Win32: symlink: add test for `symlink` attribute

To verify that the symlink is resolved correctly, we use the fact that
`git.exe` is a native Win32 program, and that `git.exe config -f <path>`
therefore uses the native symlink resolution.

Signed-off-by: Bert Belder <bertbelder@gmail.com>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

t/t2040-checkout-symlink-attr.sh

@@ -0,0 +1,46 @@
+#!/bin/sh
+
+test_description='checkout symlinks with `symlink` attribute on Windows
+
+Ensures that Git for Windows creates symlinks of the right type,
+as specified by the `symlink` attribute in `.gitattributes`.'
+
+# Tell MSYS to create native symlinks. Without this flag test-lib's
+# prerequisite detection for SYMLINKS doesn't detect the right thing.
+MSYS=winsymlinks:nativestrict && export MSYS
+
+. ./test-lib.sh
+
+if ! test_have_prereq MINGW,SYMLINKS
+then
+	skip_all='skipping $0: MinGW-only test, which requires symlink support.'
+	test_done
+fi
+
+# Adds a symlink to the index without clobbering the work tree.
+cache_symlink () {
+	sha=$(printf '%s' "$1" | git hash-object --stdin -w) &&
+	git update-index --add --cacheinfo 120000,$sha,"$2"
+}
+
+test_expect_success 'checkout symlinks with attr' '
+	cache_symlink file1 file-link &&
+	cache_symlink dir dir-link &&
+
+	printf "file-link symlink=file\ndir-link symlink=dir\n" >.gitattributes &&
+	git add .gitattributes &&
+
+	git checkout . &&
+
+	mkdir dir &&
+	echo "[a]b=c" >file1 &&
+	echo "[x]y=z" >dir/file2 &&
+
+	# MSYS2 is very forgiving, it will resolve symlinks even if the
+	# symlink type is incorrect. To make this test meaningful, try
+	# them with a native, non-MSYS executable, such as `git config`.
+	test "$(git config -f file-link a.b)" = "c" &&
+	test "$(git config -f dir-link/file2 x.y)" = "z"
+'
+
+test_done