repl: add customizable subprompt for multiline input

Add option to customize the REPL subprompt for multiline input.

Author: pckrishnadas88

lib/internal/readline/interface.js

@@ -97,7 +97,7 @@ const ESCAPE_CODE_TIMEOUT = 500;
 // Max length of the kill ring
 const kMaxLengthOfKillRing = 32;
 
-const kMultilinePrompt = Symbol('| ');
+const kMultilinePrompt = Symbol('multilinePrompt');
 
 const kAddHistory = Symbol('_addHistory');
 const kBeforeEdit = Symbol('_beforeEdit');
@@ -237,6 +237,7 @@ function InterfaceConstructor(input, output, completer, terminal) {
   this[kUndoStack] = [];
   this[kRedoStack] = [];
   this[kPreviousCursorCols] = -1;
+  this[kMultilinePrompt] ||= { description: '| ' };
 
   // The kill ring is a global list of blocks of text that were previously
   // killed (deleted). If its size exceeds kMaxLengthOfKillRing, the oldest
@@ -411,6 +412,23 @@ class Interface extends InterfaceConstructor {
     });
   }
 
+  /**
+   * Sets the multiline prompt.
+   * @param {string} prompt
+   * @returns {void}
+   */
+  setMultilinePrompt(prompt) {
+    this[kMultilinePrompt].description = prompt;
+  }
+
+  /**
+   * Returns the current multiline prompt.
+   * @returns {string}
+   */
+  getMultilinePrompt() {
+    return this[kMultilinePrompt].description;
+  }
+
   [kSetRawMode](mode) {
     const wasInRawMode = this.input.isRaw;
 
@@ -518,7 +536,7 @@ class Interface extends InterfaceConstructor {
 
       // For continuation lines, add the "|" prefix
       for (let i = 1; i < lines.length; i++) {
-        this[kWriteToOutput](`\n${kMultilinePrompt.description}` + lines[i]);
+        this[kWriteToOutput](`\n${this[kMultilinePrompt].description}` + lines[i]);
       }
     } else {
       // Write the prompt and the current buffer content.
@@ -989,7 +1007,8 @@ class Interface extends InterfaceConstructor {
         const dy = splitEnd.length + 1;
 
         // Calculate how many Xs we need to move on the right to get to the end of the line
-        const dxEndOfLineAbove = (splitBeg[splitBeg.length - 2] || '').length + kMultilinePrompt.description.length;
+        const dxEndOfLineAbove = (splitBeg[splitBeg.length - 2] || '').length +
+                                 this[kMultilinePrompt].description.length;
         moveCursor(this.output, dxEndOfLineAbove, -dy);
 
         // This is the line that was split in the middle
@@ -1010,9 +1029,9 @@ class Interface extends InterfaceConstructor {
     }
 
     if (needsRewriteFirstLine) {
-      this[kWriteToOutput](`${this[kPrompt]}${beforeCursor}\n${kMultilinePrompt.description}`);
+      this[kWriteToOutput](`${this[kPrompt]}${beforeCursor}\n${this[kMultilinePrompt].description}`);
     } else {
-      this[kWriteToOutput](kMultilinePrompt.description);
+      this[kWriteToOutput](this[kMultilinePrompt].description);
     }
 
     // Write the rest and restore the cursor to where the user left it
@@ -1024,7 +1043,7 @@ class Interface extends InterfaceConstructor {
       const formattedEndContent = StringPrototypeReplaceAll(
         afterCursor,
         '\n',
-        `\n${kMultilinePrompt.description}`,
+        `\n${this[kMultilinePrompt].description}`,
       );
 
       this[kWriteToOutput](formattedEndContent);
@@ -1085,7 +1104,7 @@ class Interface extends InterfaceConstructor {
     const curr = splitLines[rows];
     const down = direction === 1;
     const adj = splitLines[rows + direction];
-    const promptLen = kMultilinePrompt.description.length;
+    const promptLen = this[kMultilinePrompt].description.length;
     let amountToMove;
     // Clamp distance to end of current + prompt + next/prev line + newline
     const clamp = down ?
@@ -1176,7 +1195,7 @@ class Interface extends InterfaceConstructor {
         // Rows must be incremented by 1 even if offset = 0 or col = +Infinity.
         rows += MathCeil(offset / col) || 1;
         // Only add prefix offset for continuation lines in user input (not prompts)
-        offset = this[kIsMultiline] ? kMultilinePrompt.description.length : 0;
+        offset = this[kIsMultiline] ? this[kMultilinePrompt].description.length : 0;
         continue;
       }
       // Tabs must be aligned by an offset of the tab size.

lib/internal/repl.js

@@ -22,6 +22,7 @@ function createRepl(env, opts, cb) {
     ignoreUndefined: false,
     useGlobal: true,
     breakEvalOnSigint: true,
+    multilinePrompt: opts?.multilinePrompt ?? '| ',
     ...opts,
   };
 

lib/repl.js

@@ -1192,7 +1192,8 @@ class REPLServer extends Interface {
   displayPrompt(preserveCursor) {
     let prompt = this._initialPrompt;
     if (this[kBufferedCommandSymbol].length) {
-      prompt = kMultilinePrompt.description;
+    this[kMultilinePrompt].description = '| ';
+      prompt = this[kMultilinePrompt].description;
     }
 
     // Do not overwrite `_initialPrompt` here

test/parallel/test-repl-multiline-prompt.js

@@ -0,0 +1,53 @@
+'use strict';
+const common = require('../common');
+const ArrayStream = require('../common/arraystream');
+const assert = require('assert');
+const repl = require('repl');
+
+const input = [
+  'const foo = {', // start object
+  '};',            // end object
+  'foo',            // evaluate variable
+];
+
+function runPromptTest(promptStr, { useColors }) {
+  const inputStream = new ArrayStream();
+  const outputStream = new ArrayStream();
+  let output = '';
+
+  outputStream.write = (data) => { output += data.replace('\r', ''); };
+
+  const r = repl.start({
+    prompt: '',
+    input: inputStream,
+    output: outputStream,
+    terminal: true,
+    useColors
+  });
+
+  // Set the custom multiline prompt
+  r.setMultilinePrompt(promptStr);
+
+  r.on('exit', common.mustCall(() => {
+    const lines = output.split('\n');
+
+    // Validate REPL output
+    assert.ok(lines[0].endsWith(input[0])); // first line
+    assert.ok(lines[1].includes(promptStr)); // continuation line
+    assert.ok(lines[1].endsWith(input[1])); // second line content
+    assert.ok(lines[2].includes('undefined')); // first eval result
+    assert.ok(lines[3].endsWith(input[2])); // final variable
+    assert.ok(lines[4].includes('{}')); // printed object
+  }));
+
+  inputStream.run(input);
+  r.close();
+}
+
+// Test with custom `... ` prompt
+runPromptTest('... ', { useColors: true });
+runPromptTest('... ', { useColors: false });
+
+// Test with default `| ` prompt
+runPromptTest('| ', { useColors: true });
+runPromptTest('| ', { useColors: false });