fix: case _ as value shouldn't be considered a missing branch. #1860

CHANGES.rst

@@ -23,6 +23,10 @@ upgrading your version of coverage.py.
 Unreleased
 ----------
 
+- Fix: a final wildcard match/case clause assigning to a name (``case _ as
+  value``) was incorrectly marked as a missing branch.  This is now fixed,
+  closing `issue 1860`_.
+
 - Fewer things are considered branches now. Lambdas, comprehensions, and
   generator expressions are no longer marked as missing branches if they don't
   complete execution.
@@ -47,6 +51,7 @@ Unreleased
 .. _pull 1843: https://github.com/nedbat/coveragepy/pull/1843
 .. _issue 1846: https://github.com/nedbat/coveragepy/issues/1846
 .. _pull 1849: https://github.com/nedbat/coveragepy/pull/1849
+.. _issue 1860: https://github.com/nedbat/coveragepy/issues/1860
 
 
 .. scriv-start-here

coverage/parser.py

@@ -1121,6 +1121,8 @@ def _handle__Match(self, node: ast.Match) -> set[ArcStart]:
             pattern = case.pattern      # pylint: disable=undefined-loop-variable
             while isinstance(pattern, ast.MatchOr):
                 pattern = pattern.patterns[-1]
+            while isinstance(pattern, ast.MatchAs) and pattern.pattern is not None:
+                pattern = pattern.pattern
             had_wildcard = (
                 isinstance(pattern, ast.MatchAs)
                 and pattern.pattern is None

tests/test_arcs.py

@@ -1286,6 +1286,23 @@ def test_match_case_with_default(self) -> None:
         )
         assert self.stdout() == "default\nno go\ngo: n\n"
 
+    def test_match_case_with_named_default(self) -> None:
+        self.check_coverage("""\
+            for command in ["huh", "go home", "go n"]:
+                match command.split():
+                    case ["go", direction] if direction in "nesw":
+                        match = f"go: {direction}"
+                    case ["go", _]:
+                        match = "no go"
+                    case _ as value:
+                        match = "default"
+                print(match)
+            """,
+            branchz="12 1-1 34 35 56 57",
+            branchz_missing="",
+        )
+        assert self.stdout() == "default\nno go\ngo: n\n"
+
     def test_match_case_with_wildcard(self) -> None:
         self.check_coverage("""\
             for command in ["huh", "go home", "go n"]: