problem with backslash in directory name

[Joachim Durchholz <jo@durchholz.org>]

Hi all,

I'm having a problem with submodules that reside in directories that 
(unwisely) contain a backslash in their name.


Transcript:

### Arrange

$ git init main
Initialized empty Git repository in /tmp/test/main/.git/

$ git init sub\\with\\backslash
Initialized empty Git repository in /tmp/test/sub\with\backslash/.git/
# This looks okay: the shell interpreted \\ as \,
# so we get sub\with\backslash

# Create a log entry in sub\with\backslash
# (it can't be added as a submodule otherwise)
# ((actually I think it's a misfeature, my current use case would be
# easier if git didn't insist on having a log in submodules))
$ touch sub\\with\\backslash/empty.file
$ git -C sub\\with\\backslash add empty.file
$ git -C sub\\with\\backslash commit -m "Added empty.file"
[master (root-commit) a27a485] Added empty.file
  1 file changed, 0 insertions(+), 0 deletions(-)
  create mode 100644 empty.file

### Act/Assert

$ git -C main submodule add ../sub\\with\\backslash
fatal: repository '/tmp/test/sub\witackslash' does not exist
fatal: clone of '/tmp/test/sub\witackslash' into submodule path 
'sub\with\backslash' failed
# The first "fatal:" line talks about "witackslash"
# Um... "ackslash"? Now that's a nice nickname for a CVE :-)

# Okay, let's see what's actually in that message
$ git -C main submodule add ../sub\\with\\backslash 2>&1 | xxd
00000000: 6661 7461 6c3a 2072 6570 6f73 6974 6f72  fatal: repositor
00000010: 7920 272f 746d 702f 7465 7374 2f73 7562  y '/tmp/test/sub
00000020: 5c77 6974 6808 6163 6b73 6c61 7368 2720  \with.ackslash'
00000030: 646f 6573 206e 6f74 2065 7869 7374 0a66  does not exist.f
00000040: 6174 616c 3a20 636c 6f6e 6520 6f66 2027  atal: clone of '
00000050: 2f74 6d70 2f74 6573 742f 7375 625c 7769  /tmp/test/sub\wi
00000060: 7468 0861 636b 736c 6173 6827 2069 6e74  th.ackslash' int
00000070: 6f20 7375 626d 6f64 756c 6520 7061 7468  o submodule path
00000080: 2027 7375 625c 7769 7468 5c62 6163 6b73   'sub\with\backs
00000090: 6c61 7368 2720 6661 696c 6564 0a         lash' failed.

# Yeah, there's a 0x08 at offset 0x25.
# It's pretty strange that it is eliding the w following the \b,
# not the h preceding it.


So... something inside "git submodule add" is replacing the \b with a 
backspace control code.


Next I tried something nasty:

$ mv sub\\with\\backslash 'sub: $(bc)'
git -C main submodule add '../sub: $(bc)'
Cloning into ' $(bc)'...
done.

Whatever that "something" is, it is not doing shell expansion, otherwise 
it would have started an interactive calculator session.
Phew :-)
I'm still a bit uneasy because I don't know what other escape sequences 
might get interpreted, and what their effects are.