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Fix two bugs in graph.c #517

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wants to merge 2 commits into from
Closed

Fix two bugs in graph.c #517

wants to merge 2 commits into from

Commits on Jan 7, 2020

  1. graph: fix case that hit assert() 

    A failure was reported in "git log --graph --all" with the new
graph-rendering logic. The code fails an assert() statement when
collapsing multiple edges from a merge.

The assert was introduced by eaf158f (graph API: Use horizontal
lines for more compact graphs, 2009-04-21), which is quite old.
This assert is trying to say that when we complete a horizontal
line with a single slash, it is because we have reached our target.

This assertion is hit when we have two collapsing lines from the
same merge commit, as follows:

    | | | | *
    | |_|_|/|
    |/| | |/
    | | |/|
    | |/| |
    | * | |
    * | | |

It is actually the _second_ collapsing line that hits this assert.
The reason we are in this code path is because we are collapsing
the first line, and in that case we are hitting our target now
that the horizontal line is complete. However, the second line
cannot be a horizontal line, so it will collapse without horizontal
lines. In this case, it is inappropriate to assert that we have
reached our target, as we need to continue for another column
before reaching the target. Dropping the assert is safe here.

The new behavior in 0f0f389 (graph: tidy up display of
left-skewed merges, 2019-10-15) caused the behavior change that
made this assertion failure possible. In addition to making the
assert possible, it also changed how multiple edges collapse.

In a larger example, the current code will output a collapse
as follows:

	| | | | | | *
	| |_|_|_|_|/|\
	|/| | | | |/ /
	| | | | |/| /
	| | | |/| |/
	| | |/| |/|
	| |/| |/| |
	| | |/| | |
	| | * | | |

However, the intended collapse should allow multiple horizontal lines
as follows:

	| | | | | | *
	| |_|_|_|_|/|\
	|/| | | | |/ /
	| | |_|_|/| /
	| |/| | | |/
	| | | |_|/|
	| | |/| | |
	| | * | | |

This behavior is not corrected by this change, but is noted for a later
update.

Helped-by: Jeff King <peff@peff.net>
Reported-by: Bradley Smith <brad@brad-smith.co.uk>
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
    @derrickstolee
    derrickstolee committed Jan 7, 2020
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  2. 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 <peff@peff.net>
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
    @derrickstolee
    derrickstolee committed Jan 7, 2020
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