[GSoC PATCH v4 0/3] graph: add --graph-lane-limit option

[Pablo Sabater <pabloosabaterr@gmail.com>]

Repositories that have many active branches at the same time produce
wide graphs. A lane consists of two columns, the edge and the space
padding, each branch takes a lane in the graph and there is no way
to limit how many can be shown.

Add '--graph-lane-limit=<n>' option that caps the visible lanes to n. Lanes over
this limit are replaced with '.' truncation mark.

The '*' commit mark is visible when it lives on a visible lane or the first
hidden lane, any deeper lane doesn't show the commit mark but keeps the commit
message visible. 

Merges where neither the commit nor its parents live on a visible lane are skipped
because they dont carry any visible information.

The original idea to limit columns was noted as a TODO in c12172d2ea
(Add history graph API, 2008-05-04).  This does not implement
gitk-style column rearrangement, it only truncates the visual output.

Possible future improvements:

- When all branches involved in collapsing or padding are over the limit, the
  truncated lane doesn't show any information, this lane could be removed to
  make the graph more compact. Currently these lanes still appear because
  graph_output_collapsing_line() mixes state handling with rendering, so it can't
  be skipped but callers always expect a non empty buffer. Fixing it would need
  to refactor the callers to handle empty buffers instead of expecting them to
  always have content.

- Collapsing and merges lanes that start on visible lanes but end on hidden ones
  are kept to maintain the most information possible on the visible lanes, but
  the information about where they go is lost. They can be kept, removed or think
  of a way to show that information without showing the lanes.

Changes since v3:

- Rewrote commit messages to focus on reasoning rather than the
  implementation details.
- Changed graph_max_lanes to int for consistency with other
  rev_info fields like max_count.
- Zero and negative values are now accepted and silently treated
  as "no limit", following what --max-parents does with negative values.
- Removed the MINIMUM_GRAPH_COLUMNS macro.
- Fixed missing "--" prefix in the documentation.

Pablo Sabater (3):
  graph: add --graph-lane-limit option
  graph: truncate graph visual output
  graph: add documentation and tests about --graph-lane-limit

 Documentation/rev-list-options.adoc |   5 ++
 graph.c                             | 131 ++++++++++++++++++++++++----
 revision.c                          |   6 ++
 revision.h                          |   1 +
 t/t4215-log-skewed-merges.sh        |  53 +++++++++++
 5 files changed, 180 insertions(+), 16 deletions(-)


base-commit: dc6ecd5354dca88d51b6d6562777fc8fc10d77e1
-- 
2.43.0