[flang] Enumeration Type: (PR 5/5) Enable (#231641)
Enable the F2023 ENUMERATION TYPE (7.6.2) by default and remove the
development gate.
- Remove `-fenumeration-type` / `-fno-enumeration-type`,
`LanguageFeature::EnumerationType` and the experimental-support warning.
- Update tests to run without the flag.
- Update ReleaseNotes.md, Extensions.md and FortranStandardsSupport.md.
New declaration checks. An enumeration type is not a derived type, so it
is not extensible and has no type parameters. Flang now diagnoses:
- `EXTENDS(enum)`, rejected early so that no parent component is created
- `CLASS(enum)`, including in a FUNCTION prefix and in IMPLICIT
- `CLASSOF(enum)`; Flang requires an extensible type here (see
Extensions.md)
- `CLASS IS (enum)` in SELECT TYPE
- `TYPE IS (enum)` unless the selector is unlimited polymorphic
- pointer assignment of an enumeration-type pointer from a `CLASS(*)`
target
- an enumeration type as the dtv argument of a defined I/O procedure
- `SAME_TYPE_AS` / `EXTENDS_TYPE_OF` with an enumeration-type argument
- a type-param-spec-list on an enumeration type, e.g. `type(state(1))`
Compatibility: NEXT and PREVIOUS are now intrinsic functions. A
reference to an external function with either name now needs an EXTERNAL
declaration or an explicit interface. A CALL to an external subroutine
with either name is unaffected.
Known limitations:
- #231638
- #231636
- #229873
- #230617
Fixes #183789
Assisted-by: AI (Some of the implementation and feature checklist
utilized Claude).
