FuncParamType should use ValueError message in self.fail()

src/click/types.py

@@ -183,13 +183,16 @@ def convert(
     ) -> t.Any:
         try:
             return self.func(value)
-        except ValueError:
-            try:
-                value = str(value)
-            except UnicodeError:
-                value = value.decode("utf-8", "replace")
+        except ValueError as exc:
+            message = str(exc)
+
+            if not message:
+                try:
+                    message = str(value)
+                except UnicodeError:
+                    message = value.decode("utf-8", "replace")
 
-            self.fail(value, param, ctx)
+            self.fail(message, param, ctx)
 
 
 class UnprocessedParamType(ParamType):

tests/test_types.py

@@ -51,6 +51,18 @@ def test_range_fail(type, value, expect):
     assert expect in exc_info.value.message
 
 
+def test_func_param_type_uses_value_error_message():
+    def parse(value):
+        raise ValueError(f"bad value: {value}")
+
+    func_type = click.types.FuncParamType(parse)
+
+    with pytest.raises(click.BadParameter) as exc_info:
+        func_type.convert("nope", None, None)
+
+    assert "bad value: nope" in exc_info.value.message
+
+
 def test_float_range_no_clamp_open():
     with pytest.raises(TypeError):
         click.FloatRange(0, 1, max_open=True, clamp=True)