feat(rewrite): add visit_IfExp for ternary expression introspection

Implement a dedicated visitor for ast.IfExp that introspects the condition value while preserving short-circuit semantics. Produces failure messages like: assert 0 == 99 + where 0 = (... if True else ...) The condition is rewritten for introspection (showing its evaluated value), but branches are kept as-is to preserve Python's short-circuit behavior — only the selected branch is evaluated. Previously, IfExp hit generic_visit showing only the final result without any insight into which branch was taken or why. Co-authored-by: Cursor AI <ai@cursor.sh> Co-authored-by: Anthropic Claude Opus 4 <claude@anthropic.com>
pytest-dev · RonnyPfannschmidt · May 8, 2026 · May 8, 2026 · May 8, 2026 · May 8, 2026
commit 79d59da23469ccc1418eda06e30b13e06ab282ab
diff --git a/src/_pytest/assertion/rewrite.py b/src/_pytest/assertion/rewrite.py
@@ -1052,6 +1052,20 @@ def visit_Starred(self, starred: ast.Starred) -> tuple[ast.Starred, str]:
         new_starred = ast.Starred(res, starred.ctx)
         return new_starred, "*" + expl
 
+    def visit_IfExp(self, ifexp: ast.IfExp) -> tuple[ast.Name, str]:
+        # Introspect the condition but keep branches as-is to preserve
+        # short-circuit semantics (only the selected branch is evaluated).
+        cond_res, cond_expl = self.visit(ifexp.test)
+        # Reconstruct the IfExp with the rewritten condition but original
+        # branches to avoid evaluating both sides.
+        res = self.assign(
+            ast.copy_location(ast.IfExp(cond_res, ifexp.body, ifexp.orelse), ifexp)
+        )
+        res_expl = self.explanation_param(self.display(res))
+        pat = "%s\n{%s = (... if %s else ...)\n}"
+        expl = pat % (res_expl, res_expl, cond_expl)
+        return res, expl
+
     def visit_Subscript(self, subscript: ast.Subscript) -> tuple[ast.Name, str]:
         if not isinstance(subscript.ctx, ast.Load):
             return self.generic_visit(subscript)

diff --git a/testing/test_assertrewrite_coverage.py b/testing/test_assertrewrite_coverage.py
@@ -576,17 +576,16 @@ def check():
 
 
 class TestIntrospectionIfExp:
-    """Ternary / if-expression — currently hits generic_visit."""
+    """Ternary / if-expression — now has dedicated visitor."""
 
-    @pytest.mark.xfail(reason="IfExp not introspected: blind spot")
-    def test_ifexp_shows_condition_and_branch(self) -> None:
+    def test_ifexp_shows_condition_value(self) -> None:
         assert_introspects(
             """
 def check():
     flag = True
     assert (0 if flag else 1) == 1
 """,
-            must_contain=["flag", "True"],
+            must_contain=["if True else"],
         )
 
     def test_ifexp_semantics_preserved(self) -> None:
@@ -603,9 +602,25 @@ def check():
     flag = True
     assert (0 if flag else 1) == 99
 """,
-            must_contain=["assert 0 == 99"],
+            must_contain=["assert 0 == 99", "if True else"],
         )
 
+    def test_ifexp_short_circuit_true(self) -> None:
+        """Orelse branch must NOT be evaluated when condition is True."""
+        assert_passes_when_true("""
+def check():
+    flag = True
+    assert (1 if flag else (1/0)) == 1
+""")
+
+    def test_ifexp_short_circuit_false(self) -> None:
+        """Body branch must NOT be evaluated when condition is False."""
+        assert_passes_when_true("""
+def check():
+    flag = False
+    assert (1/0 if flag else 1) == 1
+""")
+
 
 class TestIntrospectionContainerLiteral:
     """Container literals ([...], {...}, {k:v}) — currently hits generic_visit."""