Re: [PATCH v2 5/8] commit-graph: not compatible with replace objects

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On 8/21/2018 1:45 PM, Junio C Hamano wrote:
Derrick Stolee <dstolee@xxxxxxxxxxxxx> writes:

Create new method commit_graph_compatible(r) to check if a given
repository r is compatible with the commit-graph feature. Fill the
method with a check to see if replace-objects exist. Test this
interaction succeeds, including ignoring an existing commit-graph and
failing to write a new commit-graph. However, we do ensure that
we write a new commit-graph by setting read_replace_refs to 0, thereby
ignoring the replace refs.

Signed-off-by: Derrick Stolee <dstolee@xxxxxxxxxxxxx>
---
  builtin/commit-graph.c  |  4 ++++
  commit-graph.c          | 21 +++++++++++++++++++++
  replace-object.c        |  2 +-
  replace-object.h        |  2 ++
  t/t5318-commit-graph.sh | 22 ++++++++++++++++++++++
  5 files changed, 50 insertions(+), 1 deletion(-)

diff --git a/builtin/commit-graph.c b/builtin/commit-graph.c
index 0bf0c48657..da737df321 100644
--- a/builtin/commit-graph.c
+++ b/builtin/commit-graph.c
@@ -120,6 +120,8 @@ static int graph_read(int argc, const char **argv)
  	return 0;
  }
+extern int read_replace_refs;
+
Why do you need this (and also in commit-graph.c)?  I thought
cache.h includes it, which you can just make use of it.


You're right. I don't know how I missed that.


+static int commit_graph_compatible(struct repository *r)
+{
+	if (read_replace_refs) {
+		prepare_replace_object(r);
+		if (hashmap_get_size(&r->objects->replace_map->map))
+			return 0;
+	}
+
+	return 1;
+}
diff --git a/replace-object.c b/replace-object.c
index 3c17864eb7..9821f1477e 100644
--- a/replace-object.c
+++ b/replace-object.c
@@ -32,7 +32,7 @@ static int register_replace_ref(struct repository *r,
  	return 0;
  }
-static void prepare_replace_object(struct repository *r)
+void prepare_replace_object(struct repository *r)
  {
  	if (r->objects->replace_map)
  		return;
The way the new caller is written, I am wondering if this function
should return "we are (or, are not) using the replace object
feature", making it unnecessary for callers on the reading side to
know about "read-replace-refs" external variable, for example.

	/*
	 * To be called on-demand from codepaths that want to make
	 * sure that replacement objects can be found as necessary.
	 *
	 * Return number of replacement defined for the repository, or
	 * -1 when !read_replace_refs tells us not to use replacement
	 * mechanism at all.
	 */
	int prepare_replace_object(struct repository *r)
	{
		if (!read_replace_refs)
			return -1;

		if (!r->objects->replace_map) {
			r->objects->replace_map =
				xmalloc(...);
			oidmap_init(r->objects->replace_map, 0);
			for_each_refplace_ref(r, register_...);
		}
		return hashmap_get_size(&r->objects->replace_map->map);
	}

This is a good idea. I can incorporate it into v3.

Then, the caller side can simply become something like:

	#define cgraph_compat(r) (prepare_replace_object(r) <= 0)

With the next two patches that add more conditions to commit_graph_compatible(), I'd prefer keeping it a method instead of a macro.

There are various writers to read_replace_refs variable, but I think
they should first be replaced with calls to something like:

	void use_replace_refs(struct repository *r, int enable);

which allows us to hide the global variable and later make it per
repository if we wanted to.

I will incorporate this into v3 as well.

Thanks,

-Stolee




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