[pinpoint] Calculate distances between Changes.

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

Index: dashboard/dashboard/pinpoint/models/change/commit.py
diff --git a/dashboard/dashboard/pinpoint/models/change/commit.py b/dashboard/dashboard/pinpoint/models/change/commit.py
index f7357279de5c7bc9385e39d07640f0d188d42657..513541031e2e715c57bcf627644ee4e35318a694 100644
--- a/dashboard/dashboard/pinpoint/models/change/commit.py
+++ b/dashboard/dashboard/pinpoint/models/change/commit.py
@@ -101,6 +101,11 @@ class Commit(collections.namedtuple('Commit', ('repository', 'git_hash'))):
   def Midpoint(cls, commit_a, commit_b):
     """Return a Commit halfway between the two given Commits.
 
+    If the range has an even number of Commits, the midpoint is the Commit just
+    before the halfway point. The range includes both commit_a and commit_b;
+    i.e. if commit_a and commit_b are adjacent or the same, the midpoint is
+    commit_a.
+
     Uses Gitiles to look up the commit range.
 
     Args:
@@ -108,16 +113,15 @@ class Commit(collections.namedtuple('Commit', ('repository', 'git_hash'))):
       commit_b: The last Commit in the range.
 
     Returns:
-      A new Commit representing the midpoint.
-      The commit before the midpoint if the range has an even number of commits.
-      commit_a if the Commits are the same or adjacent.
+      A tuple of (Commit, (left, right)). left and right are the distances
+      between the midpoint and commit_a and commit_b, respectively.
 
     Raises:
       NonLinearError: The Commits are in different repositories or commit_a does
         not come before commit_b.
     """
     if commit_a == commit_b:
-      return commit_a
+      return commit_a, (0, 0)
 
     if commit_a.repository != commit_b.repository:
       raise NonLinearError('Repositories differ between Commits: %s vs %s' %
@@ -130,11 +134,12 @@ class Commit(collections.namedtuple('Commit', ('repository', 'git_hash'))):
     if len(commits) == 0:
       raise NonLinearError('Commit "%s" does not come before commit "%s".' %
                            commit_a, commit_b)
-    if len(commits) == 1:
-      return commit_a
-    commits.pop(0)  # Remove commit_b from the range.
+    # Include both commit_a and commit_b in the range.

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

nit: Add a short reminder that the list of commits is in reverse order (i.e.
from commit_b to commit_a); took me a small bit to figure out why the lengths
below seemed to be in the wrong order.

+    commits.append({'commit': commit_a.git_hash})

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

I'm wondering whether gitiles_service.CommitRange should have an
"inclusive=True" option that basically returns '+log/{hash_a}^..{hash_b}'; so
this would be cleaner.

 
-    return cls(commit_a.repository, commits[len(commits) / 2]['commit'])
+    midpoint_index = len(commits) / 2
+    midpoint = cls(commit_a.repository, commits[midpoint_index]['commit'])
+    return midpoint, (len(commits) - midpoint_index - 1, midpoint_index)
 
 
 def _Repository(repository_url):