tree 125102a4214decd6fbad07b2afbe4c6a0f709301
parent dfb6d250b1c161b1661c9de94aed207909da0342
author Stevie Strickland <sstrickl@google.com> 1552573607 +0000
committer commit-bot@chromium.org <commit-bot@chromium.org> 1552573607 +0000

[VM] Adding regexp lookbehind assertion support.

See https://github.com/tc39/proposal-regexp-lookbehind
for a high-level description of the feature and examples.  This is one of the
features requested in https://github.com/dart-lang/sdk/issues/34935.

This work takes the feature as present in the v8 engine and appropriately
merges it into our irregexp fork. Notable changes to the irregexp codebase to
introduce this feature:

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We can no longer assume that all matching proceeds forwards, since lookbehind
matching proceeds backwards. Similarly, we cannot assume that we can only be
at the start of a string if we started matching from that point. The direction
of matching must also be taken into consideration when doing bounds checking,
which previously assumed the engine would never attempt to look before the
start of a string.

-----

We may now parse backreferences to captures before the capture they
reference, since we parse regular expressions left to right, but lookbehinds
perform captures as they evaluate the string from right to left.  Since
RegExpBackReference objects contain a pointer to their corresponding capture,
this means that we may need to create RegExpCapture objects prior to the
parsing of the corresponding captured subexpression.

Thus, RegExpCapture objects are now only initialized with their index, and the
body is set later when the subexpression is encountered and parsed. This means
any method that operates on the body of a RegExpCapture can no longer be const,
which also affects the rest of the RegExpTree class hierarchy. This also means
that we don't have a valid max_match length for backreferences based off the
capture body, and must assume they can end up being any length.

-----


Change-Id: Iffe0e71b17b1a0c6fea77235e8aee5c093005811
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/94540
Commit-Queue: Stevie Strickland <sstrickl@google.com>
Reviewed-by: Martin Kustermann <kustermann@google.com>