improve -vv repr, fix pytest-dev#9742

AUTHORS

@@ -289,6 +289,7 @@ Ruaridh Williamson
 Russel Winder
 Ryan Wooden
 Saiprasad Kale
+Samuel Colvin
 Samuel Dion-Girardeau
 Samuel Searles-Bryant
 Samuele Pedroni

changelog/9742.improvement.rst

@@ -0,0 +1 @@
+Display assertion message without escaped newline characters with ``-vv``.

extra/setup-py.test/setup.py

@@ -1,4 +1,5 @@
 import sys
+
 from distutils.core import setup
 
 if __name__ == "__main__":

src/_pytest/_io/saferepr.py

@@ -107,6 +107,20 @@ def saferepr(obj: object, maxsize: Optional[int] = DEFAULT_REPR_MAX_SIZE) -> str
     return SafeRepr(maxsize).repr(obj)
 
 
+def saferepr_unlimited(obj: object) -> str:
+    """Return an unlimited-size safe repr-string for the given object.
+
+    As with saferepr, failing __repr__ functions of user instances
+    will be represented with a short exception info.
+
+    This function is a wrapper around simple repr.
+    """
+    try:
+        return repr(obj)
+    except Exception as exc:
+        return _format_repr_exception(exc, obj)
+
+
 class AlwaysDispatchingPrettyPrinter(pprint.PrettyPrinter):
     """PrettyPrinter that always dispatches (regardless of width)."""
 

src/_pytest/assertion/util.py

@@ -14,7 +14,7 @@
 import _pytest._code
 from _pytest import outcomes
 from _pytest._io.saferepr import _pformat_dispatch
-from _pytest._io.saferepr import safeformat
+from _pytest._io.saferepr import saferepr_unlimited
 from _pytest._io.saferepr import saferepr
 from _pytest.config import Config
 
@@ -160,8 +160,8 @@ def assertrepr_compare(config, op: str, left: Any, right: Any) -> Optional[List[
     """Return specialised explanations for some operators/operands."""
     verbose = config.getoption("verbose")
     if verbose > 1:
-        left_repr = safeformat(left)
-        right_repr = safeformat(right)
+        left_repr = saferepr_unlimited(left)
+        right_repr = saferepr_unlimited(right)
     else:
         # XXX: "15 chars indentation" is wrong
         #      ("E       AssertionError: assert "); should use term width.

testing/io/test_saferepr.py

@@ -1,7 +1,7 @@
 import pytest
 from _pytest._io.saferepr import _pformat_dispatch
 from _pytest._io.saferepr import DEFAULT_REPR_MAX_SIZE
-from _pytest._io.saferepr import saferepr
+from _pytest._io.saferepr import saferepr, saferepr_unlimited
 
 
 def test_simple_repr():
@@ -179,3 +179,23 @@ def __repr__(self):
     assert saferepr(SomeClass()).startswith(
         "<[RuntimeError() raised in repr()] SomeClass object at 0x"
     )
+
+
+def test_saferepr_unlimited():
+    dict5 = {f'v{i}': i for i in range(5)}
+    assert saferepr_unlimited(dict5) == "{'v0': 0, 'v1': 1, 'v2': 2, 'v3': 3, 'v4': 4}"
+
+    dict_long = {f'v{i}': i for i in range(1_000)}
+    r = saferepr_unlimited(dict_long)
+    assert '...' not in r
+    assert '\n' not in r
+
+
+def test_saferepr_unlimited_exc():
+    class A:
+        def __repr__(self):
+            raise ValueError(42)
+
+    assert saferepr_unlimited(A()).startswith(
+        '<[ValueError(42) raised in repr()] A object at 0x'
+    )

testing/test_assertion.py

@@ -1695,3 +1695,17 @@ def test():
             "*= 1 failed in*",
         ]
     )
+
+
+def test_reprcompare_verbose_long() -> None:
+    a = {f'v{i}': i for i in range(11)}
+    b = a.copy()
+    b['v2'] += 10
+    lines = callop("==", a, b, verbose=2)
+    assert lines[0] == (
+        "{'v0': 0, 'v1': 1, 'v2': 2, 'v3': 3, 'v4': 4, 'v5': 5, "
+        "'v6': 6, 'v7': 7, 'v8': 8, 'v9': 9, 'v10': 10}"
+        " == "
+        "{'v0': 0, 'v1': 1, 'v2': 12, 'v3': 3, 'v4': 4, 'v5': 5, "
+        "'v6': 6, 'v7': 7, 'v8': 8, 'v9': 9, 'v10': 10}"
+    )