[PATCH v6 0/3] graph: indent visual roots in graph

[Pablo Sabater <pabloosabaterr@gmail.com>]

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.

There are two main limitations to predict if the next commit will be a
visual root candidate:

1. The peek only gives us the next entry reliably, we cannot see past it
   reliably in order.

2. Even if we could peek past in order, its parents might not have been
   simplified yet, so a future commit that will become a visual root is
   not detected as a visual root in peek-time.

This causes the cascading to not be set and result in a extra
indentation. For example:

Given:

	* A unrelated (visual root)
	* B child of C
	* C visual root WILL BE FILTERED OUT
	* D unrelated (visual root)

The actual output is:

	  * A
	    * B
	* D

But we wanted:

	* A
	  * B
	* D

A test has been added to t4218 and a NEEDSWORK to the lookahead function
to document this edge case but I'm not that familiar with revision.c.
Maybe there's a better way to make the lookahead more reliable.

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

V5 DIFF:

- Added new commit with lookahead functions to abstract the commit
  traverse to the graph. Changed the lookahead function from graph to
  call this new functions.
- Added new test with two unrelated branches with merges.
- Fixed test_expect_failure to have the correct expected output.
- Simplified the NEEDSWORK.

Signed-off-by: Pablo Sabater <pabloosabaterr@gmail.com>
---
Pablo Sabater (3):
      lib-log-graph: move check_graph function
      revision: add peek functions for lookahead
      graph: indent visual root in graph

 graph.c                                    | 271 +++++++++++++++++
 revision.c                                 |  38 +++
 revision.h                                 |  10 +
 t/lib-log-graph.sh                         |   5 +
 t/meson.build                              |   1 +
 t/t4215-log-skewed-merges.sh               |  33 +-
 t/t4218-log-graph-indentation.sh           | 468 +++++++++++++++++++++++++++++
 t/t6016-rev-list-graph-simplify-history.sh |  25 +-
 8 files changed, 817 insertions(+), 34 deletions(-)
---
base-commit: 95e20213faefeb95df29277c58ac1980ab68f701
change-id: 20260612-ps-pre-commit-indent-39ca72816382

Best regards,
--  
Pablo Sabater <pabloosabaterr@gmail.com>