Re: [PATCH 07/11] graph: commit and post-merge lines for left-skewed merges

[James Coglan <jcoglan@gmail.com>]

On 10/10/2019 18:49, Derrick Stolee wrote:
> On 10/10/2019 12:13 PM, James Coglan via GitGitGadget wrote:
>> From: James Coglan <jcoglan@gmail.com>
>>
>> Following the introduction of "left-skewed" merges, which are merges
>> whose first parent fuses with another edge to its left, we have some
>> more edge cases to deal with in the display of commit and post-merge
>> lines.
>>
>> The current graph code handles the following cases for edges appearing
>> to the right of the commit (*) on commit lines. A 2-way merge is usually
>> followed by vertical lines:
>>
>>         | | |
>>         | * |
>>         | |\ \
>>
>> An octopus merge (more than two parents) is always followed by edges
>> sloping to the right:
>>
>>         | |  \          | |    \
>>         | *-. \         | *---. \
>>         | |\ \ \        | |\ \ \ \
>>
>> A 2-way merge is followed by a right-sloping edge if the commit line
>> immediately follows a post-merge line for a commit that appears in the
>> same column as the current commit, or any column to the left of that:
>>
>>         | *             | * |
>>         | |\            | |\ \
>>         | * \           | | * \
>>         | |\ \          | | |\ \
>>
>> This commit introduces the following new cases for commit lines. If a
>> 2-way merge skews to the left, then the edges to its right are always
>> vertical lines, even if the commit follows a post-merge line:
>>
>>         | | |           | |\
>>         | * |           | * |
>>         |/| |           |/| |
>>
>> A commit with 3 parents that skews left is followed by vertical edges:
>>
>>         | | |
>>         | * |
>>         |/|\ \
>>
>> If a 3-way left-skewed merge commit appears immediately after a
>> post-merge line, then it may be followed the right-sloping edges, just
>> like a 2-way merge that is not skewed.
>>
>>         | |\
>>         | * \
>>         |/|\ \
>>
>> Octopus merges with 4 or more parents that skew to the left will always
>> be followed by right-sloping edges, because the existing columns need to
>> expand around the merge.
>>
>>         | |  \
>>         | *-. \
>>         |/|\ \ \
>>
>> On post-merge lines, usually all edges following the current commit
>> slope to the right:
>>
>>         | * | |
>>         | |\ \ \
>>
>> However, if the commit is a left-skewed 2-way merge, the edges to its
>> right remain vertical. We also need to display a space after the
>> vertical line descending from the commit marker, whereas this line would
>> normally be followed by a backslash.
>>
>>         | * | |
>>         |/| | |
>>
>> If a left-skewed merge has more than 2 parents, then the edges to its
>> right are still sloped as they bend around the edges introduced by the
>> merge.
>>
>>         | * | |
>>         |/|\ \ \
>>
>> To handle these new cases, we need to know not just how many parents
>> each commit has, but how many new columns it adds to the display; this
>> quantity is recorded in the `edges_added` field for the current commit,
>> and `prev_edges_added` field for the previous commit.
>>
>> Here, "column" refers to visual columns, not the logical columns of the
>> `columns` array. This is because even if all the commit's parents end up
>> fusing with existing edges, they initially introduce distinct edges in
>> the commit and post-merge lines before those edges collapse. For
>> example, a 3-way merge whose 2nd and 3rd parents fuse with existing
>> edges still introduces 2 visual columns that affect the display of edges
>> to their right.
>>
>>         | | |  \
>>         | | *-. \
>>         | | |\ \ \
>>         | |_|/ / /
>>         |/| | / /
>>         | | |/ /
>>         | |/| |
>>         | | | |
>>
>> This merge does not introduce any *logical* columns; there are 4 edges
>> before and after this commit once all edges have collapsed. But it does
>> initially introduce 2 new edges that need to be accommodated by the
>> edges to their right.
>>
>> Signed-off-by: James Coglan <jcoglan@gmail.com>
>> ---
>>  graph.c                      |  63 +++++++++++++--
>>  t/t4215-log-skewed-merges.sh | 151 +++++++++++++++++++++++++++++++++++
>>  2 files changed, 209 insertions(+), 5 deletions(-)
>>
>> diff --git a/graph.c b/graph.c
>> index 9136173e03..fb2e42850f 100644
>> --- a/graph.c
>> +++ b/graph.c
>> @@ -197,6 +197,46 @@ struct git_graph {
>>  	 * 		|/| | | | |		| | | | | *
>>  	 */
>>  	int merge_layout;
>> +	/*
>> +	 * The number of columns added to the graph by the current commit. For
>> +	 * 2-way and octopus merges, this is is usually one less than the
>> +	 * number of parents:
>> +	 *
>> +	 * 		| | |			| |    \
>> +	 *		| * |			| *---. \
>> +	 *		| |\ \			| |\ \ \ \
>> +	 *		| | | |         	| | | | | |
>> +	 *
>> +	 *		num_parents: 2		num_parents: 4
>> +	 *		edges_added: 1		edges_added: 3
>> +	 *
>> +	 * For left-skewed merges, the first parent fuses with its neighbor and
>> +	 * so one less column is added:
>> +	 *
>> +	 *		| | |			| |  \
>> +	 *		| * |			| *-. \
>> +	 *		|/| |			|/|\ \ \
>> +	 *		| | |			| | | | |
>> +	 *
>> +	 *		num_parents: 2		num_parents: 4
>> +	 *		edges_added: 0		edges_added: 2
>> +	 *
>> +	 * This number determines how edges to the right of the merge are
>> +	 * displayed in commit and post-merge lines; if no columns have been
>> +	 * added then a vertical line should be used where a right-tracking
>> +	 * line would otherwise be used.
>> +	 *
>> +	 *		| * \			| * |
>> +	 *		| |\ \			|/| |
>> +	 *		| | * \			| * |
>> +	 */
>> +	int edges_added;
>> +	/*
>> +	 * The number of columns added by the previous commit, which is used to
>> +	 * smooth edges appearing to the right of a commit in a commit line
>> +	 * following a post-merge line.
>> +	 */
>> +	int prev_edges_added;
>>  	/*
>>  	 * The maximum number of columns that can be stored in the columns
>>  	 * and new_columns arrays.  This is also half the number of entries
>> @@ -309,6 +349,8 @@ struct git_graph *graph_init(struct rev_info *opt)
>>  	graph->commit_index = 0;
>>  	graph->prev_commit_index = 0;
>>  	graph->merge_layout = 0;
>> +	graph->edges_added = 0;
>> +	graph->prev_edges_added = 0;
>>  	graph->num_columns = 0;
>>  	graph->num_new_columns = 0;
>>  	graph->mapping_size = 0;
>> @@ -670,6 +712,9 @@ void graph_update(struct git_graph *graph, struct commit *commit)
>>  	 */
>>  	graph_update_columns(graph);
>>  
>> +	graph->prev_edges_added = graph->edges_added;
>> +	graph->edges_added = graph->num_parents + graph->merge_layout - 2;
>> +
>>  	graph->expansion_row = 0;
>>  
>>  	/*
>> @@ -943,12 +988,13 @@ static void graph_output_commit_line(struct git_graph *graph, struct strbuf *sb)
>>  
>>  			if (graph->num_parents > 2)
>>  				graph_draw_octopus_merge(graph, sb);
>> -		} else if (seen_this && (graph->num_parents > 2)) {
>> +		} else if (seen_this && (graph->edges_added > 1)) {
>>  			strbuf_write_column(sb, col, '\\');
>> -		} else if (seen_this && (graph->num_parents == 2)) {
>> +		} else if (seen_this && (graph->edges_added == 1)) {
>>  			/*
>> -			 * This is a 2-way merge commit.
>> -			 * There is no GRAPH_PRE_COMMIT stage for 2-way
>> +			 * This is either a right-skewed 2-way merge
>> +			 * commit, or a left-skewed 3-way merge.
>> +			 * There is no GRAPH_PRE_COMMIT stage for such
>>  			 * merges, so this is the first line of output
>>  			 * for this commit.  Check to see what the previous
>>  			 * line of output was.
>> @@ -960,6 +1006,7 @@ static void graph_output_commit_line(struct git_graph *graph, struct strbuf *sb)
>>  			 * makes the output look nicer.
>>  			 */
>>  			if (graph->prev_state == GRAPH_POST_MERGE &&
>> +			    graph->prev_edges_added > 0 &&
>>  			    graph->prev_commit_index < i)
>>  				strbuf_write_column(sb, col, '\\');
>>  			else
>> @@ -1031,8 +1078,14 @@ static void graph_output_post_merge_line(struct git_graph *graph, struct strbuf
>>  				else
>>  					idx++;
>>  			}
>> +			if (graph->edges_added == 0)
>> +				strbuf_addch(sb, ' ');
>> +
>>  		} else if (seen_this) {
>> -			strbuf_write_column(sb, col, '\\');
>> +			if (graph->edges_added > 0)
>> +				strbuf_write_column(sb, col, '\\');
>> +			else
>> +				strbuf_write_column(sb, col, '|');
>>  			strbuf_addch(sb, ' ');
>>  		} else {
>>  			strbuf_write_column(sb, col, '|');
>> diff --git a/t/t4215-log-skewed-merges.sh b/t/t4215-log-skewed-merges.sh
>> index cfaba40f97..e479d6e676 100755
>> --- a/t/t4215-log-skewed-merges.sh
>> +++ b/t/t4215-log-skewed-merges.sh
>> @@ -39,4 +39,155 @@ test_expect_success 'log --graph with left-skewed merge' '
>>  	test_cmp expect actual
>>  '
>>  
>> +test_expect_success 'setup nested left-skewed merge' '
>> +	git checkout --orphan 1_p &&
>> +	test_commit 1_A &&
>> +	test_commit 1_B &&
>> +	test_commit 1_C &&
>> +	git checkout -b 1_q @^ && test_commit 1_D &&
>> +	git checkout 1_p && git merge --no-ff 1_q -m 1_E &&
>> +	git checkout -b 1_r @~3 && test_commit 1_F &&
>> +	git checkout 1_p && git merge --no-ff 1_r -m 1_G &&
>> +	git checkout @^^ && git merge --no-ff 1_p -m 1_H
>> +'
>> +
>> +cat > expect <<\EOF
>> +*   1_H
>> +|\
>> +| *   1_G
>> +| |\
>> +| | * 1_F
>> +| * | 1_E
>> +|/| |
>> +| * | 1_D
>> +* | | 1_C
>> +|/ /
>> +* | 1_B
>> +|/
>> +* 1_A
>> +EOF
>> +
>> +test_expect_success 'log --graph with nested left-skewed merge' '
>> +	git log --graph --pretty=tformat:%s | sed "s/ *$//" > actual &&
>> +	test_cmp expect actual
>> +'
> 
> I should have noticed in your earlier commits, but why don't you keep
> the output inside the test suite? You can start with "cat >expect <<-EOF"
> to have it ignore leading whitespace. Sorry if there's something else about
> this that is causing issues.

I was following a pattern used in t/t4202-log.sh. I believe it was easier to debug these tests with the setup and expectations split into separate blocks, but I wouldn't be opposed to merging them.

>> +
>> +test_expect_success 'setup nested left-skewed merge following normal merge' '
>> +	git checkout --orphan 2_p &&
>> +	test_commit 2_A &&
>> +	test_commit 2_B &&
>> +	test_commit 2_C &&
>> +	git checkout -b 2_q @^^ &&
>> +	test_commit 2_D &&
>> +	test_commit 2_E &&
>> +	git checkout -b 2_r @^ && test_commit 2_F &&
>> +	git checkout 2_q &&
>> +	git merge --no-ff 2_r -m 2_G &&
>> +	git merge --no-ff 2_p^ -m 2_H &&
>> +	git checkout -b 2_s @^^ && git merge --no-ff 2_q -m 2_J &&
>> +	git checkout 2_p && git merge --no-ff 2_s -m 2_K
>> +'
>> +
>> +cat > expect <<\EOF
>> +*   2_K
>> +|\
>> +| *   2_J
>> +| |\
>> +| | *   2_H
>> +| | |\
>> +| | * | 2_G
>> +| |/| |
>> +| | * | 2_F
>> +| * | | 2_E
>> +| |/ /
>> +| * | 2_D
>> +* | | 2_C
>> +| |/
>> +|/|
>> +* | 2_B
>> +|/
>> +* 2_A
>> +EOF
>> +
>> +test_expect_success 'log --graph with nested left-skewed merge following normal merge' '
>> +	git log --graph --pretty=tformat:%s | sed "s/ *$//" > actual &&
>> +	test_cmp expect actual
>> +'
>> +
>> +test_expect_success 'setup nested right-skewed merge following left-skewed merge' '
>> +	git checkout --orphan 3_p &&
>> +	test_commit 3_A &&
>> +	git checkout -b 3_q &&
>> +	test_commit 3_B &&
>> +	test_commit 3_C &&
>> +	git checkout -b 3_r @^ &&
>> +	test_commit 3_D &&
>> +	git checkout 3_q && git merge --no-ff 3_r -m 3_E &&
>> +	git checkout 3_p && git merge --no-ff 3_q -m 3_F &&
>> +	git checkout 3_r && test_commit 3_G &&
>> +	git checkout 3_p && git merge --no-ff 3_r -m 3_H &&
>> +	git checkout @^^ && git merge --no-ff 3_p -m 3_J
>> +'
>> +
>> +cat > expect <<\EOF
>> +*   3_J
>> +|\
>> +| *   3_H
>> +| |\
>> +| | * 3_G
>> +| * | 3_F
>> +|/| |
>> +| * |   3_E
>> +| |\ \
>> +| | |/
>> +| | * 3_D
>> +| * | 3_C
>> +| |/
>> +| * 3_B
>> +|/
>> +* 3_A
>> +EOF
>> +
>> +test_expect_success 'log --graph with nested right-skewed merge following left-skewed merge' '
>> +	git log --graph --pretty=tformat:%s | sed "s/ *$//" > actual &&
>> +	test_cmp expect actual
>> +'
>> +
>> +test_expect_success 'setup right-skewed merge following a left-skewed one' '
>> +	git checkout --orphan 4_p &&
>> +	test_commit 4_A &&
>> +	test_commit 4_B &&
>> +	test_commit 4_C &&
>> +	git checkout -b 4_q @^^ && test_commit 4_D &&
>> +	git checkout -b 4_r 4_p^ && git merge --no-ff 4_q -m 4_E &&
>> +	git checkout -b 4_s 4_p^^ &&
>> +	git merge --no-ff 4_r -m 4_F &&
>> +	git merge --no-ff 4_p -m 4_G &&
>> +	git checkout @^^ && git merge --no-ff 4_s -m 4_H
>> +'
>> +
>> +cat > expect <<\EOF
>> +*   4_H
>> +|\
>> +| *   4_G
>> +| |\
>> +| * | 4_F
>> +|/| |
>> +| * |   4_E
>> +| |\ \
>> +| | * | 4_D
>> +| |/ /
>> +|/| |
>> +| | * 4_C
>> +| |/
>> +| * 4_B
>> +|/
>> +* 4_A
>> +EOF
>> +
>> +test_expect_success 'log --graph with right-skewed merge following a left-skewed one' '
>> +	git log --graph --date-order --pretty=tformat:%s | sed "s/ *$//" > actual &&
>> +	test_cmp expect actual
>> +'
>> +
>>  test_done
>>
>