On Fri, Jan 03, 2020 at 04:13:31PM -0800, Jonathan Nieder wrote:

To follow up on Junio's hint in his review: callers can inject
additional cached objects by using pretend_object_file.  Junio
described how this would make sense as a mechanism for building
the virtual ancestor object, but we don't do that.  In fact, the
only caller is fake_working_tree_commit in "git blame", a read-only
code path. *phew*

-- >8 --
Subject: sha1-file: document how to use pretend_object_file
[...]
+/*
+ * Add an object file to the in-memory object store, without writing it
+ * to disk.
+ *
+ * Callers are responsible for calling write_object_file to record the
+ * object in persistent storage before writing any other new objects
+ * that reference it.
+ */
 int pretend_object_file(void *, unsigned long, enum object_type,
 			struct object_id *oid);
 

I think this is an improvement over the status quo, but it's still a
potential trap for code which happens to run in the same process (see my
other email in the thread).

Should the message perhaps be even more scary?

-Peff