graph: fix lack of color in horizontal lines

In some cases, horizontal lines in rendered graphs can lose their
coloring. This is due to a use of graph_line_addch() instead of
graph_line_write_column(). Using a ternary operator to pick the
character is nice for compact code, but we actually need a column to
provide the color.

Add a test to t4215-log-skewed-merges.sh to prevent regression.

Reported-by: Jeff King <[email protected]>
Signed-off-by: Derrick Stolee <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: derrickstolee

graph.c

@@ -1063,7 +1063,7 @@ static void graph_output_post_merge_line(struct git_graph *graph, struct graph_l
 	int i, j;
 
 	struct commit_list *first_parent = first_interesting_parent(graph);
-	int seen_parent = 0;
+	struct column *parent_col = NULL;
 
 	/*
 	 * Output the post-merge row
@@ -1117,12 +1117,17 @@ static void graph_output_post_merge_line(struct git_graph *graph, struct graph_l
 			graph_line_addch(line, ' ');
 		} else {
 			graph_line_write_column(line, col, '|');
-			if (graph->merge_layout != 0 || i != graph->commit_index - 1)
-				graph_line_addch(line, seen_parent ? '_' : ' ');
+			if (graph->merge_layout != 0 || i != graph->commit_index - 1) {
+				if (parent_col)
+					graph_line_write_column(
+						line, parent_col, '_');
+				else
+					graph_line_addch(line, ' ');
+			}
 		}
 
 		if (col_commit == first_parent->item)
-			seen_parent = 1;
+			parent_col = col;
 	}
 
 	/*

t/t4215-log-skewed-merges.sh

@@ -282,4 +282,33 @@ test_expect_success 'log --graph with multiple tips' '
 	EOF
 '
 
+test_expect_success 'log --graph with multiple tips and colors' '
+	test_config log.graphColors red,green,yellow,blue,magenta,cyan &&
+	cat >expect.colors <<-\EOF &&
+	*   6_I
+	<RED>|<RESET><GREEN>\<RESET>
+	<RED>|<RESET> <GREEN>|<RESET> *   6_H
+	<RED>|<RESET> <GREEN>|<RESET> <YELLOW>|<RESET><BLUE>\<RESET>
+	<RED>|<RESET> <GREEN>|<RESET> <YELLOW>|<RESET> * 6_G
+	<RED>|<RESET> <GREEN>|<RESET> <YELLOW>|<RESET> <BLUE>|<RESET> * 6_F
+	<RED>|<RESET> <GREEN>|<RESET><RED>_<RESET><YELLOW>|<RESET><RED>_<RESET><BLUE>|<RESET><RED>/<RESET><GREEN>|<RESET>
+	<RED>|<RESET><RED>/<RESET><GREEN>|<RESET> <YELLOW>|<RESET> <BLUE>|<RESET><GREEN>/<RESET>
+	<RED>|<RESET> <GREEN>|<RESET> <YELLOW>|<RESET><GREEN>/<RESET><BLUE>|<RESET>
+	<RED>|<RESET> <GREEN>|<RESET><GREEN>/<RESET><YELLOW>|<RESET> <BLUE>|<RESET>
+	<RED>|<RESET> <GREEN>|<RESET> * <BLUE>|<RESET> 6_E
+	<RED>|<RESET> * <CYAN>|<RESET> <BLUE>|<RESET> 6_D
+	<RED>|<RESET> <BLUE>|<RESET> <CYAN>|<RESET><BLUE>/<RESET>
+	<RED>|<RESET> <BLUE>|<RESET><BLUE>/<RESET><CYAN>|<RESET>
+	* <BLUE>|<RESET> <CYAN>|<RESET> 6_C
+	<CYAN>|<RESET> <BLUE>|<RESET><CYAN>/<RESET>
+	<CYAN>|<RESET><CYAN>/<RESET><BLUE>|<RESET>
+	* <BLUE>|<RESET> 6_B
+	<BLUE>|<RESET><BLUE>/<RESET>
+	* 6_A
+	EOF
+	git log --color=always --graph --date-order --pretty=tformat:%s 6_1 6_3 6_5 >actual.colors.raw &&
+	test_decode_color <actual.colors.raw | sed "s/ *\$//" >actual.colors &&
+	test_cmp expect.colors actual.colors
+'
+
 test_done