def Midpoint(cls, change_a, change_b):
"""Returns a Change halfway between the two given Changes.
This function does two passes over the Changes' Commits:
* The first pass attempts to match the lengths of the Commit lists by
expanding DEPS to fill in any repositories that are missing from one,
but included in the other.
* The second pass takes the midpoint of every matched pair of Commits,
expanding DEPS rolls as it comes across them.
A NonLinearError is raised if there is no valid midpoint. The Changes are
not linear if any of the following is true:
* They have different patches.
* Their repositories don't match even after expanding DEPS rolls.
* The left Change comes after the right Change.
* They are the same or adjacent.
See change_test.py for examples of linear and nonlinear Changes.
Args:
change_a: The first Change in the range.
change_b: The last Change in the range.
Returns:
A new Change representing the midpoint.
The Change before the midpoint if the range has an even number of commits.
Raises:
NonLinearError: The Changes are not linear.
"""
if change_a.patch != change_b.patch:
raise commit_module.NonLinearError(
'Change A has patch "%s" and Change B has patch "%s".' %
(change_a.patch, change_b.patch))
commits_a = list(change_a.commits)
commits_b = list(change_b.commits)
_ExpandDepsToMatchRepositories(commits_a, commits_b)
commits_midpoint = _FindMidpoints(commits_a, commits_b)
if commits_a == commits_midpoint:
raise commit_module.NonLinearError(
'Changes are the same or adjacent.')
return cls(commits_midpoint, change_a.patch)
def _FindMidpoints(commits_a, commits_b):
"""Returns the midpoint of two Commit lists.
Loops through each pair of Commits and takes the midpoint. If the repositories
don't match, a NonLinearError is raised. If the Commits are adjacent and
represent a DEPS roll, the differing DEPs are added to the end of the lists.
Args:
commits_a: A list of Commits.
commits_b: A list of Commits.
Returns:
A list of Commits, each of which is the midpoint of the respective Commit in
commits_a and commits_b.
Raises:
NonLinearError: The lists have a different number of commits even after
expanding DEPS rolls, a Commit pair contains differing repositories, or a
Commit pair is in the wrong order.
"""
commits_midpoint = []
for commit_a, commit_b in zip_longest(commits_a, commits_b):
if not (commit_a and commit_b):
# If the commit lists are not the same length, bail out. That could happen
# if commits_b has a repository that was not found in the DEPS of
# commits_a (or vice versa); or a DEPS roll added or removed a DEP.
raise commit_module.NonLinearError(
'Changes have a different number of commits.')
commit_midpoint = commit_module.Commit.Midpoint(commit_a, commit_b)
commits_midpoint.append(commit_midpoint)
if commit_a == commit_midpoint and commit_midpoint != commit_b:
# Commits are adjacent.
# Add any DEPS changes to the commit lists.
deps_a = commit_a.Deps()
deps_b = commit_b.Deps()
dep_commits_a = sorted(
commit_module.Commit.FromDep(dep)
for dep in deps_a.difference(deps_b) if
not _FindRepositoryUrlInCommits(commits_a, dep.repository_url))
dep_commits_b = sorted(
commit_module.Commit.FromDep(dep)
for dep in deps_b.difference(deps_a) if
not _FindRepositoryUrlInCommits(commits_b, dep.repository_url))
commits_a += [c for c in dep_commits_a if c is not None]
commits_b += [c for c in dep_commits_b if c is not None]
return commits_midpoint
