txt2regex autopkgtest regression with bash 5.2

[Nick Rosbrook]

Here is a link to a failed autopkgtest log: https://autopkgtest.ubuntu.com/results/autopkgtest-kinetic/kinetic/amd64/t/txt2regex/20220827_144122_eb850@/log.gz. The relevant snippet is this:

[FAILED #53, line 77] txt2regex --all --history '241¤\'
@@ -1,23 +1,23 @@
- Regex awk : [\\]
- Regex chicken : [\\\\]
+ Regex awk : [\]
+ Regex chicken : [\\]
  Regex ed : [\]
  Regex egrep : [\]
- Regex emacs : [\\\\]
- Regex expect : [\\]
+ Regex emacs : [\\]
+ Regex expect : [\]
  Regex find : [\]
- Regex gawk : [\\]
+ Regex gawk : [\]
  Regex grep : [\]
- Regex javascript: [\\]
- Regex lex : [\\]
- Regex mawk : [\\]
- Regex mysql : [\\\\]
- Regex perl : [\\]
- Regex php : [\\\\]
- Regex postgres : [\\]
+ Regex javascript: [\]
+ Regex lex : [\]
+ Regex mawk : [\]
+ Regex mysql : [\\]
+ Regex perl : [\]
+ Regex php : [\\]
+ Regex postgres : [\]
  Regex procmail : [\]
- Regex python : [\\]
+ Regex python : [\]
  Regex sed : [\]
- Regex tcl : [\\]
+ Regex tcl : [\]
  Regex vi : [\]
- Regex vim : [\\]
+ Regex vim : [\]

The issue comes down to how the following expression -- which is simulating a section of txt2regex.sh -- is evaluated in bash 5.2 vs prior versions:

$ uin='[\]'; escape_metachar='\\'; echo ${uin/\\/$escape_metachar$escape_metachar}

Namely, we have:

  $ bash --version | head -1
  GNU bash, version 5.2.0(1)-rc2 (x86_64-pc-linux-gnu)
  $ uin='[\]'; escape_metachar='\\'; echo ${uin/\\/$escape_metachar$escape_metachar}
  [\\]

  vs.

  $ bash --version | head -1
  GNU bash, version 5.1.16(1)-release (x86_64-pc-linux-gnu)
  $ uin='[\]'; escape_metachar='\\'; echo ${uin/\\/$escape_metachar$escape_metachar}
  [\\\\]

[Nick Rosbrook (enr0n)]

The attached patch solves the issue. This PPA autopkgtest log verifies it: https://autopkgtest.ubuntu.com/results/autopkgtest-kinetic-enr0n-proposed-migration/kinetic/amd64/t/txt2regex/20220902_180733_f0883@/log.gz.

[Graham Inggs (ginggs)]

Your upstream PR was picked up by txt2regex's Debian maintainer, and someone else already sync'd it.