add check and replace on already visited variables that have been changing by the walrus operator

src/_pytest/assertion/rewrite.py

@@ -657,6 +657,7 @@ class AssertionRewriter(ast.NodeVisitor):
         else:
             self.enable_assertion_pass_hook = False
         self.source = source
+        self.overwrite: Dict[str, str] = {}
 
     def run(self, mod: ast.Module) -> None:
         """Find all assert statements in *mod* and rewrite them."""
@@ -943,8 +944,8 @@ class AssertionRewriter(ast.NodeVisitor):
         return self.statements
 
     def visit_NamedExpr(self, name: namedExpr) -> Tuple[namedExpr, str]:
-        # Display the repr of the target name if it's a local variable or
-        # _should_repr_global_name() thinks it's acceptable.
+        # This method handles the 'walrus operator' repr of the target
+        # name if it's a local variable or _should_repr_global_name() thinks it's acceptable.
         locs = ast.Call(self.builtin("locals"), [], [])
         target_id = name.target.id  # type: ignore[attr-defined]
         inlocs = ast.Compare(ast.Str(target_id), [ast.In()], [locs])
@@ -973,12 +974,32 @@ class AssertionRewriter(ast.NodeVisitor):
         levels = len(boolop.values) - 1
         self.push_format_context()
         # Process each operand, short-circuiting if needed.
+        pytest_temp = None
         for i, v in enumerate(boolop.values):
             if i:
                 fail_inner: List[ast.stmt] = []
                 # cond is set in a prior loop iteration below
                 self.expl_stmts.append(ast.If(cond, fail_inner, []))  # noqa
                 self.expl_stmts = fail_inner
+                if isinstance(v, ast.Compare):
+                    if isinstance(v.left, ast.NamedExpr) and (
+                        v.left.target.id
+                        in [
+                            ast_expr.id
+                            for ast_expr in boolop.values[:i]
+                            if hasattr(ast_expr, "id")
+                        ]
+                        or v.left.target.id == pytest_temp
+                    ):
+                        pytest_temp = f"pytest_{v.left.target.id}_temp"
+                        self.overwrite[v.left.target.id] = pytest_temp
+                        v.left.target.id = pytest_temp
+
+                    elif isinstance(v.left, ast.Name) and (
+                        pytest_temp is not None
+                        and v.left.id == pytest_temp.lstrip("pytest_").rstrip("_temp")
+                    ):
+                        v.left.id = pytest_temp
             self.push_format_context()
             res, expl = self.visit(v)
             body.append(ast.Assign([ast.Name(res_var, ast.Store())], res))
@@ -1054,6 +1075,8 @@ class AssertionRewriter(ast.NodeVisitor):
 
     def visit_Compare(self, comp: ast.Compare) -> Tuple[ast.expr, str]:
         self.push_format_context()
+        if isinstance(comp.left, ast.Name) and comp.left.id in self.overwrite:
+            comp.left.id = self.overwrite[comp.left.id]
         left_res, left_expl = self.visit(comp.left)
         if isinstance(comp.left, (ast.Compare, ast.BoolOp)):
             left_expl = f"({left_expl})"
@@ -1065,6 +1088,13 @@ class AssertionRewriter(ast.NodeVisitor):
         syms = []
         results = [left_res]
         for i, op, next_operand in it:
+            if (
+                isinstance(next_operand, ast.NamedExpr)
+                and isinstance(left_res, ast.Name)
+                and next_operand.target.id == left_res.id
+            ):
+                next_operand.target.id = f"pytest_{left_res.id}_temp"
+                self.overwrite[left_res.id] = next_operand.target.id
             next_res, next_expl = self.visit(next_operand)
             if isinstance(next_operand, (ast.Compare, ast.BoolOp)):
                 next_expl = f"({next_expl})"

testing/test_assertrewrite.py

@@ -1374,8 +1374,7 @@ class TestIssue10743:
         )
         result = pytester.runpytest()
         assert result.ret == 1
-        # This is not optimal as error message but it depends on how the rewrite is structured
-        result.stdout.fnmatch_lines(["*AssertionError: assert 'hello' == 'hello'"])
+        result.stdout.fnmatch_lines(["*AssertionError: assert 'Hello' == 'hello'"])
 
     def test_assertion_walrus_operator_boolean_composite(
         self, pytester: Pytester
@@ -1385,7 +1384,7 @@ class TestIssue10743:
             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()
@@ -1403,8 +1402,7 @@ class TestIssue10743:
         )
         result = pytester.runpytest()
         assert result.ret == 1
-        # This is not optimal as error message but it depends on how the rewrite is structured
-        result.stdout.fnmatch_lines(["*assert not (False)"])
+        result.stdout.fnmatch_lines(["*assert not (True and False is False)"])
 
     def test_assertion_walrus_operator_boolean_none_fails(
         self, pytester: Pytester
@@ -1418,8 +1416,7 @@ class TestIssue10743:
         )
         result = pytester.runpytest()
         assert result.ret == 1
-        # This is not optimal as error message but it depends on how the rewrite is structured
-        result.stdout.fnmatch_lines(["*assert not (None)"])
+        result.stdout.fnmatch_lines(["*assert not (True and None is None)"])
 
 
 @pytest.mark.skipif(