Trying to Search using variable length look-behind suggests enabling search.usePCRE2, but no such setting

• VSCode Version: 1.37.0

Steps to Reproduce:

1. ⇧⌘F (Open Find in Files)
2. Enter a regex with a non-constant length look-behind, such as (?<!a.*)b
3. 
4. Click Open Settings
5. 

Does this issue occur when all extensions are disabled?: Yes

[vscodebot]

(Experimental duplicate detection)
Thanks for submitting this issue. Please also check if it is already covered by an existing one, like:

• [REGEX] Non fixed-length lookbehind support (#76502)

[IllusionMH]

/needsMoreInfo

This flag was deprecated in 1.37 because these features should be enabled automatically https://code.visualstudio.com/updates/v1_37#_search-regex-features

Do you see any errors in DevTools (Help > Toggle Developer Tools) when you performs search?

[vscodebot]

Thanks for creating this issue! We figured it's missing some basic information or in some other way doesn't follow our issue reporting guidelines. Please take the time to review these and update the issue.

Happy Coding!

@IllusionMH No errors in the DevTools Console. I have also tried the same on the Insiders' build ba69d8dcccaebbfaa94906503728eb7c3e45b9c1 without plugins, can also reproduce there.

Realised that fixed-length look-behinds work, this only happens with variable-length ones.

Update: OK, it turns out PCRE (and most other regex libraries except .Net's) doesn't support infinite-length look-behind expressions...

[IllusionMH]

Oh, looks like it is
/duplicate of #70156

[vscodebot]

Thanks for creating this issue! We figured it's covering the same as another one we already have. Thus, we closed this one as a duplicate. You can search for existing issues here. See also our issue reporting guidelines.

Happy Coding!

[IllusionMH]

@peteVo do you see error message under the search field?

Probably I erroneously marked this as duplicate, because while inability to use variable length lookbehind can't be fixed, it make sense to use this issue to remove irrelevant error message in notification. @roblourens what do you think?

[roblourens]

Yeah so when search returns a regex parse error, we suggest trying the PCRE2 setting because that supports some features that ripgrep by default doesn't. But, now that setting is deprecated because ripgrep is able to fall back on PCRE2 automatically. So this notification needs to be removed.

We could parse a better error message out of ripgrep's output but it's a bit of a pain and wouldn't be localized. e.g. in this case it looks like

regex could not be compiled with either the default regex engine or with PCRE2.

default regex engine error:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
regex parse error:
    (?<!a.*)b
    ^^^^
error: look-around, including look-ahead and look-behind, is not supported
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

PCRE2 regex engine error:
PCRE2: error compiling pattern at offset 0: lookbehind assertion is not fixed length