Re: [GSoC PATCH v4 1/3] graph: add --graph-lane-limit option

["SZEDER Gábor" <szeder.dev@gmail.com>]

On Mon, Mar 23, 2026 at 10:59:33PM +0100, Pablo Sabater wrote:
> Repositories that have many active branches at the same time produce
> wide graphs. A lane consists of two columns, the edge and the space
> padding, each branch takes a lane in the graph and there is no way
> to limit how many can be shown.
> 
> Add '--graph-lane-limit=<n>' revision option that caps the number
> of visible lanes to n. This option requires '--graph', without it
> a limit to the graph has no meaning, in this case error out.
> 
> Zero and negative values are valid inputs but silently ignored
> treating them as "no limit", the same as not using the option.
> This follows what '--max-parents' does with negative values.
> 
> Signed-off-by: Pablo Sabater <pabloosabaterr@gmail.com>
> ---
>  graph.c    | 9 +++++++++
>  revision.c | 6 ++++++
>  revision.h | 1 +
>  3 files changed, 16 insertions(+)
> 
> diff --git a/graph.c b/graph.c
> index 26f6fbf000..e7c1151ac0 100644
> --- a/graph.c
> +++ b/graph.c
> @@ -317,6 +317,15 @@ struct git_graph {
>  	struct strbuf prefix_buf;
>  };
>  
> +static int graph_needs_truncation(struct git_graph *graph, int lane)
> +{
> +	int max = graph->revs->graph_max_lanes;
> +	/*
> +	 * Ignore values <= 0, meaning no limit.
> +	 */
> +	return max > 0 && lane >= max;
> +}

This patch adds this static function, but it doesn't add any callers.
This breaks the build with DEVELOPER=1:

  $ make DEVELOPER=1 graph.o
      CC graph.o
  graph.c:320:12: error: ‘graph_needs_truncation’ defined but not used [-Werror=unused-function]
    320 | static int graph_needs_truncation(struct git_graph *graph, int lane)
        |            ^~~~~~~~~~~~~~~~~~~~~~
  cc1: all warnings being treated as errors
  make: *** [Makefile:2923: graph.o] Error 1

>  static const char *diff_output_prefix_callback(struct diff_options *opt, void *data)
>  {
>  	struct git_graph *graph = data;
> diff --git a/revision.c b/revision.c
> index 31808e3df0..952edb031e 100644
> --- a/revision.c
> +++ b/revision.c
> @@ -2605,6 +2605,8 @@ static int handle_revision_opt(struct rev_info *revs, int argc, const char **arg
>  	} else if (!strcmp(arg, "--no-graph")) {
>  		graph_clear(revs->graph);
>  		revs->graph = NULL;
> +	} else if (skip_prefix(arg, "--graph-lane-limit=", &optarg)) {
> +		revs->graph_max_lanes = parse_count(optarg);
>  	} else if (!strcmp(arg, "--encode-email-headers")) {
>  		revs->encode_email_headers = 1;
>  	} else if (!strcmp(arg, "--no-encode-email-headers")) {
> @@ -3172,6 +3174,10 @@ int setup_revisions(int argc, const char **argv, struct rev_info *revs, struct s
>  
>  	if (revs->no_walk && revs->graph)
>  		die(_("options '%s' and '%s' cannot be used together"), "--no-walk", "--graph");
> +
> +	if (revs->graph_max_lanes > 0 && !revs->graph)
> +		die(_("option '%s' requires '%s'"), "--graph-lane-limit", "--graph");
> +
>  	if (!revs->reflog_info && revs->grep_filter.use_reflog_filter)
>  		die(_("the option '%s' requires '%s'"), "--grep-reflog", "--walk-reflogs");
>  
> diff --git a/revision.h b/revision.h
> index 69242ecb18..874ccce625 100644
> --- a/revision.h
> +++ b/revision.h
> @@ -304,6 +304,7 @@ struct rev_info {
>  
>  	/* Display history graph */
>  	struct git_graph *graph;
> +	int graph_max_lanes;
>  
>  	/* special limits */
>  	int skip_count;
> -- 
> 2.43.0
>