Ban ]
as literal first character of custom character class
#404
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
PCRE, Oniguruma, and ICU allow
]
to appear as the first member of a custom character class, and treat it as literal, due to empty character classes being invalid.However this behavior isn't particularly intuitive, and makes lexing heuristics such as swiftlang/swift#58835 harder to implement properly. Instead, reject such character classes as being empty, and require escaping if
]
is meant as the first character.