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* regexp: document and implement that invalid UTF-8 bytes are the same as U+FFFDRuss Cox2021-10-111-0/+7
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | What should it mean to run a regexp match on invalid UTF-8 bytes? The coherent behavior options are: 1. Invalid UTF-8 does not match any character classes, nor a U+FFFD literal (nor \x{fffd}). 2. Each byte of invalid UTF-8 is treated identically to a U+FFFD in the input, as a utf8.DecodeRune loop might. RE2 uses Rule 1. Because it works byte at a time, it can also provide \C to match any single byte of input, which matches invalid UTF-8 as well. This provides the nice property that a match for a regexp without \C is guaranteed to be valid UTF-8. Unfortunately, today Go has an incoherent mix of these two, although mostly Rule 2. This is a deviation from RE2, and it gives up the nice property, but we probably can't correct that at this point. In particular .* already matches entire inputs today, valid UTF-8 or not, and I doubt we can break that. This CL adopts Rule 2 officially, fixing the few places that deviate from it. Fixes #48749. Change-Id: I96402527c5dfb1146212f568ffa09dde91d71244 Reviewed-on: https://go-review.googlesource.com/c/go/+/354569 Trust: Russ Cox <rsc@golang.org> Run-TryBot: Russ Cox <rsc@golang.org> TryBot-Result: Go Bot <gobot@golang.org> Reviewed-by: Rob Pike <r@golang.org>
* regexp: fix repeat of preferred empty matchRuss Cox2021-05-131-0/+1
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | In Perl mode, (|a)* should match an empty string at the start of the input. Instead it matches as many a's as possible. Because (|a)+ is handled correctly, matching only an empty string, this leads to the paradox that e* can match more text than e+ (for e = (|a)) and that e+ is sometimes different from ee*. This is a very old bug that ultimately derives from the picture I drew for e* in https://swtch.com/~rsc/regexp/regexp1.html. The picture is correct for longest-match (POSIX) regexps but subtly wrong for preferred-match (Perl) regexps in the case where e has a preferred empty match. Pointed out by Andrew Gallant in private mail. The current code treats e* and e+ as the same structure, with different entry points. In the case of e* the preference list ends up not quite in the right order, in part because the “before e” and “after e” states are the same state. Splitting them apart fixes the preference list, and that can be done by compiling e* as if it were (e+)?. Like with any bug fix, there is a very low chance of breaking a program that accidentally depends on the buggy behavior. RE2, Go, and Rust all have this bug, and we've all agreed to fix it, to keep the implementations in sync. Fixes #46123. Change-Id: I70e742e71e0a23b626593b16ddef3c1e73b413b0 Reviewed-on: https://go-review.googlesource.com/c/go/+/318750 Trust: Russ Cox <rsc@golang.org> Run-TryBot: Russ Cox <rsc@golang.org> Reviewed-by: Rob Pike <r@golang.org> TryBot-Result: Go Bot <gobot@golang.org>
* regexp: limit the capacity of slices of bytes returned by FindXFrancesc Campoy2019-02-261-4/+16
| | | | | | | | | | | | | | | | | | This change limits the capacity of the slices of bytes returned by: - Find - FindAll - FindAllSubmatch to be the same as their length. Fixes #30169 Change-Id: I07b632757d2bfeab42fce0d42364e2a16c597360 Reviewed-on: https://go-review.googlesource.com/c/161877 Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org> Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org> TryBot-Result: Gobot Gobot <gobot@golang.org>
* build: move package sources from src/pkg to srcRuss Cox2014-09-081-0/+498
Preparation was in CL 134570043. This CL contains only the effect of 'hg mv src/pkg/* src'. For more about the move, see golang.org/s/go14nopkg.