feat(repl): improve support of multi-line statements

gnovm/cmd/gno/repl.go

@@ -2,10 +2,11 @@ package main
 
 import (
 	"bufio"
-	"bytes"
 	"context"
+	"errors"
 	"flag"
 	"fmt"
+	"go/scanner"
 	"os"
 	"strings"
 
@@ -88,91 +89,71 @@ func execRepl(cfg *replCfg, args []string) error {
 //   gno> import "gno.land/p/demo/avl"     // import the p/demo/avl package
 //   gno> func a() string { return "a" }   // declare a new function named a
 //   gno> /src                             // print current generated source
-//   gno> /editor                          // enter in editor mode to add several lines
 //   gno> /reset                           // remove all previously inserted code
 //   gno> println(a())                     // print the result of calling a()
-//   gno> /exit
+//   gno> /exit                            // alternative to <Ctrl-D>
 `)
 	}
 
 	return runRepl(cfg)
 }
 
 func runRepl(cfg *replCfg) error {
-	// init repl state
 	r := repl.NewRepl()
 
 	if cfg.initialCommand != "" {
 		handleInput(r, cfg.initialCommand)
 	}
 
-	var multiline bool
-	for {
-		fmt.Fprint(os.Stdout, "gno> ")
+	fmt.Fprint(os.Stdout, "gno> ")
 
-		input, err := getInput(multiline)
-		if err != nil {
-			return err
+	prevline := ""
+	liner := bufio.NewScanner(os.Stdin)
+
+	for liner.Scan() {
+		line := liner.Text()
+		if prevline != "" {
+			line = prevline + "\n" + line
+			prevline = ""
+		}
+
+		if err := handleInput(r, line); err != nil {
+			var goScanError scanner.ErrorList
+			if errors.As(err, &goScanError) {
+				// We assume that a Go scanner error indicates an incomplete Go statement.
+				// Append next line and retry.
+				prevline = line
+			} else {
+				fmt.Fprintln(os.Stderr, err)
+			}
 		}
 
-		multiline = handleInput(r, input)
+		if prevline == "" {
+			fmt.Fprint(os.Stdout, "gno> ")
+		} else {
+			fmt.Fprint(os.Stdout, "... ")
+		}
 	}
+	return nil
 }
 
-// handleInput reads the input string and parses it depending if it
-// is a specific command, or source code. It returns true if the following
-// input is expected to be on more than one line.
-func handleInput(r *repl.Repl, input string) bool {
+// handleInput executes specific "/" commands, or evaluates input as Gno source code.
+func handleInput(r *repl.Repl, input string) error {
 	switch strings.TrimSpace(input) {
 	case "/reset":
 		r.Reset()
 	case "/src":
 		fmt.Fprintln(os.Stdout, r.Src())
 	case "/exit":
 		os.Exit(0)
-	case "/editor":
-		fmt.Fprintln(os.Stdout, "// Entering editor mode (^D to finish)")
-		return true
 	case "":
-		// avoid to increase the repl execution counter if sending empty content
-		fmt.Fprintln(os.Stdout, "")
-		return false
+		// Avoid to increase the repl execution counter if no input.
 	default:
 		out, err := r.Process(input)
 		if err != nil {
-			fmt.Fprintln(os.Stderr, err)
+			return err
 		}
 		fmt.Fprintln(os.Stdout, out)
 	}
-
-	return false
-}
-
-const (
-	inputBreaker = "^D"
-	nl           = "\n"
-)
-
-func getInput(ml bool) (string, error) {
-	s := bufio.NewScanner(os.Stdin)
-	var mlOut bytes.Buffer
-	for s.Scan() {
-		line := s.Text()
-		if !ml {
-			return line, nil
-		}
-
-		if line == inputBreaker {
-			break
-		}
-
-		mlOut.WriteString(line)
-		mlOut.WriteString(nl)
-	}
-
-	if err := s.Err(); err != nil {
-		return "", err
-	}
-
-	return mlOut.String(), nil
+	return nil
 }

gnovm/pkg/repl/repl.go

@@ -161,7 +161,7 @@ func (r *Repl) Process(input string) (out string, err error) {
 		return r.handleExpression(exp)
 	}
 
-	return "", fmt.Errorf("error parsing code:\n\t- as expression (error: %q)\n\t- as declarations (error: %q)", expErr.Error(), declErr.Error())
+	return "", fmt.Errorf("error parsing code:\n\t- as expression: %w\n\t- as declarations: %w", expErr, declErr)
 }
 
 func (r *Repl) handleExpression(e *ast.File) (string, error) {