mcedit search/replace: captured group reference `\1` not replaced if surrounded by `\{` ... `\}`

[GfEW]

Is there an existing issue for this?

• I have searched the existing issues

Midnight Commander version and build configuration

$ mc -V
GNU Midnight Commander 4.8.33-1
Built with GLib 2.84.0
Built with ncurses 6.5
Built with libssh2 1.11.1
With builtin editor
With subshell support as default
With support for background operations
With mouse support on xterm
With support for X11 events
With multiple codepages support
Virtual File Systems:
 cpiofs, tarfs, sfs, extfs, ftpfs, sftpfs, shell
Data types:
 char: 8; int: 32; long: 64; void *: 64; size_t: 64; off_t: 64; uintmax_t: 64;
$ apt info mc 2>&- | grep Version
Version: 4.8.33-1

Operating system

Linux localhost 4.19.157-perf-[...]-dirty [...] SMP PREEMPT [...] aarch64 Android

Is this issue reproducible using the latest version of Midnight Commander?

• I confirm the issue is still reproducible with the latest version of Midnight Commander

How to reproduce

capture group not replaced if surrounded by '{ ... }'

• example line:
  echo $foo_bar
• search pattern:
  \$(\w+)
• replace pattern:
  \$\{\1\}

Expected behavior

• expected result:
  echo ${foo_bar}

Actual behavior

• actual result:
  echo ${\1}

Additional context

If the braces are not escaped, the replacement works as expected:

• replace pattern:
  \${\1}
• actual result:
  echo ${foo_bar}

Whilst braces in the replacement string don't need to be escaped, doing so should certainly not break captured group references.

[zyv]

Which version of mc is that?

[zyv]

I just tried gedit and it shows the following error:

I think the glib regex library we use under the hood doesn't like the replacement. If you think this is wrong, you should talk to them.

However, I wonder why we don't show an error message. Perhaps we don't handle replacement pattern errors, only search pattern errors?

[GfEW]

Which version of mc is that?

Curiously enough, mc -V doesn't show. apt info claims 4.8.33-1, I've updated the OP accordingly.

[GfEW]

I just tried gedit and it shows the following error:

Apparently, gedit doesn't even allow \$ in replacement patterns, which IMHO is overly restrictive, as escaped chars that are not special in the replacement pattern should simply mean themselves (i. e. the idle backslash be removed).

I think the glib regex library we use under the hood doesn't like the replacement. If you think this is wrong, you should talk to them.

I'm just a regular mc user with little clue about its intestines, but I'll try.

However, I wonder why we don't show an error message. Perhaps we don't handle replacement pattern errors, only search pattern errors?

Moreover, some replacements do happen - after all, the braces are inserted correctly, and the captured group is replaced incorrectly by the broken reference. Such surprises could turn out nasty if matches are scattered across a larger file.

[zyv]

Reproducible on latest master (2f41edb).

[mc-worker]

This behavior is correct (but unfortunately undocumented).

The \{} in used for octal digits in replacement pattern:

• example line
  echo $foo_bar
• search pattern:
  \$(\w+)
• replace pattern:
  \$\{41}
• result
  echo $!

Same for hexadecimal:

• example line
  echo $foo_bar
• search pattern:
  \$(\w+)
• replace pattern:
  \$\x{21}
• result
  echo $!

Octal 41 and hex 21 is the ! character.

Since replacement pattern \{\1\} contains an invalid octal sequence \1\, it applied as is, but perhaps result should be \1\.