tests: introduce test_ln_s_add

Add a new function that creates a symbolic link and adds it to the index
to be used in cases where a symbolic link is not required on the file
system. We will use it to remove many SYMLINKS prerequisites from test
cases.

Signed-off-by: Johannes Sixt <j6t@kdbg.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/README

@@ -592,6 +592,20 @@ library for your script to use.
 		test_cmp expected actual
 	'
 
+ - test_ln_s_add <path1> <path2>
+
+   This function helps systems whose filesystem does not support symbolic
+   links. Use it to add a symbolic link entry to the index when it is not
+   important that the file system entry is a symbolic link, i.e., instead
+   of the sequence
+
+	ln -s foo bar &&
+	git add bar
+
+   Sometimes it is possible to split a test in a part that does not need
+   the symbolic link in the file system and a part that does; then only
+   the latter part need be protected by a SYMLINKS prerequisite (see below).
+
 Prerequisites
 -------------
 

t/test-lib-functions.sh

@@ -679,3 +679,20 @@ test_create_repo () {
 		mv .git/hooks .git/hooks-disabled
 	) || exit
 }
+
+# This function helps on symlink challenged file systems when it is not
+# important that the file system entry is a symbolic link.
+# Use test_ln_s_add instead of "ln -s x y && git add y" to add a
+# symbolic link entry y to the index.
+
+test_ln_s_add () {
+	if test_have_prereq SYMLINKS
+	then
+		ln -s "$1" "$2" &&
+		git update-index --add "$2"
+	else
+		printf '%s' "$1" >"$2" &&
+		ln_s_obj=$(git hash-object -w "$2") &&
+		git update-index --add --cacheinfo 120000 $ln_s_obj "$2"
+	fi
+}