wip

6 files changed, 267 insertions, 3 deletions

diff --git a/coverage/collector.py b/coverage/collector.py
index 2f8c1752..1082b30b 100644
--- a/coverage/collector.py
+++ b/coverage/collector.py
@@ -21,6 +21,7 @@ from coverage.debug import short_stack
 from coverage.disposition import FileDisposition
 from coverage.exceptions import ConfigError
 from coverage.misc import human_sorted_items, isolate_module
+from coverage.pep669_tracer import Pep669Tracer
 from coverage.plugin import CoveragePlugin
 from coverage.pytracer import PyTracer
 from coverage.types import (
@@ -144,8 +145,12 @@ class Collector:
         if HAS_CTRACER and not timid:
             use_ctracer = True
 
-        #if HAS_CTRACER and self._trace_class is CTracer:
-        if use_ctracer:
+        if env.PYBEHAVIOR.pep669 and self.should_start_context is None:
+            self._trace_class = Pep669Tracer
+            self.file_disposition_class = FileDisposition
+            self.supports_plugins = False
+            self.packed_arcs = False
+        elif use_ctracer:
             self._trace_class = CTracer
             self.file_disposition_class = CFileDisposition
             self.supports_plugins = True
diff --git a/coverage/env.py b/coverage/env.py
index bdc2c785..6abfb43a 100644
--- a/coverage/env.py
+++ b/coverage/env.py
@@ -137,6 +137,10 @@ class PYBEHAVIOR:
     # only a 0-number line, which is ignored, giving a truly empty module.
     empty_is_empty = (PYVERSION >= (3, 11, 0, "beta", 4))
 
+    # PEP669 Low Impact Monitoring: https://peps.python.org/pep-0669/
+    pep669 = bool(getattr(sys, "monitoring", None))
+
+
 # Coverage.py specifics.
 
 # Are we using the C-implemented trace function?
diff --git a/coverage/pep669_tracer.py b/coverage/pep669_tracer.py
new file mode 100644
index 00000000..9591f5d9
--- /dev/null
+++ b/coverage/pep669_tracer.py
@@ -0,0 +1,245 @@
+# Licensed under the Apache License: http://www.apache.org/licenses/LICENSE-2.0
+# For details: https://github.com/nedbat/coveragepy/blob/master/NOTICE.txt
+
+"""Raw data collector for coverage.py."""
+
+from __future__ import annotations
+
+import atexit
+import inspect
+import sys
+import threading
+import traceback
+
+from types import CodeType, FrameType, ModuleType
+from typing import Any, Callable, Dict, List, Optional, Set, Tuple, cast
+
+from coverage import env
+from coverage.types import (
+    TArc, TFileDisposition, TLineNo, TTraceData, TTraceFileData, TTraceFn,
+    TTracer, TWarnFn,
+)
+
+# When running meta-coverage, this file can try to trace itself, which confuses
+# everything.  Don't trace ourselves.
+
+THIS_FILE = __file__.rstrip("co")
+
+
+def log(msg):
+    with open("/tmp/pan.out", "a") as f:
+        print(msg, file=f)
+
+def panopticon(meth):
+    def _wrapped(self, *args, **kwargs):
+        assert not kwargs
+        log(f"{meth.__name__}{args!r}")
+        try:
+            return meth(self, *args, **kwargs)
+        except:
+            with open("/tmp/pan.out", "a") as f:
+                traceback.print_exception(sys.exception(), file=f)
+                sys.monitoring.set_events(sys.monitoring.COVERAGE_ID, 0)
+            raise
+    return _wrapped
+
+
+class Pep669Tracer(TTracer):
+    """Python implementation of the raw data tracer for PEP669 implementations."""
+
+    def __init__(self) -> None:
+        # pylint: disable=super-init-not-called
+        # Attributes set from the collector:
+        self.data: TTraceData
+        self.trace_arcs = False
+        self.should_trace: Callable[[str, FrameType], TFileDisposition]
+        self.should_trace_cache: Dict[str, Optional[TFileDisposition]]
+        self.should_start_context: Optional[Callable[[FrameType], Optional[str]]] = None
+        self.switch_context: Optional[Callable[[Optional[str]], None]] = None
+        self.warn: TWarnFn
+
+        # The threading module to use, if any.
+        self.threading: Optional[ModuleType] = None
+
+        self.cur_file_data: Optional[TTraceFileData] = None
+        self.last_line: TLineNo = 0
+        self.cur_file_name: Optional[str] = None
+        #self.context: Optional[str] = None
+
+        self.code_cache: Dict[CodeType, Tuple[bool, Optional[TTraceFileData]]] = {}
+
+        # The frame_stack parallels the Python call stack. Each entry is
+        # information about an active frame, a three-element tuple:
+        #   [0] The TTraceData for this frame's file. Could be None if we
+        #           aren't tracing this frame.
+        #   [1] The current file name for the frame. None if we aren't tracing
+        #           this frame.
+        #   [2] The last line number executed in this frame.
+        self.frame_stack: List[Tuple[Optional[TTraceFileData], Optional[str], TLineNo]] = []
+        self.thread: Optional[threading.Thread] = None
+        self.stopped = False
+        self._activity = False
+
+        self.in_atexit = False
+        # On exit, self.in_atexit = True
+        atexit.register(setattr, self, "in_atexit", True)
+
+    def __repr__(self) -> str:
+        me = id(self)
+        points = sum(len(v) for v in self.data.values())
+        files = len(self.data)
+        return f"<Pep669Tracer at 0x{me:x}: {points} data points in {files} files>"
+
+    def log(self, marker: str, *args: Any) -> None:
+        """For hard-core logging of what this tracer is doing."""
+        with open("/tmp/debug_trace.txt", "a") as f:
+            f.write("{} {}[{}]".format(
+                marker,
+                id(self),
+                len(self.frame_stack),
+            ))
+            if 0:   # if you want thread ids..
+                f.write(".{:x}.{:x}".format(                    # type: ignore[unreachable]
+                    self.thread.ident,
+                    self.threading.current_thread().ident,
+                ))
+            f.write(" {}".format(" ".join(map(str, args))))
+            if 0:   # if you want callers..
+                f.write(" | ")                                  # type: ignore[unreachable]
+                stack = " / ".join(
+                    (fname or "???").rpartition("/")[-1]
+                    for _, fname, _, _ in self.frame_stack
+                )
+                f.write(stack)
+            f.write("\n")
+
+    def start(self) -> TTraceFn:
+        """Start this Tracer.
+
+        Return a Python function suitable for use with sys.settrace().
+
+        """
+        self.stopped = False
+        if self.threading:
+            if self.thread is None:
+                self.thread = self.threading.current_thread()
+            else:
+                if self.thread.ident != self.threading.current_thread().ident:
+                    # Re-starting from a different thread!? Don't set the trace
+                    # function, but we are marked as running again, so maybe it
+                    # will be ok?
+                    #self.log("~", "starting on different threads")
+                    return self._cached_bound_method_trace
+
+        self.myid = sys.monitoring.COVERAGE_ID
+        sys.monitoring.use_tool_id(self.myid, "coverage.py")
+        events = sys.monitoring.events
+        sys.monitoring.set_events(self.myid, events.PY_START)
+        sys.monitoring.register_callback(self.myid, events.PY_START, self.sysmon_py_start)
+        # Use PY_START globally, then use set_local_event(LINE) for interesting
+        # frames, so i might not need to bookkeep which are the interesting frame.
+        sys.monitoring.register_callback(self.myid, events.PY_RESUME, self.sysmon_py_resume)
+        sys.monitoring.register_callback(self.myid, events.PY_RETURN, self.sysmon_py_return)
+        sys.monitoring.register_callback(self.myid, events.PY_YIELD, self.sysmon_py_yield)
+        # UNWIND is like RETURN/YIELD
+        sys.monitoring.register_callback(self.myid, events.LINE, self.sysmon_line)
+        #sys.monitoring.register_callback(self.myid, events.BRANCH, self.sysmon_branch)
+
+    def stop(self) -> None:
+        """Stop this Tracer."""
+        sys.monitoring.set_events(self.myid, 0)
+        sys.monitoring.free_tool_id(self.myid)
+
+    def activity(self) -> bool:
+        """Has there been any activity?"""
+        return self._activity
+
+    def reset_activity(self) -> None:
+        """Reset the activity() flag."""
+        self._activity = False
+
+    def get_stats(self) -> Optional[Dict[str, int]]:
+        """Return a dictionary of statistics, or None."""
+        return None
+
+    @panopticon
+    def sysmon_py_start(self, code, instruction_offset: int):
+        # Entering a new frame.  Decide if we should trace in this file.
+        self._activity = True
+
+        self.frame_stack.append((self.cur_file_data, self.cur_file_name, self.last_line))
+
+        if code in self.code_cache:
+            tracing_code, self.cur_file_data = self.code_cache[code]
+        else:
+            tracing_code = self.cur_file_data = None
+
+        if tracing_code is None:
+            self.cur_file_name = filename = code.co_filename
+            disp = self.should_trace_cache.get(filename)
+            if disp is None:
+                frame = inspect.currentframe()
+                disp = self.should_trace(filename, frame)
+                self.should_trace_cache[filename] = disp
+
+            tracing_code = disp.trace
+            if tracing_code:
+                tracename = disp.source_filename
+                assert tracename is not None
+                if tracename not in self.data:
+                    self.data[tracename] = set()    # type: ignore[assignment]
+                self.cur_file_data = self.data[tracename]
+            else:
+                self.cur_file_data = None
+
+        self.code_cache[code] = (tracing_code, self.cur_file_data)
+
+        if tracing_code:
+            events = sys.monitoring.events
+            log(f"set_local_events({code!r})")
+            sys.monitoring.set_local_events(
+                self.myid,
+                code,
+                (
+                    sys.monitoring.events.LINE |
+                    sys.monitoring.events.PY_RETURN |
+                    sys.monitoring.events.PY_RESUME |
+                    sys.monitoring.events.PY_YIELD
+                )
+            )
+
+        self.last_line = -code.co_firstlineno
+
+    @panopticon
+    def sysmon_py_resume(self, code, instruction_offset: int):
+        self.frame_stack.append((self.cur_file_data, self.cur_file_name, self.last_line))
+        frame = inspect.currentframe()
+        self.last_line = frame.f_lineno
+
+    @panopticon
+    def sysmon_py_return(self, code, instruction_offset: int, retval: object):
+        if self.cur_file_data is not None:
+            cast(Set[TArc], self.cur_file_data).add((self.last_line, -code.co_firstlineno))
+
+        # Leaving this function, pop the filename stack.
+        self.cur_file_data, self.cur_file_name, self.last_line = (
+            self.frame_stack.pop()
+        )
+
+    def sysmon_py_yield(self, code, instruction_offset: int, retval: object):
+        ...
+
+    @panopticon
+    def sysmon_line(self, code, line_number: int):
+        #assert self.cur_file_data is not None
+        if self.cur_file_data is not None:
+            if self.trace_arcs:
+                cast(Set[TArc], self.cur_file_data).add((self.last_line, line_number))
+            else:
+                cast(Set[TLineNo], self.cur_file_data).add(line_number)
+            self.last_line = line_number
+        return sys.monitoring.DISABLE
+
+    @panopticon
+    def sysmon_branch(self, code, instruction_offset: int, destination_offset: int):
+        ...
diff --git a/coverage/pytracer.py b/coverage/pytracer.py
index 81832b0f..543a6128 100644
--- a/coverage/pytracer.py
+++ b/coverage/pytracer.py
@@ -71,6 +71,14 @@ class PyTracer(TTracer):
         self.context: Optional[str] = None
         self.started_context = False
 
+        # The data_stack parallels the Python call stack. Each entry is
+        # information about an active frame, a four-element tuple:
+        #   [0] The TTraceData for this frame's file. Could be None if we
+        #           aren't tracing this frame.
+        #   [1] The current file name for the frame. None if we aren't tracing
+        #           this frame.
+        #   [2] The last line number executed in this frame.
+        #   [3] Boolean: did this frame start a new context?
         self.data_stack: List[Tuple[Optional[TTraceFileData], Optional[str], TLineNo, bool]] = []
         self.thread: Optional[threading.Thread] = None
         self.stopped = False
diff --git a/coverage/types.py b/coverage/types.py
index 828ab20b..05dca065 100644
--- a/coverage/types.py
+++ b/coverage/types.py
@@ -83,7 +83,7 @@ TTraceFileData = Union[Set[TLineNo], Set[TArc], Set[int]]
 TTraceData = Dict[str, TTraceFileData]
 
 class TTracer(Protocol):
-    """Either CTracer or PyTracer."""
+    """TODO: Either CTracer or PyTracer."""
 
     data: TTraceData
     trace_arcs: bool
diff --git a/tests/coveragetest.py b/tests/coveragetest.py
index 9d1ef06f..f67e445a 100644
--- a/tests/coveragetest.py
+++ b/tests/coveragetest.py
@@ -173,6 +173,8 @@ class CoverageTest(
         # Coverage.py wants to deal with things as modules with file names.
         modname = self.get_module_name()
 
+        #import dis,textwrap; dis.dis(textwrap.dedent(text))
+
         self.make_file(modname + ".py", text)
 
         if arcs is None and arcz is not None: