[all-commits] [llvm/llvm-project] c90e19: Fix parsing of enum-base to follow C++11 rules.

[Richard Smith via All-commits]

  Branch: refs/heads/master
  Home:   https://github.com/llvm/llvm-project
  Commit: c90e198107431f64b73686bdce31c293e3380ac7
      https://github.com/llvm/llvm-project/commit/c90e198107431f64b73686bdce31c293e3380ac7
  Author: Richard Smith <richard at metafoo.co.uk>
  Date:   2020-05-08 (Fri, 08 May 2020)

  Changed paths:
    M clang/include/clang/Basic/DiagnosticParseKinds.td
    M clang/include/clang/Basic/DiagnosticSemaKinds.td
    M clang/include/clang/Parse/Parser.h
    M clang/lib/Parse/ParseDecl.cpp
    M clang/lib/Parse/ParseDeclCXX.cpp
    M clang/lib/Parse/ParseTentative.cpp
    M clang/lib/Sema/SemaDecl.cpp
    M clang/test/CXX/drs/dr15xx.cpp
    M clang/test/CXX/drs/dr19xx.cpp
    M clang/test/CXX/drs/dr21xx.cpp
    M clang/test/CXX/expr/expr.prim/expr.prim.general/p8-0x.cpp
    M clang/test/Parser/c1x-generic-selection.c
    M clang/test/Parser/cxx0x-ambig.cpp
    M clang/test/Parser/cxx0x-decl.cpp
    M clang/test/SemaCXX/enum-bitfield.cpp
    M clang/test/SemaCXX/enum-scoped.cpp
    M clang/test/SemaObjC/enum-fixed-type.m
    M clang/www/cxx_dr_status.html

  Log Message:
  -----------
  Fix parsing of enum-base to follow C++11 rules.

Previously we implemented non-standard disambiguation rules to
distinguish an enum-base from a bit-field but otherwise treated a :
after an elaborated-enum-specifier as introducing an enum-base. That
misparses various examples (anywhere an elaborated-type-specifier can
appear followed by a colon, such as within a ternary operator or
_Generic).

We now implement the C++11 rules, with the old cases accepted as
extensions where that seemed reasonable. These amount to:
 * an enum-base must always be accompanied by an enum definition (except
   in a standalone declaration of the form 'enum E : T;')
 * in a member-declaration, 'enum E :' always introduces an enum-base,
   never a bit-field
 * in a type-specifier (or similar context), 'enum E :' is not
   permitted; the colon means whatever else it would mean in that
   context.

Fixed underlying types for enums are also permitted in Objective-C and
under MS extensions, plus as a language extension in all other modes.
The behavior in ObjC and MS extensions modes is unchanged (but the
bit-field disambiguation is a bit better); remaining language modes
follow the C++11 rules.

Fixes PR45726, PR39979, PR19810, PR44941, and most of PR24297, plus C++
core issues 1514 and 1966.