Subject: Re: [PATCH 1/4] merge-tree: fail with a non-zero exit code on missing tree objects

From: Patrick Steinhardt <[email-masked]>
Date: Wed, 7 Feb 2024 08:42:30 +0100

On Tue, Feb 06, 2024 at 09:49:38AM +0000, Johannes Schindelin via GitGitGadget wrote:
> From: Johannes Schindelin <[email-masked]>
> 
> When `git merge-tree` encounters a missing tree object, it should error
> out and not continue quietly as if nothing had happened.
> 
> However, as of time of writing, `git merge-tree` _does_ continue, and
> then offers the empty tree as result.
> 
> Let's fix this.
> 
> Signed-off-by: Johannes Schindelin <[email-masked]>
> ---
>  merge-ort.c                      |  7 ++++---
>  t/t4301-merge-tree-write-tree.sh | 10 ++++++++++
>  2 files changed, 14 insertions(+), 3 deletions(-)
> 
> diff --git a/merge-ort.c b/merge-ort.c
> index 6491070d965..c37fc035f13 100644
> --- a/merge-ort.c
> +++ b/merge-ort.c
> @@ -1659,9 +1659,10 @@ static int collect_merge_info(struct merge_options *opt,
>  	info.data = opt;
>  	info.show_all_errors = 1;
>  
> -	parse_tree(merge_base);
> -	parse_tree(side1);
> -	parse_tree(side2);
> +	if (parse_tree(merge_base) < 0 ||
> +	    parse_tree(side1) < 0 ||
> +	    parse_tree(side2) < 0)
> +		return -1;

I was wondering whether we also want to print an error in this case. But
`parse_tree()` calls `parse_tree_gently(tree, 0)`, where the second
parameter instructs the function to print an error message when the tree
is missing.

>  	init_tree_desc(t + 0, merge_base->buffer, merge_base->size);
>  	init_tree_desc(t + 1, side1->buffer, side1->size);
>  	init_tree_desc(t + 2, side2->buffer, side2->size);
> diff --git a/t/t4301-merge-tree-write-tree.sh b/t/t4301-merge-tree-write-tree.sh
> index 7d0fa74da74..4ea1b74445d 100755
> --- a/t/t4301-merge-tree-write-tree.sh
> +++ b/t/t4301-merge-tree-write-tree.sh
> @@ -950,5 +950,15 @@ test_expect_success '--merge-base with tree OIDs' '
>  	git merge-tree --merge-base=side1^^{tree} side1^{tree} side3^{tree} >with-trees &&
>  	test_cmp with-commits with-trees
>  '

Nit: missing newline.

> +test_expect_success 'error out on missing tree objects' '
> +	git init --bare missing-tree.git &&
> +	(
> +		git rev-list side3 &&
> +		git rev-parse side3^:
> +	) | git pack-objects missing-tree.git/objects/pack/side3-tree-is-missing &&
> +	side3=$(git rev-parse side3) &&
> +	test_must_fail git --git-dir=missing-tree.git merge-tree $side3^ $side3 >actual &&
> +	test_must_be_empty actual
> +'

Can't we avoid the subshell by using curly braces to pipe the outputs

Patrick