sha1-file: document how to use pretend_object_file

Like in-memory alternates, pretend_object_file contains a trap for the
unwary: careless callers can use it to create references to an object
that does not exist in the on-disk object store.

Add a comment documenting how to use the function without risking such
problems.

The only current caller is blame, which uses pretend_object_file to
create an in-memory commit representing the working tree state.
Noticed during a discussion of how to safely use this function in
operations like "git merge" which, unlike blame, are not read-only.

Inspired-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Jonathan Nieder 2020-01-03 16:13:31 -08:00 committed by Junio C Hamano
parent 53a06cf39b
commit 60440d72db

View File

@ -187,6 +187,14 @@ int hash_object_file_literally(const void *buf, unsigned long len,
const char *type, struct object_id *oid,
unsigned flags);
/*
* 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);