Handle symlinks graciously

This patch converts a stat() to an lstat() call, thereby fixing the case
when the date of a symlink was not the same as the one recorded in the
index. The included test case demonstrates this.

This is for the case that the symlink points to a non-existing file. If
the file exists, worse things than just an error message happen.

Signed-off-by: Johannes Schindelin <Johannes.Schindelin@gmx.de>
Signed-off-by: Junio C Hamano <junkio@cox.net>

diff.c

@@ -650,7 +650,7 @@ static void diff_fill_sha1_info(struct diff_filespec *one)
 	if (DIFF_FILE_VALID(one)) {
 		if (!one->sha1_valid) {
 			struct stat st;
-			if (stat(one->path, &st) < 0)
+			if (lstat(one->path, &st) < 0)
 				die("stat %s", one->path);
 			if (index_path(one->sha1, one->path, &st, 0))
 				die("cannot hash %s\n", one->path);

t/t4011-diff-symlink.sh

@@ -0,0 +1,85 @@
+#!/bin/sh
+#
+# Copyright (c) 2005 Johannes Schindelin
+#
+
+test_description='Test diff of symlinks.
+
+'
+. ./test-lib.sh
+. ../diff-lib.sh
+
+cat > expected << EOF
+diff --git a/frotz b/frotz
+new file mode 120000
+index 0000000..7c465af
+--- /dev/null
++++ b/frotz
+@@ -0,0 +1 @@
++xyzzy
+\ No newline at end of file
+EOF
+
+test_expect_success \
+    'diff new symlink' \
+    'ln -s xyzzy frotz &&
+    git-update-index &&
+    tree=$(git-write-tree) &&
+    git-update-index --add frotz &&
+    GIT_DIFF_OPTS=--unified=0 git-diff-index -M -p $tree > current &&
+    compare_diff_patch current expected'
+
+test_expect_success \
+    'diff unchanged symlink' \
+    'tree=$(git-write-tree) &&
+    git-update-index frotz &&
+    test -z "$(git-diff-index --name-only $tree)"'
+
+cat > expected << EOF
+diff --git a/frotz b/frotz
+deleted file mode 120000
+index 7c465af..0000000
+--- a/frotz
++++ /dev/null
+@@ -1 +0,0 @@
+-xyzzy
+\ No newline at end of file
+EOF
+
+test_expect_success \
+    'diff removed symlink' \
+    'rm frotz &&
+    git-diff-index -M -p $tree > current &&
+    compare_diff_patch current expected'
+
+cat > expected << EOF
+diff --git a/frotz b/frotz
+EOF
+
+test_expect_success \
+    'diff identical, but newly created symlink' \
+    'sleep 1 &&
+    ln -s xyzzy frotz &&
+    git-diff-index -M -p $tree > current &&
+    compare_diff_patch current expected'
+
+cat > expected << EOF
+diff --git a/frotz b/frotz
+index 7c465af..df1db54 120000
+--- a/frotz
++++ b/frotz
+@@ -1 +1 @@
+-xyzzy
+\ No newline at end of file
++yxyyz
+\ No newline at end of file
+EOF
+
+test_expect_success \
+    'diff different symlink' \
+    'rm frotz &&
+    ln -s yxyyz frotz &&
+    git-diff-index -M -p $tree > current &&
+    compare_diff_patch current expected'
+
+test_done