Fix git subtree on Windows

In the topic branch ls/subtree, we saw a lot of improvements of the git subtree command, and some cleaning up, too. For example, 22d550749361 (subtree: don't fuss with PATH, 2021-04-27) carefully laid out a history of changes intended to work around issues where the git-subtree script was not in the intended location, and removed a statement modifying PATH in favor of a conditional warning (contingent on the PATH being in an unexpected shape).

This particular condition, however, was never tested on Windows, and it broke git subtree in Git for Windows v2.32.0, as reported here
[https://github.com/git-for-windows/git/issues/3260]. Now, every invocation of git subtree, with or without command-line arguments, results in output like this:

It looks like either your git installation or your git-subtree installation is broken.

Tips:
- If git --exec-path does not print the correct path to
your git install directory, then set the GIT_EXEC_PATH
environment variable to the correct directory.
- Make sure that your git-core\git-subtree file is either in your
PATH or in your git exec path (C:/Users/harry/Downloads/PortableGit/mingw64/libexec/git-core).
- You should run git-subtree as git core\git-subtree,
not as git-core\git-subtree.

This patch series provides a fix for that symptom, and is based on ls/subtree.

Changes since v1:

* Instead of using the Windows-specific cygpath construct, we now instead fall back to verify that GIT_EXEC_PATH and the first component of PATH refer to the same entity (via the -ef operator, which compares inodes). Since the bug affects only Windows, as far as we know, the non-portability of the -ef operator does not matter because Git for Windows' Bash does have support for it.

Johannes Schindelin (2):
subtree: fix the GIT_EXEC_PATH sanity check to work on Windows
subtree: fix assumption about the directory separator

 contrib/subtree/git-subtree.sh | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

base-commit: 9a3e3ca2ba869f9fef9f8be390ed45457565ccd1
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-978%2Fdscho%2Ffix-subtree-on-windows-v2
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-978/dscho/fix-subtree-on-windows-v2
Pull-Request: https://github.com/gitgitgadget/git/pull/978

Range-diff vs v1:

1: a91ac6c18938 ! 1: 5f2d9434b4eb subtree: fix the GIT_EXEC_PATH sanity check to work on Windows
@@ Commit message
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.
+ Let's make extra certain that $GIT_EXEC_PATH and the first component
+ of $PATH refer to different entities before erroring out.

- 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.
+ We do that by using the test <path1> -ef <path2> command that verifies
+ that the inode of <path1> and of <path2> is the same.
+
+ Sadly, this construct is non-portable, according to
+ https://pubs.opengroup.org/onlinepubs/009695399/utilities/test.html.
+ However, it does not matter in practice because we still first look
+ whether $GIT_EXEC_PREFIX is string-identical to the first component of
+ $PATH. This will give us the expected result everywhere but in Git for
+ Windows, and Git for Windows' own Bash _does_ handle the -ef operator.
+
+ Just in case that we _do_ need to show the error message _and_ are
+ running in a shell that lacks support for -ef, we simply suppress the
+ error output for that part.

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

@@ contrib/subtree/git-subtree.sh
#

-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"
++if test -z "$GIT_EXEC_PATH" || ! test -f "$GIT_EXEC_PATH/git-sh-setup" || {
++ test "${PATH#"${GIT_EXEC_PATH}:"}" = "$PATH" &&
++ test ! "$GIT_EXEC_PATH" -ef "${PATH%%:*}" 2>/dev/null
++}
then
echo >&2 'It looks like either your git installation or your'
echo >&2 'git-subtree installation is broken.'
2: 4e1a569c9fa4 ! 2: a6f7aa40485f subtree: fix assumption about the directory separator

     @@ Commit message
          Signed-off-by: Johannes Schindelin <[email protected]>
      
       ## contrib/subtree/git-subtree.sh ##
     -@@ contrib/subtree/git-subtree.sh: if test -z "$GIT_EXEC_PATH" || {
     - 	}
     - } || ! test -f "$GIT_EXEC_PATH/git-sh-setup"
     +@@ contrib/subtree/git-subtree.sh: if test -z "$GIT_EXEC_PATH" || ! test -f "$GIT_EXEC_PATH/git-sh-setup" || {
     + 	test ! "$GIT_EXEC_PATH" -ef "${PATH%%:*}" 2>/dev/null
     + }
       then
     -+	base=${0##*/}
     -+	base=${base##*\\}
     ++	basename=${0##*[/\\]}
       	echo >&2 'It looks like either your git installation or your'
       	echo >&2 'git-subtree installation is broken.'
       	echo >&2
     @@ contrib/subtree/git-subtree.sh: then
       	echo >&2 "   your git install directory, then set the GIT_EXEC_PATH"
       	echo >&2 "   environment variable to the correct directory."
      -	echo >&2 " - Make sure that your \`${0##*/}\` file is either in your"
     -+	echo >&2 " - Make sure that your \`$base\` file is either in your"
     ++	echo >&2 " - Make sure that your \`$basename\` file is either in your"
       	echo >&2 "   PATH or in your git exec path (\`$(git --exec-path)\`)."
      -	echo >&2 " - You should run git-subtree as \`git ${0##*/git-}\`,"
      -	echo >&2 "   not as \`${0##*/}\`." >&2
     -+	echo >&2 " - You should run git-subtree as \`git ${base#git-}\`,"
     -+	echo >&2 "   not as \`$base\`." >&2
     ++	echo >&2 " - You should run git-subtree as \`git ${basename#git-}\`,"
     ++	echo >&2 "   not as \`$basename\`." >&2
       	exit 126
       fi

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