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.

Author: Theo-Steiner

lib/internal/readline/interface.js

@@ -20,6 +20,7 @@ const {
   MathMaxApply,
   NumberIsFinite,
   ObjectSetPrototypeOf,
+  RegExp,
   RegExpPrototypeExec,
   StringPrototypeCodePointAt,
   StringPrototypeEndsWith,
@@ -72,7 +73,7 @@ const kHistorySize = 30;
 const kMaxUndoRedoStackSize = 2048;
 const kMincrlfDelay = 100;
 // \r\n, \n, or \r followed by something other than \n
-const lineEnding = /\r?\n|\r(?!\n)/g;
+const lineEndingPattern = '\r?\n|\r(?!\n)';
 
 const kLineObjectStream = Symbol('line object stream');
 const kQuestionCancel = Symbol('kQuestionCancel');
@@ -585,6 +586,7 @@ class Interface extends InterfaceConstructor {
     }
 
     // Run test() on the new string chunk, not on the entire line buffer.
+    const lineEnding = new RegExp(lineEndingPattern, 'g');
     let newPartContainsEnding = RegExpPrototypeExec(lineEnding, string);
     if (newPartContainsEnding !== null) {
       if (this[kLine_buffer]) {
@@ -1322,18 +1324,24 @@ class Interface extends InterfaceConstructor {
         // falls through
         default:
           if (typeof s === 'string' && s) {
+            /**
+             * Use Regular Expression scoped to this block, as lastIndex and the state for RegExpPrototypeExec
+             * will be overwritten if the same RegEx instance is reused in recursive function calls.
+             */
+            const lineEnding = new RegExp(lineEndingPattern, 'g');
             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));
+                this[kLine]();
                 ({ lastIndex } = lineEnding);
-              }
-              if (lastIndex === s.length) this[kLine]();
-            } else {
-              this[kInsertString](s);
+              } while ((nextMatch = RegExpPrototypeExec(lineEnding, s)) !== null);
             }
           }
       }

lib/repl.js

@@ -861,6 +861,7 @@ function REPLServer(prompt,
       // code alignment
       const matches = self._sawKeyPress ?
         RegExpPrototypeExec(/^\s+/, cmd) : null;
+      // Preserve indentation in editorMode
       if (matches) {
         const prefix = matches[0];
         self.write(prefix);

test/parallel/test-repl-load-multiline-function.js

@@ -0,0 +1,47 @@
+'use strict';
+const common = require('../common');
+const ArrayStream = require('../common/arraystream');
+const assert = require('assert');
+const join = require('path').join;
+const fs = require('fs');
+
+common.skipIfDumbTerminal();
+
+const tmpdir = require('../common/tmpdir');
+tmpdir.refresh();
+
+const terminalCode = '(\u001b[1G\u001b[0J \u001b[1G)';
+const terminalCodeRegex = new RegExp(terminalCode.replace(/\[/g, '\\['), 'g');
+
+const repl = require('repl');
+
+const inputStream = new ArrayStream();
+const outputStream = new ArrayStream();
+
+const r = repl.start({
+  prompt: '',
+  input: inputStream,
+  output: outputStream,
+  terminal: true,
+  useColors: false
+});
+
+const testFile = 'function a(b) {\n  return b }\na(1)\n';
+const testFileName = join(tmpdir.path, 'foo.js');
+fs.writeFileSync(testFileName, testFile);
+
+const command = `.load ${testFileName}\n`;
+let accum = '';
+outputStream.write = (data) => accum += data.replace('\r', '');
+
+
+r.write(command);
+
+const expected = command +
+'function a(b) {\n' +
+'  return b }\n' +
+'a(1)\n' +
+'\n' +
+'1\n';
+assert.strictEqual(accum.replace(terminalCodeRegex, ''), expected);
+r.close();