Subject: Re: [PATCH v4] write-tree: integrate with sparse index

From: Victoria Dye <[email-masked]>
Date: Fri, 21 Apr 2023 14:42:34 -0700

Shuqi Liang wrote:
> Update 'git write-tree' to allow using the sparse-index in memory
> without expanding to a full one.
> 
> The recursive algorithm for update_one() was already updated in 2de37c5
> (cache-tree: integrate with sparse directory entries, 2021-03-03) to
> handle sparse directory entries in the index. Hence we can just set the
> requires-full-index to false for "write-tree".
> 
> The `p2000` tests demonstrate a ~96% execution time reduction for 'git
> write-tree' using a sparse index:
> 
> Test                                           before  after
> -----------------------------------------------------------------
> 2000.78: git write-tree (full-v3)              0.34    0.33 -2.9%
> 2000.79: git write-tree (full-v4)              0.32    0.30 -6.3%
> 2000.80: git write-tree (sparse-v3)            0.47    0.02 -95.8%
> 2000.81: git write-tree (sparse-v4)            0.45    0.02 -95.6%

Please update your commit message to explain only the incremental updates on
top of 1a65b41b38a (write-tree: integrate with sparse index, 2023-04-03);
that patch's message (what you have here) does not accurately describe what
_this_ patch is doing.

> diff --git a/builtin/write-tree.c b/builtin/write-tree.c
> index 32e302a813..a9d5c20cde 100644
> --- a/builtin/write-tree.c
> +++ b/builtin/write-tree.c
> @@ -38,12 +38,15 @@ int cmd_write_tree(int argc, const char **argv, const char *cmd_prefix)
>  	};
>  
>  	git_config(git_default_config, NULL);
> +	
> +	if (the_repository->gitdir) {
> +		prepare_repo_settings(the_repository);
> +		the_repository->settings.command_requires_full_index = 0;
> +	}
> +
>  	argc = parse_options(argc, argv, cmd_prefix, write_tree_options,
>  			     write_tree_usage, 0);
>  
> -	prepare_repo_settings(the_repository);
> -	the_repository->settings.command_requires_full_index = 0;
> -

What is the functional benefit of this change? AFAICT, we don't need
'command_requires_full_index' to be set before 'parse_options' in this case,
so this won't have any effect on the behavior of 'write-tree'.

> diff --git a/t/t1092-sparse-checkout-compatibility.sh b/t/t1092-sparse-checkout-compatibility.sh
> index 9bbc0d646b..d3eb31326b 100755
> --- a/t/t1092-sparse-checkout-compatibility.sh
> +++ b/t/t1092-sparse-checkout-compatibility.sh
> @@ -2055,22 +2055,32 @@ test_expect_success 'grep sparse directory within submodules' '
>  	test_cmp actual expect
>  '
>  
> -test_expect_success 'write-tree on all' '
> +test_expect_success 'write-tree' '
>  	init_repos &&
>  
> +	test_all_match git write-tree &&
> +
>  	write_script edit-contents <<-\EOF &&
>  	echo text >>"$1"
>  	EOF
>  
> +	# make a change inside the sparse cone
>  	run_on_all ../edit-contents deep/a &&
> -	run_on_all git update-index deep/a &&
> +	test_all_match git update-index deep/a &&
>  	test_all_match git write-tree &&
> +	test_all_match git status --porcelain=v2 &&
>  
> +	# make a change outside the sparse cone
>  	run_on_all mkdir -p folder1 &&
>  	run_on_all cp a folder1/a &&
>  	run_on_all ../edit-contents folder1/a &&
> -	run_on_all git update-index folder1/a &&
> -	test_all_match git write-tree
> +	test_all_match git update-index folder1/a &&
> +	test_all_match git write-tree &&
> +	test_all_match git status --porcelain=v2 &&
> +	
> +	# check that SKIP_WORKTREE files are not materialized
> +	test_path_is_missing sparse-checkout/folder2/a &&
> +	test_path_is_missing sparse-index/folder2/a

Test updates look good!

>  '
>  
>  test_expect_success 'sparse-index is not expanded: write-tree' '
> @@ -2080,7 +2090,7 @@ test_expect_success 'sparse-index is not expanded: write-tree' '
>  
>  	echo "test1" >>sparse-index/a &&
>  	git -C sparse-index update-index a &&
> -	ensure_not_expanded write-tree
> +	ensure_not_expanded write-tree 

nit: trailing whitespace should be removed

>  '
>  test_done