[Predator] Make ``CallStackDetector`` return a namedtuple.

appengine/findit/crash/chromecrash_parser.py

 # Copyright 2016 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import math
 import re
 
 from crash import callstack_detectors
 from crash import callstack_filters
 from crash.stacktrace import CallStackBuffer
@@ skipping 14 matching lines @@
     # Filters to filter callstack buffers.
     filters = [callstack_filters.FilterInlineFunction(),
                callstack_filters.KeepTopNFrames(top_n_frames or
                                                 DEFAULT_TOP_N_FRAMES)]
     stacktrace_buffer = StacktraceBuffer(signature=signature, filters=filters)
 
     stack_detector = callstack_detectors.ChromeCrashStackDetector()
     # Initial background callstack which is not to be added into Stacktrace.
     stack_buffer = CallStackBuffer()
     for line in stacktrace_string.splitlines():
-      is_new_callstack, priority, format_type, language_type, metadata = (
-          stack_detector.IsStartOfNewCallStack(line))
+      start_of_callstack = stack_detector(line)
 
-      if is_new_callstack:
+      if start_of_callstack:
         stacktrace_buffer.AddFilteredStack(stack_buffer)
-        stack_buffer = CallStackBuffer(priority=priority,
-                                       format_type=format_type,
-                                       language_type=language_type,
-                                       metadata=metadata)
+        stack_buffer = CallStackBuffer(
+            priority=start_of_callstack.priority,
+            format_type=start_of_callstack.format_type,
+            language_type=start_of_callstack.language_type,
+            metadata=start_of_callstack.metadata)

[wrengr, 2016/12/29 20:13:02]

Since we're just passing all the parts through, why not have the stack_detector
return the new CallStackBuffer (or None) directly?

[Sharu Jiang, 2016/12/29 21:40:14]

I think it would be more clear that the ``stack_detector`` only detects the
``StartOfCallstack``, and let the ``Parser`` takes care of the whole
``stack_buffer`` (including creating the ``stack_buffer`` based
``StartOfCallStack`` and adding all the frames.)

       else:
         frame = StackFrame.Parse(stack_buffer.language_type,
                                  stack_buffer.format_type, line, deps,
                                  len(stack_buffer.frames))
         if frame is not None:
           stack_buffer.frames.append(frame)
 
     # Add the last stack to stacktrace.
     stacktrace_buffer.AddFilteredStack(stack_buffer)
     return stacktrace_buffer.ToStacktrace()