refactor: use a single implementation for checking cnb/herokuish images

Also use a plugin trigger for testing whether an image is herokuish or not rather than trying to mess around with sourced files.

plugins/builder/.gitignore

@@ -7,4 +7,4 @@
 /install
 /post-*
 /report
-/builder-detect
+/builder-*

plugins/builder/Makefile

@@ -1,5 +1,5 @@
 SUBCOMMANDS = subcommands/report subcommands/set
-TRIGGERS = triggers/builder-detect triggers/core-post-extract triggers/install triggers/post-app-clone-setup triggers/post-app-rename-setup triggers/post-delete triggers/report
+TRIGGERS = triggers/builder-detect triggers/builder-image-is-cnb triggers/builder-image-is-herokuish triggers/core-post-extract triggers/install triggers/post-app-clone-setup triggers/post-app-rename-setup triggers/post-delete triggers/report
 BUILD = commands subcommands triggers
 PLUGIN_NAME = builder
 

plugins/builder/src/triggers/triggers.go

@@ -21,6 +21,14 @@ func main() {
 	case "builder-detect":
 		appName := flag.Arg(0)
 		err = builder.TriggerBuilderDetect(appName)
+	case "builder-image-is-cnb":
+		appName := flag.Arg(0)
+		image := flag.Arg(1)
+		err = builder.TriggerBuilderImageIsCNB(appName, image)
+	case "builder-image-is-herokuish":
+		appName := flag.Arg(0)
+		image := flag.Arg(1)
+		err = builder.TriggerBuilderImageIsHerokuish(appName, image)
 	case "core-post-extract":
 		appName := flag.Arg(0)
 		sourceWorkDir := flag.Arg(1)

plugins/builder/triggers.go

@@ -26,6 +26,28 @@ func TriggerBuilderDetect(appName string) error {
 	return nil
 }
 
+// TriggerBuilderImageIsCNB prints true if an image is cnb based, false otherwise
+func TriggerBuilderImageIsCNB(appName string, image string) error {
+	if common.IsImageCnbBased(image) {
+		fmt.Println("true")
+	} else {
+		fmt.Println("false")
+	}
+
+	return nil
+}
+
+// TriggerBuilderImageIsHerokuish prints true if an image is herokuish based, false otherwise
+func TriggerBuilderImageIsHerokuish(appName string, image string) error {
+	if common.IsImageHerokuishBased(image, appName) {
+		fmt.Println("true")
+	} else {
+		fmt.Println("false")
+	}
+
+	return nil
+}
+
 // TriggerCorePostExtract moves a configured build-dir to be in the app root dir
 func TriggerCorePostExtract(appName string, sourceWorkDir string) error {
 	buildDir := strings.Trim(reportComputedBuildDir(appName), "/")