repl: repl clobbers RegExp.$1

[bnoordhuis]

$ out/Release/iojs
> RegExp.$1
'RegExp.$1'
> eval(RegExp.$1)
# snip
    at <error: RangeError: Maximum call stack size exceeded>

[vkurchatkin]

is this the same issue: nodejs/node-v0.x-archive#4088 ?

[bnoordhuis]

Yes, it is. I'd forgotten about that other issue, actually.

[vkurchatkin]

As an idea: we can execute regexps in a different context

[chrisdickinson]

Given that we have a patch, this would make a good first bug for anyone with the time to PR it in.

[thefourtheye]

I was looking at it the other day, I was able to reproduce the problem but couldn't understand the fix suggested. I ll spend sometime this week to understand it.

[bnoordhuis]

Reproducing here for posterity:

diff --git a/lib/repl.js b/lib/repl.js
index 361745f..fe3077c 100644
--- a/lib/repl.js
+++ b/lib/repl.js
@@ -104,9 +104,14 @@ function REPLServer(prompt, stream, eval_, useGlobal, ignoreUndefined) {

   self.useGlobal = !!useGlobal;
   self.ignoreUndefined = !!ignoreUndefined;
+  self._saved = [];

   self.eval = eval_ || function(code, context, file, cb) {
     var err, result;
+
+    // restore RegExp.$1 to RegExp.$9
+    /^\u0000(.*)\u0000(.*)\u0000(.*)\u0000(.*)\u0000(.*)\u0000(.*)\u0000(.*)\u0000(.*)\u0000(.*)$/.test(self._saved.join('\u0000'));
+
     try {
       if (self.useGlobal) {
         result = vm.runInThisContext(code, file);
@@ -116,6 +121,11 @@ function REPLServer(prompt, stream, eval_, useGlobal, ignoreUndefined) {
     } catch (e) {
       err = e;
     }
+
+    for (var i = 1; i <= 9; ++i) {
+      self._saved[i] = RegExp['$' + i];
+    }
+
     cb(err, result);
   };

@thefourtheye It works by creating a string from the 9 saved values, then doing a capturing match against that, thereby restoring the values of RegExp.$1 to RegExp.$9.

Aside: using '\u0000' as the separator is probably not unique enough in practice.

[thefourtheye]

@bnoordhuis Thanks for helping me understand :-)