List - Address review feedback for --json output

- Filter non-job lines (comments, env vars) from JSON output so it
  matches the table output behavior. Creates a shallow copy of each
  crontab with only job lines before marshaling.
- Return error from printListAsJSON instead of calling os.Exit directly,
  making the error path testable.
- Check w.Write return value instead of discarding it.
- Add TestPrintListAsJSONExcludesNonJobLines test.

https://claude.ai/code/session_01K2duHV2B2CrFFVC5SYU6pH

Author: claude

cmd/list.go

@@ -42,7 +42,10 @@ Example:
 		}
 
 		if printJSON {
-			printListAsJSON(os.Stdout, crontabs)
+			if err := printListAsJSON(os.Stdout, crontabs); err != nil {
+				fmt.Fprintf(os.Stderr, "Error encoding JSON: %s\n", err)
+				os.Exit(1)
+			}
 		} else {
 			printListAsTable(os.Stdout, crontabs)
 		}
@@ -123,24 +126,30 @@ func printListAsTable(w io.Writer, crontabs []*lib.Crontab) {
 }
 
 // printListAsJSON marshals crontabs to JSON and writes to w.
-// Only crontabs with job lines are included.
-func printListAsJSON(w io.Writer, crontabs []*lib.Crontab) {
-	var output []*lib.Crontab
+// Only crontabs with job lines are included, and within each crontab
+// only job lines are emitted (matching the table output behavior).
+func printListAsJSON(w io.Writer, crontabs []*lib.Crontab) error {
+	var output []lib.Crontab
 	for _, crontab := range crontabs {
-		if len(jobLines(crontab)) > 0 {
-			output = append(output, crontab)
+		jobs := jobLines(crontab)
+		if len(jobs) == 0 {
+			continue
 		}
+		// Shallow copy with only job lines so comments/env vars are excluded
+		filtered := *crontab
+		filtered.Lines = jobs
+		output = append(output, filtered)
 	}
 
 	if output == nil {
-		output = []*lib.Crontab{}
+		output = []lib.Crontab{}
 	}
 
 	data, err := json.MarshalIndent(output, "", "  ")
 	if err != nil {
-		fmt.Fprintf(os.Stderr, "Error encoding JSON: %s\n", err)
-		os.Exit(1)
+		return err
 	}
 	data = append(data, '\n')
-	w.Write(data)
+	_, err = w.Write(data)
+	return err
 }

cmd/list_test.go

@@ -83,7 +83,9 @@ func TestPrintListAsJSONValidOutput(t *testing.T) {
 	}
 
 	var buf bytes.Buffer
-	printListAsJSON(&buf, crontabs)
+	if err := printListAsJSON(&buf, crontabs); err != nil {
+		t.Fatalf("printListAsJSON returned error: %v", err)
+	}
 
 	if buf.Len() == 0 {
 		t.Fatal("printListAsJSON produced no output")
@@ -102,7 +104,9 @@ func TestPrintListAsJSONStructure(t *testing.T) {
 	}
 
 	var buf bytes.Buffer
-	printListAsJSON(&buf, crontabs)
+	if err := printListAsJSON(&buf, crontabs); err != nil {
+		t.Fatalf("printListAsJSON returned error: %v", err)
+	}
 
 	var parsed []json.RawMessage
 	if err := json.Unmarshal(buf.Bytes(), &parsed); err != nil {
@@ -137,7 +141,9 @@ func TestPrintListAsJSONStructure(t *testing.T) {
 
 func TestPrintListAsJSONEmptyCrontabs(t *testing.T) {
 	var buf bytes.Buffer
-	printListAsJSON(&buf, []*lib.Crontab{})
+	if err := printListAsJSON(&buf, []*lib.Crontab{}); err != nil {
+		t.Fatalf("printListAsJSON returned error: %v", err)
+	}
 
 	var parsed []json.RawMessage
 	if err := json.Unmarshal(buf.Bytes(), &parsed); err != nil {
@@ -150,7 +156,9 @@ func TestPrintListAsJSONEmptyCrontabs(t *testing.T) {
 
 func TestPrintListAsJSONNilCrontabs(t *testing.T) {
 	var buf bytes.Buffer
-	printListAsJSON(&buf, nil)
+	if err := printListAsJSON(&buf, nil); err != nil {
+		t.Fatalf("printListAsJSON returned error: %v", err)
+	}
 
 	var parsed []json.RawMessage
 	if err := json.Unmarshal(buf.Bytes(), &parsed); err != nil {
@@ -175,7 +183,9 @@ func TestPrintListAsJSONSkipsEmptyCrontabs(t *testing.T) {
 	}
 
 	var buf bytes.Buffer
-	printListAsJSON(&buf, crontabs)
+	if err := printListAsJSON(&buf, crontabs); err != nil {
+		t.Fatalf("printListAsJSON returned error: %v", err)
+	}
 
 	var parsed []json.RawMessage
 	if err := json.Unmarshal(buf.Bytes(), &parsed); err != nil {
@@ -186,6 +196,38 @@ func TestPrintListAsJSONSkipsEmptyCrontabs(t *testing.T) {
 	}
 }
 
+func TestPrintListAsJSONExcludesNonJobLines(t *testing.T) {
+	crontabs := []*lib.Crontab{
+		makeCrontab("/etc/crontab", false, []*lib.Line{
+			makeLine("0 * * * *", "/usr/bin/backup"),
+			// Comment line (no command)
+			{IsComment: true, FullLine: "# this is a comment", LineNumber: 2},
+			// Env var line (no command)
+			{FullLine: "SHELL=/bin/bash", LineNumber: 3},
+			makeLine("30 2 * * *", "/usr/bin/cleanup"),
+		}),
+	}
+
+	var buf bytes.Buffer
+	if err := printListAsJSON(&buf, crontabs); err != nil {
+		t.Fatalf("printListAsJSON returned error: %v", err)
+	}
+
+	var parsed []struct {
+		Lines []json.RawMessage `json:"lines"`
+	}
+	if err := json.Unmarshal(buf.Bytes(), &parsed); err != nil {
+		t.Fatalf("failed to parse JSON: %v", err)
+	}
+
+	if len(parsed) != 1 {
+		t.Fatalf("expected 1 crontab, got %d", len(parsed))
+	}
+	if len(parsed[0].Lines) != 2 {
+		t.Errorf("expected 2 job lines (excluding comment and env var), got %d", len(parsed[0].Lines))
+	}
+}
+
 func TestPrintListAsJSONContainsCommandText(t *testing.T) {
 	crontabs := []*lib.Crontab{
 		makeCrontab("/etc/crontab", false, []*lib.Line{
@@ -194,7 +236,9 @@ func TestPrintListAsJSONContainsCommandText(t *testing.T) {
 	}
 
 	var buf bytes.Buffer
-	printListAsJSON(&buf, crontabs)
+	if err := printListAsJSON(&buf, crontabs); err != nil {
+		t.Fatalf("printListAsJSON returned error: %v", err)
+	}
 
 	if !bytes.Contains(buf.Bytes(), []byte("/usr/bin/test arg1 arg2")) {
 		t.Errorf("expected command in JSON output, got: %s", buf.String())