Re: [PATCH v4 04/14] qapi/introspect.py: guard against ifcond/comment misuse

[Markus Armbruster <armbru@redhat.com>]

John Snow <jsnow@redhat.com> writes:

> _tree_to_qlit is called recursively on dict values alone; at such a
> point in generating output it is too late to apply an ifcond. Similarly,
> comments do not necessarily have a "tidy" place they can be printed in
> such a circumstance.
>
> Forbid this usage.
>
> Signed-off-by: John Snow <jsnow@redhat.com>
> ---
>  scripts/qapi/introspect.py | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/scripts/qapi/introspect.py b/scripts/qapi/introspect.py
> index 4749f65ea3c..ccdf4f1c0d0 100644
> --- a/scripts/qapi/introspect.py
> +++ b/scripts/qapi/introspect.py
> @@ -43,6 +43,12 @@ def indent(level):
>          ifobj, extra = obj
>          ifcond = extra.get('if')
>          comment = extra.get('comment')
> +
> +        # NB: _tree_to_qlit is called recursively on the values of a key:value
> +        # pair; those values can't be decorated with comments or conditionals.
> +        msg = "dict values cannot have attached comments or if-conditionals."
> +        assert not suppress_first_indent, msg
> +
>          ret = ''
>          if comment:
>              ret += indent(level) + '/* %s */\n' % comment

This uses @suppress_first_indent as a proxy for "@obj is a value in a
dict".  Works, because we pass suppress_first_indent=True exactly
there.  Took me a minute to see, though.

Do you need this assertion to help mypy over the hump?

Perhaps we'd be better off with two functions, one that takes possibly
annotated @obj, and one that takes only plain @obj.  "Yes, but not now"
woule be one acceptable answer to that.