       bool              // log the output from docker run