_compare_eq_iterable: use AlwaysDispatchingPrettyPrinter (#6151)

src/_pytest/assertion/util.py

@@ -28,6 +28,27 @@ _reprcompare = None  # type: Optional[Callable[[str, object, object], Optional[s
 _assertion_pass = None  # type: Optional[Callable[[int, str, str], None]]
 
 
+class AlwaysDispatchingPrettyPrinter(pprint.PrettyPrinter):
+    """PrettyPrinter that always dispatches (regardless of width)."""
+
+    def _format(self, object, stream, indent, allowance, context, level):
+        p = self._dispatch.get(type(object).__repr__, None)
+
+        objid = id(object)
+        if objid in context or p is None:
+            return super()._format(object, stream, indent, allowance, context, level)
+
+        context[objid] = 1
+        p(self, object, stream, indent, allowance, context, level + 1)
+        del context[objid]
+
+
+def _pformat_dispatch(object, indent=1, width=80, depth=None, *, compact=False):
+    return AlwaysDispatchingPrettyPrinter(
+        indent=1, width=80, depth=None, compact=False
+    ).pformat(object)
+
+
 def format_explanation(explanation: str) -> str:
     """This formats an explanation
 
@@ -270,15 +291,8 @@ def _compare_eq_iterable(
     lines_left = len(left_formatting)
     lines_right = len(right_formatting)
     if lines_left != lines_right:
-        if lines_left > lines_right:
+        left_formatting = _pformat_dispatch(left).splitlines()
-            max_width = min(len(x) for x in left_formatting)
+        right_formatting = _pformat_dispatch(right).splitlines()
-        else:
-            max_width = min(len(x) for x in right_formatting)
-
-        right_formatting = pprint.pformat(right, width=max_width).splitlines()
-        lines_right = len(right_formatting)
-        left_formatting = pprint.pformat(left, width=max_width).splitlines()
-        lines_left = len(left_formatting)
 
     if lines_left > 1 or lines_right > 1:
         _surrounding_parens_on_own_lines(left_formatting)

testing/test_assertion.py

@@ -462,6 +462,29 @@ class TestAssert_reprcompare:
             "  ]",
         ]
 
+    def test_list_dont_wrap_strings(self):
+        long_a = "a" * 10
+        l1 = ["a"] + [long_a for _ in range(0, 7)]
+        l2 = ["should not get wrapped"]
+        diff = callequal(l1, l2, verbose=True)
+        assert diff == [
+            "['a', 'aaaaaa...aaaaaaa', ...] == ['should not get wrapped']",
+            "At index 0 diff: 'a' != 'should not get wrapped'",
+            "Left contains 7 more items, first extra item: 'aaaaaaaaaa'",
+            "Full diff:",
+            "  [",
+            "+  'should not get wrapped',",
+            "-  'a',",
+            "-  'aaaaaaaaaa',",
+            "-  'aaaaaaaaaa',",
+            "-  'aaaaaaaaaa',",
+            "-  'aaaaaaaaaa',",
+            "-  'aaaaaaaaaa',",
+            "-  'aaaaaaaaaa',",
+            "-  'aaaaaaaaaa',",
+            "  ]",
+        ]
+
     def test_dict_wrap(self):
         d1 = {"common": 1, "env": {"env1": 1}}
         d2 = {"common": 1, "env": {"env1": 1, "env2": 2}}
@@ -479,22 +502,20 @@ class TestAssert_reprcompare:
         ]
 
         long_a = "a" * 80
-        sub = {"long_a": long_a, "sub1": {"long_a": "substring that gets wrapped"}}
+        sub = {"long_a": long_a, "sub1": {"long_a": "substring that gets wrapped " * 2}}
         d1 = {"env": {"sub": sub}}
         d2 = {"env": {"sub": sub}, "new": 1}
         diff = callequal(d1, d2, verbose=True)
         assert diff == [
-            "{'env': {'sub...s wrapped'}}}} == {'env': {'sub...}}}, 'new': 1}",
+            "{'env': {'sub... wrapped '}}}} == {'env': {'sub...}}}, 'new': 1}",
             "Omitting 1 identical items, use -vv to show",
             "Right contains 1 more item:",
             "{'new': 1}",
             "Full diff:",
             "  {",
             "   'env': {'sub': {'long_a': '" + long_a + "',",
-            "                   'sub1': {'long_a': 'substring '",
+            "                   'sub1': {'long_a': 'substring that gets wrapped substring '",
-            "                                      'that '",
+            "                                      'that gets wrapped '}}},",
-            "                                      'gets '",
-            "                                      'wrapped'}}},",
             "+  'new': 1,",
             "  }",
         ]