presubmit checks: skip computing the diff if possible

tests/presubmit_unittest.py

Index: tests/presubmit_unittest.py
===================================================================
--- tests/presubmit_unittest.py	(revision 82663)
+++ tests/presubmit_unittest.py	(working copy)
@@ -1374,27 +1374,45 @@
     self.assertEquals(results2[0].__class__, error_type)
 
   def ContentTest(self, check, content1, content2, error_type):
+    """Runs a test of a content-checking rule.
+
+      Args:
+        check: the check to run.
+        content1: content which is expected to pass the check.
+        content2: content which is expected to fail the check.
+        error_type: the type of the error expected for content2.
+    """
     change1 = presubmit.Change(
         'foo1', 'foo1\n', self.fake_root_dir, None, 0, 0, None)
     input_api1 = self.MockInputApi(change1, False)
     affected_file = self.mox.CreateMock(presubmit.SvnAffectedFile)
-    affected_file.LocalPath().AndReturn('foo.cc')
-    # Format is (file, line number, line content)
-    output1 = [
-      (affected_file, 42, 'yo, ' + content1),
-      (affected_file, 43, 'yer'),
-      (affected_file, 23, 'ya'),
-    ]
-    input_api1.RightHandSideLines(mox.IgnoreArg()).AndReturn(output1)
+    input_api1.AffectedFiles(mox.IgnoreArg(), include_deletes=False).AndReturn(
+        [affected_file])
+    affected_file.NewContents().AndReturn([
+        'ahoy',
+        'yo' + content1,
+        'hay',
+        'yer',
+        'ya'])
+
     change2 = presubmit.Change(
         'foo2', 'foo2\n', self.fake_root_dir, None, 0, 0, None)
     input_api2 = self.MockInputApi(change2, False)
-    output2 = [
-      (affected_file, 42, 'yo, ' + content2),
-      (affected_file, 43, 'yer'),
-      (affected_file, 23, 'ya'),
-    ]
-    input_api2.RightHandSideLines(mox.IgnoreArg()).AndReturn(output2)
+
+    input_api2.AffectedFiles(mox.IgnoreArg(), include_deletes=False).AndReturn(
+        [affected_file])
+    affected_file.NewContents().AndReturn([
+        'ahoy',
+        'yo' + content2,
+        'hay',
+        'yer',
+        'ya'])
+    affected_file.ChangedContents().AndReturn([
+        (42, 'yo, ' + content2),
+        (43, 'yer'),
+        (23, 'ya')])
+    affected_file.LocalPath().AndReturn('foo.cc')
+
     self.mox.ReplayAll()
 
     results1 = check(input_api1, presubmit.OutputApi, None)
@@ -1565,20 +1583,21 @@
     # Only this one will trigger.
     affected_file4 = self.mox.CreateMock(presubmit.SvnAffectedFile)
     affected_file4.LocalPath().AndReturn('makefile.foo')
+    affected_file1.NewContents().AndReturn(['yo, '])
+    affected_file4.NewContents().AndReturn(['ye\t'])
+    affected_file4.ChangedContents().AndReturn([(46, 'ye\t')])
     affected_file4.LocalPath().AndReturn('makefile.foo')
-    output1 = [
-      (affected_file1, 42, 'yo, '),
-      (affected_file2, 43, 'yer\t'),
-      (affected_file3, 45, 'yr\t'),
-      (affected_file4, 46, 'ye\t'),
-    ]
-    def test(source_filter):
-      for i in output1:
-        if source_filter(i[0]):
-          yield i
+    affected_files = (affected_file1, affected_file2,
+                      affected_file3, affected_file4)
+
+    def test(source_filter, include_deletes):
+      self.assertFalse(include_deletes)
+      for x in affected_files:
+        if source_filter(x):
+          yield x
     # Override the mock of these functions.
     input_api1.FilterSourceFile = lambda x: x
-    input_api1.RightHandSideLines = test
+    input_api1.AffectedFiles = test
     self.mox.ReplayAll()
 
     results1 = presubmit_canned_checks.CheckChangeHasNoTabs(input_api1,