graph: tidy up display of left-skewed merges

Currently, when we display a merge whose first parent is already present
in a column to the left of the merge commit, we display the first parent
as a vertical pipe `|` in the GRAPH_POST_MERGE line and then immediately
enter the GRAPH_COLLAPSING state. The first-parent line tracks to the
left and all the other parent lines follow it; this creates a "kink" in
those lines:

        | *---.
        | |\ \ \
        |/ / / /
        | | | *

This change tidies the display of such commits such that if the first
parent appears to the left of the merge, we render it as a `/` and the
second parent as a `|`. This reduces the horizontal and vertical space
needed to render the merge, and makes the resulting lines easier to
read.

        | *-.
        |/|\ \
        | | | *

If the first parent is separated from the merge by several columns, a
horizontal line is drawn in a similar manner to how the GRAPH_COLLAPSING
state displays the line.

        | | | *-.
        | |_|/|\ \
        |/| | | | *

This effect is applied to both "normal" two-parent merges, and to
octopus merges. It also reduces the vertical space needed for pre-commit
lines, as the merge occupies one less column than usual.

        Before:         After:

        | *             | *
        | |\            | |\
        | | \           | * \
        | |  \          |/|\ \
        | *-. \
        | |\ \ \

Signed-off-by: James Coglan <jcoglan@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 8 insertions, 12 deletions

diff --git a/t/t4214-log-graph-octopus.sh b/t/t4214-log-graph-octopus.sh
index 3ae8e51e50..1b96276894 100755
--- a/t/t4214-log-graph-octopus.sh
+++ b/t/t4214-log-graph-octopus.sh
@@ -26,9 +26,8 @@ test_expect_success 'set up merge history' '
 test_expect_success 'log --graph with tricky octopus merge, no color' '
 	cat >expect.uncolored <<-\EOF &&
 	* left
-	| *---.   octopus-merge
-	| |\ \ \
-	|/ / / /
+	| *-.   octopus-merge
+	|/|\ \
 	| | | * 4
 	| | * | 3
 	| | |/
@@ -47,9 +46,8 @@ test_expect_success 'log --graph with tricky octopus merge with colors' '
 	test_config log.graphColors red,green,yellow,blue,magenta,cyan &&
 	cat >expect.colors <<-\EOF &&
 	* left
-	<RED>|<RESET> *<BLUE>-<RESET><BLUE>-<RESET><MAGENTA>-<RESET><MAGENTA>.<RESET>   octopus-merge
-	<RED>|<RESET> <RED>|<RESET><YELLOW>\<RESET> <BLUE>\<RESET> <MAGENTA>\<RESET>
-	<RED>|<RESET><RED>/<RESET> <YELLOW>/<RESET> <BLUE>/<RESET> <MAGENTA>/<RESET>
+	<RED>|<RESET> *<MAGENTA>-<RESET><MAGENTA>.<RESET>   octopus-merge
+	<RED>|<RESET><RED>/<RESET><YELLOW>|<RESET><BLUE>\<RESET> <MAGENTA>\<RESET>
 	<RED>|<RESET> <YELLOW>|<RESET> <BLUE>|<RESET> * 4
 	<RED>|<RESET> <YELLOW>|<RESET> * <MAGENTA>|<RESET> 3
 	<RED>|<RESET> <YELLOW>|<RESET> <MAGENTA>|<RESET><MAGENTA>/<RESET>
@@ -147,9 +145,8 @@ test_expect_success 'log --graph with tricky octopus merge and its child, no col
 	cat >expect.uncolored <<-\EOF &&
 	* left
 	| * after-merge
-	| *---.   octopus-merge
-	| |\ \ \
-	|/ / / /
+	| *-.   octopus-merge
+	|/|\ \
 	| | | * 4
 	| | * | 3
 	| | |/
@@ -169,9 +166,8 @@ test_expect_failure 'log --graph with tricky octopus merge and its child with co
 	cat >expect.colors <<-\EOF &&
 	* left
 	<RED>|<RESET> * after-merge
-	<RED>|<RESET> *<MAGENTA>-<RESET><MAGENTA>-<RESET><CYAN>-<RESET><CYAN>.<RESET>   octopus-merge
-	<RED>|<RESET> <RED>|<RESET><BLUE>\<RESET> <MAGENTA>\<RESET> <CYAN>\<RESET>
-	<RED>|<RESET><RED>/<RESET> <BLUE>/<RESET> <MAGENTA>/<RESET> <CYAN>/<RESET>
+	<RED>|<RESET> *<CYAN>-<RESET><CYAN>.<RESET>   octopus-merge
+	<RED>|<RESET><RED>/<RESET><BLUE>|<RESET><MAGENTA>\<RESET> <CYAN>\<RESET>
 	<RED>|<RESET> <BLUE>|<RESET> <MAGENTA>|<RESET> * 4
 	<RED>|<RESET> <BLUE>|<RESET> * <CYAN>|<RESET> 3
 	<RED>|<RESET> <BLUE>|<RESET> <CYAN>|<RESET><CYAN>/<RESET>