[PATCH 1/2] subtree: fix the GIT_EXEC_PATH sanity check to work on Windows

["Johannes Schindelin via GitGitGadget" <gitgitgadget@gmail.com>]

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

In 22d550749361 (subtree: don't fuss with PATH, 2021-04-27), `git
subtree` was broken thoroughly on Windows.

The reason is that it assumes Unix semantics, where `PATH` is
colon-separated, and it assumes that `$GIT_EXEC_PATH:` is a verbatim
prefix of `$PATH`. Neither are true, the latter in particular because
`GIT_EXEC_PATH` is a Windows-style path, while `PATH` is a Unix-style
path list.

Let's keep the original spirit, and hack together something that
unbreaks the logic on Windows.

A more thorough fix would look at the inode of `$GIT_EXEC_PATH` and of
the first component of `$PATH`, to make sure that they are identical,
but that is even trickier to do in a portable way.

This fixes https://github.com/git-for-windows/git/issues/3260

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
---
 contrib/subtree/git-subtree.sh | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/contrib/subtree/git-subtree.sh b/contrib/subtree/git-subtree.sh
index b06782bc7955..6bd689a6bb92 100755
--- a/contrib/subtree/git-subtree.sh
+++ b/contrib/subtree/git-subtree.sh
@@ -5,7 +5,13 @@
 # Copyright (C) 2009 Avery Pennarun <apenwarr@gmail.com>
 #
 
-if test -z "$GIT_EXEC_PATH" || test "${PATH#"${GIT_EXEC_PATH}:"}" = "$PATH" || ! test -f "$GIT_EXEC_PATH/git-sh-setup"
+if test -z "$GIT_EXEC_PATH" || {
+	test "${PATH#"${GIT_EXEC_PATH}:"}" = "$PATH" && {
+		# On Windows, PATH might be Unix-style, GIT_EXEC_PATH not
+		! type -p cygpath >/dev/null 2>&1 ||
+		test "${PATH#$(cygpath -au "$GIT_EXEC_PATH"):}" = "$PATH"
+	}
+} || ! test -f "$GIT_EXEC_PATH/git-sh-setup"
 then
 	echo >&2 'It looks like either your git installation or your'
 	echo >&2 'git-subtree installation is broken.'
-- 
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