[PATCH v8 0/4] graph: indent visual roots in graph

When rendering a graph, if the history contains multiple "visual roots",
actual roots or commits that look like roots (i.e. have their parents
filtered out) can end up being vertically adjacent to unrelated commits,
falsely appearing to be related.

A fix for this issue was already attempted [1] a while ago.

This series adds indentation to the visual root commits, so they cannot be
vertically adjacent anymore making it easier to identify them.

Before indentation:

	* A
	* B1
	* B2
	* C1
	* C2

After indentation:

	  * A
	* B1
	 \
	  * B2
	* C1
	* C2

Indents the visual root commits that have still commits to show after
them, and if they have children it connects them with an edge at a new
row.

If there are multiple visual roots adjacent in history, the indentation
starts with the second one, avoiding redundant indentation of the first
one and cascades after the second.

	* A
	  * B
	    * C
	* D1
	* D2

This series first commit is a cleanup that brings a common function
from t4215 and t6016 to a graph functions file which they both use, so
the new test file for indentation, t4218, can use it as well.

GitHub CI: https://github.com/pabloosabaterr/git/actions/runs/29082267633

[1]: https://lore.kernel.org/git/xmqqwnwajbuj.fsf@gitster.c.googlers.com/ (local)

V7 DIFF:

- New commit (2nd) "revision: add next_commit_to_show()" I wanted to
  drop (!revs->max_count_stage && !revs->reverse_output_stage) because
  --reverse is not compatible with --graph and I wanted the indentation
  to work with --max-count-oldest. Dropping it broke tests at t4202
  because the lookahead buffer was being populated from a different
  source.
  This new commit adds a helper to get the commits for the lookahead
  from the same source.
- Typos and style.
- Added --max-count and --max-count-oldest tests.
- graph_get_lookahead_room() now uses ARRAY_SIZE() instead of the
  hardcoded size 2.
- Added an assert on graph_pop_lookahead()

Signed-off-by: Pablo Sabater <redacted>
---
Pablo Sabater (4):
      lib-log-graph: move check_graph function
      revision: add next_commit_to_show()
      graph: add a 2 commit buffer for lookahead
      graph: indent visual root in graph

 graph.c                                    | 286 +++++++++++++++++
 graph.h                                    |  17 ++
 revision.c                                 |  48 ++-
 t/lib-log-graph.sh                         |   5 +
 t/meson.build                              |   1 +
 t/t4215-log-skewed-merges.sh               |  33 +-
 t/t4218-log-graph-indentation.sh           | 473 +++++++++++++++++++++++++++++
 t/t6016-rev-list-graph-simplify-history.sh |  25 +-
 8 files changed, 843 insertions(+), 45 deletions(-)

base-commit: f85a7e662054a7b0d9070e432508831afa214b47