Add python coverage module to third_party

third_party/pycoverage/coverage/collector.py

Index: third_party/pycoverage/coverage/collector.py
diff --git a/third_party/pycoverage/coverage/collector.py b/third_party/pycoverage/coverage/collector.py
new file mode 100644
index 0000000000000000000000000000000000000000..8ba7d87cd4e055b2e11efccd487bc7493f58d19d
--- /dev/null
+++ b/third_party/pycoverage/coverage/collector.py
@@ -0,0 +1,353 @@
+"""Raw data collector for Coverage."""
+
+import os, sys, threading
+
+try:
+    # Use the C extension code when we can, for speed.
+    from coverage.tracer import CTracer         # pylint: disable=F0401,E0611
+except ImportError:
+    # Couldn't import the C extension, maybe it isn't built.
+    if os.getenv('COVERAGE_TEST_TRACER') == 'c':
+        # During testing, we use the COVERAGE_TEST_TRACER env var to indicate
+        # that we've fiddled with the environment to test this fallback code.
+        # If we thought we had a C tracer, but couldn't import it, then exit
+        # quickly and clearly instead of dribbling confusing errors. I'm using
+        # sys.exit here instead of an exception because an exception here
+        # causes all sorts of other noise in unittest.
+        sys.stderr.write(
+            "*** COVERAGE_TEST_TRACER is 'c' but can't import CTracer!\n"
+            )
+        sys.exit(1)
+    CTracer = None
+
+
+class PyTracer(object):
+    """Python implementation of the raw data tracer."""
+
+    # Because of poor implementations of trace-function-manipulating tools,
+    # the Python trace function must be kept very simple.  In particular, there
+    # must be only one function ever set as the trace function, both through
+    # sys.settrace, and as the return value from the trace function.  Put
+    # another way, the trace function must always return itself.  It cannot
+    # swap in other functions, or return None to avoid tracing a particular
+    # frame.
+    #
+    # The trace manipulator that introduced this restriction is DecoratorTools,
+    # which sets a trace function, and then later restores the pre-existing one
+    # by calling sys.settrace with a function it found in the current frame.
+    #
+    # Systems that use DecoratorTools (or similar trace manipulations) must use
+    # PyTracer to get accurate results.  The command-line --timid argument is
+    # used to force the use of this tracer.
+
+    def __init__(self):
+        self.data = None
+        self.should_trace = None
+        self.should_trace_cache = None
+        self.warn = None
+        self.cur_file_data = None
+        self.last_line = 0
+        self.data_stack = []
+        self.last_exc_back = None
+        self.last_exc_firstlineno = 0
+        self.arcs = False
+        self.thread = None
+        self.stopped = False
+
+    def _trace(self, frame, event, arg_unused):
+        """The trace function passed to sys.settrace."""
+
+        if self.stopped:
+            return
+
+        if 0:
+            sys.stderr.write("trace event: %s %r @%d\n" % (
+                event, frame.f_code.co_filename, frame.f_lineno
+            ))
+
+        if self.last_exc_back:
+            if frame == self.last_exc_back:
+                # Someone forgot a return event.
+                if self.arcs and self.cur_file_data:
+                    pair = (self.last_line, -self.last_exc_firstlineno)
+                    self.cur_file_data[pair] = None
+                self.cur_file_data, self.last_line = self.data_stack.pop()
+            self.last_exc_back = None
+
+        if event == 'call':
+            # Entering a new function context.  Decide if we should trace
+            # in this file.
+            self.data_stack.append((self.cur_file_data, self.last_line))
+            filename = frame.f_code.co_filename
+            if filename not in self.should_trace_cache:
+                tracename = self.should_trace(filename, frame)
+                self.should_trace_cache[filename] = tracename
+            else:
+                tracename = self.should_trace_cache[filename]
+            #print("called, stack is %d deep, tracename is %r" % (
+            #               len(self.data_stack), tracename))
+            if tracename:
+                if tracename not in self.data:
+                    self.data[tracename] = {}
+                self.cur_file_data = self.data[tracename]
+            else:
+                self.cur_file_data = None
+            # Set the last_line to -1 because the next arc will be entering a
+            # code block, indicated by (-1, n).
+            self.last_line = -1
+        elif event == 'line':
+            # Record an executed line.
+            if self.cur_file_data is not None:
+                if self.arcs:
+                    #print("lin", self.last_line, frame.f_lineno)
+                    self.cur_file_data[(self.last_line, frame.f_lineno)] = None
+                else:
+                    #print("lin", frame.f_lineno)
+                    self.cur_file_data[frame.f_lineno] = None
+            self.last_line = frame.f_lineno
+        elif event == 'return':
+            if self.arcs and self.cur_file_data:
+                first = frame.f_code.co_firstlineno
+                self.cur_file_data[(self.last_line, -first)] = None
+            # Leaving this function, pop the filename stack.
+            self.cur_file_data, self.last_line = self.data_stack.pop()
+            #print("returned, stack is %d deep" % (len(self.data_stack)))
+        elif event == 'exception':
+            #print("exc", self.last_line, frame.f_lineno)
+            self.last_exc_back = frame.f_back
+            self.last_exc_firstlineno = frame.f_code.co_firstlineno
+        return self._trace
+
+    def start(self):
+        """Start this Tracer.
+
+        Return a Python function suitable for use with sys.settrace().
+
+        """
+        self.thread = threading.currentThread()
+        sys.settrace(self._trace)
+        return self._trace
+
+    def stop(self):
+        """Stop this Tracer."""
+        self.stopped = True
+        if self.thread != threading.currentThread():
+            # Called on a different thread than started us: we can't unhook
+            # ourseves, but we've set the flag that we should stop, so we won't
+            # do any more tracing.
+            return
+
+        if hasattr(sys, "gettrace") and self.warn:
+            if sys.gettrace() != self._trace:
+                msg = "Trace function changed, measurement is likely wrong: %r"
+                self.warn(msg % (sys.gettrace(),))
+        #print("Stopping tracer on %s" % threading.current_thread().ident)
+        sys.settrace(None)
+
+    def get_stats(self):
+        """Return a dictionary of statistics, or None."""
+        return None
+
+
+class Collector(object):
+    """Collects trace data.
+
+    Creates a Tracer object for each thread, since they track stack
+    information.  Each Tracer points to the same shared data, contributing
+    traced data points.
+
+    When the Collector is started, it creates a Tracer for the current thread,
+    and installs a function to create Tracers for each new thread started.
+    When the Collector is stopped, all active Tracers are stopped.
+
+    Threads started while the Collector is stopped will never have Tracers
+    associated with them.
+
+    """
+
+    # The stack of active Collectors.  Collectors are added here when started,
+    # and popped when stopped.  Collectors on the stack are paused when not
+    # the top, and resumed when they become the top again.
+    _collectors = []
+
+    def __init__(self, should_trace, timid, branch, warn):
+        """Create a collector.
+
+        `should_trace` is a function, taking a filename, and returning a
+        canonicalized filename, or None depending on whether the file should
+        be traced or not.
+
+        If `timid` is true, then a slower simpler trace function will be
+        used.  This is important for some environments where manipulation of
+        tracing functions make the faster more sophisticated trace function not
+        operate properly.
+
+        If `branch` is true, then branches will be measured.  This involves
+        collecting data on which statements followed each other (arcs).  Use
+        `get_arc_data` to get the arc data.
+
+        `warn` is a warning function, taking a single string message argument,
+        to be used if a warning needs to be issued.
+
+        """
+        self.should_trace = should_trace
+        self.warn = warn
+        self.branch = branch
+        self.reset()
+
+        if timid:
+            # Being timid: use the simple Python trace function.
+            self._trace_class = PyTracer
+        else:
+            # Being fast: use the C Tracer if it is available, else the Python
+            # trace function.
+            self._trace_class = CTracer or PyTracer
+
+    def __repr__(self):
+        return "<Collector at 0x%x>" % id(self)
+
+    def tracer_name(self):
+        """Return the class name of the tracer we're using."""
+        return self._trace_class.__name__
+
+    def reset(self):
+        """Clear collected data, and prepare to collect more."""
+        # A dictionary mapping filenames to dicts with linenumber keys,
+        # or mapping filenames to dicts with linenumber pairs as keys.
+        self.data = {}
+
+        # A cache of the results from should_trace, the decision about whether
+        # to trace execution in a file. A dict of filename to (filename or
+        # None).
+        self.should_trace_cache = {}
+
+        # Our active Tracers.
+        self.tracers = []
+
+    def _start_tracer(self):
+        """Start a new Tracer object, and store it in self.tracers."""
+        tracer = self._trace_class()
+        tracer.data = self.data
+        tracer.arcs = self.branch
+        tracer.should_trace = self.should_trace
+        tracer.should_trace_cache = self.should_trace_cache
+        tracer.warn = self.warn
+        fn = tracer.start()
+        self.tracers.append(tracer)
+        return fn
+
+    # The trace function has to be set individually on each thread before
+    # execution begins.  Ironically, the only support the threading module has
+    # for running code before the thread main is the tracing function.  So we
+    # install this as a trace function, and the first time it's called, it does
+    # the real trace installation.
+
+    def _installation_trace(self, frame_unused, event_unused, arg_unused):
+        """Called on new threads, installs the real tracer."""
+        # Remove ourselves as the trace function
+        sys.settrace(None)
+        # Install the real tracer.
+        fn = self._start_tracer()
+        # Invoke the real trace function with the current event, to be sure
+        # not to lose an event.
+        if fn:
+            fn = fn(frame_unused, event_unused, arg_unused)
+        # Return the new trace function to continue tracing in this scope.
+        return fn
+
+    def start(self):
+        """Start collecting trace information."""
+        if self._collectors:
+            self._collectors[-1].pause()
+        self._collectors.append(self)
+        #print("Started: %r" % self._collectors, file=sys.stderr)
+
+        # Check to see whether we had a fullcoverage tracer installed.
+        traces0 = []
+        if hasattr(sys, "gettrace"):
+            fn0 = sys.gettrace()
+            if fn0:
+                tracer0 = getattr(fn0, '__self__', None)
+                if tracer0:
+                    traces0 = getattr(tracer0, 'traces', [])
+
+        # Install the tracer on this thread.
+        fn = self._start_tracer()
+
+        for args in traces0:
+            (frame, event, arg), lineno = args
+            try:
+                fn(frame, event, arg, lineno=lineno)
+            except TypeError:
+                raise Exception(
+                    "fullcoverage must be run with the C trace function."
+                )
+
+        # Install our installation tracer in threading, to jump start other
+        # threads.
+        threading.settrace(self._installation_trace)
+
+    def stop(self):
+        """Stop collecting trace information."""
+        #print >>sys.stderr, "Stopping: %r" % self._collectors
+        assert self._collectors
+        assert self._collectors[-1] is self
+
+        self.pause()
+        self.tracers = []
+
+        # Remove this Collector from the stack, and resume the one underneath
+        # (if any).
+        self._collectors.pop()
+        if self._collectors:
+            self._collectors[-1].resume()
+
+    def pause(self):
+        """Pause tracing, but be prepared to `resume`."""
+        for tracer in self.tracers:
+            tracer.stop()
+            stats = tracer.get_stats()
+            if stats:
+                print("\nCoverage.py tracer stats:")
+                for k in sorted(stats.keys()):
+                    print("%16s: %s" % (k, stats[k]))
+        threading.settrace(None)
+
+    def resume(self):
+        """Resume tracing after a `pause`."""
+        for tracer in self.tracers:
+            tracer.start()
+        threading.settrace(self._installation_trace)
+
+    def get_line_data(self):
+        """Return the line data collected.
+
+        Data is { filename: { lineno: None, ...}, ...}
+
+        """
+        if self.branch:
+            # If we were measuring branches, then we have to re-build the dict
+            # to show line data.
+            line_data = {}
+            for f, arcs in self.data.items():
+                line_data[f] = ldf = {}
+                for l1, _ in list(arcs.keys()):
+                    if l1:
+                        ldf[l1] = None
+            return line_data
+        else:
+            return self.data
+
+    def get_arc_data(self):
+        """Return the arc data collected.
+
+        Data is { filename: { (l1, l2): None, ...}, ...}
+
+        Note that no data is collected or returned if the Collector wasn't
+        created with `branch` true.
+
+        """
+        if self.branch:
+            return self.data
+        else:
+            return {}