fix(codegen): ignore transient invalid watch input

Co-Authored-By: Virgil <virgil@lethean.io>

cmd/codegen/main.go

@@ -81,6 +81,7 @@ func runDaemon(ctx context.Context, inputPath, outputPath string, emitTypes bool
 	}
 
 	var lastInput string
+	var lastOutput string
 	for {
 		input, err := coreio.Local.Read(inputPath)
 		if err != nil {
@@ -90,12 +91,18 @@ func runDaemon(ctx context.Context, inputPath, outputPath string, emitTypes bool
 		if input != lastInput {
 			out, err := generate([]byte(input), emitTypes)
 			if err != nil {
-				return err
+				// Watch mode should keep running through transient bad edits.
+				log.Error("codegen watch skipped invalid input", "err", err)
+				lastInput = input
+			} else {
+				if out != lastOutput {
+					if err := coreio.Local.Write(outputPath, out); err != nil {
+						return log.E("codegen", "writing output file", err)
+					}
+					lastOutput = out
+				}
+				lastInput = input
 			}
-			if err := coreio.Local.Write(outputPath, out); err != nil {
-				return log.E("codegen", "writing output file", err)
-			}
-			lastInput = input
 		}
 
 		select {

cmd/codegen/main_test.go

@@ -96,6 +96,36 @@ func TestRunDaemon_WritesBundle(t *testing.T) {
 	require.NoError(t, <-done)
 }
 
+func TestRunDaemon_RecoversFromInvalidJSON(t *testing.T) {
+	dir := t.TempDir()
+	inputPath := dir + "/slots.json"
+	outputPath := dir + "/bundle.js"
+
+	require.NoError(t, writeTestFile(inputPath, `not json`))
+
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
+	done := make(chan error, 1)
+	go func() {
+		done <- runDaemon(ctx, inputPath, outputPath, false, 5*time.Millisecond)
+	}()
+
+	time.Sleep(20 * time.Millisecond)
+	require.NoError(t, writeTestFile(inputPath, `{"H":"nav-bar","C":"main-content"}`))
+
+	require.Eventually(t, func() bool {
+		got, err := readTestFile(outputPath)
+		if err != nil {
+			return false
+		}
+		return strings.Contains(got, "NavBar") && strings.Contains(got, "MainContent")
+	}, time.Second, 10*time.Millisecond)
+
+	cancel()
+	require.NoError(t, <-done)
+}
+
 func TestRunDaemon_MissingPaths(t *testing.T) {
 	err := runDaemon(context.Background(), "", "", false, time.Millisecond)
 	require.Error(t, err)