feat: allow exiting on build failure with fallback

This adds support for exiting envbuilder on build failure
even when a `FALLBACK_IMAGE` is specified.

envbuilder.go

@@ -137,6 +137,12 @@ type Options struct {
 	// a Dockerfile is not found.
 	FallbackImage string `env:"FALLBACK_IMAGE"`
 
+	// ExitOnBuildFailure terminates the container upon a build failure.
+	// This is handy when preferring the `FALLBACK_IMAGE` in cases where
+	// no devcontainer.json or image is provided. However, it ensures
+	// that the container stops if the build process encounters an error.
+	ExitOnBuildFailure bool `env:"EXIT_ON_BUILD_FAILURE"`
+
 	// ForceSafe ignores any filesystem safety checks.
 	// This could cause serious harm to your system!
 	// This is used in cases where bypass is needed
@@ -633,7 +639,7 @@ func Run(ctx context.Context, options Options) error {
 		case strings.Contains(err.Error(), "unexpected status code 401 Unauthorized"):
 			logf(codersdk.LogLevelError, "Unable to pull the provided image. Ensure your registry credentials are correct!")
 		}
-		if !fallback {
+		if !fallback || options.ExitOnBuildFailure {
 			return err
 		}
 		logf(codersdk.LogLevelError, "Failed to build: %s", err)

integration/integration_test.go

@@ -336,6 +336,23 @@ RUN exit 1`,
 	})
 }
 
+func TestExitBuildOnFailure(t *testing.T) {
+	t.Parallel()
+	url := createGitServer(t, gitServerOptions{
+		files: map[string]string{
+			"Dockerfile": "bad syntax",
+		},
+	})
+	_, err := runEnvbuilder(t, options{env: []string{
+		"GIT_URL=" + url,
+		"DOCKERFILE_PATH=Dockerfile",
+		"FALLBACK_IMAGE=alpine",
+		// Ensures that the fallback doesn't work when an image is specified.
+		"EXIT_ON_BUILD_FAILURE=true",
+	}})
+	require.ErrorContains(t, err, "parsing dockerfile")
+}
+
 func TestPrivateRegistry(t *testing.T) {
 	t.Parallel()
 	t.Run("NoAuth", func(t *testing.T) {