[PATCH v2 7/7] technical/shallow: describe why shallow cannot use replace refs

From: Johannes Schindelin <johannes.schindelin@gmx.de>
Date: Apr 19, 2018, 08:21 UTC
Message-ID: <c041db4e62283e520a29039ddfec24d77d023d70.1524125760.git.johannes.schindelin@gmx.de>
In-Reply-To: <cover.1524125760.git.johannes.schindelin@gmx.de>

It is tempting to do away with commit_graft altogether (in the long haul), now that grafts are deprecated.

However, the shallow feature needs a couple of things that the replace refs cannot fulfill. Let's point that out in the documentation.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
---

	By the way, I did not squash this into the previous patch on
	purpose: in my mind, describing the relationship with replace refs
	is different enough from pointing out from the goal of this here
	patch to merit a separate commit. And that goal is: to describe
	why "shallow" cannot be implemented on top of "replace refs".

 Documentation/technical/shallow.txt | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/Documentation/technical/shallow.txt b/Documentation/technical/shallow.txt
index b3ff23c25f6..cb79181c2bb 100644
--- a/Documentation/technical/shallow.txt
+++ b/Documentation/technical/shallow.txt
@@ -25,6 +25,13 @@ Each line contains exactly one SHA-1. When read, a commit_graft
 will be constructed, which has nr_parent < 0 to make it easier
 to discern from user provided grafts.
 
+Note that the shallow feature could not be changed easily to
+use replace refs: a commit containing a `mergetag` is not allowed
+to be replaced, not even by a root commit. Such a commit can be
+made shallow, though. Also, having a `shallow` file explicitly
+listing all the commits made shallow makes it a *lot* easier to
+do shallow-specific things such as to deepen the history.
+
 Since fsck-objects relies on the library to read the objects,
 it honours shallow commits automatically.

-- 
2.17.0.windows.1.4.g7e4058d72e3