From 1a172e4ac1719a068c76384bd077ee65d915ebea Mon Sep 17 00:00:00 2001
From: Johannes Schindelin <johannes.schindelin@gmx.de>
Date: Wed, 1 Nov 2017 18:10:30 +0100
Subject: mingw: optionally redirect stderr/stdout via the same handle

The "2>&1" notation in Powershell and in Unix shells implies that stderr
is redirected to the same handle into which stdout is already written.

Let's use this special value to allow the same trick with
GIT_REDIRECT_STDERR and GIT_REDIRECT_STDOUT: if the former's value is
`2>&1`, then stderr will simply be written to the same handle as stdout.

The functionality was suggested by Jeff Hostetler.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/compat/mingw.c b/compat/mingw.c
index 6c6c779..2d44d21 100644
--- a/compat/mingw.c
+++ b/compat/mingw.c
@@ -2160,6 +2160,21 @@ static void maybe_redirect_std_handle(const wchar_t *key, DWORD std_id, int fd,
 			CloseHandle(handle);
 		return;
 	}
+	if (std_id == STD_ERROR_HANDLE && !wcscmp(buf, L"2>&1")) {
+		handle = GetStdHandle(STD_OUTPUT_HANDLE);
+		if (handle == INVALID_HANDLE_VALUE) {
+			close(fd);
+			handle = GetStdHandle(std_id);
+			if (handle != INVALID_HANDLE_VALUE)
+				CloseHandle(handle);
+		} else {
+			int new_fd = _open_osfhandle((intptr_t)handle, O_BINARY);
+			SetStdHandle(std_id, handle);
+			dup2(new_fd, fd);
+			/* do *not* close the new_fd: that would close stdout */
+		}
+		return;
+	}
 	handle = CreateFileW(buf, desired_access, 0, NULL, create_flag,
 			     flags, NULL);
 	if (handle != INVALID_HANDLE_VALUE) {
diff --git a/t/t0001-init.sh b/t/t0001-init.sh
index 0fd2fc4..c413bff 100755
--- a/t/t0001-init.sh
+++ b/t/t0001-init.sh
@@ -456,7 +456,13 @@ test_expect_success 're-init from a linked worktree' '
 test_expect_success MINGW 'redirect std handles' '
 	GIT_REDIRECT_STDOUT=output.txt git rev-parse --git-dir &&
 	test .git = "$(cat output.txt)" &&
-	test -z "$(GIT_REDIRECT_STDOUT=off git rev-parse --git-dir)"
+	test -z "$(GIT_REDIRECT_STDOUT=off git rev-parse --git-dir)" &&
+	test_must_fail env \
+		GIT_REDIRECT_STDOUT=output.txt \
+		GIT_REDIRECT_STDERR="2>&1" \
+		git rev-parse --git-dir --verify refs/invalid &&
+	printf ".git\nfatal: Needed a single revision\n" >expect &&
+	test_cmp expect output.txt
 '
 
 test_done
-- 
cgit v0.10.2-6-g49f6