rename: Break filepairs with different types.

When we consider if a path has been totally rewritten, we did not
touch changes from symlinks to files or vice versa.  But a change
that modifies even the type of a blob surely should count as a
complete rewrite.

While we are at it, modernise diffcore-break to be aware of gitlinks (we
do not want to touch them).

Signed-off-by: Junio C Hamano <gitster@pobox.com>

cache.h

@@ -192,6 +192,13 @@ enum object_type {
 	OBJ_MAX,
 };
 
+static inline enum object_type object_type(unsigned int mode)
+{
+	return S_ISDIR(mode) ? OBJ_TREE :
+		S_ISGITLINK(mode) ? OBJ_COMMIT :
+		OBJ_BLOB;
+}
+
 #define GIT_DIR_ENVIRONMENT "GIT_DIR"
 #define GIT_WORK_TREE_ENVIRONMENT "GIT_WORK_TREE"
 #define DEFAULT_GIT_DIR_ENVIRONMENT ".git"

diffcore-break.c

@@ -52,8 +52,10 @@ static int should_break(struct diff_filespec *src,
 			     * is the default.
 			     */
 
-	if (!S_ISREG(src->mode) || !S_ISREG(dst->mode))
-		return 0; /* leave symlink rename alone */
+	if (S_ISREG(src->mode) != S_ISREG(dst->mode)) {
+		*merge_score_p = (int)MAX_SCORE;
+		return 1; /* even their types are different */
+	}
 
 	if (src->sha1_valid && dst->sha1_valid &&
 	    !hashcmp(src->sha1, dst->sha1))
@@ -168,11 +170,13 @@ void diffcore_break(int break_score)
 		struct diff_filepair *p = q->queue[i];
 		int score;
 
-		/* We deal only with in-place edit of non directory.
+		/*
+		 * We deal only with in-place edit of blobs.
 		 * We do not break anything else.
 		 */
 		if (DIFF_FILE_VALID(p->one) && DIFF_FILE_VALID(p->two) &&
-		    !S_ISDIR(p->one->mode) && !S_ISDIR(p->two->mode) &&
+		    object_type(p->one->mode) == OBJ_BLOB &&
+		    object_type(p->two->mode) == OBJ_BLOB &&
 		    !strcmp(p->one->path, p->two->path)) {
 			if (should_break(p->one, p->two,
 					 break_score, &score)) {

t/t4008-diff-break-rewrite.sh

@@ -122,11 +122,11 @@ test_expect_success \
     'run diff with -B -M' \
     'git diff-index -B -M "$tree" >current'
 
-# This should not mistake file0 as the copy source of new file1
-# due to type differences.
+# file0 changed from regular to symlink.  file1 is very close to the preimage of file0.
+# because we break file0, file1 can become a rename of it.
 cat >expected <<\EOF
 :100644 120000 f5deac7be59e7eeab8657fd9ae706fd6a57daed2 67be421f88824578857624f7b3dc75e99a8a1481 T	file0
-:100644 100644 6ff87c4664981e4397625791c8ea3bbb5f2279a3 f5deac7be59e7eeab8657fd9ae706fd6a57daed2 M100	file1
+:100644 100644 6ff87c4664981e4397625791c8ea3bbb5f2279a3 f5deac7be59e7eeab8657fd9ae706fd6a57daed2 R	file0	file1
 EOF
 
 test_expect_success \

t/t4023-diff-rename-typechange.sh

@@ -0,0 +1,86 @@
+#!/bin/sh
+
+test_description='typechange rename detection'
+
+. ./test-lib.sh
+
+test_expect_success setup '
+
+	rm -f foo bar &&
+	cat ../../COPYING >foo &&
+	ln -s linklink bar &&
+	git add foo bar &&
+	git commit -a -m Initial &&
+	git tag one &&
+
+	rm -f foo bar &&
+	cat ../../COPYING >bar &&
+	ln -s linklink foo &&
+	git add foo bar &&
+	git commit -a -m Second &&
+	git tag two &&
+
+	rm -f foo bar &&
+	cat ../../COPYING >foo &&
+	git add foo &&
+	git commit -a -m Third &&
+	git tag three &&
+
+	mv foo bar &&
+	ln -s linklink foo &&
+	git add foo bar &&
+	git commit -a -m Fourth &&
+	git tag four &&
+
+	# This is purely for sanity check
+
+	rm -f foo bar &&
+	cat ../../COPYING >foo &&
+	cat ../../Makefile >bar &&
+	git add foo bar &&
+	git commit -a -m Fifth &&
+	git tag five &&
+
+	rm -f foo bar &&
+	cat ../../Makefile >foo &&
+	cat ../../COPYING >bar &&
+	git add foo bar &&
+	git commit -a -m Sixth &&
+	git tag six
+
+'
+
+test_expect_success 'cross renames to be detected for regular files' '
+
+	git diff-tree five six -r --name-status -B -M | sort >actual &&
+	{
+		echo "R100	foo	bar"
+		echo "R100	bar	foo"
+	} | sort >expect &&
+	diff -u expect actual
+
+'
+
+test_expect_success 'cross renames to be detected for typechange' '
+
+	git diff-tree one two -r --name-status -B -M | sort >actual &&
+	{
+		echo "R100	foo	bar"
+		echo "R100	bar	foo"
+	} | sort >expect &&
+	diff -u expect actual
+
+'
+
+test_expect_success 'moves and renames' '
+
+	git diff-tree three four -r --name-status -B -M | sort >actual &&
+	{
+		echo "R100	foo	bar"
+		echo "T100	foo"
+	} | sort >expect &&
+	diff -u expect actual
+
+'
+
+test_done

tree-walk.h

@@ -7,13 +7,6 @@ struct name_entry {
 	unsigned int mode;
 };
 
-static inline enum object_type object_type(unsigned int mode)
-{
-	return S_ISDIR(mode) ? OBJ_TREE :
-		S_ISGITLINK(mode) ? OBJ_COMMIT :
-		OBJ_BLOB;
-}
-
 struct tree_desc {
 	const void *buffer;
 	struct name_entry entry;