dap: return error from evaluate command in repl context

In the repl context, we will now return the error instead of directly
printing it. We also suppress reporting errors from cobra. The logic
flow has also been changed to prevent returning errors from cobra unless
there was something related to the command line invocation so usage will
only be printed when a command was typed wrong and it will not show up
for every error.

Signed-off-by: Jonathan A. Sternberg <jonathan.sternberg@docker.com>

dap/eval.go

@@ -29,43 +29,70 @@ func (d *Adapter[C]) Evaluate(ctx Context, req *dap.EvaluateRequest, resp *dap.E
 		return nil
 	}
 
-	var t *thread
-	if req.Arguments.FrameId > 0 {
-		if t = d.getThreadByFrameID(req.Arguments.FrameId); t == nil {
-			return errors.Errorf("no thread with frame id %d", req.Arguments.FrameId)
-		}
-	} else {
-		if t = d.getFirstThread(); t == nil {
-			return errors.New("no paused thread")
-		}
-	}
-
-	cmd := d.replCommands(ctx, t, resp)
+	var retErr error
+	cmd := d.replCommands(ctx, req, resp, &retErr)
 	cmd.SetArgs(args)
 	cmd.SetErr(d.Out())
 	if err := cmd.Execute(); err != nil {
-		fmt.Fprintf(d.Out(), "ERROR: %+v\n", err)
+		// This error should only happen if there was something command
+		// related that malfunctioned as it will also print usage.
+		// Normal errors should set retErr from replCommands.
+		return err
 	}
-	return nil
+	return retErr
 }
 
-func (d *Adapter[C]) replCommands(ctx Context, t *thread, resp *dap.EvaluateResponse) *cobra.Command {
-	rootCmd := &cobra.Command{}
+func (d *Adapter[C]) replCommands(ctx Context, req *dap.EvaluateRequest, resp *dap.EvaluateResponse, retErr *error) *cobra.Command {
+	rootCmd := &cobra.Command{
+		SilenceErrors: true,
+	}
 
-	execCmd := &cobra.Command{
-		Use: "exec",
-		RunE: func(cmd *cobra.Command, args []string) error {
-			if !d.supportsExec {
-				return errors.New("cannot exec without runInTerminal client capability")
-			}
-			return t.Exec(ctx, args, resp)
-		},
+	execCmd, execOpts := replCmd(ctx, "exec", resp, retErr, d.execCmd)
+	execCmd.PreRun = func(cmd *cobra.Command, args []string) {
+		execOpts.FrameID = req.Arguments.FrameId
 	}
 	rootCmd.AddCommand(execCmd)
 	return rootCmd
 }
 
-func (t *thread) Exec(ctx Context, args []string, eresp *dap.EvaluateResponse) (retErr error) {
+type execOptions struct {
+	FrameID int
+}
+
+func (d *Adapter[C]) execCmd(ctx Context, args []string, flags execOptions) (string, error) {
+	if !d.supportsExec {
+		return "", errors.New("cannot exec without runInTerminal client capability")
+	}
+
+	var t *thread
+	if flags.FrameID > 0 {
+		if t = d.getThreadByFrameID(flags.FrameID); t == nil {
+			return "", errors.Errorf("no thread with frame id %d", flags.FrameID)
+		}
+	} else {
+		if t = d.getFirstThread(); t == nil {
+			return "", errors.New("no paused thread")
+		}
+	}
+	return t.Exec(ctx, args)
+}
+
+func replCmd[Flags any, RetVal any](ctx Context, name string, resp *dap.EvaluateResponse, retErr *error, fn func(ctx Context, args []string, flags Flags) (RetVal, error)) (*cobra.Command, *Flags) {
+	flags := new(Flags)
+	return &cobra.Command{
+		Use: name,
+		Run: func(cmd *cobra.Command, args []string) {
+			v, err := fn(ctx, args, *flags)
+			if err != nil {
+				*retErr = err
+				return
+			}
+			resp.Body.Result = fmt.Sprint(v)
+		},
+	}, flags
+}
+
+func (t *thread) Exec(ctx Context, args []string) (message string, retErr error) {
 	cfg := &build.InvokeConfig{Tty: true}
 	if len(cfg.Entrypoint) == 0 && len(cfg.Cmd) == 0 {
 		cfg.Entrypoint = []string{"/bin/sh"} // launch shell by default
@@ -75,7 +102,7 @@ func (t *thread) Exec(ctx Context, args []string, eresp *dap.EvaluateResponse) (
 
 	ctr, err := build.NewContainer(ctx, t.rCtx, cfg)
 	if err != nil {
-		return err
+		return "", err
 	}
 	defer func() {
 		if retErr != nil {
@@ -85,7 +112,7 @@ func (t *thread) Exec(ctx Context, args []string, eresp *dap.EvaluateResponse) (
 
 	dir, err := os.MkdirTemp("", "buildx-dap-exec")
 	if err != nil {
-		return err
+		return "", err
 	}
 	defer func() {
 		if retErr != nil {
@@ -96,7 +123,7 @@ func (t *thread) Exec(ctx Context, args []string, eresp *dap.EvaluateResponse) (
 	socketPath := filepath.Join(dir, "s.sock")
 	l, err := net.Listen("unix", socketPath)
 	if err != nil {
-		return err
+		return "", err
 	}
 
 	go func() {
@@ -121,11 +148,11 @@ func (t *thread) Exec(ctx Context, args []string, eresp *dap.EvaluateResponse) (
 
 	resp := ctx.Request(req)
 	if !resp.GetResponse().Success {
-		return errors.New(resp.GetResponse().Message)
+		return "", errors.New(resp.GetResponse().Message)
 	}
 
-	eresp.Body.Result = fmt.Sprintf("Started process attached to %s.", socketPath)
-	return nil
+	message = fmt.Sprintf("Started process attached to %s.", socketPath)
+	return message, nil
 }
 
 func (t *thread) runExec(l net.Listener, ctr *build.Container, cfg *build.InvokeConfig) {