[5.9] Optimize search for start-anchored regexes #684
Conversation
When a regex is anchored to the start of a subject, there's no need to search throughout a string for the pattern when searching for the first match: a prefix match is sufficient. This adds a regex compilation-time check about whether a match can only be found at the start of a subject, and then uses that to choose whether to defer to `prefixMatch` from within `firstMatch`.
|
@swift-ci Please test |
|
@swift-ci Please test macOS platform |
1 similar comment
|
@swift-ci Please test macOS platform |
natecook1000
force-pushed
the
anchor_prefix_match_5_9
branch
from
e114521 to
b58c24c
Compare
|
@swift-ci Please test macOS platform |
|
@swift-ci Please test macOS platform |
1 similar comment
|
@swift-ci Please test macOS platform |
natecook1000
force-pushed
the
anchor_prefix_match_5_9
branch
from
9d0d9f5 to
12a8c9b
Compare
|
@swift-ci Please test macOS platform |
1 similar comment
|
@swift-ci Please test macOS platform |
The order of this property in MEProgram seems to determine whether or not it persists from the time it's stored to when it's accessed in RegexDSLTests. Clearly something else is going on here, but this works around the issue for now.
|
@swift-ci Please test |
| /// - `nil`: This node is inconclusive about where it can match. | ||
| /// | ||
| /// In particular, non-required groups and option-setting groups are | ||
| /// inconclusive about where they can match. |
There was a problem hiding this comment.
How is nil actually different from false? What can the caller do with a nil result that they cannot do with a false result?
There was a problem hiding this comment.
Returning nil means that the node doesn't determine the result either way. For example, in /(?i)^foo/, the (?i) node is encountered as the first child of a concatenation, and doesn't affect whether or not the pattern can only match at the start. Returning nil means that the search for a definitive answer can continue to the next sibling.
Note that callers don't have access to this method; the one they call just returns a Bool.
When a regex is anchored to the start of a subject, there's no need to search throughout a string for the pattern when searching for the first match: a prefix match is sufficient.
This adds a regex compilation-time check about whether a match can only be found at the start of a subject, and then uses that to choose whether to defer to
prefixMatchfrom withinfirstMatch.(This is a cherry-pick of #682.)