threads / bug / 55971

Bug: branch checkout is detached if the case doesn't match

Subject: Bug: branch checkout is detached if the case doesn't match

## tl;dr

6 messages between Jun 20, 2021 and Jun 23, 2021.

replies: 5people: 3as markdown or json

Tim Hutt· Jun 20, 2021, 19:45 UTC · lore

If you try to switch to a branch (e.g. `master`), but get the case wrong, e.g:

    git switch MASTER
    git checkout MASTER
    git switch Master
    git checkout Master

etc. then it autocorrects the case (bad idea but ok), but it also enables the `--detach` flag! In other words

    git switch Master

acts like

    git switch -d master

Very unexpected!

Cheers,

Tim

[System Info] git version: git version 2.32.0 cpu: x86_64 no commit associated with this build sizeof-long: 8 sizeof-size_t: 8 shell-path: /bin/sh uname: Darwin 20.4.0 Darwin Kernel Version 20.4.0: Fri Mar 5 01:14:14 PST 2021; root:xnu-7195.101.1~3/RELEASE_X86_64 x86_64 compiler info: clang: 12.0.5 (clang-1205.0.22.9) libc info: no libc information available $SHELL (typically, interactive shell): /bin/zsh

[Enabled Hooks]

Ævar Arnfjörð Bjarmason· Jun 20, 2021, 22:03 UTC · re: Tim Hutt · lore

Re: Bug: branch checkout is detached if the case doesn't match

On Sun, Jun 20 2021, Tim Hutt wrote:

Show 17 quoted lines

> If you try to switch to a branch (e.g. `master`), but get the case wrong, e.g:
>
>     git switch MASTER
>     git checkout MASTER
>     git switch Master
>     git checkout Master
>
> etc. then it autocorrects the case (bad idea but ok), but it also
> enables the `--detach` flag! In other words
>
>     git switch Master
>
> acts like
>
>     git switch -d master
>
> Very unexpected!

This behavior isn't intentionaly, but ultimately isn't with Git, but with your running of Git on a filesystem that doesn't respect POSIX semantics.

The default FS on OSX is case insensitive, we store the "master" reference (unpacked) under that name on the FS, so this is emergent behavior. Can you reproduce this after a:

    git pack-refs --all

Even after that we'll have a .git/HEAD, and I know on OSX e.g. "git log head...<branch>" unintentionally resolved to "HEAD" too at some point (probably still).

There's various workarounds in git's code to deal with funny behavior on OSX, but it's hard to catch them all as it means having to second-guess standard library calls. I think you're best off creating a case-sensitive partition on your computer and using git there if you want to avoid these cases entirely.

Show 15 quoted lines

> [System Info]
> git version:
> git version 2.32.0
> cpu: x86_64
> no commit associated with this build
> sizeof-long: 8
> sizeof-size_t: 8
> shell-path: /bin/sh
> uname: Darwin 20.4.0 Darwin Kernel Version 20.4.0: Fri Mar  5 01:14:14
> PST 2021; root:xnu-7195.101.1~3/RELEASE_X86_64 x86_64
> compiler info: clang: 12.0.5 (clang-1205.0.22.9)
> libc info: no libc information available
> $SHELL (typically, interactive shell): /bin/zsh
>
> [Enabled Hooks]

Tim Hutt· Jun 21, 2021, 17:20 UTC · re: Ævar Arnfjörð Bjarmason · lore

Re: Bug: branch checkout is detached if the case doesn't match

Ah of course!

> git pack-refs --all

Yeah that "fixes" things so you get `fatal: invalid reference: MASTER`.

I guess `git checkout` checks whether `MASTER` exists (yes, according to MacOS), but git log checks whether the current branch (`MASTER`) matches `master` (it doesn't).

Very unfortunate, but I guess it's not worth fixing.

Cheers,

Tim

On Sun, 20 Jun 2021 at 23:09, Ævar Arnfjörð Bjarmason <avarab@gmail.com> wrote:

Show 60 quoted lines

>
>
> On Sun, Jun 20 2021, Tim Hutt wrote:
>
> > If you try to switch to a branch (e.g. `master`), but get the case wrong, e.g:
> >
> >     git switch MASTER
> >     git checkout MASTER
> >     git switch Master
> >     git checkout Master
> >
> > etc. then it autocorrects the case (bad idea but ok), but it also
> > enables the `--detach` flag! In other words
> >
> >     git switch Master
> >
> > acts like
> >
> >     git switch -d master
> >
> > Very unexpected!
>
> This behavior isn't intentionaly, but ultimately isn't with Git, but
> with your running of Git on a filesystem that doesn't respect POSIX
> semantics.
>
> The default FS on OSX is case insensitive, we store the "master"
> reference (unpacked) under that name on the FS, so this is emergent
> behavior. Can you reproduce this after a:
>
>     git pack-refs --all
>
> ?
>
> Even after that we'll have a .git/HEAD, and I know on OSX e.g. "git log
> head...<branch>" unintentionally resolved to "HEAD" too at some point
> (probably still).
>
> There's various workarounds in git's code to deal with funny behavior on
> OSX, but it's hard to catch them all as it means having to second-guess
> standard library calls. I think you're best off creating a
> case-sensitive partition on your computer and using git there if you
> want to avoid these cases entirely.
>
> > [System Info]
> > git version:
> > git version 2.32.0
> > cpu: x86_64
> > no commit associated with this build
> > sizeof-long: 8
> > sizeof-size_t: 8
> > shell-path: /bin/sh
> > uname: Darwin 20.4.0 Darwin Kernel Version 20.4.0: Fri Mar  5 01:14:14
> > PST 2021; root:xnu-7195.101.1~3/RELEASE_X86_64 x86_64
> > compiler info: clang: 12.0.5 (clang-1205.0.22.9)
> > libc info: no libc information available
> > $SHELL (typically, interactive shell): /bin/zsh
> >
> > [Enabled Hooks]
>

brian m. carlson· Jun 23, 2021, 02:38 UTC · re: Tim Hutt · lore

Re: Bug: branch checkout is detached if the case doesn't match

On 2021-06-21 at 17:20:28, Tim Hutt wrote:

Show 11 quoted lines

> Ah of course!
> 
> > git pack-refs --all
> 
> Yeah that "fixes" things so you get `fatal: invalid reference: MASTER`.
> 
> I guess `git checkout` checks whether `MASTER` exists (yes, according
> to MacOS), but git log checks whether the current branch (`MASTER`)
> matches `master` (it doesn't).
> 
> Very unfortunate, but I guess it's not worth fixing.

I should point out that there is work underway to add a ref backend called reftable that doesn't store things in the file system and hence doesn't suffer from this problem. It's just a big project and it involves touching a lot of code, so it's slow going, but when it's completed, people who are using that won't have this problem ("MASTER" will be rejected if the branch is "master").

You aren't the first person to report this problem in some variation (it comes up quite frequently); we've known about it a long time, but fixing it just isn't trivial. In the mean time, you may prefer to adopt a naming convention for your project branches; for example, even though I use Linux and don't have this problem, I always use lowercase, which makes things easier for colleagues on other systems (and is also easier to type).

-- 
brian m. carlson (he/him or they/them)
Toronto, Ontario, CA

Tim Hutt· Jun 23, 2021, 11:00 UTC · re: brian m. carlson · lore

Re: Bug: branch checkout is detached if the case doesn't match

On Wed, 23 Jun 2021 at 03:38, brian m. carlson <sandals@crustytoothpaste.net> wrote:

> I should point out that there is work underway to add a ref backend
> called reftable that doesn't store things in the file system and hence
> doesn't suffer from this problem.

Ah nice - good luck!

Ævar Arnfjörð Bjarmason· Jun 23, 2021, 13:00 UTC · re: brian m. carlson · lore

Re: Bug: branch checkout is detached if the case doesn't match

On Wed, Jun 23 2021, brian m. carlson wrote:

> [...] In the mean time, you may prefer to adopt a naming convention
> for your project branches; for example, even though I use Linux and
> don't have this problem, I always use lowercase, which makes things
> easier for colleagues on other systems (and is also easier to type).

The reported issue is one that doesn't have to do with the naming of the branch itself, but git accepting it due to how the ref backend interacts with the FS.

As noted I've run into e.g. people writing unportable "head.." code, which we happily resolve to "HEAD"., ditto "master", "Master", "MASTER" etc. on OSX.