Don't leak TypeError from Coerce when the type is a non-class callable

[chuenchen309]

Problem

Coerce accepts any callable (type: Union[type, Callable]), and its docstring says a ValueError/TypeError from the constructor marks the value Invalid. But when the callable is a plain function (not a class), the failure path raises a raw, uncaught TypeError instead:

from voluptuous import Schema, Coerce
import datetime

Schema(Coerce(datetime.datetime.fromisoformat))('not-a-date')
# TypeError: issubclass() arg 1 must be a class    <-- escapes; not an Invalid

def parse_int(v): return int(v)
Schema(Coerce(parse_int))('foo')
# TypeError: issubclass() arg 1 must be a class

Coerce(int)('foo') (a class) correctly yields MultipleInvalid: expected int. The only difference is class-vs-function, so the two are analogous — and functions are explicitly supported by the signature.

Cause

In Coerce.__call__, the except handler calls issubclass(self.type, Enum) to optionally list Enum values in the message. issubclass() requires a class as its first argument, so when self.type is a function it raises TypeError. That call is outside the try (which only wraps self.type(v)), so it propagates raw, bypassing CoerceInvalid, error paths, and humanize.

Note Coerce(func, msg="...") didn't hit this, because not self.msg short-circuits before issubclass — only the default-message path was affected.

Fix

Guard the Enum check with isinstance(self.type, type):

if not self.msg and Enum and isinstance(self.type, type) and issubclass(self.type, Enum):

The class path (including the Enum value-listing message, e.g. expected Color or one of 1, 2) is unchanged; non-class callables now produce MultipleInvalid: expected <name> as documented.

Testing

Added test_coerce_callable_marks_invalid_without_msg (red before, green after). Full suite: 182 passed. black, isort, flake8, mypy all clean.

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Disclosure: authored by an AI coding agent (Claude Code) running on this account — it found the bug, ran the repro, wrote the test and this description. I review every change and am accountable for it; the verification above is real and re-runnable from the diff. If this isn't a change you want, say so and I'll close it.