readline: add getPrompt to get the current prompt

Since there is a setPrompt() there should be a getPrompt().
There are use-cases where it is needed to know what the
current prompt is. Adding a getPrompt() negates the need
to store the set prompt externally or read the internal
_prompt which would be bad practice.

Co-authored-by: Colin Ihrig <cjihrig@gmail.com>

PR-URL: #33675
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Anto Aravinth <anto.aravinth.cse@gmail.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Juan José Arboleda <soyjuanarbol@gmail.com>

doc/api/readline.md

@@ -283,6 +283,15 @@ added: v0.1.98
 The `rl.setPrompt()` method sets the prompt that will be written to `output`
 whenever `rl.prompt()` is called.
 
+### `rl.getPrompt()`
+<!-- YAML
+added: REPLACEME
+-->
+
+* Returns: {string} the current prompt string
+
+The `rl.getPrompt()` method returns the current prompt used by `rl.prompt()`.
+
 ### `rl.write(data[, key])`
 <!-- YAML
 added: v0.1.98

lib/internal/repl/utils.js

@@ -144,7 +144,7 @@ function setupPreview(repl, contextSymbol, bufferSymbol, active) {
   let escaped = null;
 
   function getPreviewPos() {
-    const displayPos = repl._getDisplayPos(`${repl._prompt}${repl.line}`);
+    const displayPos = repl._getDisplayPos(`${repl.getPrompt()}${repl.line}`);
     const cursorPos = repl.line.length !== repl.cursor ?
       repl.getCursorPos() :
       displayPos;
@@ -177,7 +177,7 @@ function setupPreview(repl, contextSymbol, bufferSymbol, active) {
         rows = pos.displayPos.rows - pos.cursorPos.rows;
         moveCursor(repl.output, 0, rows);
       }
-      const totalLine = `${repl._prompt}${repl.line}${completionPreview}`;
+      const totalLine = `${repl.getPrompt()}${repl.line}${completionPreview}`;
       const newPos = repl._getDisplayPos(totalLine);
       // Minimize work for the terminal. It is enough to clear the right part of
       // the current line in case the preview is visible on a single line.
@@ -263,7 +263,7 @@ function setupPreview(repl, contextSymbol, bufferSymbol, active) {
       }
       repl.output.write(result);
       cursorTo(repl.output, cursorPos.cols);
-      const totalLine = `${repl._prompt}${repl.line}${suffix}`;
+      const totalLine = `${repl.getPrompt()}${repl.line}${suffix}`;
       const newPos = repl._getDisplayPos(totalLine);
       const rows = newPos.rows - cursorPos.rows - (newPos.cols === 0 ? 1 : 0);
       moveCursor(repl.output, 0, -rows);
@@ -611,7 +611,7 @@ function setupReverseSearch(repl) {
     let rows = 0;
     if (lastMatch !== -1) {
       const line = repl.history[lastMatch].slice(0, lastCursor);
-      rows = repl._getDisplayPos(`${repl._prompt}${line}`).rows;
+      rows = repl._getDisplayPos(`${repl.getPrompt()}${line}`).rows;
       cursorTo(repl.output, promptPos.cols);
     } else if (isInReverseSearch && repl.line !== '') {
       rows = repl.getCursorPos().rows;
@@ -631,7 +631,7 @@ function setupReverseSearch(repl) {
 
     // To know exactly how many rows we have to move the cursor back we need the
     // cursor rows, the output rows and the input rows.
-    const prompt = repl._prompt;
+    const prompt = repl.getPrompt();
     const cursorLine = `${prompt}${outputLine.slice(0, cursor)}`;
     const cursorPos = repl._getDisplayPos(cursorLine);
     const outputPos = repl._getDisplayPos(`${prompt}${outputLine}`);
@@ -682,7 +682,7 @@ function setupReverseSearch(repl) {
     if (!isInReverseSearch) {
       if (key.ctrl && checkAndSetDirectionKey(key.name)) {
         historyIndex = repl.historyIndex;
-        promptPos = repl._getDisplayPos(`${repl._prompt}`);
+        promptPos = repl._getDisplayPos(`${repl.getPrompt()}`);
         print(repl.line, `${labels[dir]}_`);
         isInReverseSearch = true;
       }

lib/readline.js

@@ -291,6 +291,11 @@ Interface.prototype.setPrompt = function(prompt) {
 };
 
 
+Interface.prototype.getPrompt = function() {
+  return this._prompt;
+};
+
+
 Interface.prototype._setRawMode = function(mode) {
   const wasInRawMode = this.input.isRaw;
 

test/parallel/test-readline-interface.js

@@ -898,6 +898,16 @@ for (let i = 0; i < 12; i++) {
     });
   }
 
+  // Calling the getPrompt method
+  {
+    const expectedPrompts = ['$ ', '> '];
+    const [rli] = getInterface({ terminal });
+    for (const prompt of expectedPrompts) {
+      rli.setPrompt(prompt);
+      assert.strictEqual(rli.getPrompt(), prompt);
+    }
+  }
+
   {
     const expected = terminal ?
       ['\u001b[1G', '\u001b[0J', '$ ', '\u001b[3G'] :
@@ -920,7 +930,7 @@ for (let i = 0; i < 12; i++) {
 
     rl.prompt();
 
-    assert.strictEqual(rl._prompt, '$ ');
+    assert.strictEqual(rl.getPrompt(), '$ ');
   }
 
   {

test/parallel/test-repl-options.js

@@ -104,7 +104,7 @@ assert.throws(r3, {
 // 4, Verify that defaults are used when no arguments are provided
 const r4 = repl.start();
 
-assert.strictEqual(r4._prompt, '> ');
+assert.strictEqual(r4.getPrompt(), '> ');
 assert.strictEqual(r4.input, process.stdin);
 assert.strictEqual(r4.output, process.stdout);
 assert.strictEqual(r4.terminal, !!r4.output.isTTY);