Investigate "default dodginess"

[schrockn]

Found a comment that indicates a bug in test_system_config.py so creating an issue to track it down.

[schrockn]

Grep the file for the issue number

[natekupp]

There's still a comment for this issue in the codebase, but looks like the test is enabled—is this still an issue?

[schrockn]

Yes it's still an issue:

The config system claims that:

    @solid(
        name='int_config_solid',
        config=Field(Int, is_required=False),
        input_defs=[],
        output_defs=[],
    )
    def int_config_solid(_):
        return None

Has provided a default

[schrockn]

assert int_solid_field.default_provided

[sryza]

Is there a user-facing consequence to this?

I took a brief look at this, and as far as I can tell at least some part of the internals believe that this is the expected behavior - or at least we have code that explicitly tries to make it the case. I.e. the code snippets below go out of their way to make it the case that a Shape config field whose interior fields are all optional gets a default value of {}.

If I don't hear back, I'll post a PR that removes the comment and then close this issue.

Relevant snippets:

        if is_required is None:
            is_optional = has_implicit_default(self.config_type) or self.default_provided
            is_required = not is_optional

            # on implicitly optional - set the default value
            # by resolving the defaults of the type
            if is_optional and not self.default_provided:
                evr = resolve_defaults(self.config_type, None)
                if not evr.success:
                    raise DagsterInvalidConfigError(
                        "Unable to resolve implicit default_value for Field.",
                        evr.errors,
                        None,
                    )
                self._default_value = evr.value

def has_implicit_default(config_type):
    if config_type.kind == ConfigTypeKind.NONEABLE:
        return True

    return all_optional_type(config_type)

def all_optional_type(config_type: ConfigType) -> bool:
    check.inst_param(config_type, "config_type", ConfigType)

    if ConfigTypeKind.is_shape(config_type.kind):
        for field in config_type.fields.values():  # type: ignore
            if field.is_required:
                return False
        return True

    if ConfigTypeKind.is_selector(config_type.kind):
        if len(config_type.fields) == 1:  # type: ignore
            for field in config_type.fields.values():  # type: ignore
                if field.is_required:
                    return False
            return True

    return False