repl: fix .load infinite loop caused by shared use of lineEnding RegExp

Since the lineEnding Regular Expression is declared on the module scope,
recursive invocations of its `[kTtyWrite]` method share one instance of
this Regular Expression.
Since the state of a RegExp is managed by instance,
alternately calling RegExpPrototypeExec with the same RegExp on
different strings can lead to the state changing unexpectedly.
This is the root cause of this infinite loop bug when calling .load on
javascript files of certain shapes.

PR-URL: #46742
Fixes: #46731
Reviewed-By: Kohei Ueno <[email protected]>
Reviewed-By: Antoine du Hamel <[email protected]>

Author: Theo-Steiner

lib/internal/readline/interface.js

@@ -1329,18 +1329,22 @@ class Interface extends InterfaceConstructor {
         // falls through
         default:
           if (typeof s === 'string' && s) {
+            // Erase state of previous searches.
+            lineEnding.lastIndex = 0;
             let nextMatch = RegExpPrototypeExec(lineEnding, s);
-            if (nextMatch !== null) {
-              this[kInsertString](StringPrototypeSlice(s, 0, nextMatch.index));
-              let { lastIndex } = lineEnding;
-              while ((nextMatch = RegExpPrototypeExec(lineEnding, s)) !== null) {
-                this[kLine]();
+            // If no line endings are found, just insert the string as is.
+            if (nextMatch === null) {
+              this[kInsertString](s);
+            } else {
+              // Keep track of the end of the last match.
+              let lastIndex = 0;
+              do {
                 this[kInsertString](StringPrototypeSlice(s, lastIndex, nextMatch.index));
                 ({ lastIndex } = lineEnding);
-              }
-              if (lastIndex === s.length) this[kLine]();
-            } else {
-              this[kInsertString](s);
+                this[kLine]();
+                // Restore lastIndex as the call to kLine could have mutated it.
+                lineEnding.lastIndex = lastIndex;
+              } while ((nextMatch = RegExpPrototypeExec(lineEnding, s)) !== null);
             }
           }
       }

test/parallel/test-readline-interface-recursive-writes.js

@@ -0,0 +1,33 @@
+'use strict';
+const common = require('../common');
+const ArrayStream = require('../common/arraystream');
+const assert = require('assert');
+
+common.skipIfDumbTerminal();
+
+const readline = require('readline');
+const rli = new readline.Interface({
+  terminal: true,
+  input: new ArrayStream(),
+});
+
+let recursionDepth = 0;
+
+// Minimal reproduction for #46731
+const testInput = ' \n}\n';
+const numberOfExpectedLines = testInput.match(/\n/g).length;
+
+rli.on('line', () => {
+  // Abort in case of infinite loop
+  if (recursionDepth > numberOfExpectedLines) {
+    return;
+  }
+  recursionDepth++;
+  // Write something recursively to readline
+  rli.write('foo');
+});
+
+
+rli.write(testInput);
+
+assert.strictEqual(recursionDepth, numberOfExpectedLines);