Truncate InvalidCallbackReturnValue size

Truncate the stringified value of `bad_val`,
in order to avoid excessive output on the debug pop-up.

Fixes #2658

Signed-off-by: Stavros Ntentos <[email protected]>

Author: stdedos

dash/_validate.py

@@ -2,6 +2,8 @@
 import re
 from textwrap import dedent
 from keyword import iskeyword
+from typing import Any, Final
+
 import flask
 
 from ._grouping import grouping_len, map_grouping
@@ -15,6 +17,8 @@
     clean_property_name,
 )
 
+TRUNCATE_AT: Final[int] = 100
+
 
 def validate_callback(outputs, inputs, state, extra_args, types):
     Input, Output, State = types
@@ -209,11 +213,23 @@ def validate_multi_return(output_lists, output_values, callback_id):
                 )
 
 
+def truncate_object(obj: Any, at: int) -> str:
+    """Return a truncated string representation of an object."""
+    obj_stringified = str(obj)
+    size = len(obj_stringified)
+
+    if size <= at:
+        return obj_stringified
+
+    return obj_stringified[:at] + f"... (truncated - {size} characters total)"
+
+
 def fail_callback_output(output_value, output):
     valid_children = (str, int, float, type(None), Component)
     valid_props = (str, int, float, type(None), tuple, MutableSequence)
 
     def _raise_invalid(bad_val, outer_val, path, index=None, toplevel=False):
+        bad_val_stringified = truncate_object(bad_val, TRUNCATE_AT)
         bad_type = type(bad_val).__name__
         outer_id = f"(id={outer_val.id:s})" if getattr(outer_val, "id", False) else ""
         outer_type = type(outer_val).__name__
@@ -244,7 +260,7 @@ def _raise_invalid(bad_val, outer_val, path, index=None, toplevel=False):
 
                 {location}
                 and has string representation
-                `{bad_val}`
+                `{bad_val_stringified}`
 
                 In general, Dash properties can only be
                 dash components, strings, dictionaries, numbers, None,