Re: [PATCH 3/3] commit-graph: error out on invalid commit oids in 'write --stdin-commits'

> While 'git commit-graph write --stdin-commits' expects commit object
> ids as input, it accepts and silently skips over any invalid commit
> object ids, and still exits with success:
> 
>   # nonsense
>   $ echo not-a-commit-oid | git commit-graph write --stdin-commits
>   $ echo $?
>   0
>   # sometimes I forgot that refs are not good...
>   $ echo HEAD | git commit-graph write --stdin-commits
>   $ echo $?
>   0
>   # valid tree OID, but not a commit OID
>   $ git rev-parse HEAD^{tree} | git commit-graph write --stdin-commits
>   $ echo $?
>   0
>   $ ls -l .git/objects/info/commit-graph
>   ls: cannot access '.git/objects/info/commit-graph': No such file or directory
> 
> Check that all input records are indeed valid commit object ids and
> return with error otherwise, the same way '--stdin-packs' handles
> invalid input; see e103f7276f (commit-graph: return with errors during
> write, 2019-06-12).

> Note that it should only return with error when encountering an
> invalid commit object id coming from standard input.  However,
> '--reachable' uses the same code path to process object ids pointed to
> by all refs, and that includes tag object ids as well, which should
> still be skipped over.  Therefore add a new flag to 'enum
> commit_graph_write_flags' and a corresponding field to 'struct
> write_commit_graph_context', so we can differentiate between those two
> cases.

> @@ -1215,20 +1216,21 @@ static void fill_oids_from_commit_hex(struct write_commit_graph_context *ctx,
>  		struct commit *result;
>  
>  		display_progress(ctx->progress, i + 1);
> -		if (commit_hex->items[i].string &&
> -		    parse_oid_hex(commit_hex->items[i].string, &oid, &end))
> -			continue;
> -
> -		result = lookup_commit_reference_gently(ctx->r, &oid, 1);
> -
> -		if (result) {
> +		if (!parse_oid_hex(commit_hex->items[i].string, &oid, &end) &&
> +		    (result = lookup_commit_reference_gently(ctx->r, &oid, 1))) {
>  			ALLOC_GROW(ctx->oids.list, ctx->oids.nr + 1, ctx->oids.alloc);
>  			oidcpy(&ctx->oids.list[ctx->oids.nr], &(result->object.oid));
>  			ctx->oids.nr++;
> +		} else if (ctx->check_oids) {
> +			error(_("invalid commit object id: %s"),
> +			    commit_hex->items[i].string);
> +			return -1;
>  		}
>  	}
>  	stop_progress(&ctx->progress);
>  	strbuf_release(&progress_title);
> +
> +	return 0;
>  }

> @@ -1775,6 +1777,7 @@ int write_commit_graph(const char *obj_dir,
>  	ctx->append = flags & COMMIT_GRAPH_WRITE_APPEND ? 1 : 0;
>  	ctx->report_progress = flags & COMMIT_GRAPH_WRITE_PROGRESS ? 1 : 0;
>  	ctx->split = flags & COMMIT_GRAPH_WRITE_SPLIT ? 1 : 0;
> +	ctx->check_oids = flags & COMMIT_GRAPH_WRITE_CHECK_OIDS ? 1 : 0;
>  	ctx->split_opts = split_opts;

> @@ -1829,8 +1832,10 @@ int write_commit_graph(const char *obj_dir,
>  			goto cleanup;
>  	}
>  
> -	if (commit_hex)
> -		fill_oids_from_commit_hex(ctx, commit_hex);
> +	if (commit_hex) {
> +		if ((res = fill_oids_from_commit_hex(ctx, commit_hex)))
> +			goto cleanup;
> +	}