In some situations run-command will incorrectly try (and fail) to
execute a directory instead of an executable file.  This was observed by
having a directory called "ssh" in $PATH before the real ssh and trying
to use ssh protoccol, reslting in the following:

        $ git ls-remote ssh://url
        fatal: cannot exec 'ssh': Permission denied

It ends up being worse and run-command will even try to execute a
non-executable file if it preceeds the executable version of a file on
the PATH.  For example, if PATH=~/bin1:~/bin2:~/bin3 and there exists a
directory 'git-hello' in 'bin1', a non-executable file 'git-hello' in
bin2 and an executable file 'git-hello' (which prints "Hello World!") in
bin3 the following will occur:

        $ git hello
        fatal: cannot exec 'git-hello': Permission denied

This is due to only checking 'access()' when locating an executable in
PATH, which doesn't distinguish between files and directories.  Instead
use 'is_executable()' which check that the path is to a regular,
executable file.  Now run-command won't try to execute the directory or
non-executable file 'git-hello':

        $ git hello
        Hello World!

Reported-by: Brian Hatfield <bhatfi...@google.com>
Signed-off-by: Brandon Williams <bmw...@google.com>
---
 run-command.c          |  2 +-
 t/t0061-run-command.sh | 23 +++++++++++++++++++++++
 2 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/run-command.c b/run-command.c
index a97d7bf9f..ec08e0951 100644
--- a/run-command.c
+++ b/run-command.c
@@ -137,7 +137,7 @@ static char *locate_in_PATH(const char *file)
                }
                strbuf_addstr(&buf, file);
 
-               if (!access(buf.buf, F_OK))
+               if (is_executable(buf.buf))
                        return strbuf_detach(&buf, NULL);
 
                if (!*end)
diff --git a/t/t0061-run-command.sh b/t/t0061-run-command.sh
index 98c09dd98..fd5e43766 100755
--- a/t/t0061-run-command.sh
+++ b/t/t0061-run-command.sh
@@ -37,6 +37,29 @@ test_expect_success !MINGW 'run_command can run a script 
without a #! line' '
        test_cmp empty err
 '
 
+test_expect_success 'run_command should not try to execute a directory' '
+       test_when_finished "rm -rf bin1 bin2 bin3" &&
+       mkdir -p bin1/greet bin2 bin3 &&
+       write_script bin2/greet <<-\EOF &&
+       cat bin2/greet
+       EOF
+       chmod -x bin2/greet &&
+       write_script bin3/greet <<-\EOF &&
+       cat bin3/greet
+       EOF
+
+       # Test that run-command does not try to execute the "greet" directory in
+       # "bin1", or the non-executable file "greet" in "bin2", but rather
+       # correcty executes the "greet" script located in bin3.
+       (
+               PATH=$PWD/bin1:$PWD/bin2:$PWD/bin3:$PATH &&
+               export PATH &&
+               test-run-command run-command greet >actual 2>err
+       ) &&
+       test_cmp bin3/greet actual &&
+       test_cmp empty err
+'
+
 test_expect_success POSIXPERM 'run_command reports EACCES' '
        cat hello-script >hello.sh &&
        chmod -x hello.sh &&
-- 
2.13.0.rc0.306.g87b477812d-goog

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