commit e260cc033050d08b8c6137db963b25fc622f8bd4
author Lasse R.H. Nielsen <lrn@google.com> Thu Oct 03 14:01:41 2024 +0000
committer Commit Queue <dart-scoped@luci-project-accounts.iam.gserviceaccount.com> Thu Oct 03 14:01:41 2024 +0000
tree 53b13576ae91e5aad2c0c600a560f5ed4df1e752
parent 7909ef1225819db34d2a1681d7d6953a612e4e3f

Reset regexp `lastIndex` before using it again.

The way JS RegExps handle anchored matches is to have a separate RegExp
with `|()` added at the end, which means it either matches at that point,
or the `()` matches at that point, and that's visible in the captures
as a non-`null` last capture group.

The same RegExp is used to find the number of captures a RegExp has,
by running it on an empty string, and seeing the length of the capture
array, even if it contains nothing but `null` and `""` values.

The RegExp is as JS global regexp, which is what allows it to start matching
at a specific point, which we use for `startsWith(Pattern, start)`.
Every *normal* use of that RegExp remembers to set the `lastIndex` of the
regexp before using it, but the `regExpCaptureCount` used the "anchored
regexp" directly, and forgot to set the `lastIndex`, and since it had just
been used and failed to match at a position *later* than the current input
string's length, the "unfailable" test on the empty string failed, returning
`null` where no `null` was expected.

So now `regExpCaptureCount` sets `lastIndex` to zero before using the RegExp,
like every use of a shared RegExp should.

Fixes #56834

Bug: https://dartbug/com/56834
Change-Id: Ib649b70db5922c277950d7b7cfd4d157788d11cc
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/388002
Commit-Queue: Lasse Nielsen <lrn@google.com>
Reviewed-by: Ömer Ağacan <omersa@google.com>