Subject: Re: [PATCH 2/2] sparse-index.c: don't call prepare_repo_settings() twice in a row

From: Ævar Arnfjörð Bjarmason <[email-masked]>
Date: Thu, 06 May 2021 10:49:59 +0200

On Wed, May 05 2021, Derrick Stolee wrote:

> On 5/5/2021 8:11 AM, Ævar Arnfjörð Bjarmason wrote:
>> Change code added in 58300f47432 (sparse-index: add index.sparse
>> config option, 2021-03-30) to only call prepare_repo_settings()
>> once. We know that our own set_sparse_index_config() has just finished
>> calling it, so we don't need to call it if we're acting on "test_env".
>
> I'm not sure about the value here. prepare_repo_settings() returns
> quickly if the settings have already been prepared, so a second call
> is negligible in cost.

I changed that while I was at it to make it easier to read, it's not an
optimization. I.e. one wonders what the side-effect is of calling
prepare_repo_settings() twice, discovers there isn't one...

>> @@ -133,11 +133,12 @@ int convert_to_sparse(struct index_state *istate)
>>  	test_env = git_env_bool("GIT_TEST_SPARSE_INDEX", -1);
>>  	if (test_env >= 0)
>>  		set_sparse_index_config(istate->repo, test_env);
>> +	else
>> +		prepare_repo_settings(istate->repo);
>
> The change presented here to either call set_sparse_index_config()
> _or_ prepare_repo_settings() seems like it knows too much about
> how set_sparse_index_config() works.

It seems reasonable to assume that a function to set config has
initialized (or died, if it couldn't) enough of our config state to do
its job.

Besides, it's a few lines above the changed code in the same file. 

But looking at this again 2/3 callers of set_sparse_index_config()
aren't checking the return value. Wouldn't something like [1] on top be
a good idea here?

Also, is GIT_TEST_SPARSE_INDEX=true itself supposed to work? Running the
test suite with it fails 3 test files for me, all /sparse/, i.e. tests
that (presumably) assume it's not already turned on by this code.

1. 

diff --git a/builtin/sparse-checkout.c b/builtin/sparse-checkout.c
index a4bdd7c4940..bea1e7dd00e 100644
--- a/builtin/sparse-checkout.c
+++ b/builtin/sparse-checkout.c
@@ -280,8 +280,9 @@ static int set_config(enum sparse_checkout_mode mode)
 				      "core.sparseCheckoutCone",
 				      mode == MODE_CONE_PATTERNS ? "true" : NULL);
 
-	if (mode == MODE_NO_PATTERNS)
-		set_sparse_index_config(the_repository, 0);
+	if (mode == MODE_NO_PATTERNS &&
+	    set_sparse_index_config(the_repository, 0) < 0)
+		die(_("could not set index.sparse=0"));
 
 	return 0;
 }
diff --git a/sparse-index.c b/sparse-index.c
index 5bad05de645..3938bcec962 100644
--- a/sparse-index.c
+++ b/sparse-index.c
@@ -131,10 +131,13 @@ int convert_to_sparse(struct index_state *istate)
 	 * index.sparse config variable to be on.
 	 */
 	test_env = git_env_bool("GIT_TEST_SPARSE_INDEX", -1);
-	if (test_env >= 0)
-		set_sparse_index_config(istate->repo, test_env);
-	else
+	if (test_env >= 0) {
+		if (set_sparse_index_config(istate->repo, test_env) < 0)
+			die(_("could not set index.sparse based on GIT_TEST_SPARSE_INDEX=%d"),
+			    test_env);
+	} else {
 		prepare_repo_settings(istate->repo);
+	}
 
 	/*
 	 * Only convert to sparse if index.sparse is set.