Sorry for not replying earlier in the series.

From: "Christian Couder" <>
Users replacing an object with one of a different type were not
prevented to do so, even if it was obvious, and stated in the doc,
that bad things would result from doing that.

To avoid mistakes, it is better to just forbid that though.

If one object is replaced with one of a different type, the only way
to keep the history valid is to also replace all the other objects
that point to the replaced object.

Isn't this a recursion problem? Taken in that order one unravels the whole DAG.

However if considered in the reverse direction, one can replace an existing object within the DAG with a carefully crafted alternative of the same type, but which then wrongly references other dangling objects which are then replaced by objects which have the right type (this last replacement requires -f force).

That's because:

* Annotated tags contain the type of the tagged object.

* The tree/parent lines in commits must be a tree and commits, resp.

* The object types referred to by trees are specified in the 'mode'
   100644 and 100755    blob
   160000               commit
   040000               tree
 (these are the only valid modes)

* Blobs don't point at anything.

The doc will be updated in a later patch.

Acked-by: Philip Oakley <>
Signed-off-by: Christian Couder <>
builtin/replace.c | 10 ++++++++++
1 file changed, 10 insertions(+)

diff --git a/builtin/replace.c b/builtin/replace.c
index 59d3115..9a94769 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 (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))
 else if (!force)

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