core: add concept of Flavour to core::str_bytes - #161759
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Right now things are undertested and underspecified. Some of the library code would get in a loop if searcher starts returning empty rejects. And there's no tests for backwards multi byte char matchers. Pull request I'm reviving had a problem implementing that, so making sure it's tested before the actual code lands. Right now it is possible to break both tests (and user code) without breaking anything else in the test suite I think.
Add a Haystack trait describing something that can be searched in and make core::str::Pattern (and related types) generic on that trait. This will allow Pattern to be used for types other than str (most notably OsStr). This somewhat follows the Pattern API 2.0 design. While that design is apparently abandoned (?), it is somewhat helpful when going for patterns on OsStr, so I’m going with it unless someone tells me otherwise. ;) For now leave Pattern, Haystack et al in core::str::pattern. Since they are no longer str-specific, I’ll move them to core::pattern in future commit. This one leaves them in place to make the diff smaller. @pacak: I moved some (or all new) of the `P: Pattern<&'a str> constraints into where clause to keep things narrower: ``` pub fn foo<'a, P: Pattern<&'a str>>(&'a self, pat: P, ...) ... ``` to ``` pub fn replacen<'a, P>(&'a self, pat: P, ...) ... where P: Pattern<&'a str>, ``` Original code had indices in Haystack abstracted as an associated type Cursor. Replaced with usize - Cursor adds noise with not much value. Changed wording in 2-3 places - for example Searcher is generic over a few types so it makes more sense to talk about split points in general with utf8 split points as an example for `&str`.
Pattern is no longer str-specific, so move it from core::str::pattern module to a new core::pattern module. This introduces no changes in behaviour or implementation. Just moves stuff around and adjusts documentation.
Introduce core::pattern::Split and core::pattern::SplitN internal types which can be used to implement iterators splitting haystack into parts. Convert str’s Split-family of iterators to use them. In the future, more haystacks will use those internal types. Co-authored-by: Peter Jaszkowiak <p.jaszkow@gmail.com> @pacak: Fixed some typos, added a few `#[inline]`. Since there's no `H::Cursor` - I had to add `ctx: PhantomData<H>`.
This reverts commit 85cf233ced0d0fe02734c8a83b6d79ccc5432d06. Gone for now, I'll reimplement it later in str_bytes.rs, will confirm with the benchmarks included that the optimization still applies
Introduce core::pattern::EmptyNeedleSearcher internal type which implements logic for matching an empty pattern against a haystack. Convert core::str::pattern::StrSearcher to use it. In future more implementations will take advantage of it. Also adapt and rework TwoWayStrategy into an internal SearchResult trait which abstracts differences between Searcher’s next, next_match and next_rejects methods. It makes it simpler to write a single generic method implementing optimised versions of all those calls. @pacak: - Fixed a few typos. - There's no H::Cursor parameter so code gets a bit simplified. - Added a test to assert how TwoWaySearcher runs with EmptyNeedleSearcher
@pacak: - made more things const fn - there was a (copy-paste?) error in try_finish_byte_sequence so I added a test that checks try_next_code_point(_reverse) with some values, including invalid ones. - reworded a few comments (passive voice, etc) Also different comments: since former is public and later is private due to historical reasons. > This is different than [`next_code_point`] in that it doesn't assume > This is different than `next_code_point_reverse` in that it doesn't assume
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Introduce a new core::str_bytes module with types and functions which handle string-like bytes slices. String-like means that they code treats UTF-8 byte sequences as characters within such slices but doesn't assume that the slices are well-formed. A `str` is trivially a bytes sequence that the module can handle but so is OsStr (which is WTF-8 on Windows and unstructured bytes on Unix). Move bunch of code (most notably implementation of the two-way string-matching algorithm) from core::str to core::str_bytes. Note that this likely introduces regression in some of the str function performance (since the new code cannot assume well-formed UTF-8). This is going to be rectified by following commit which will make it again possible for the code to assume bytes format. This is not done in this commit to keep it smaller. @pacak: - Added a few comments - tried to hide internal types from the diagnostic And then there's two different bugs where it would report matched areas as rejected. This broke str::trim_end_matches and who knows what else. Caught it thanks to tests in the previous commit. And one underflow bug on invalid input.
It works right now, but original implementation of the next commit breaks them with none of existing tests catching this regression.
Since core::str_bytes module cannot assume byte slices it deals with are well-formed UTF-8 (or even WTF-8), the code must be defensive and accept invalid sequences. This eliminates optimisations which would be otherwise possible. Introduce a `Flavour` trait which tags `Bytes` type with information about the byte sequence. For example, if a `Bytes` object is created from `&str` it’s tagged with `Utf8` flavour which gives the code freedom to assume data is well-formed UTF-8. This brings back all the optimisations removed in previous commit. @pacak: - removed IS_WTF8 associated constant - unused - fixed a bug related to multibyte reverse matching: `next_code_point_reverse` reads the input via Iterator::next_back, passing `bytes.iter().rev()` reverses it a second time. Not good.
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Since core::str_bytes module cannot assume byte slices it deals with
are well-formed UTF-8 (or even WTF-8), the code must be defensive and
accept invalid sequences. This eliminates optimisations which would
be otherwise possible.
Introduce a
Flavourtrait which tagsBytestype with informationabout the byte sequence. For example, if a
Bytesobject is createdfrom
&strit’s tagged withUtf8flavour which gives the codefreedom to assume data is well-formed UTF-8.
This brings back all the optimisations removed in previous commit.
@pacak:
next_code_point_reversereads the input via Iterator::next_back,passing
bytes.iter().rev()reverses it a second time. Not good.This PR is part of a stack containing 16 PRs:
main