Add Saferepr to tracer class

Author: Anusha Shekhar

src/pluggy/_tracing.py

@@ -7,6 +7,7 @@
 from typing import Callable
 from typing import Sequence
 from typing import Tuple
+import reprlib
 
 
 _Writer = Callable[[str], object]
@@ -59,6 +60,96 @@ def setprocessor(self, tags: str | tuple[str, ...], processor: _Processor) -> No
             assert isinstance(tags, tuple)
         self._tags2proc[tags] = processor
 
+def _try_repr_or_str(obj: object) -> str:
+    try:
+        return repr(obj)
+    except (KeyboardInterrupt, SystemExit):
+        raise
+    except BaseException:
+        return f'{type(obj).__name__}("{obj}")'
+
+def _format_repr_exception(exc: BaseException, obj: object) -> str:
+    try:
+        exc_info = _try_repr_or_str(exc)
+    except (KeyboardInterrupt, SystemExit):
+        raise
+    except BaseException as exc:
+        exc_info = f"unpresentable exception ({_try_repr_or_str(exc)})"
+    return "<[{} raised in repr()] {} object at 0x{:x}>".format(
+        exc_info, type(obj).__name__, id(obj)
+    )
+
+def _ellipsize(s: str, maxsize: int) -> str:
+    if len(s) > maxsize:
+        i = max(0, (maxsize - 3) // 2)
+        j = max(0, maxsize - 3 - i)
+        return s[:i] + "..." + s[len(s) - j :]
+    return s
+
+class SafeRepr(reprlib.Repr):
+    """
+    repr.Repr that limits the resulting size of repr() and includes
+    information on exceptions raised during the call.
+    """
+
+    def __init__(self, maxsize: Optional[int], use_ascii: bool = False) -> None:
+        """
+        :param maxsize:
+            If not None, will truncate the resulting repr to that specific size, using ellipsis
+            somewhere in the middle to hide the extra text.
+            If None, will not impose any size limits on the returning repr.
+        """
+        super().__init__()
+        # ``maxstring`` is used by the superclass, and needs to be an int; using a
+        # very large number in case maxsize is None, meaning we want to disable
+        # truncation.
+        self.maxstring = maxsize if maxsize is not None else 1_000_000_000
+        self.maxsize = maxsize
+        self.use_ascii = use_ascii
+
+    def repr(self, x: object) -> str:
+        try:
+            if self.use_ascii:
+                s = ascii(x)
+            else:
+                s = super().repr(x)
+
+        except (KeyboardInterrupt, SystemExit):
+            raise
+        except BaseException as exc:
+            s = _format_repr_exception(exc, x)
+        if self.maxsize is not None:
+            s = _ellipsize(s, self.maxsize)
+        return s
+
+    def repr_instance(self, x: object, level: int) -> str:
+        try:
+            s = repr(x)
+        except (KeyboardInterrupt, SystemExit):
+            raise
+        except BaseException as exc:
+            s = _format_repr_exception(exc, x)
+        if self.maxsize is not None:
+            s = _ellipsize(s, self.maxsize)
+        return s
+
+
+# Maximum size of overall repr of objects to display during assertion errors.
+DEFAULT_REPR_MAX_SIZE = 240
+def saferepr(
+    obj: object, maxsize: Optional[int] = DEFAULT_REPR_MAX_SIZE, use_ascii: bool = False
+) -> str:
+    """Return a size-limited safe repr-string for the given object.
+
+    Failing __repr__ functions of user instances will be represented
+    with a short exception info and 'saferepr' generally takes
+    care to never raise exceptions itself.
+
+    This function is a wrapper around the Repr/reprlib functionality of the
+    stdlib.
+    """
+
+    return SafeRepr(maxsize, use_ascii).repr(obj)
 
 class TagTracerSub:
     def __init__(self, root: TagTracer, tags: tuple[str, ...]) -> None: