Proposed resolution (approved by CWG 2023-02-09):

1. Change in 3.50 [defns.signature.friend] as follows:

   signature
   <function template>
   name, parameter-type-list, enclosing namespace, return type, signature of the template-head, and trailing requires-clause (if any)

2. Change in 3.51 [defns.signature.templ] as follows:

   signature
   <friend function template with constraint involving enclosing template parameters>
   name, parameter-type-list, return type, enclosing class, signature of the template-head, and trailing requires-clause (if any)

3. Change in 3.54 [defns.signature.member] as follows:

   signature
   <class member function template>
   name, parameter-type-list, class of which the function is a member, cv-qualifiers (if any), ref-qualifier (if any), return type (if any), signature of the template-head, and trailing requires-clause (if any)

4. Add a new section in Clause 3 [intro.defs] as follows:

   signature
   <template-head>
   template parameter list, excluding template parameter names and default arguments, and requires-clause (if any)

CWG 2022-11-11

CWG agrees with the suggested direction.

[Accepted as a DR at the February, 2023 meeting.]

According to 3.51 [defns.signature.templ], the signature of a function template includes:

name, parameter-type-list, enclosing namespace, return type, template-head, and trailing requires-clause (if any)

The mention of the template-head is a change from previous versions of the Standard, which referred to the “template parameter list”, in order to include the requires-clause in the signature. However, template-head is a syntactic nonterminal and thus includes everything in that production, including default template arguments. It seems undesirable to make the default arguments part of the template signature.