Merge branch 'cc/replace-with-the-same-type'

* cc/replace-with-the-same-type:
  Doc: 'replace' merge and non-merge commits
  t6050-replace: use some long option names
  replace: allow long option names
  Documentation/replace: add Creating Replacement Objects section
  t6050-replace: add test to clean up all the replace refs
  t6050-replace: test that objects are of the same type
  Documentation/replace: state that objects must be of the same type
  replace: forbid replacing an object with one of a different type

3 files changed, 61 insertions, 9 deletions

diff --git a/Documentation/git-replace.txt b/Documentation/git-replace.txt
index e0b4057976..f373ab48d4 100644
--- a/Documentation/git-replace.txt
+++ b/Documentation/git-replace.txt
@@ -20,8 +20,14 @@ The name of the 'replace' reference is the SHA-1 of the object that is
 replaced. The content of the 'replace' reference is the SHA-1 of the
 replacement object.
 
+The replaced object and the replacement object must be of the same type.
+This restriction can be bypassed using `-f`.
+
 Unless `-f` is given, the 'replace' reference must not yet exist.
 
+There is no other restriction on the replaced and replacement objects.
+Merge commits can be replaced by non-merge commits and vice versa.
+
 Replacement references will be used by default by all Git commands
 except those doing reachability traversal (prune, pack transfer and
 fsck).
@@ -49,18 +55,34 @@ achieve the same effect as the `--no-replace-objects` option.
 OPTIONS
 -------
 -f::
+--force::
 	If an existing replace ref for the same object exists, it will
 	be overwritten (instead of failing).
 
 -d::
+--delete::
 	Delete existing replace refs for the given objects.
 
 -l <pattern>::
+--list <pattern>::
 	List replace refs for objects that match the given pattern (or
 	all if no pattern is given).
 	Typing "git replace" without arguments, also lists all replace
 	refs.
 
+CREATING REPLACEMENT OBJECTS
+----------------------------
+
+linkgit:git-filter-branch[1], linkgit:git-hash-object[1] and
+linkgit:git-rebase[1], among other git commands, can be used to create
+replacement objects from existing objects.
+
+If you want to replace many blobs, trees or commits that are part of a
+string of commits, you may just want to create a replacement string of
+commits and then only replace the commit at the tip of the target
+string of commits with the commit at the tip of the replacement string
+of commits.
+
 BUGS
 ----
 Comparing blobs or trees that have been replaced with those that
@@ -69,12 +91,13 @@ go back to a replaced commit will move the branch to the replacement
 commit instead of the replaced commit.
 
 There may be other problems when using 'git rev-list' related to
-pending objects. And of course things may break if an object of one
-type is replaced by an object of another type (for example a blob
-replaced by a commit).
+pending objects.
 
 SEE ALSO
 --------
+linkgit:git-hash-object[1]
+linkgit:git-filter-branch[1]
+linkgit:git-rebase[1]
 linkgit:git-tag[1]
 linkgit:git-branch[1]
 linkgit:git[1]
diff --git a/builtin/replace.c b/builtin/replace.c
index 301b45ce6a..b1bd3ef994 100644
--- a/builtin/replace.c
+++ b/builtin/replace.c
@@ -85,6 +85,7 @@ static int replace_object(const char *object_ref, const char *replace_ref,
 			  int force)
 {
 	unsigned char object[20], prev[20], repl[20];
+	enum object_type obj_type, repl_type;
 	char ref[PATH_MAX];
 	struct ref_lock *lock;
 
@@ -100,6 +101,15 @@ static int replace_object(const char *object_ref, const char *replace_ref,
 	if (check_refname_format(ref, 0))
 		die("'%s' is not a valid ref name.", ref);
 
+	obj_type = sha1_object_info(object, NULL);
+	repl_type = sha1_object_info(repl, NULL);
+	if (!force && obj_type != repl_type)
+		die("Objects must be of the same type.\n"
+		    "'%s' points to a replaced object of type '%s'\n"
+		    "while '%s' points to a replacement object of type '%s'.",
+		    object_ref, typename(obj_type),
+		    replace_ref, typename(repl_type));
+
 	if (read_ref(ref, prev))
 		hashclr(prev);
 	else if (!force)
@@ -118,9 +128,9 @@ int cmd_replace(int argc, const char **argv, const char *prefix)
 {
 	int list = 0, delete = 0, force = 0;
 	struct option options[] = {
-		OPT_BOOL('l', NULL, &list, N_("list replace refs")),
-		OPT_BOOL('d', NULL, &delete, N_("delete replace refs")),
-		OPT_BOOL('f', NULL, &force, N_("replace the ref if it exists")),
+		OPT_BOOL('l', "list", &list, N_("list replace refs")),
+		OPT_BOOL('d', "delete", &delete, N_("delete replace refs")),
+		OPT_BOOL('f', "force", &force, N_("replace the ref if it exists")),
 		OPT_END()
 	};
 
diff --git a/t/t6050-replace.sh b/t/t6050-replace.sh
index decdc33c52..7d47984352 100755
--- a/t/t6050-replace.sh
+++ b/t/t6050-replace.sh
@@ -122,9 +122,9 @@ test_expect_success '"git replace" listing and deleting' '
      test "$HASH2" = "$(git replace -l)" &&
      test "$HASH2" = "$(git replace)" &&
      aa=${HASH2%??????????????????????????????????????} &&
-     test "$HASH2" = "$(git replace -l "$aa*")" &&
+     test "$HASH2" = "$(git replace --list "$aa*")" &&
      test_must_fail git replace -d $R &&
-     test_must_fail git replace -d &&
+     test_must_fail git replace --delete &&
      test_must_fail git replace -l -d $HASH2 &&
      git replace -d $HASH2 &&
      git show $HASH2 | grep "A U Thor" &&
@@ -147,7 +147,7 @@ test_expect_success '"git replace" resolves sha1' '
      git show $HASH2 | grep "O Thor" &&
      test_must_fail git replace $HASH2 $R &&
      git replace -f $HASH2 $R &&
-     test_must_fail git replace -f &&
+     test_must_fail git replace --force &&
      test "$HASH2" = "$(git replace)"
 '
 
@@ -263,4 +263,23 @@ test_expect_success 'not just commits' '
 	test_cmp file.replaced file
 '
 
+test_expect_success 'replaced and replacement objects must be of the same type' '
+	test_must_fail git replace mytag $HASH1 &&
+	test_must_fail git replace HEAD^{tree} HEAD~1 &&
+	BLOB=$(git rev-parse :file) &&
+	test_must_fail git replace HEAD^ $BLOB
+'
+
+test_expect_success '-f option bypasses the type check' '
+	git replace -f mytag $HASH1 &&
+	git replace --force HEAD^{tree} HEAD~1 &&
+	git replace -f HEAD^ $BLOB
+'
+
+test_expect_success 'replace ref cleanup' '
+	test -n "$(git replace)" &&
+	git replace -d $(git replace) &&
+	test -z "$(git replace)"
+'
+
 test_done