This introduces a new mechanism for evaluating lookbehind assertions by
adding four new bytecode opcodes: SetStepBack, IncStepBack,
CheckStepBack, and CheckSavedPosition.
These opcodes replace the previous GoBack-based approach and enables
correct handling of variable-length lookbehind patterns,
where the match length cannot be known statically.
Track lookbehind greediness in the parser and propagate it to bytecode
generation. Allow controlled backtracking in lookbehind bodies while
avoiding incorrect captures during step-back execution.
Partially fix issue: #3459
ca2f0141f6 removed only the execution side
of this, which made it skip some optimisations for pure string searches.
This commit implements it properly for utf16 strings instead.
Previously, we used restoration based on character position in parser.
This caused the lexer to re-tokenize from the middle of multi-character
tokens like escape sequences, and led to incorrect parse failures for
patterns like `[\[\]]`. We would backtrack to before the first `\[`
token, then re-lex the `[` as a separate token instead of part of the
`\[` escape.
Now we save and restore the actual token object along with the lexer
index, so we keep correct token state when backtracking.
We were incorrectly checking for negated character class when string
properties appeared in nested classes. Now we track negation state in
the parser and correctly reject invalid string properties in negated
classes.
This commit implements support for forward references to named capture
groups. We now allow patterns like \k<name>(?<name>x) and
self-references like (?<name>\k<name>x).
Previously, named capture groups in RegExp results did not always follow
their source order, and unmatched groups were omitted. According to the
spec, all named capture groups must appear in the result object in the
order they are defined, even if they did not participate in the match.
This commit makes sure we follow this requirement.
Take record of the named capture group prior to parsing the group's
body. This requires removal of the recorded minimum length of the named
capture group directly, and now needs to be looked up via the group
minimu lengths table.
This commit is a mix of several commits, squashed into one because the
commits before 'Move regex to own Library and fix all the broken stuff'
were not fixable in any elegant way.
The commits are listed below for "historical" purposes:
- AK: Add options/flags and Errors for regular expressions
Flags can be provided for any possible flavour by adding a new scoped enum.
Handling of flags is done by templated Options class and the overloaded
'|' and '&' operators.
- AK: Add Lexer for regular expressions
The lexer parses the input and extracts tokens needed to parse a regular
expression.
- AK: Add regex Parser and PosixExtendedParser
This patchset adds a abstract parser class that can be derived to implement
different parsers. A parser produces bytecode to be executed within the
regex matcher.
- AK: Add regex matcher
This patchset adds an regex matcher based on the principles of the T-REX VM.
The bytecode pruduced by the respective Parser is put into the matcher and
the VM will recursively execute the bytecode according to the available OpCodes.
Possible improvement: the recursion could be replaced by multi threading capabilities.
To match a Regular expression, e.g. for the Posix standard regular expression matcher
use the following API:
```
Pattern<PosixExtendedParser> pattern("^.*$");
auto result = pattern.match("Well, hello friends!\nHello World!"); // Match whole needle
EXPECT(result.count == 1);
EXPECT(result.matches.at(0).view.starts_with("Well"));
EXPECT(result.matches.at(0).view.end() == "!");
result = pattern.match("Well, hello friends!\nHello World!", PosixFlags::Multiline); // Match line by line
EXPECT(result.count == 2);
EXPECT(result.matches.at(0).view == "Well, hello friends!");
EXPECT(result.matches.at(1).view == "Hello World!");
EXPECT(pattern.has_match("Well,....")); // Just check if match without a result, which saves some resources.
```
- AK: Rework regex to work with opcodes objects
This patchsets reworks the matcher to work on a more structured base.
For that an abstract OpCode class and derived classes for the specific
OpCodes have been added. The respective opcode logic is contained in
each respective execute() method.
- AK: Add benchmark for regex
- AK: Some optimization in regex for runtime and memory
- LibRegex: Move regex to own Library and fix all the broken stuff
Now regex works again and grep utility is also in place for testing.
This commit also fixes the use of regex.h in C by making `regex_t`
an opaque (-ish) type, which makes its behaviour consistent between
C and C++ compilers.
Previously, <regex.h> would've blown C compilers up, and even if it
didn't, would've caused a leak in C code, and not in C++ code (due to
the existence of `OwnPtr` inside the struct).
To make this whole ordeal easier to deal with (for now), this pulls the
definitions of `reg*()` into LibRegex.
pros:
- The circular dependency between LibC and LibRegex is broken
- Eaiser to test (without accidentally pulling in the host's libc!)
cons:
- Using any of the regex.h functions will require the user to link -lregex
- The symbols will be missing from libc, which will be a big surprise
down the line (especially with shared libs).
Co-Authored-By: Ali Mohammad Pur <ali.mpfard@gmail.com>
