Clang-built Gawk 5.2.1 regex oddity

[Kenton Groombridge]

Hi,

Recently I started observing some strange behavior with gawk 5.2.1 and a
particular regex pattern found in plymouth[1]. For some reason when I
build gawk using clang 15.0.6 and try to run plymouth's
'plymouth-set-default-theme' script, I see the following error:

awk: cmd. line:3: fatal: invalid character class

This doesn't happen with gawk 5.1.1. Strangely, I can "fix" the above
error by building gawk using gcc. I've managed to reproduce this
behavior on 3 different Gentoo systems. Here is a simple test case:

head /dev/zero | awk 'BEGIN { RS="[[][:blank:]]" }'

When I build gawk with clang and run this command, I see the
aforementioned error. When I build gawk with gcc and run it, there is no
error and gawk exits cleanly.

---
Kenton Groombridge
Gentoo Linux Developer, SELinux Project

[1] 
https://gitlab.freedesktop.org/plymouth/plymouth/-/blob/main/scripts/plymouth-set-default-theme.in#L50

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