fix: sysmon should ignore GeneratorExit

Also, don't use dis in production, it's changed often.

coverage/sysmon.py

@@ -6,7 +6,6 @@
 from __future__ import annotations
 
 import dataclasses
-import dis
 import functools
 import inspect
 import os
@@ -168,12 +167,10 @@ class CodeInfo:
 def bytes_to_lines(code: CodeType) -> Dict[int, int]:
     """Make a dict mapping byte code offsets to line numbers."""
     b2l = {}
-    cur_line = 0
-    for inst in dis.get_instructions(code):
-        if inst.starts_line is not None:
-            cur_line = inst.starts_line
-        b2l[inst.offset] = cur_line
-    log(f"  --> bytes_to_lines: {b2l!r}")
+    for bstart, bend, lineno in code.co_lines():
+        if lineno is not None:
+            for boffset in range(bstart, bend, 2):
+                b2l[boffset] = lineno
     return b2l
 
 
@@ -379,26 +376,30 @@ def sysmon_py_return_arcs(
             last_line = self.last_lines.get(frame)
             if last_line is not None:
                 arc = (last_line, -code.co_firstlineno)
+                # log(f"adding {arc=}")
                 cast(Set[TArc], code_info.file_data).add(arc)
 
         # Leaving this function, no need for the frame any more.
         self.last_lines.pop(frame, None)
 
-    @panopticon("code", "@", None)
+    @panopticon("code", "@", "exc")
     def sysmon_py_unwind_arcs(
         self, code: CodeType, instruction_offset: int, exception: BaseException
     ) -> MonitorReturn:
         """Handle sys.monitoring.events.PY_UNWIND events for branch coverage."""
         frame = self.callers_frame()
+        # Leaving this function.
+        last_line = self.last_lines.pop(frame, None)
+        if isinstance(exception, GeneratorExit):
+            # We don't want to count generator exits as arcs.
+            return
         code_info = self.code_infos.get(id(code))
         if code_info is not None and code_info.file_data is not None:
-            last_line = self.last_lines.get(frame)
             if last_line is not None:
                 arc = (last_line, -code.co_firstlineno)
+                # log(f"adding {arc=}")
                 cast(Set[TArc], code_info.file_data).add(arc)
 
-        # Leaving this function.
-        self.last_lines.pop(frame, None)
 
     @panopticon("code", "line")
     def sysmon_line_lines(self, code: CodeType, line_number: int) -> MonitorReturn:

tests/test_arcs.py

@@ -7,7 +7,6 @@
 
 import pytest
 
-from tests import testenv
 from tests.coveragetest import CoverageTest
 from tests.helpers import assert_count_equal, xfail_pypy38
 
@@ -1308,7 +1307,6 @@ def gen(inp):
             arcz=".1 19 9.  .2 23 34 45 56 63 37 7.",
         )
 
-    @pytest.mark.xfail(testenv.SYS_MON, reason="TODO: fix this for sys.monitoring")
     def test_abandoned_yield(self) -> None:
         # https://github.com/nedbat/coveragepy/issues/440
         self.check_coverage("""\
@@ -1651,7 +1649,6 @@ def test_pathologically_long_code_object(self, n: int) -> None:
         self.check_coverage(code, arcs=[(-1, 1), (1, 2*n+4), (2*n+4, -1)])
         assert self.stdout() == f"{n}\n"
 
-    @pytest.mark.xfail(testenv.SYS_MON, reason="TODO: fix this for sys.monitoring")
     def test_partial_generators(self) -> None:
         # https://github.com/nedbat/coveragepy/issues/475
         # Line 2 is executed completely.

tests/test_coverage.py

@@ -11,7 +11,6 @@
 from coverage import env
 from coverage.exceptions import NoDataError
 
-from tests import testenv
 from tests.coveragetest import CoverageTest
 
 
@@ -1407,7 +1406,6 @@ def test_excluding_try_except_stranded_else(self) -> None:
             arcz_missing=arcz_missing,
         )
 
-    @pytest.mark.xfail(testenv.SYS_MON, reason="TODO: fix this for sys.monitoring")
     def test_excluded_comprehension_branches(self) -> None:
         # https://github.com/nedbat/coveragepy/issues/1271
         self.check_coverage("""\