repl: avoid parsing division operator as regex

This improves the heuristic used in multiline-prompt mode to determine
whether a given slash character is at the beginning of a regular
expression.

PR-URL: #10103
Reviewed-By: Prince John Wesley <princejohnwesley@gmail.com>
Reviewed-By: James M Snell <jasnell@keybase.io>
Fixes: #9300

lib/repl.js

@@ -93,6 +93,7 @@ class LineParser {
     this.shouldFail = false;
     this.blockComment = false;
     this.regExpLiteral = false;
+    this.prevTokenChar = null;
   }
 
   parseLine(line) {
@@ -132,7 +133,11 @@ class LineParser {
         if (previous === '/') {
           if (current === '*') {
             this.blockComment = true;
-          } else {
+          } else if (
+            // Distinguish between a division operator and the start of a regex
+            // by examining the non-whitespace character that precedes the /
+            [null, '(', '[', '{', '}', ';'].includes(this.prevTokenChar)
+          ) {
             this.regExpLiteral = true;
           }
           previous = null;
@@ -147,6 +152,8 @@ class LineParser {
         this._literal = this._literal || current;
       }
 
+      if (current.trim() && current !== '/') this.prevTokenChar = current;
+
       previous = current;
     }
 

test/parallel/test-repl.js

@@ -352,6 +352,16 @@ function error_test() {
 
     { client: client_unix, send: 'function * foo() {}; foo().next()',
       expect: '{ value: undefined, done: true }' },
+
+    // https://github.com/nodejs/node/issues/9300
+    { client: client_unix, send: 'function foo() {\nvar bar = 1 / 1; // "/"\n}',
+      expect: prompt_multiline + prompt_multiline + 'undefined\n' + prompt_unix },
+
+    { client: client_unix, send: '(function() {\nreturn /foo/ / /bar/;\n}())',
+      expect: prompt_multiline + prompt_multiline + 'NaN\n' + prompt_unix },
+
+    { client: client_unix, send: '(function() {\nif (false) {} /bar"/;\n}())',
+      expect: prompt_multiline + prompt_multiline + 'undefined\n' + prompt_unix }
   ]);
 }