Re: [PATCH] allow setting GIT_WORK_TREE to "no work tree"

[Johannes Sixt <j.sixt@viscovery.net>]

Johannes Schindelin schrieb:
> Hi,
> 
> On Wed, 6 Feb 2008, Johannes Sixt wrote:
> 
>> Jeff King schrieb:
>>> In setup_git_directory_gently, we have a special rule that says "if 
>>> GIT_DIR is set but GIT_WORK_TREE is not, then use the current working 
>>> directory as the work tree." This is the intended behavior for the 
>>> user perspective.
>>>
>>> However, setup_git_directory_gently sets GIT_DIR itself, meaning that 
>>> further setups (either because we are executing a command via alias, 
>>> or in a subprocess) will see the non-existent GIT_WORK_TREE and assume 
>>> we fall into the "current working directory is the working tree" 
>>> codepath.
>>>
>>> Instead, we now use a special value of GIT_WORK_TREE to indicate that 
>>> we have already checked for a worktree and that there isn't one, 
>>> setting it when we set GIT_DIR and checking for it in the special case 
>>> path.
>>>
>>> The special value is a blank GIT_WORK_TREE; it could be any value, but 
>>> this should not conflict with any user values (and as a bonus, you can 
>>> now tell git "I don't have a work tree" with "GIT_WORK_TREE= git", 
>>> though I suspect the use case for that is limited).
>> Hrm. Unfortunately, on Windows there is no such thing as an empty 
>> environment string. setenv(x, "") *removes* the environment variable.
> 
> That might be a shortcoming of our implementation of setenv():

No, it is not. It's Windows's putenv(), and it's even documented.

> -- snip --
> cd /git
> 
> cat > a1.c << EOF
> #include <stdio.h>
> #include "compat/setenv.c"
> #include "compat/unsetenv.c"
> 
> static void p()
> {
> 	const char *abc = getenv("ABC");
> 	printf("env ABC: %s\n", abc ? abc : "(null)");
> }
> 
> int main()
> {
> 	p();
> 	gitsetenv("ABC", "Hello", 1);
> 	p();
> 	gitsetenv("ABC", "", 1);
> 	p();
> 	gitunsetenv("ABC");
> 	p();
> 	return 0;
> }
> EOF
> 
> gcc -DNO_MMAP=1 -I. -Icompat -o a1.exe a1.c
> 
> ABC="" ./a1.exe 
> -- snap --
> 
> This will show
> 
> env ABC: 
> env ABC: Hello
> env ABC: (null)
> env ABC: (null)
> 
> So it seems that environment variables _can_ be empty.  Just our 
> relatively stupid implementation of setenv() does not do it.
> 
> Maybe something like compat/unsetenv.c is needed in setenv(), too.

This only shows that, yes, variables _can_ be empty - if the setenv/putenv
implementation is "sane", like MSYS/bash's.

That said, we probably should modify environ directly in gitsetenv().

-- Hannes