Re: [PATCH 6/7] diff: handle sha1 abbreviations outside of repository

[Jeff King <peff@peff.net>]

On Thu, Oct 20, 2016 at 02:21:25AM -0400, Jeff King wrote:

> diff --git a/diff.c b/diff.c
> index 8f0f309..ef11001 100644
> --- a/diff.c
> +++ b/diff.c
> @@ -3049,6 +3049,19 @@ static int similarity_index(struct diff_filepair *p)
>  	return p->score * 100 / MAX_SCORE;
>  }
>  
> +static const char *diff_abbrev_oid(const struct object_id *oid, int abbrev)
> +{
> +	if (startup_info->have_repository)
> +		return find_unique_abbrev(oid->hash, abbrev);
> +	else {
> +		char *hex = oid_to_hex(oid);
> +		if (abbrev < 0 || abbrev > GIT_SHA1_HEXSZ)
> +			die("BUG: oid abbreviation out of range: %d", abbrev);
> +		hex[abbrev] = '\0';
> +		return hex;
> +	}
> +}

Note that this function has a semantic (but not textual) conflict with
lt/auto-abbrev in 'next', as it sets DEFAULT_ABBREV to -1.

The resolution is:

diff --git a/diff.c b/diff.c
index cab811e..4c09314 100644
--- a/diff.c
+++ b/diff.c
@@ -3102,7 +3102,9 @@ static const char *diff_abbrev_oid(const struct object_id *oid, int abbrev)
 		return find_unique_abbrev(oid->hash, abbrev);
 	else {
 		char *hex = oid_to_hex(oid);
-		if (abbrev < 0 || abbrev > GIT_SHA1_HEXSZ)
+		if (abbrev < 0)
+			abbrev = FALLBACK_DEFAULT_ABBREV;
+		if (abbrev > GIT_SHA1_HEXSZ)
 			die("BUG: oid abbreviation out of range: %d", abbrev);
 		hex[abbrev] = '\0';
 		return hex;

This logic could be pushed down into the find_unique_abbrev() code
(where it _would_ just cause a textual conflict). I preferred to keep it
up here because other callers could conceivably want to handle the
non-repo case in some different way (e.g., by not abbreviating at all).

-Peff