This change adds the git_commit_graph_writer_* functions to allow to
write and create `commit-graph` files from `.idx`/`.pack` files or
`git_revwalk`s.
Part of: #5757
This change introduces a new API function
`git_graph_reachable_from_any()`, that answers the question whether a
commit is reachable from any of the provided commits through following
parent edges.
This function can take advantage of optimizations provided by the
existence of a `commit-graph` file, since it makes it faster to know
whether, given two commits X and Y, X cannot possibly be an reachable
from Y.
Part of: #5757
This change does a medium-size refactor of the git_commit_graph_file and
the interaction with the ODB. Now instead of the ODB owning a direct
reference to the git_commit_graph_file, there will be an intermediate
git_commit_graph. The main advantage of that is that now end users can
explicitly set a git_commit_graph that is eagerly checked for errors,
while still being able to lazily use the commit-graph in a regular ODB,
if the file is present.
This change introduces a function that allows the caller to know whether
the `commit-graph` file has not been modified since it was parsed.
Part of: #5757
This change introduces `git_commit_graph_entry_find()` and
`git_commit_graph_entry_parent()`. These two functions allow a much
faster lookup of commits by ID, since the ODB does not need to be
consulted, the commit object does not need to be inflated, and the
contents of the commit object do not need to be parsed.
Part of: #5757
This change is the first in a series to add support for git's
commit-graph. This should speed up commit graph traversals by avoiding
object parsing and allowing some operations to terminate earlier.
Part of: #5757
