patchProactively fix a test issue with v3.x of the MSYS2 runtime

I saw this in one of my builds that followed the bleeding edge of Git for Windows' SDK: git.exe has a different idea of the test script's PID than the test script itself. Yet another of the quirks Git for Windows has to deal with...

Johannes Schindelin (1):
  t6500(mingw): use the Windows PID of the shell

 t/t6500-gc.sh | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

base-commit: 8104ec994ea3849a968b4667d072fedd1e688642
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-185%2Fdscho%2Ft6500-and-msys2-runtime-v3.x-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-185/dscho/t6500-and-msys2-runtime-v3.x-v1
Pull-Request: https://github.com/gitgitgadget/git/pull/185

From: Johannes Schindelin <johannes.schindelin@gmx.de>

In Git for Windows, we use the MSYS2 Bash which inherits a non-standard PID model from Cygwin's POSIX emulation layer: every MSYS2 process has a regular Windows PID, and in addition it has an MSYS2 PID (which corresponds to a shadow process that emulates Unix-style signal handling).

With the upgrade to the MSYS2 runtime v3.x, this shadow process cannot be accessed via `OpenProcess()` any longer, and therefore t6500 thought incorrectly that the process referenced in `gc.pid` (which is not actually a real `gc` process in this context, but the current shell) no longer exists.

Let's fix this by making sure that the Windows PID is written into `gc.pid` in this test script soo that `git.exe` is able to understand that that process does indeed still exist.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
---
 t/t6500-gc.sh | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

On Tue, May 7, 2019 at 5:51 PM Johannes Schindelin via GitGitGadget <gitgitgadget@gmail.com> wrote:

I wonder if it would make sense to abstract this away behind a shell function named shell_pid() which can be specialized for MINGW, much like the shell function pwd() is specialized on Windows.

Eric Sunshine <sunshine@sunshineco.com> writes:

It would be, especially when we need the next such invocation. I'd find it easier to follow if it were

	if test_have_prereq ...
	then
		shell_pid=$(cat /proc/$$/winpid)
	else
		shell_pid=$$
	fi &&
	...

simply because in each of the cases the mental burden gets smaller (those trying to see what happens on MINGW do not have to recall shell_pid was originally taken from $$ after seeing 'then'; others do not have to wonder if lack of 'else' to cover the platforms they are reading for is deliberate and shell_pid is the only thing expected out of the if/then/fi construct)

And I would suggest doing such a rewrite when it becomes a helper shell function, but what is written here is good enough until then, I would think.

Junio C Hamano <gitster@pobox.com> writes:

I amended s/soo/so/ while queuing; I did not make any other changes, as I described why in the message I am responding to.

Thanks.