Allow error code on action failure (#102)

Explained in the readme. This is mainly useful for our own CI, but can
also be used when running the action.

Signed-off-by: Galo Navarro <anglorvaroa@gmail.com>

.github/workflows/build.yml

@@ -30,6 +30,7 @@ jobs:
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
           INPUT_CONFIG_PATH: ./.github/labeler.yml
+          INPUT_FAIL_ON_ERROR: true
         run: ./action
 
       - name: Check that the docker image builds

README.md

@@ -137,9 +137,20 @@ will read the config file from the local checkout.
 
 ## Troubleshooting
 
-This action will avoid failing in all cases, so if you're experiencing
-unexpected behaviour it's worth looking at execution logs. Typical
-errors are related to non-existing configuration file or invalid yaml.
+To avoid blocking CI pipelines, the action will never return an error
+code and just log information about the problem. Typical errors are
+related to non-existing configuration file or invalid yaml.
+
+If you wish to make the action fail the pipeline, you can override this
+behaviour thus:
+
+    steps:
+    - uses: srvaroa/labeler@master
+      with:
+        fail_on_error: true
+
+When `fail_on_error` is enabled, any failure inside the action will
+exit the action process with an error code.
 
 ## Configuring matching rules
 

cmd/action.go

@@ -16,10 +16,20 @@ import (
 
 func main() {
 
+	// Determine if we want the action to fail on error, or be silent to
+	// prevent blocking Ci pipelines
+	failCode := 0
+	failOnError, err := strconv.ParseBool(os.Getenv("INPUT_FAIL_ON_ERROR"))
+	if err != nil {
+		log.Printf("INPUT_FAIL_ON_ERROR not set, defaulting to silent failures")
+	} else if failOnError {
+		log.Printf("INPUT_FAIL_ON_ERROR enabled, the action will exit with an error code on failure")
+		failCode = 1
+	}
 	gh, err := getGithubClient()
 	if err != nil {
 		log.Printf("Failed to retrieve a GitHub client: %+v", err)
-		return
+		os.Exit(failCode)
 	}
 	eventPayload := getEventPayload()
 	eventName := os.Getenv("GITHUB_EVENT_NAME")
@@ -39,7 +49,7 @@ func main() {
 		contents, err := ioutil.ReadFile(configFile)
 		if err != nil {
 			log.Printf("Error reading configuration from local file: %s", err)
-			return
+			os.Exit(failCode)
 		}
 		configRaw = &contents
 	} else {
@@ -58,14 +68,15 @@ func main() {
 
 		if err != nil {
 			log.Printf("Error reading configuration from default branch: %s", err)
-			return
+			os.Exit(failCode)
 		}
 
 	}
 
 	config, err := getLabelerConfigV1(configRaw)
 	if err != nil {
-		return
+		log.Printf("Unable to parse configuration")
+		os.Exit(failCode)
 	}
 
 	log.Printf("Re-evaluating labels on %s@%s",