Merge branch 'ps/graph-lane-limit' into seen

The graph output from commands like "git log --graph" can now be
limited to a specified number of lanes, preventing overly wide output
in repositories with many branches.

* ps/graph-lane-limit:
  graph: add truncation mark to capped lanes
  graph: add --graph-lane-limit option
  graph: limit the graph width to a hard-coded max

Documentation/rev-list-options.adoc

@@ -1259,6 +1259,12 @@ This implies the `--topo-order` option by default, but the
 	in between them in that case. If _<barrier>_ is specified, it
 	is the string that will be shown instead of the default one.
 
+`--graph-lane-limit=<n>`::
+	When `--graph` is used, limit the number of graph lanes to be shown.
+	Lanes over the limit are replaced with a truncation mark '~'.
+	By default it is set to 0 (no limit), zero and negative values
+	are ignored and treated as no limit.
+
 ifdef::git-rev-list[]
 `--count`::
 	Print a number stating how many commits would have been

graph.c

@@ -317,6 +317,15 @@ struct git_graph {
 	struct strbuf prefix_buf;
 };
 
+static inline 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;
+}
+
 static const char *diff_output_prefix_callback(struct diff_options *opt, void *data)
 {
 	struct git_graph *graph = data;
@@ -696,6 +705,19 @@ static void graph_update_columns(struct git_graph *graph)
 		}
 	}
 
+	/*
+	 * If graph_max_lanes is set, cap the width
+	 */
+	if (graph->revs->graph_max_lanes > 0) {
+		/*
+		 * width of "| " per lanes plus truncation mark "~ ".
+		 * Allow commits from merges to align to the merged lane.
+		 */
+		int max_width = graph->revs->graph_max_lanes * 2 + 2;
+		if (graph->width > max_width)
+			graph->width = max_width;
+	}
+
 	/*
 	 * Shrink mapping_size to be the minimum necessary
 	 */
@@ -846,6 +868,10 @@ static void graph_output_padding_line(struct git_graph *graph,
 	 * Output a padding row, that leaves all branch lines unchanged
 	 */
 	for (i = 0; i < graph->num_new_columns; i++) {
+		if (graph_needs_truncation(graph, i)) {
+			graph_line_addstr(line, "~ ");
+			break;
+		}
 		graph_line_write_column(line, &graph->new_columns[i], '|');
 		graph_line_addch(line, ' ');
 	}
@@ -903,6 +929,9 @@ static void graph_output_pre_commit_line(struct git_graph *graph,
 			seen_this = 1;
 			graph_line_write_column(line, col, '|');
 			graph_line_addchars(line, ' ', graph->expansion_row);
+		} else if (seen_this && graph_needs_truncation(graph, i)) {
+			graph_line_addstr(line, "~ ");
+			break;
 		} else if (seen_this && (graph->expansion_row == 0)) {
 			/*
 			 * This is the first line of the pre-commit output.
@@ -994,6 +1023,16 @@ static void graph_draw_octopus_merge(struct git_graph *graph, struct graph_line
 		col = &graph->new_columns[j];
 
 		graph_line_write_column(line, col, '-');
+
+		/*
+		 * Commit is at commit_index, each iteration move one lane to
+		 * the right from the commit.
+		 */
+		if (graph_needs_truncation(graph, graph->commit_index + 1 + i)) {
+			graph_line_addstr(line, "~ ");
+			break;
+		}
+
 		graph_line_write_column(line, col, (i == dashed_parents - 1) ? '.' : '-');
 	}
 
@@ -1028,8 +1067,17 @@ static void graph_output_commit_line(struct git_graph *graph, struct graph_line
 			seen_this = 1;
 			graph_output_commit_char(graph, line);
 
+			if (graph_needs_truncation(graph, i)) {
+				graph_line_addch(line, ' ');
+				break;
+			}
+
 			if (graph->num_parents > 2)
 				graph_draw_octopus_merge(graph, line);
+		} else if (graph_needs_truncation(graph, i)) {
+			graph_line_addstr(line, "~ ");
+			seen_this = 1;
+			break;
 		} else if (seen_this && (graph->edges_added > 1)) {
 			graph_line_write_column(line, col, '\\');
 		} else if (seen_this && (graph->edges_added == 1)) {
@@ -1065,13 +1113,46 @@ static void graph_output_commit_line(struct git_graph *graph, struct graph_line
 
 	/*
 	 * Update graph->state
+	 *
+	 * If the commit is a merge and the first parent is in a visible lane,
+	 * then the GRAPH_POST_MERGE is needed to draw the merge lane.
+	 *
+	 * If the commit is over the truncation limit, but the first parent is on
+	 * a visible lane, then we still need the merge lane but truncated.
+	 *
+	 * If both commit and first parent are over the truncation limit, then
+	 * there's no need to draw the merge lane because it would work as a
+	 * padding lane.
 	 */
-	if (graph->num_parents > 1)
-		graph_update_state(graph, GRAPH_POST_MERGE);
-	else if (graph_is_mapping_correct(graph))
+	if (graph->num_parents > 1) {
+		if (!graph_needs_truncation(graph, graph->commit_index)) {
+			graph_update_state(graph, GRAPH_POST_MERGE);
+		} else {
+			struct commit_list *p = first_interesting_parent(graph);
+			int lane;
+
+			/*
+			 * graph->num_parents are found using first_interesting_parent
+			 * and next_interesting_parent so it can't be a scenario
+			 * where num_parents > 1 and there are no interesting parents
+			 */
+			if (!p)
+				BUG("num_parents > 1 but no interesting parent");
+
+			lane = graph_find_new_column_by_commit(graph, p->item);
+
+			if (!graph_needs_truncation(graph, lane))
+				graph_update_state(graph, GRAPH_POST_MERGE);
+			else if (graph_is_mapping_correct(graph))
+				graph_update_state(graph, GRAPH_PADDING);
+			else
+				graph_update_state(graph, GRAPH_COLLAPSING);
+		}
+	} else if (graph_is_mapping_correct(graph)) {
 		graph_update_state(graph, GRAPH_PADDING);
-	else
+	} else {
 		graph_update_state(graph, GRAPH_COLLAPSING);
+	}
 }
 
 static const char merge_chars[] = {'/', '|', '\\'};
@@ -1109,6 +1190,7 @@ static void graph_output_post_merge_line(struct git_graph *graph, struct graph_l
 			int par_column;
 			int idx = graph->merge_layout;
 			char c;
+			int truncated = 0;
 			seen_this = 1;
 
 			for (j = 0; j < graph->num_parents; j++) {
@@ -1117,23 +1199,56 @@ static void graph_output_post_merge_line(struct git_graph *graph, struct graph_l
 
 				c = merge_chars[idx];
 				graph_line_write_column(line, &graph->new_columns[par_column], c);
+
+				/*
+				 * j counts parents, it needs to be halved to be
+				 * comparable with i. Don't truncate if there are
+				 * no more lanes to print (end of the lane)
+				 */
+				if (graph_needs_truncation(graph, j / 2 + i) &&
+				    j / 2 + i <= graph->num_columns) {
+					if ((j + i * 2) % 2 != 0)
+						graph_line_addch(line, ' ');
+					graph_line_addstr(line, "~ ");
+					truncated = 1;
+					break;
+				}
+
 				if (idx == 2) {
-					if (graph->edges_added > 0 || j < graph->num_parents - 1)
+					/*
+					 * Check if the next lane needs truncation
+					 * to avoid having the padding doubled
+					 */
+					if (graph_needs_truncation(graph, (j + 1) / 2 + i) &&
+					    j < graph->num_parents - 1) {
+						graph_line_addstr(line, "~ ");
+						truncated = 1;
+						break;
+					} else if (graph->edges_added > 0 || j < graph->num_parents - 1)
 						graph_line_addch(line, ' ');
 				} else {
 					idx++;
 				}
 				parents = next_interesting_parent(graph, parents);
 			}
+			if (truncated)
+				break;
 			if (graph->edges_added == 0)
 				graph_line_addch(line, ' ');
-
+		} else if (graph_needs_truncation(graph, i)) {
+			graph_line_addstr(line, "~ ");
+			break;
 		} else if (seen_this) {
 			if (graph->edges_added > 0)
 				graph_line_write_column(line, col, '\\');
 			else
 				graph_line_write_column(line, col, '|');
-			graph_line_addch(line, ' ');
+			/*
+			 * If it's between two lanes and next would be truncated,
+			 * don't add space padding.
+			 */
+			if (!graph_needs_truncation(graph, i + 1))
+				graph_line_addch(line, ' ');
 		} else {
 			graph_line_write_column(line, col, '|');
 			if (graph->merge_layout != 0 || i != graph->commit_index - 1) {
@@ -1164,6 +1279,7 @@ static void graph_output_collapsing_line(struct git_graph *graph, struct graph_l
 	short used_horizontal = 0;
 	int horizontal_edge = -1;
 	int horizontal_edge_target = -1;
+	int truncated = 0;
 
 	/*
 	 * Swap the mapping and old_mapping arrays
@@ -1279,26 +1395,35 @@ static void graph_output_collapsing_line(struct git_graph *graph, struct graph_l
 	 */
 	for (i = 0; i < graph->mapping_size; i++) {
 		int target = graph->mapping[i];
-		if (target < 0)
-			graph_line_addch(line, ' ');
-		else if (target * 2 == i)
-			graph_line_write_column(line, &graph->new_columns[target], '|');
-		else if (target == horizontal_edge_target &&
-			 i != horizontal_edge - 1) {
-				/*
-				 * Set the mappings for all but the
-				 * first segment to -1 so that they
-				 * won't continue into the next line.
-				 */
-				if (i != (target * 2)+3)
-					graph->mapping[i] = -1;
-				used_horizontal = 1;
-			graph_line_write_column(line, &graph->new_columns[target], '_');
+
+		if (!truncated && graph_needs_truncation(graph, i / 2)) {
+			graph_line_addstr(line, "~ ");
+			truncated = 1;
+		}
+
+		if (target < 0) {
+			if (!truncated)
+				graph_line_addch(line, ' ');
+		} else if (target * 2 == i) {
+			if (!truncated)
+				graph_line_write_column(line, &graph->new_columns[target], '|');
+		} else if (target == horizontal_edge_target &&
+			   i != horizontal_edge - 1) {
+			/*
+			 * Set the mappings for all but the
+			 * first segment to -1 so that they
+			 * won't continue into the next line.
+			 */
+			if (i != (target * 2)+3)
+				graph->mapping[i] = -1;
+			used_horizontal = 1;
+			if (!truncated)
+				graph_line_write_column(line, &graph->new_columns[target], '_');
 		} else {
 			if (used_horizontal && i < horizontal_edge)
 				graph->mapping[i] = -1;
-			graph_line_write_column(line, &graph->new_columns[target], '/');
-
+			if (!truncated)
+				graph_line_write_column(line, &graph->new_columns[target], '/');
 		}
 	}
 
@@ -1372,6 +1497,11 @@ static void graph_padding_line(struct git_graph *graph, struct strbuf *sb)
 	for (i = 0; i < graph->num_columns; i++) {
 		struct column *col = &graph->columns[i];
 
+		if (graph_needs_truncation(graph, i)) {
+			graph_line_addstr(&line, "~ ");
+			break;
+		}
+
 		graph_line_write_column(&line, col, '|');
 
 		if (col->commit == graph->commit && graph->num_parents > 2) {

revision.c

@@ -2606,6 +2606,8 @@ 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")) {
@@ -3175,6 +3177,10 @@ 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(_("the 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");
 

revision.h

@@ -305,6 +305,7 @@ struct rev_info {
 
 	/* Display history graph */
 	struct git_graph *graph;
+	int graph_max_lanes;
 
 	/* special limits */
 	int skip_count;

t/t4215-log-skewed-merges.sh

@@ -370,4 +370,148 @@ test_expect_success 'log --graph with multiple tips' '
 	EOF
 '
 
+test_expect_success 'log --graph --graph-lane-limit=2 limited to two lanes' '
+	check_graph --graph-lane-limit=2 M_7 <<-\EOF
+	*-.   7_M4
+	|\ \
+	| | * 7_G
+	| | * 7_F
+	| * ~ 7_E
+	| * ~ 7_D
+	* | ~ 7_C
+	| |/
+	|/|
+	* | 7_B
+	|/
+	* 7_A
+	EOF
+'
+
+test_expect_success 'log --graph --graph-lane-limit=1 truncate mid octopus merge' '
+	check_graph --graph-lane-limit=1 M_7 <<-\EOF
+	*-~  7_M4
+	|\~
+	| ~ 7_G
+	| ~ 7_F
+	| * 7_E
+	| * 7_D
+	* ~ 7_C
+	| ~
+	|/~
+	* ~ 7_B
+	|/
+	* 7_A
+	EOF
+'
+
+test_expect_success 'log --graph --graph-lane-limit=3 limited to three lanes' '
+	check_graph --graph-lane-limit=3 M_1 M_3 M_5 M_7 <<-\EOF
+	*   7_M1
+	|\
+	| | *   7_M2
+	| | |\
+	| | | * 7_H
+	| | | ~ 7_M3
+	| | | ~ 7_J
+	| | | ~ 7_I
+	| | | ~ 7_M4
+	| |_|_~
+	|/| | ~
+	| | |_~
+	| |/| ~
+	| | | ~
+	| | |/~
+	| | * ~ 7_G
+	| | | ~
+	| | |/~
+	| | * ~ 7_F
+	| * | ~ 7_E
+	| | |/~
+	| |/| ~
+	| * | ~ 7_D
+	| | |/
+	| |/|
+	* | | 7_C
+	| |/
+	|/|
+	* | 7_B
+	|/
+	* 7_A
+	EOF
+'
+
+test_expect_success 'log --graph --graph-lane-limit=6 check if it only shows first of 3 parent merge' '
+	check_graph --graph-lane-limit=6 M_1 M_3 M_5 M_7 <<-\EOF
+	*   7_M1
+	|\
+	| | *   7_M2
+	| | |\
+	| | | * 7_H
+	| | | | *   7_M3
+	| | | | |\
+	| | | | | * 7_J
+	| | | | * | 7_I
+	| | | | | | * 7_M4
+	| |_|_|_|_|/~
+	|/| | | | |/~
+	| | |_|_|/| ~
+	| |/| | | |/
+	| | | |_|/|
+	| | |/| | |
+	| | * | | | 7_G
+	| | | |_|/
+	| | |/| |
+	| | * | | 7_F
+	| * | | | 7_E
+	| | |/ /
+	| |/| |
+	| * | | 7_D
+	| | |/
+	| |/|
+	* | | 7_C
+	| |/
+	|/|
+	* | 7_B
+	|/
+	* 7_A
+	EOF
+'
+
+test_expect_success 'log --graph --graph-lane-limit=7 check if it shows all 3 parent merge' '
+	check_graph --graph-lane-limit=7 M_1 M_3 M_5 M_7 <<-\EOF
+	*   7_M1
+	|\
+	| | *   7_M2
+	| | |\
+	| | | * 7_H
+	| | | | *   7_M3
+	| | | | |\
+	| | | | | * 7_J
+	| | | | * | 7_I
+	| | | | | | *   7_M4
+	| |_|_|_|_|/|\
+	|/| | | | |/ /
+	| | |_|_|/| /
+	| |/| | | |/
+	| | | |_|/|
+	| | |/| | |
+	| | * | | | 7_G
+	| | | |_|/
+	| | |/| |
+	| | * | | 7_F
+	| * | | | 7_E
+	| | |/ /
+	| |/| |
+	| * | | 7_D
+	| | |/
+	| |/|
+	* | | 7_C
+	| |/
+	|/|
+	* | 7_B
+	|/
+	* 7_A
+	EOF
+'
+
 test_done