fix: Python3.12 now inlines comprehensions

6 files changed, 47 insertions, 14 deletions

diff --git a/CHANGES.rst b/CHANGES.rst
index 8aefb88f..4a1570a7 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -20,7 +20,9 @@ development at the same time, such as 4.5.x and 5.0.
 Unreleased
 ----------
 
-Nothing yet.
+- Python 3.12 beta 1 now inlines comprehensions.  Previously they were compiled
+  as invisible functions and coverage.py would warn you if they weren't
+  completely executed.  This no longer happens under Python 3.12.
 
 
 .. scriv-start-here
diff --git a/coverage/env.py b/coverage/env.py
index bdc2c785..9f9b2553 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))
 
+    # 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))
+
 # Coverage.py specifics.
 
 # Are we using the C-implemented trace function?
diff --git a/coverage/parser.py b/coverage/parser.py
index e653a9cc..e8d51a9b 100644
--- a/coverage/parser.py
+++ b/coverage/parser.py
@@ -1343,9 +1343,10 @@ class AstArcAnalyzer:
 
     _code_object__Lambda = _make_expression_code_method("lambda")
     _code_object__GeneratorExp = _make_expression_code_method("generator expression")
-    _code_object__DictComp = _make_expression_code_method("dictionary comprehension")
-    _code_object__SetComp = _make_expression_code_method("set comprehension")
-    _code_object__ListComp = _make_expression_code_method("list comprehension")
+    if env.PYBEHAVIOR.comprehensions_are_functions:
+        _code_object__DictComp = _make_expression_code_method("dictionary comprehension")
+        _code_object__SetComp = _make_expression_code_method("set comprehension")
+        _code_object__ListComp = _make_expression_code_method("list comprehension")
 
 
 # Code only used when dumping the AST for debugging.
diff --git a/doc/migrating.rst b/doc/migrating.rst
index 5bbc1f33..443afac6 100644
--- a/doc/migrating.rst
+++ b/doc/migrating.rst
@@ -39,3 +39,16 @@ Consider these changes when migrating to coverage.py 7.x:
   entire list.  Newer versions of coverage.py will be adding to the default set
   of exclusions.  Using ``exclude_also`` will let you benefit from those
   updates.
+
+
+.. _migrating_py312:
+
+Migrating to Python 3.12
+------------------------
+
+Keep these things in mind when running under Python 3.12:
+
+- Python 3.12 now inlines list, dict, and set comprehensions.  Previously, they
+  were compiled as functions that were called internally.  Coverage.py would
+  warn you if comprehensions weren't fully completed, but this no longer
+  happens with Python 3.12.
diff --git a/tests/test_arcs.py b/tests/test_arcs.py
index d80a4637..d4c1ba9d 100644
--- a/tests/test_arcs.py
+++ b/tests/test_arcs.py
@@ -559,6 +559,10 @@ class LoopArcTest(CoverageTest):
         )
 
     def test_confusing_for_loop_bug_175(self) -> None:
+        if env.PYBEHAVIOR.comprehensions_are_functions:
+            extra_arcz = " -22 2-2"
+        else:
+            extra_arcz = ""
         self.check_coverage("""\
             o = [(1,2), (3,4)]
             o = [a for a in o]
@@ -566,7 +570,7 @@ class LoopArcTest(CoverageTest):
                 x = tup[0]
                 y = tup[1]
             """,
-            arcz=".1 -22 2-2 12 23 34 45 53 3.",
+            arcz=".1 12 23 34 45 53 3." + extra_arcz,
         )
         self.check_coverage("""\
             o = [(1,2), (3,4)]
@@ -574,7 +578,7 @@ class LoopArcTest(CoverageTest):
                 x = tup[0]
                 y = tup[1]
             """,
-            arcz=".1 12 -22 2-2 23 34 42 2.",
+            arcz=".1 12 23 34 42 2." + extra_arcz,
         )
 
     # https://bugs.python.org/issue44672
@@ -639,6 +643,10 @@ class LoopArcTest(CoverageTest):
         )
 
     def test_other_comprehensions(self) -> None:
+        if env.PYBEHAVIOR.comprehensions_are_functions:
+            extra_arcz = " -22 2-2"
+        else:
+            extra_arcz = ""
         # Set comprehension:
         self.check_coverage("""\
             o = ((1,2), (3,4))
@@ -647,7 +655,7 @@ class LoopArcTest(CoverageTest):
                 x = tup[0]
                 y = tup[1]
             """,
-            arcz=".1 -22 2-2 12 23 34 45 53 3.",
+            arcz=".1 12 23 34 45 53 3." + extra_arcz,
         )
         # Dict comprehension:
         self.check_coverage("""\
@@ -657,10 +665,14 @@ class LoopArcTest(CoverageTest):
                 x = tup[0]
                 y = tup[1]
             """,
-            arcz=".1 -22 2-2 12 23 34 45 53 3.",
+            arcz=".1 12 23 34 45 53 3." + extra_arcz,
         )
 
     def test_multiline_dict_comp(self) -> None:
+        if env.PYBEHAVIOR.comprehensions_are_functions:
+            extra_arcz = " 2-2"
+        else:
+            extra_arcz = ""
         # Multiline dict comp:
         self.check_coverage("""\
             # comment
@@ -675,7 +687,7 @@ class LoopArcTest(CoverageTest):
             }
             x = 11
             """,
-            arcz="-22 2B B-2   2-2"
+            arcz="-22 2B B-2" + extra_arcz,
         )
         # Multi dict comp:
         self.check_coverage("""\
@@ -695,7 +707,7 @@ class LoopArcTest(CoverageTest):
             }
             x = 15
             """,
-            arcz="-22 2F F-2   2-2"
+            arcz="-22 2F F-2" + extra_arcz,
         )
 
 
diff --git a/tests/test_parser.py b/tests/test_parser.py
index f74420b5..d461cb6c 100644
--- a/tests/test_parser.py
+++ b/tests/test_parser.py
@@ -322,10 +322,11 @@ class ParserMissingArcDescriptionTest(CoverageTest):
         assert expected == parser.missing_arc_description(2, -2)
         expected = "line 3 didn't finish the generator expression on line 3"
         assert expected == parser.missing_arc_description(3, -3)
-        expected = "line 4 didn't finish the dictionary comprehension on line 4"
-        assert expected == parser.missing_arc_description(4, -4)
-        expected = "line 5 didn't finish the set comprehension on line 5"
-        assert expected == parser.missing_arc_description(5, -5)
+        if env.PYBEHAVIOR.comprehensions_are_functions:
+            expected = "line 4 didn't finish the dictionary comprehension on line 4"
+            assert expected == parser.missing_arc_description(4, -4)
+            expected = "line 5 didn't finish the set comprehension on line 5"
+            assert expected == parser.missing_arc_description(5, -5)
 
     def test_missing_arc_descriptions_for_exceptions(self) -> None:
         parser = self.parse_text("""\