refactor: don't test arcs, test branches

This required some other changes:

- `with` statements jump back to the with when leaving, but that
  confuses the branches, so fix the arcs to hide that fact.

CHANGES.rst

@@ -23,7 +23,10 @@ upgrading your version of coverage.py.
 Unreleased
 ----------
 
-Nothing yet.
+- Fewer things are considered branches now:
+
+  - Lambdas, comprehensions, and generator expressions are no longer marked as
+    missing branches if they don't complete execution.
 
 
 .. scriv-start-here

coverage/core.py

@@ -14,7 +14,11 @@
 from coverage.exceptions import ConfigError
 from coverage.pytracer import PyTracer
 from coverage.sysmon import SysMonitor
-from coverage.types import TFileDisposition, Tracer,  TWarnFn
+from coverage.types import (
+    TFileDisposition,
+    Tracer,
+    TWarnFn,
+)
 
 
 try:
@@ -45,7 +49,14 @@ class Core:
     packed_arcs: bool
     systrace: bool
 
-    def __init__(self, warn: TWarnFn, timid: bool, metacov: bool) -> None:
+    def __init__(self,
+        warn: TWarnFn,
+        timid: bool,
+        metacov: bool,
+    ) -> None:
+        # Defaults
+        self.tracer_kwargs = {}
+
         core_name: str | None
         if timid:
             core_name = "pytrace"
@@ -74,14 +85,12 @@ def __init__(self, warn: TWarnFn, timid: bool, metacov: bool) -> None:
             self.systrace = False
         elif core_name == "ctrace":
             self.tracer_class = CTracer
-            self.tracer_kwargs = {}
             self.file_disposition_class = CFileDisposition
             self.supports_plugins = True
             self.packed_arcs = True
             self.systrace = True
         elif core_name == "pytrace":
             self.tracer_class = PyTracer
-            self.tracer_kwargs = {}
             self.file_disposition_class = FileDisposition
             self.supports_plugins = False
             self.packed_arcs = False

coverage/env.py

@@ -64,15 +64,6 @@ class PYBEHAVIOR:
     # 3.7 changed how functions with only docstrings are numbered.
     docstring_only_function = (not PYPY) and (PYVERSION <= (3, 10))
 
-    # When a break/continue/return statement in a try block jumps to a finally
-    # block, does the finally jump back to the break/continue/return (pre-3.10)
-    # to do the work?
-    finally_jumps_back = (PYVERSION < (3, 10))
-
-    # CPython 3.11 now jumps to the decorator line again while executing
-    # the decorator.
-    trace_decorator_line_again = (CPYTHON and PYVERSION > (3, 11, 0, "alpha", 3, 0))
-
     # CPython 3.9a1 made sys.argv[0] and other reported files absolute paths.
     report_absolute_files = (
         (CPYTHON or (PYPY and PYPYVERSION >= (7, 3, 10)))
@@ -112,10 +103,6 @@ class PYBEHAVIOR:
     # only a 0-number line, which is ignored, giving a truly empty module.
     empty_is_empty = (PYVERSION >= (3, 11, 0, "beta", 4))
 
-    # Are comprehensions inlined (new) or compiled as called functions (old)?
-    # Changed in https://github.com/python/cpython/pull/101441
-    comprehensions_are_functions = (PYVERSION <= (3, 12, 0, "alpha", 7, 0))
-
     # PEP669 Low Impact Monitoring: https://peps.python.org/pep-0669/
     pep669 = bool(getattr(sys, "monitoring", None))
 

coverage/execfile.py

@@ -288,13 +288,13 @@ def run_python_file(args: list[str]) -> None:
 
 def make_code_from_py(filename: str) -> CodeType:
     """Get source from `filename` and make a code object of it."""
-    # Open the source file.
     try:
         source = get_python_source(filename)
     except (OSError, NoSource) as exc:
         raise NoSource(f"No file to run: '{filename}'") from exc
 
-    return compile(source, filename, "exec", dont_inherit=True)
+    code = compile(source, filename, mode="exec", dont_inherit=True)
+    return code
 
 
 def make_code_from_pyc(filename: str) -> CodeType: