[dcl.fct.def.general] Non-templated functions cannot have a requires-clause CWG2831

[sdkrystian]

CA378 intended to prohibited constraining non-templated functions. As a result, the following wording was changed in [dcl.decl] p4:

The optional requires-clause in an init-declarator or member-declarator shall be present only if the declarator declares a templated function.

Consider a function-definition. It has neither an init-declarator nor a member-declarator, and the "a function definition must be a valid declaration" rule doesn't account for the requires-clause.

I think the cleanest way to fix this is to add a sentence to [dcl.fct.def.general] p3 explicitly prohibiting this rather than dancing around the "definition must be a valid declaration" rule as context would have to be accounted for.

[jensmaurer]

I would prefer if we could inherit the rules for declarations into the function-definition case instead of re-stating the rules. (There are certainly other rules for requires-clause that apply to both definitions and only-declarations.)

[tkoeppe]

CWG meeting consensus, Nov 11: This is not editorial and requires a core issue. This is fixing a bug.

[jensmaurer]

CWG2831

[frederick-vs-ja]

Superseded by #6906 (5b089c3).