[pinpoint] Calculate distances between Changes.

dashboard/dashboard/pinpoint/models/change/change.py

Index: dashboard/dashboard/pinpoint/models/change/change.py
diff --git a/dashboard/dashboard/pinpoint/models/change/change.py b/dashboard/dashboard/pinpoint/models/change/change.py
index ade1c48f1d047df26e855b10a0d0caceaa5c8f11..b8ca94c3473e03a45ce73e8bd5fe4b0efe4712f1 100644
--- a/dashboard/dashboard/pinpoint/models/change/change.py
+++ b/dashboard/dashboard/pinpoint/models/change/change.py
@@ -86,17 +86,21 @@ class Change(collections.namedtuple('Change', ('commits', 'patch'))):
     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.
+      * The left Change does not come before the right Change.
     See change_test.py for examples of linear and nonlinear Changes.
 
+    If the range has an even number of Changes, the midpoint is the Change just
+    before the halfway point. The range includes both change_a and change_b;
+    i.e. if change_a and change_b are adjacent or the same, the midpoint is
+    change_a.
+
     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.
+      A tuple of (Change, (left, right)). left and right are the distances

[perezju, 2017/09/19 15:58:05]

I think it's cleaner if it returns just (change, left, right)

+      between the midpoint and change_a and change_b, respectively.
 
     Raises:
       NonLinearError: The Changes are not linear.
@@ -110,12 +114,12 @@ class Change(collections.namedtuple('Change', ('commits', 'patch'))):
     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.')
+    midpoints = _FindMidpoints(commits_a, commits_b)
+    commits_midpoint, distances = zip(*midpoints)
 
-    return cls(commits_midpoint, change_a.patch)
+    midpoint = cls(commits_midpoint, change_a.patch)
+    distances = tuple(map(max, zip(*distances)))
+    return midpoint, distances
 
 
 def _ExpandDepsToMatchRepositories(commits_a, commits_b):
@@ -159,7 +163,7 @@ def _ExpandDepsToMatchRepositories(commits_a, commits_b):
 
 
 def _FindMidpoints(commits_a, commits_b):
-  """Returns the midpoint of two Commit lists.
+  """Returns the midpoints 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
@@ -170,15 +174,14 @@ def _FindMidpoints(commits_a, commits_b):
     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.
+    A list of tuples. Each tuple is the result of Commit.Midpoint().
 
   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 = []
+  midpoints = []
 
   for commit_a, commit_b in itertools.izip_longest(commits_a, commits_b):
     if not (commit_a and commit_b):
@@ -188,9 +191,10 @@ def _FindMidpoints(commits_a, commits_b):
       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 != commit_b:
+    midpoint, distances = commit_module.Commit.Midpoint(commit_a, commit_b)
+    midpoints.append((midpoint, distances))
+
+    if sum(distances) == 1:
       # Commits are adjacent.
       # Add any DEPS changes to the commit lists.
       deps_a = commit_a.Deps()
@@ -202,7 +206,7 @@ def _FindMidpoints(commits_a, commits_b):
           dep for dep in deps_b.difference(deps_a)
           if not _FindCommitWithRepository(commits_b, dep.repository))
 
-  return commits_midpoint
+  return midpoints
 
 
 def _FindCommitWithRepository(commits, repository):