fix(rewrite): short-circuit chained comparisons

changelog/14445.bugfix.rst

@@ -0,0 +1,3 @@
+Fixed assertion rewriting evaluating walrus operator (``:=``) expressions multiple times, causing incorrect test results when the expression had side effects (e.g., incrementing a counter or calling a function).
+
+Operands preceding a walrus operator are now evaluated -- and reported -- before it rebinds their name, so ``assert value != identity(value := value.lower())`` keeps Python's left-to-right evaluation order.

changelog/14814.bugfix.rst

@@ -0,0 +1 @@
+Fixed assertion rewriting evaluating a walrus operator (``:=``) or a starred argument out of order when a later argument assigned to the same name, so ``assert collect(*items, identity(items := [9]))`` now passes the pre-assignment ``items``.

changelog/14815.improvement.rst

@@ -0,0 +1,4 @@
+Assertion failure messages now decompose subscript expressions, showing the container and the key that produced a value::
+
+    assert 1 == 99
+     +  where 1 = {'a': 1, 'b': 2}['a']

changelog/14816.improvement.rst

@@ -0,0 +1,4 @@
+Assertion failure messages now show the condition of a conditional expression::
+
+    assert 0 == 99
+     +  where 0 = (... if True else ...)

changelog/14817.improvement.rst

@@ -0,0 +1,4 @@
+Assertion failure messages now show a method call on a single line, without the bound method as a separate intermediate::
+
+    assert 42 == 100
+     +  where 42 = Obj().compute()

changelog/14821.bugfix.rst

@@ -0,0 +1 @@
+Fixed assertion rewriting reading an operand after a later call had rebound its name, so ``assert count == bump()`` compares the ``count`` Python would have compared even when ``bump()`` assigns to it via ``global`` or ``nonlocal``.

changelog/14822.bugfix.rst

@@ -0,0 +1 @@
+Chained comparisons in an ``assert`` now short-circuit the way Python does: in ``assert a < b < c``, ``c`` is no longer evaluated when ``a < b`` is false. Previously ``assert 1 < 0 < 1 / 0`` raised ``ZeroDivisionError`` instead of ``AssertionError``, and a call in an unreached position ran anyway.

testing/python/raises_group.py

@@ -1237,11 +1237,10 @@ def test_assert_matches() -> None:
         match=wrap_escape(
             "`ValueError()` is not an instance of `TypeError`\n"
             "assert False\n"
-            " +  where False = matches(ValueError())\n"
-            " +    where matches = RaisesExc(TypeError).matches"
+            " +  where False = RaisesExc(TypeError).matches(ValueError())"
         ),
     ):
-        # you'd need to do this arcane incantation
+        # binding the RaisesExc is still how you get at ``fail_reason``
         assert (m := RaisesExc(TypeError)).matches(e), m.fail_reason
 
     # but even if we add assert_matches, will people remember to use it?

testing/test_assertrewrite.py

@@ -1637,190 +1637,29 @@ def test_simple_failure():
         result.stdout.fnmatch_lines(["*E*assert (1 + 1) == 3"])
 
 
-class TestAssertionRewriteWalrusOperator:
-    """See #10743"""
-
-    def test_assertion_walrus_operator(self, pytester: Pytester) -> None:
-        pytester.makepyfile(
-            """
-            def my_func(before, after):
-                return before == after
-
-            def change_value(value):
-                return value.lower()
-
-            def test_walrus_conversion():
-                a = "Hello"
-                assert not my_func(a, a := change_value(a))
-                assert a == "hello"
-        """
-        )
-        result = pytester.runpytest()
-        assert result.ret == 0
-
-    def test_assertion_walrus_operator_dont_rewrite(self, pytester: Pytester) -> None:
-        pytester.makepyfile(
-            """
-            'PYTEST_DONT_REWRITE'
-            def my_func(before, after):
-                return before == after
-
-            def change_value(value):
-                return value.lower()
-
-            def test_walrus_conversion_dont_rewrite():
-                a = "Hello"
-                assert not my_func(a, a := change_value(a))
-                assert a == "hello"
-        """
-        )
-        result = pytester.runpytest()
-        assert result.ret == 0
-
-    def test_assertion_inline_walrus_operator(self, pytester: Pytester) -> None:
-        pytester.makepyfile(
-            """
-            def my_func(before, after):
-                return before == after
-
-            def test_walrus_conversion_inline():
-                a = "Hello"
-                assert not my_func(a, a := a.lower())
-                assert a == "hello"
-        """
-        )
-        result = pytester.runpytest()
-        assert result.ret == 0
-
-    def test_assertion_inline_walrus_operator_reverse(self, pytester: Pytester) -> None:
-        pytester.makepyfile(
-            """
-            def my_func(before, after):
-                return before == after
-
-            def test_walrus_conversion_reverse():
-                a = "Hello"
-                assert my_func(a := a.lower(), a)
-                assert a == 'hello'
-        """
-        )
-        result = pytester.runpytest()
-        assert result.ret == 0
-
-    def test_assertion_walrus_no_variable_name_conflict(
-        self, pytester: Pytester
-    ) -> None:
-        pytester.makepyfile(
-            """
-            def test_walrus_conversion_no_conflict():
-                a = "Hello"
-                assert a == (b := a.lower())
-        """
-        )
-        result = pytester.runpytest()
-        assert result.ret == 1
-        result.stdout.fnmatch_lines(["*AssertionError: assert 'Hello' == 'hello'"])
-
-    def test_assertion_walrus_operator_true_assertion_and_changes_variable_value(
-        self, pytester: Pytester
-    ) -> None:
-        pytester.makepyfile(
-            """
-            def test_walrus_conversion_succeed():
-                a = "Hello"
-                assert a != (a := a.lower())
-                assert a == 'hello'
-        """
-        )
-        result = pytester.runpytest()
-        assert result.ret == 0
-
-    def test_assertion_walrus_operator_fail_assertion(self, pytester: Pytester) -> None:
-        pytester.makepyfile(
-            """
-            def test_walrus_conversion_fails():
-                a = "Hello"
-                assert a == (a := a.lower())
-        """
-        )
-        result = pytester.runpytest()
-        assert result.ret == 1
-        result.stdout.fnmatch_lines(["*AssertionError: assert 'Hello' == 'hello'"])
-
-    def test_assertion_walrus_operator_boolean_composite(
-        self, pytester: Pytester
-    ) -> None:
-        pytester.makepyfile(
-            """
-            def test_walrus_operator_change_boolean_value():
-                a = True
-                assert a and True and ((a := False) is False) and (a is False) and ((a := None) is None)
-                assert a is None
-        """
-        )
-        result = pytester.runpytest()
-        assert result.ret == 0
-
-    def test_assertion_walrus_operator_compare_boolean_fails(
-        self, pytester: Pytester
-    ) -> None:
-        pytester.makepyfile(
-            """
-            def test_walrus_operator_change_boolean_value():
-                a = True
-                assert not (a and ((a := False) is False))
-        """
-        )
-        result = pytester.runpytest()
-        assert result.ret == 1
-        result.stdout.fnmatch_lines(["*assert not (True and False is False)"])
+def test_walrus_rebinding_does_not_outlive_its_statement(
+    pytester: Pytester,
+) -> None:
+    """A walrus target must not be rebound by a later, unrelated assertion.
 
-    def test_assertion_walrus_operator_boolean_none_fails(
-        self, pytester: Pytester
-    ) -> None:
-        pytester.makepyfile(
-            """
-            def test_walrus_operator_change_boolean_value():
-                a = True
-                assert not (a and ((a := None) is None))
+    The rest of #10743's suite moved to the coverage matrix, which runs
+    in-process.  This one stays here because it needs two tests in one module
+    to say anything: the rewriter may keep no state that survives a statement,
+    let alone a test.  The matrix cannot express that.
+    """
+    pytester.makepyfile(
         """
-        )
-        result = pytester.runpytest()
-        assert result.ret == 1
-        result.stdout.fnmatch_lines(["*assert not (True and None is None)"])
+        def test_walrus_operator_change_value():
+            a = True
+            assert (a := None) is None
 
-    def test_assertion_walrus_operator_value_changes_cleared_after_each_test(
-        self, pytester: Pytester
-    ) -> None:
-        pytester.makepyfile(
-            """
-            def test_walrus_operator_change_value():
-                a = True
-                assert (a := None) is None
-
-            def test_walrus_operator_not_override_value():
-                a = True
-                assert a is True
-        """
-        )
-        result = pytester.runpytest()
-        assert result.ret == 0
-
-    def test_assertion_namedexpr_compare_left_overwrite(
-        self, pytester: Pytester
-    ) -> None:
-        pytester.makepyfile(
-            """
-            def test_namedexpr_compare_left_overwrite():
-                a = "Hello"
-                b = "World"
-                c = "Test"
-                assert (a := b) == c and (a := "Test") == "Test"
-            """
-        )
-        result = pytester.runpytest()
-        assert result.ret == 1
-        result.stdout.fnmatch_lines(["*assert ('World' == 'Test'*"])
+        def test_walrus_operator_not_override_value():
+            a = True
+            assert a is True
+    """
+    )
+    result = pytester.runpytest()
+    assert result.ret == 0
 
 
 class TestIssue11028:
@@ -1931,6 +1770,49 @@ def test_2():
         assert result.ret == 0
 
 
+class TestIssue14445:
+    """Regression tests for #14445: walrus operator double evaluation."""
+
+    def test_walrus_no_double_eval_basic(self, pytester: Pytester) -> None:
+        """Walrus captures the value at assignment time, not re-evaluated later."""
+        pytester.makepyfile(
+            """
+            class Counter:
+                def __init__(self):
+                    self.value = 0
+                def increment(self):
+                    self.value += 1
+
+            def test_walrus_in_assertion_basic():
+                c = Counter()
+                assert (before := c.value) == 0
+                c.increment()
+                assert before != (after := c.value)
+        """
+        )
+        result = pytester.runpytest()
+        assert result.ret == 0
+
+    def test_walrus_no_double_eval_running_counter(self, pytester: Pytester) -> None:
+        """Walrus increments fire exactly once per assert statement."""
+        pytester.makepyfile(
+            """
+            def test_walrus_running_counter():
+                count = 0
+                items = []
+                items.append("a")
+                assert (count := count + 1) == len(items)
+                items.append("b")
+                assert (count := count + 1) == len(items)
+                items.append("c")
+                assert (count := count + 1) == len(items)
+                assert count == 3
+        """
+        )
+        result = pytester.runpytest()
+        assert result.ret == 0
+
+
 @pytest.mark.skipif(
     sys.maxsize <= (2**31 - 1), reason="Causes OverflowError on 32bit systems"
 )