Merge branch 'jc/maint-diff-patch-header' into maint

"git diff-index" and its friends at the plumbing level showed the
"diff --git" header and nothing else for a path whose cached stat
info is dirty without actual difference when asked to produce a
patch. This was a longstanding bug that we could have fixed long
time ago.

By Junio C Hamano
* jc/maint-diff-patch-header:
  diff -p: squelch "diff --git" header for stat-dirty paths
  t4011: illustrate "diff-index -p" on stat-dirty paths
  t4011: modernise style

diff.c

@@ -2210,7 +2210,7 @@ static void builtin_diff(const char *name_a,
 		struct emit_callback ecbdata;
 		const struct userdiff_funcname *pe;
 
-		if (!DIFF_XDL_TST(o, WHITESPACE_FLAGS) || must_show_header) {
+		if (must_show_header) {
 			fprintf(o->file, "%s", header.buf);
 			strbuf_reset(&header);
 		}

t/t4011-diff-symlink.sh

@@ -9,7 +9,8 @@ test_description='Test diff of symlinks.
 . ./test-lib.sh
 . "$TEST_DIRECTORY"/diff-lib.sh
 
-cat > expected << EOF
+test_expect_success SYMLINKS 'diff new symlink and file' '
+	cat >expected <<-\EOF &&
 	diff --git a/frotz b/frotz
 	new file mode 120000
 	index 0000000..7c465af
@@ -18,24 +19,31 @@ index 0000000..7c465af
 	@@ -0,0 +1 @@
 	+xyzzy
 	\ No newline at end of file
+	diff --git a/nitfol b/nitfol
+	new file mode 100644
+	index 0000000..7c465af
+	--- /dev/null
+	+++ b/nitfol
+	@@ -0,0 +1 @@
+	+xyzzy
 	EOF
-
+	ln -s xyzzy frotz &&
-test_expect_success SYMLINKS \
+	echo xyzzy >nitfol &&
-    'diff new symlink' \
-    'ln -s xyzzy frotz &&
 	git update-index &&
 	tree=$(git write-tree) &&
-    git update-index --add frotz &&
+	git update-index --add frotz nitfol &&
 	GIT_DIFF_OPTS=--unified=0 git diff-index -M -p $tree >current &&
-    compare_diff_patch current expected'
+	compare_diff_patch expected current
+'
 
-test_expect_success SYMLINKS \
+test_expect_success SYMLINKS 'diff unchanged symlink and file'  '
-    'diff unchanged symlink' \
+	tree=$(git write-tree) &&
-    'tree=$(git write-tree) &&
+	git update-index frotz nitfol &&
-    git update-index frotz &&
+	test -z "$(git diff-index --name-only $tree)"
-    test -z "$(git diff-index --name-only $tree)"'
+'
 
-cat > expected << EOF
+test_expect_success SYMLINKS 'diff removed symlink and file' '
+	cat >expected <<-\EOF &&
 	diff --git a/frotz b/frotz
 	deleted file mode 120000
 	index 7c465af..0000000
@@ -44,25 +52,36 @@ index 7c465af..0000000
 	@@ -1 +0,0 @@
 	-xyzzy
 	\ No newline at end of file
+	diff --git a/nitfol b/nitfol
+	deleted file mode 100644
+	index 7c465af..0000000
+	--- a/nitfol
+	+++ /dev/null
+	@@ -1 +0,0 @@
+	-xyzzy
 	EOF
-
+	mv frotz frotz2 &&
-test_expect_success SYMLINKS \
+	mv nitfol nitfol2 &&
-    'diff removed symlink' \
-    'mv frotz frotz2 &&
 	git diff-index -M -p $tree >current &&
-    compare_diff_patch current expected'
+	compare_diff_patch expected current
+'
 
-cat > expected << EOF
+test_expect_success SYMLINKS 'diff identical, but newly created symlink and file' '
-diff --git a/frotz b/frotz
+	>expected &&
-EOF
+	rm -f frotz nitfol &&
-
+	echo xyzzy >nitfol &&
-test_expect_success SYMLINKS \
+	test-chmtime +10 nitfol &&
-    'diff identical, but newly created symlink' \
+	ln -s xyzzy frotz &&
-    'ln -s xyzzy frotz &&
 	git diff-index -M -p $tree >current &&
-    compare_diff_patch current expected'
+	compare_diff_patch expected current &&
 
-cat > expected << EOF
+	>expected &&
+	git diff-index -M -p -w $tree >current &&
+	compare_diff_patch expected current
+'
+
+test_expect_success SYMLINKS 'diff different symlink and file' '
+	cat >expected <<-\EOF &&
 	diff --git a/frotz b/frotz
 	index 7c465af..df1db54 120000
 	--- a/frotz
@@ -72,22 +91,28 @@ index 7c465af..df1db54 120000
 	\ No newline at end of file
 	+yxyyz
 	\ No newline at end of file
+	diff --git a/nitfol b/nitfol
+	index 7c465af..df1db54 100644
+	--- a/nitfol
+	+++ b/nitfol
+	@@ -1 +1 @@
+	-xyzzy
+	+yxyyz
 	EOF
-
+	rm -f frotz &&
-test_expect_success SYMLINKS \
-    'diff different symlink' \
-    'rm frotz &&
 	ln -s yxyyz frotz &&
+	echo yxyyz >nitfol &&
 	git diff-index -M -p $tree >current &&
-    compare_diff_patch current expected'
+	compare_diff_patch expected current
+'
 
-test_expect_success SYMLINKS \
+test_expect_success SYMLINKS 'diff symlinks with non-existing targets' '
-    'diff symlinks with non-existing targets' \
+	ln -s narf pinky &&
-    'ln -s narf pinky &&
 	ln -s take\ over brain &&
 	test_must_fail git diff --no-index pinky brain >output 2>output.err &&
 	grep narf output &&
-    ! grep error output.err'
+	! test -s output.err
+'
 
 test_expect_success SYMLINKS 'setup symlinks with attributes' '
 	echo "*.bin diff=bin" >>.gitattributes &&
@@ -96,7 +121,8 @@ test_expect_success SYMLINKS 'setup symlinks with attributes' '
 	git add -N file.bin link.bin
 '
 
-cat >expect <<'EOF'
+test_expect_success SYMLINKS 'symlinks do not respect userdiff config by path' '
+	cat >expect <<-\EOF &&
 	diff --git a/file.bin b/file.bin
 	index e69de29..d95f3ad 100644
 	Binary files a/file.bin and b/file.bin differ
@@ -108,7 +134,6 @@ index e69de29..dce41ec 120000
 	+file.bin
 	\ No newline at end of file
 	EOF
-test_expect_success SYMLINKS 'symlinks do not respect userdiff config by path' '
 	git config diff.bin.binary true &&
 	git diff file.bin link.bin >actual &&
 	test_cmp expect actual