Subject: Re: [PATCH 2/2] midx-write.c: assume checksum-invalid MIDXs require an update

From: Patrick Steinhardt <[email-masked]>
Date: Tue, 13 Jan 2026 08:38:23 +0100

On Mon, Jan 12, 2026 at 06:45:06PM -0500, Taylor Blau wrote:
> diff --git a/midx-write.c b/midx-write.c
> index 87b97c70872..6485cb67068 100644
> --- a/midx-write.c
> +++ b/midx-write.c
> @@ -1011,6 +1011,20 @@ static bool midx_needs_update(struct multi_pack_index *midx, struct write_midx_c
>  	struct strbuf buf = STRBUF_INIT;
>  	bool needed = true;
>  
> +	/*
> +	 * Ensure that we have a valid checksum before consulting the
> +	 * exisiting MIDX in order to determine if we can avoid an
> +	 * update.
> +	 *
> +	 * This is necessary because the given MIDX is loaded directly
> +	 * from the object store (because we still compare our proposed
> +	 * update to any on-disk MIDX regardless of whether or not we
> +	 * have assigned "ctx.m") and is thus not guaranteed to have a
> +	 * valid checksum.
> +	 */
> +	if (!midx_checksum_valid(midx))
> +		goto out;
> +
>  	/*
>  	 * Ignore incremental updates for now. The assumption is that any
>  	 * incremental update would be either empty (in which case we will bail

This looks sensible to me, thanks for the fix!

Patrick