[7.4.x] Improve reporting from __iter__ exceptions (#11749)

changelog/7966.bugfix.rst

@@ -0,0 +1 @@
+Removed unhelpful error message from assertion rewrite mechanism when exceptions are raised in ``__iter__`` methods. Now they are treated un-iterable instead.

src/_pytest/assertion/util.py

@@ -132,7 +132,7 @@ def isiterable(obj: Any) -> bool:
     try:
         iter(obj)
         return not istext(obj)
-    except TypeError:
+    except Exception:
         return False
 
 

testing/test_assertrewrite.py

@@ -686,6 +686,25 @@ def myany(x) -> bool:
         assert msg is not None
         assert "<MY42 object> < 0" in msg
 
+    def test_assert_handling_raise_in__iter__(self, pytester: Pytester) -> None:
+        pytester.makepyfile(
+            """\
+            class A:
+                def __iter__(self):
+                    raise ValueError()
+
+                def __eq__(self, o: object) -> bool:
+                    return self is o
+
+                def __repr__(self):
+                    return "<A object>"
+
+            assert A() == A()
+            """
+        )
+        result = pytester.runpytest()
+        result.stdout.fnmatch_lines(["*E*assert <A object> == <A object>"])
+
     def test_formatchar(self) -> None:
         def f() -> None:
             assert "%test" == "test"  # type: ignore[comparison-overlap]