fix: missing exceptions through with statements in 3.10 aren't consid…

…ered missing branches. #1205

CHANGES.rst

@@ -37,13 +37,18 @@ Unreleased
   now warnings, to ease the use of coverage across versions.  Fixes `issue
   1035`_.
 
+- Fix handling of exceptions through context managers in Python 3.10. A missing
+  exception is no longer considered a missing branch from the with statement.
+  Fixes `issue 1205`_.
+
 - Fix another rarer instance of "Error binding parameter 0 - probably
   unsupported type." (`issue 1010`_).
 
 .. _issue 1035: https://github.com/nedbat/coveragepy/issues/1035
 .. _issue 1105: https://github.com/nedbat/coveragepy/issues/1105
 .. _issue 1163: https://github.com/nedbat/coveragepy/issues/1163
 .. _issue 1195: https://github.com/nedbat/coveragepy/issues/1195
+.. _issue 1205: https://github.com/nedbat/coveragepy/issues/1205
 
 
 .. _changes_60b1:

coverage/parser.py

@@ -556,14 +556,14 @@ def __init__(self, start):
         # that need to go through the with-statement while exiting.
         self.break_from = set()
         self.continue_from = set()
-        self.raise_from = set()
         self.return_from = set()
 
-    def _process_exits(self, exits, add_arc, from_set):
+    def _process_exits(self, exits, add_arc, from_set=None):
         """Helper to process the four kinds of exits."""
         for xit in exits:
             add_arc(xit.lineno, self.start, xit.cause)
-        from_set.update(exits)
+        if from_set is not None:
+            from_set.update(exits)
         return True
 
     def process_break_exits(self, exits, add_arc):
@@ -573,7 +573,7 @@ def process_continue_exits(self, exits, add_arc):
         return self._process_exits(exits, add_arc, self.continue_from)
 
     def process_raise_exits(self, exits, add_arc):
-        return self._process_exits(exits, add_arc, self.raise_from)
+        return self._process_exits(exits, add_arc)
 
     def process_return_exits(self, exits, add_arc):
         return self._process_exits(exits, add_arc, self.return_from)
@@ -1232,10 +1232,6 @@ def _handle__With(self, node):
                 self.process_continue_exits(
                     self._combine_finally_starts(with_block.continue_from, with_exit)
                     )
-            if with_block.raise_from:
-                self.process_raise_exits(
-                    self._combine_finally_starts(with_block.raise_from, with_exit)
-                    )
             if with_block.return_from:
                 self.process_return_exits(
                     self._combine_finally_starts(with_block.return_from, with_exit)

tests/test_arcs.py

@@ -279,6 +279,62 @@ def test_continue_through_with(self):
             arcz=arcz,
             )
 
+    def test_raise_through_with(self):
+        if env.PYBEHAVIOR.exit_through_with:
+            arcz = ".1 12 27 78 8. 9A A.  -23 34 45 53 6-2"
+            arcz_missing = "6-2 8."
+            arcz_unpredicted = "3-2 89"
+        else:
+            arcz = ".1 12 27 78 8. 9A A.  -23 34 45 5-2 6-2"
+            arcz_missing = "6-2 8."
+            arcz_unpredicted = "89"
+        cov = self.check_coverage("""\
+            from contextlib import suppress
+            def f(x):
+                with suppress():    # used as a null context manager
+                    print(4)
+                    raise Exception("Boo6")
+                print(6)
+            try:
+                f(8)
+            except Exception:
+                print("oops 10")
+            """,
+            arcz=arcz,
+            arcz_missing=arcz_missing,
+            arcz_unpredicted=arcz_unpredicted,
+            )
+        expected = "line 3 didn't jump to the function exit"
+        assert self.get_missing_arc_description(cov, 3, -2) == expected
+
+    def test_untaken_raise_through_with(self):
+        if env.PYBEHAVIOR.exit_through_with:
+            #arcz = ".1 12 28 89 9. AB B.  -23 3-2 34 45 56 53 63 37 7-2"
+            arcz = ".1 12 28 89 9. AB B.  -23 34 45 56 53 63 37 7-2"
+            #arcz_missing = "3-2 56 63 AB B."
+            arcz_missing = "56 63 AB B."
+        else:
+            arcz = ".1 12 28 89 9. AB B.  -23 34 45 56 6-2 57 7-2"
+            arcz_missing = "56 6-2 AB B."
+        cov = self.check_coverage("""\
+            from contextlib import suppress
+            def f(x):
+                with suppress():    # used as a null context manager
+                    print(4)
+                    if x == 5:
+                        raise Exception("Boo6")
+                print(7)
+            try:
+                f(9)
+            except Exception:
+                print("oops 11")
+            """,
+            arcz=arcz,
+            arcz_missing=arcz_missing,
+            )
+        expected = "line 3 didn't jump to the function exit"
+        assert self.get_missing_arc_description(cov, 3, -2) == expected
+
 
 class LoopArcTest(CoverageTest):
     """Arc-measuring tests involving loops."""