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Russ Cox 702e337174 regexp: document and implement that invalid UTF-8 bytes are the same as U+FFFD
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>
2021-10-11 15:28:50 +00:00
.github .github: update IRC server 2021-09-30 19:56:27 +00:00
api net/http: add Cookie.Valid method 2021-10-06 23:26:57 +00:00
doc cmd/go: add release note for 'go get' changes 2021-09-28 17:19:19 +00:00
lib/time lib/time: fix RFC 6557 url 2021-08-15 02:18:46 +00:00
misc misc/cgo/testshared: pass the testing.T to goCmd when available 2021-10-08 15:27:20 +00:00
src regexp: document and implement that invalid UTF-8 bytes are the same as U+FFFD 2021-10-11 15:28:50 +00:00
test cmd/compile: eliminate successive swaps 2021-10-09 01:04:29 +00:00
.gitattributes all: treat all files as binary, but check in .bat with CRLF 2020-06-08 15:31:43 +00:00
.gitignore internal/buildcfg: move build configuration out of cmd/internal/objabi 2021-04-16 19:20:53 +00:00
AUTHORS A+C: update name to real name and add to AUTHORS 2021-09-16 23:57:28 +00:00
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CONTRIBUTORS A+C: update name to real name and add to AUTHORS 2021-09-16 23:57:28 +00:00
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README.md README.md: update contribute URL 2021-09-30 13:33:21 +00:00
SECURITY.md SECURITY.md: update go versions 2019-09-26 15:34:57 +00:00
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