Choose one: is this a bug report or feature request? a bug

Expected Behavior

By default, babel-register creates a cache in the user's home directory, .babel.json. This cache appears to be unmanaged based on looking at ./babel-register/lib/cache.js. The cache should manage itself to avoid growing to an extremely large size.

Current Behavior

I started experiencing v8 crashes when running mocha tests using --compilers js:babel-core/register as below:

<--- Last few GCs --->

   82518 ms: Mark-sweep 807.1 (1039.7) -> 802.3 (1038.7) MB, 149.2 / 0.0 ms [allocation failure] [GC in old space requested].
   82668 ms: Mark-sweep 802.3 (1038.7) -> 802.3 (1036.7) MB, 150.6 / 0.0 ms [allocation failure] [GC in old space requested].
   82838 ms: Mark-sweep 802.3 (1036.7) -> 802.2 (993.7) MB, 169.7 / 0.0 ms [last resort gc].
   82989 ms: Mark-sweep 802.2 (993.7) -> 802.2 (982.7) MB, 150.6 / 0.0 ms [last resort gc].


<--- JS stacktrace --->

==== JS stack trace =========================================

Security context: 0000024EE58CFB61 <JS Object>
    1: SparseJoinWithSeparatorJS(aka SparseJoinWithSeparatorJS) [native array.js:~75] [pc=000002B8298FC057] (this=0000024EE5804381 <undefined>,w=0000011715C4D061 <JS Array[7440]>,F=000003681BBC8B19 <JS Array[7440]>,x=7440,I=0000024EE58B46F1 <JS Function ConvertToString (SharedFunctionInfo 0000024EE5852DC9)>,J=000003681BBC8AD9 <String[4]\: ,\n  >)
    2: DoJoin(aka DoJoin) [native array.js:137...

FATAL ERROR: CALL_AND_RETRY_LAST Allocation failed - JavaScript heap out of memory

I traced these to babel-register/lib/cache.js code calling JSON.stringify on the cache object.

  try {
    serialised = (0, _stringify2.default)(data, null, "  ");
  } catch (err) {

My .cache.json was over 200 megabytes. Deleting it immediately resolved the problem.

Possible Solution

• cache should periodically expire old things and have a maximum size
• cache could be implemented using some kind of simple database that's more efficient than reading the entire cache into memory & rewriting it at the end of a session

Context

Prevents inline transpilation from working properly, and performance suffers significantly as the cache size grows and each operation requires reading/writing a huge file.

Because it's very difficult to trace the source of v8 crashes, this is a rather insidious bug. There is at least one other bug report in a random package that is almost certainly this issue:

caolan/async#1311

This would primarily become an issue for people running large test suites using babel-register in a single environment that is never purged (e.g. a dev workstation). I expect even though it may not manifest very often, there are certainly performance and stability implications for a large number of users for never pruning the cache.

Your Environment

Windows 10
Node 6.10.2
Npm 4.2.0
Babel 6.18.2