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regexp/syntax: (?:A) doesn't compile #64668

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dolmen opened this issue Dec 12, 2023 · 2 comments
Closed

regexp/syntax: (?:A) doesn't compile #64668

dolmen opened this issue Dec 12, 2023 · 2 comments
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NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one.

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@dolmen
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dolmen commented Dec 12, 2023

Go version

go version go1.21.5 darwin/arm64

What operating system and processor architecture are you using (go env)?

N/A

What did you do?

From regexp/syntax:

(?:re)         non-capturing group

https://go.dev/play/p/YKM2yyDC2Bm

import "regexp/syntax"

fmt.Println(syntax.Parse("(?:A)", 0))

Output:

<nil> error parsing regexp: missing argument to repetition operator: `?`

$ perl -E 'say ("A" =~ /(?:A)/)'
1
$ go run github.com/dolmen-go/goeval@latest -i=regexp/syntax -i=fmt 'fmt.Println(syntax.Parse("(A)", 0))'
(A) <nil>
$ go run github.com/dolmen-go/goeval@latest -i=regexp/syntax -i=fmt 'fmt.Println(syntax.Parse("(?:A)", 0))'  
<nil> error parsing regexp: missing argument to repetition operator: `?`

What did you expect to see?

no error

What did you see instead?

Output:

<nil> error parsing regexp: missing argument to repetition operator: `?`
@dolmen dolmen mentioned this issue Dec 12, 2023
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@mauri870 mauri870 added the NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. label Dec 12, 2023
@Jorropo
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Jorropo commented Dec 12, 2023

Doing this works:

import "regexp/syntax"

fmt.Println(syntax.Parse("(?:A)", syntax.Perl))

(this is what regexp.Compile uses)

0 is posix syntax:

go/src/regexp/syntax/parse.go

Line 72 in b18b058

POSIX Flags = 0 // POSIX syntax

Which does not have support for non capturing groups as far as I checked.

There is this text which attempts to explain this.
https://pkg.go.dev/regexp/syntax#hdr-Syntax

I guess each feature could explain under which syntax it is supposed to work. In a table form it might even be digest.

@dolmen
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dolmen commented Dec 12, 2023

OK, closing. I will see instead about submitting documentation improvements.

@dolmen dolmen closed this as completed Dec 12, 2023
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