fix: display the correct response for coder list (#16547)

Closes https://github.com/coder/coder/issues/16312

We intend to modify the behavior of the CLI handler based on the
specified output format. However, the output format is currently only
accessible within the `OutputFormatter` structure. Therefore, I propose
extending `OutputFormatter` by introducing a public `FormatID` method,
which will allow us to retrieve the format identifier and use it to
customize the behavior of the CLI handler accordingly.

cli/cliui/output.go

@@ -83,6 +83,12 @@ func (f *OutputFormatter) Format(ctx context.Context, data any) (string, error)
 	return "", xerrors.Errorf("unknown output format %q", f.formatID)
 }
 
+// FormatID will return the ID of the format selected by `--output`.
+// If no flag is present, it returns the 'default' formatter.
+func (f *OutputFormatter) FormatID() string {
+	return f.formatID
+}
+
 type tableFormat struct {
 	defaultColumns []string
 	allColumns     []string

cli/list.go

@@ -112,7 +112,7 @@ func (r *RootCmd) list() *serpent.Command {
 				return err
 			}
 
-			if len(res) == 0 {
+			if len(res) == 0 && formatter.FormatID() != cliui.JSONFormat().ID() {
 				pretty.Fprintf(inv.Stderr, cliui.DefaultStyles.Prompt, "No workspaces found! Create one:\n")
 				_, _ = fmt.Fprintln(inv.Stderr)
 				_, _ = fmt.Fprintln(inv.Stderr, "  "+pretty.Sprint(cliui.DefaultStyles.Code, "coder create <name>"))

cli/list_test.go

@@ -74,4 +74,30 @@ func TestList(t *testing.T) {
 		require.NoError(t, json.Unmarshal(out.Bytes(), &workspaces))
 		require.Len(t, workspaces, 1)
 	})
+
+	t.Run("NoWorkspacesJSON", func(t *testing.T) {
+		t.Parallel()
+		client := coderdtest.New(t, nil)
+		owner := coderdtest.CreateFirstUser(t, client)
+		member, _ := coderdtest.CreateAnotherUser(t, client, owner.OrganizationID)
+
+		inv, root := clitest.New(t, "list", "--output=json")
+		clitest.SetupConfig(t, member, root)
+
+		ctx, cancelFunc := context.WithTimeout(context.Background(), testutil.WaitLong)
+		defer cancelFunc()
+
+		stdout := bytes.NewBuffer(nil)
+		stderr := bytes.NewBuffer(nil)
+		inv.Stdout = stdout
+		inv.Stderr = stderr
+		err := inv.WithContext(ctx).Run()
+		require.NoError(t, err)
+
+		var workspaces []codersdk.Workspace
+		require.NoError(t, json.Unmarshal(stdout.Bytes(), &workspaces))
+		require.Len(t, workspaces, 0)
+
+		require.Len(t, stderr.Bytes(), 0)
+	})
 }