feat: Quit REPL when Ctrl-D is pressed on an empty prompt (#1674)

Signed-off-by: Andrew Haines <haines@cerbos.dev>

cmd/cerbos/repl/internal/repl.go

@@ -108,7 +108,16 @@ func (r *REPL) Loop() error {
 	r.output.Println()
 
 	for {
-		input := r.readInput()
+		input, err := r.readInput()
+		if err != nil {
+			if errors.Is(err, errExit) {
+				return nil
+			}
+
+			r.output.PrintErr("Failed to read input", err)
+			continue
+		}
+
 		if input == "" {
 			continue
 		}
@@ -126,25 +135,33 @@ func (r *REPL) Loop() error {
 	}
 }
 
-func (r *REPL) readInput() string {
+func (r *REPL) readInput() (string, error) {
 	var input strings.Builder
 	currPrompt := prompt
 
 	stack := &runeStack{}
 	for {
 		line, err := r.reader.Prompt(currPrompt)
 		if err != nil {
-			if errors.Is(err, io.EOF) || errors.Is(err, liner.ErrPromptAborted) {
-				return ""
+			if errors.Is(err, io.EOF) {
+				if stack.IsEmpty() {
+					return "", errExit
+				}
+
+				r.output.Println()
+				return "", nil
 			}
 
-			r.output.PrintErr("Failed to read input", err)
-			return ""
+			if errors.Is(err, liner.ErrPromptAborted) {
+				return "", nil
+			}
+
+			return "", err
 		}
 
 		line = strings.TrimSpace(line)
 		if line == "" {
-			return input.String()
+			return input.String(), nil
 		}
 
 		l, terminated := isTerminated(line, stack)
@@ -154,7 +171,7 @@ func (r *REPL) readInput() string {
 			currPrompt = secondaryPrompt
 		} else {
 			input.WriteString(l)
-			return input.String()
+			return input.String(), nil
 		}
 	}
 }

cmd/cerbos/repl/repl.go

@@ -31,6 +31,7 @@ func (c *Cmd) Run(k *kong.Kong) error {
 	histFile := getHistoryFile(c.History)
 
 	reader := liner.NewLiner()
+	reader.SetCtrlCAborts(true)
 	reader.SetMultiLineMode(true)
 
 	defer func() {