Add PRESUBMIT check if modified UMA histogram name can be found (2)

PRESUBMIT.py

Index: PRESUBMIT.py
diff --git a/PRESUBMIT.py b/PRESUBMIT.py
index 33008be52923f9a0fb57c56b30139857bb76d6b4..f6da5907d5ca06a0e230887002a6061680026090 100644
--- a/PRESUBMIT.py
+++ b/PRESUBMIT.py
@@ -359,6 +359,71 @@ def _CheckNoUNIT_TESTInSourceFiles(input_api, output_api):
       '\n'.join(problems))]
 
 
+def _FindHistogramNameInLine(histogram_name, line):
+  """Helper function to smartly try to find a histogram name or prefix in a
+  line."""

[Alexei Svitkine (slow), 2015/02/02 15:12:08]

Nit: No fit into one line - e.g. no need to start with "Helper function.", just
... "Tries to find a histogram name"...

[mcasas, 2015/02/02 19:24:14]

Done.

+  if not "affected-histogram" in line:
+    return histogram_name in line
+  # A histogram_suffixes tag type has an affected-histogram name as a prefix of
+  # the histogram_name.
+  if not '"' in line:
+    return False
+  histogram_prefix = line.split('\"')[1]
+  return histogram_prefix in histogram_name
+
+
+def _CheckUmaHistogramChanges(input_api, output_api):
+  """Check that UMA histogram names in touched lines can still be found in other
+  lines of the patch or in histograms.xml. Note that this check would not catch
+  the reverse: changes in histograms.xml not matched in the code itself."""
+  touched_histograms = []
+  histograms_xml_modifications = []
+  pattern = input_api.re.compile('UMA_HISTOGRAM.*\("(.*)"')
+  for f in input_api.AffectedFiles():
+    # If histograms.xml itself is modified, keep the modified lines for later.
+    if f.LocalPath().endswith(('histograms.xml')):
+      histograms_xml_modifications = f.ChangedContents()
+      continue
+    if not f.LocalPath().endswith(('cc', 'mm', 'cpp')):
+      continue
+    for line_num, line in f.ChangedContents():
+      found = pattern.search(line)
+      if found:
+        touched_histograms.append([found.group(1), f, line_num])
+
+  # Search for the touched histogram names in the local modifications to
+  # histograms.xml, and, if not found, on the base histograms.xml file.
+  problems = []
+  for histogram_info in touched_histograms:
+    histogram_name_found = False
+    for line_num, line in histograms_xml_modifications:
+      histogram_name_found = _FindHistogramNameInLine(histogram_info[0], line)
+      if histogram_name_found:
+        break
+    if histogram_name_found:
+      touched_histograms.remove(histogram_info)

[Alexei Svitkine (slow), 2015/02/02 15:12:07]

Is it actually safe to remove an item from the list you're iterating over?

[mcasas, 2015/02/02 19:24:14]

It turns out that the iterator-like semantics are a 
bit more involved than what we thought. My idea was to
avoid creating a new list of unmatched-histograms but
meh. 

I changed it to building up a list of unmatched 
histograms.

+      continue
+
+  if touched_histograms:
+    with open('tools/metrics/histograms/histograms.xml') as histograms_xml:
+      for histogram_name, f, line_num in touched_histograms:
+        histogram_name_found = False;

[Alexei Svitkine (slow), 2015/02/02 15:12:08]

No ;

[mcasas, 2015/02/02 19:24:14]

Argh! Done :)

+        for line in histograms_xml:
+          histogram_name_found = _FindHistogramNameInLine(histogram_name, line);
+          if histogram_name_found:
+            break
+        if histogram_name_found:
+          continue

[Alexei Svitkine (slow), 2015/02/02 15:12:08]

Nit: Just reverse the condition and put the next line in the if.

[mcasas, 2015/02/02 19:24:14]

Done.

+        problems.append(' [%s:%d] %s' %
+                        (f.LocalPath(), line_num, histogram_name))
+
+  if not problems:
+    return []
+  return [output_api.PresubmitPromptWarning('Some UMA_HISTOGRAM lines have '
+    'been modified and the associated histogram name has no match in either '
+    'metrics/histograms.xml or the modifications of it:',  problems)]
+
+
 def _CheckNoNewWStrings(input_api, output_api):
   """Checks to make sure we don't introduce use of wstrings."""
   problems = []
@@ -1585,6 +1650,7 @@ def CheckChangeOnUpload(input_api, output_api):
   results.extend(_CheckJavaStyle(input_api, output_api))
   results.extend(
       input_api.canned_checks.CheckGNFormatted(input_api, output_api))
+  results.extend(_CheckUmaHistogramChanges(input_api, output_api))
   return results