Misc

mdl/repl/color.go

@@ -0,0 +1,73 @@
+// SPDX-License-Identifier: Apache-2.0
+
+package repl
+
+import (
+	"os"
+
+	"golang.org/x/term"
+)
+
+// ANSI escape codes.
+const (
+	ansiReset    = "\033[0m"
+	ansiBold     = "\033[1m"
+	ansiBoldCyan = "\033[1;36m"
+	ansiRed      = "\033[31m"
+	ansiGray     = "\033[90m"
+)
+
+// rlIgnoreStart / rlIgnoreEnd bracket invisible characters in readline prompts
+// so readline counts the display width correctly.
+const (
+	rlIgnoreStart = "\001"
+	rlIgnoreEnd   = "\002"
+)
+
+// colorPalette applies ANSI colors when stdout is a real TTY and NO_COLOR is unset.
+type colorPalette struct {
+	enabled bool
+}
+
+// newColorPalette returns a palette active only when stdout is a terminal and
+// the NO_COLOR environment variable is absent.
+func newColorPalette() colorPalette {
+	if os.Getenv("NO_COLOR") != "" {
+		return colorPalette{}
+	}
+	return colorPalette{enabled: term.IsTerminal(int(os.Stdout.Fd()))}
+}
+
+func (c colorPalette) wrap(code, s string) string {
+	if !c.enabled {
+		return s
+	}
+	return code + s + ansiReset
+}
+
+// Bold returns s in bold.
+func (c colorPalette) Bold(s string) string { return c.wrap(ansiBold, s) }
+
+// Red returns s in red (used for errors).
+func (c colorPalette) Red(s string) string { return c.wrap(ansiRed, s) }
+
+// Gray returns s in dark gray (used for secondary text).
+func (c colorPalette) Gray(s string) string { return c.wrap(ansiGray, s) }
+
+// PromptPrimary returns a readline-safe bold-cyan prompt string.
+// The \001…\002 markers tell readline not to count the escape bytes in the
+// visible line width, preventing cursor positioning bugs.
+func (c colorPalette) PromptPrimary(s string) string {
+	if !c.enabled {
+		return s
+	}
+	return rlIgnoreStart + ansiBoldCyan + rlIgnoreEnd + s + rlIgnoreStart + ansiReset + rlIgnoreEnd
+}
+
+// PromptContinue returns a readline-safe gray continuation prompt string.
+func (c colorPalette) PromptContinue(s string) string {
+	if !c.enabled {
+		return s
+	}
+	return rlIgnoreStart + ansiGray + rlIgnoreEnd + s + rlIgnoreStart + ansiReset + rlIgnoreEnd
+}

mdl/repl/repl.go

@@ -29,6 +29,7 @@ type REPL struct {
 	prompt   string
 	rl       *readline.Instance
 	logger   *diaglog.Logger
+	c        colorPalette
 }
 
 // SetLogger sets the diagnostics logger for the REPL and its executor.
@@ -41,11 +42,13 @@ func (r *REPL) SetLogger(l *diaglog.Logger) {
 func New(input io.Reader, output io.Writer) *REPL {
 	exec := executor.New(output)
 	exec.SetBackendFactory(func() backend.FullBackend { return mprbackend.New() })
+	c := newColorPalette()
 	return &REPL{
 		executor: exec,
 		input:    input,
 		output:   output,
 		prompt:   "mdl> ",
+		c:        c,
 	}
 }
 
@@ -80,7 +83,7 @@ func (r *REPL) Run() error {
 				if errors.Is(err, executor.ErrExit) {
 					return nil
 				}
-				fmt.Fprintf(r.output, "Error: %v\n", err)
+				fmt.Fprintf(r.output, "%s\n", r.c.Red("Error: "+err.Error()))
 			}
 			buffer.Reset()
 		}
@@ -92,7 +95,7 @@ func (r *REPL) Run() error {
 		if strings.TrimSpace(input) != "" {
 			err := r.execute(input)
 			if err != nil && !errors.Is(err, executor.ErrExit) {
-				fmt.Fprintf(r.output, "Error: %v\n", err)
+				fmt.Fprintf(r.output, "%s\n", r.c.Red("Error: "+err.Error()))
 			}
 		}
 	}
@@ -130,17 +133,17 @@ func (r *REPL) RunWithReadline() error {
 
 	var buffer strings.Builder
 
-	fmt.Fprintln(r.output, "MDL REPL - Mendix Definition Language")
-	fmt.Fprintln(r.output, "Type 'help' or '?' for commands, 'exit' or 'quit' to quit")
-	fmt.Fprintln(r.output, "Tab: autocomplete, ↑↓: history, Ctrl+R: search history")
+	fmt.Fprintln(r.output, r.c.Bold("MDL REPL")+" — Mendix Definition Language")
+	fmt.Fprintln(r.output, r.c.Gray("Type 'help' or '?' for commands, 'exit' or 'quit' to quit"))
+	fmt.Fprintln(r.output, r.c.Gray("Tab: autocomplete, ↑↓: history, Ctrl+R: search history"))
 	fmt.Fprintln(r.output)
 
 	for {
 		// Set prompt based on whether we're continuing a multi-line statement
 		if buffer.Len() == 0 {
-			rl.SetPrompt(r.prompt)
+			rl.SetPrompt(r.c.PromptPrimary(r.prompt))
 		} else {
-			rl.SetPrompt("...> ")
+			rl.SetPrompt(r.c.PromptContinue("...> "))
 		}
 
 		// Read line with readline (supports history, arrow keys, etc.)
@@ -189,7 +192,7 @@ func (r *REPL) RunWithReadline() error {
 					fmt.Fprintln(r.output, "Goodbye!")
 					return nil
 				}
-				fmt.Fprintf(r.output, "Error: %v\n", err)
+				fmt.Fprintf(r.output, "%s\n", r.c.Red("Error: "+err.Error()))
 			}
 			buffer.Reset()
 		}
@@ -218,7 +221,7 @@ func (r *REPL) execute(input string) error {
 	prog, errs := visitor.Build(input)
 	if len(errs) > 0 {
 		for _, err := range errs {
-			fmt.Fprintf(r.output, "Parse error: %v\n", err)
+			fmt.Fprintf(r.output, "%s\n", r.c.Red("Parse error: "+err.Error()))
 		}
 		r.logger.ParseError(input, errs)
 		return nil // Don't return error, just print and continue