[GSoC PATCH WIP RFC v3 1/3] graph: add --graph-lane-limit option

[Pablo Sabater <pabloosabaterr@gmail.com>]

Repositories that have many active branches produce very wide outputs
with 'git log --graph --all' making it difficult to read.

Add MINIMUM_GRAPH_COLUMNS = 1

Add '--graph-lane-limit=<n>' to the revision options, this option
needs --graph explicitly and rejects values under MINIMUM_GRAPH_COLUMNS.

Add graph_max_lanes to rev_info and store what the user set

Add graph_needs_truncation() and teach it to know when a column is
over the limit following graph_max_lanes, if the limit is 0, treat it like
no limit.

Signed-off-by: Pablo Sabater <pabloosabaterr@gmail.com>
---
 graph.c    |  6 ++++++
 graph.h    |  2 ++
 revision.c | 11 +++++++++++
 revision.h |  1 +
 4 files changed, 20 insertions(+)

diff --git a/graph.c b/graph.c
index 26f6fbf000..a95c0a9a73 100644
--- a/graph.c
+++ b/graph.c
@@ -317,6 +317,12 @@ struct git_graph {
 	struct strbuf prefix_buf;
 };
 
+static int graph_needs_truncation(struct git_graph *graph, int col)
+{
+	int max = graph->revs->graph_max_lanes;
+	return max > 0 && col >= max;
+}
+
 static const char *diff_output_prefix_callback(struct diff_options *opt, void *data)
 {
 	struct git_graph *graph = data;
diff --git a/graph.h b/graph.h
index 3fd1dcb2e9..9a4551dd29 100644
--- a/graph.h
+++ b/graph.h
@@ -262,4 +262,6 @@ void graph_show_commit_msg(struct git_graph *graph,
 			   FILE *file,
 			   struct strbuf const *sb);
 
+#define MINIMUM_GRAPH_COLUMNS 1
+
 #endif /* GRAPH_H */
diff --git a/revision.c b/revision.c
index 31808e3df0..aeddf2d166 100644
--- a/revision.c
+++ b/revision.c
@@ -2605,6 +2605,13 @@ 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 ((argcount = parse_long_opt("graph-lane-limit", argv, &optarg))) {
+		int max_lanes = parse_count(optarg);
+		if (max_lanes < MINIMUM_GRAPH_COLUMNS)
+			die(_("minimum lanes is %d, cannot be set to %d"),
+			    MINIMUM_GRAPH_COLUMNS, max_lanes);
+		revs->graph_max_lanes = max_lanes;
+		return argcount;
 	} else if (!strcmp(arg, "--encode-email-headers")) {
 		revs->encode_email_headers = 1;
 	} else if (!strcmp(arg, "--no-encode-email-headers")) {
@@ -3172,6 +3179,10 @@ 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..597116f885 100644
--- a/revision.h
+++ b/revision.h
@@ -304,6 +304,7 @@ struct rev_info {
 
 	/* Display history graph */
 	struct git_graph *graph;
+	unsigned int graph_max_lanes;
 
 	/* special limits */
 	int skip_count;
-- 
2.43.0