[all-commits] [llvm/llvm-project] f1f0a0: Diagnose extensions in 'offsetof'

[Aaron Ballman via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: f1f0a0d8e8fdd2e534d9423b2e64c6b8aaa53aee
      https://github.com/llvm/llvm-project/commit/f1f0a0d8e8fdd2e534d9423b2e64c6b8aaa53aee
  Author: Aaron Ballman <aaron at aaronballman.com>
  Date:   2023-01-17 (Tue, 17 Jan 2023)

  Changed paths:
    M clang/docs/LanguageExtensions.rst
    M clang/docs/ReleaseNotes.rst
    M clang/include/clang/Basic/DiagnosticGroups.td
    M clang/include/clang/Basic/DiagnosticParseKinds.td
    M clang/include/clang/Basic/DiagnosticSemaKinds.td
    M clang/include/clang/Parse/Parser.h
    M clang/include/clang/Parse/RAIIObjectsForParser.h
    M clang/include/clang/Sema/Sema.h
    M clang/lib/Parse/ParseDecl.cpp
    M clang/lib/Parse/ParseDeclCXX.cpp
    M clang/lib/Parse/ParseExpr.cpp
    M clang/lib/Sema/SemaDecl.cpp
    M clang/lib/Sema/SemaDeclCXX.cpp
    M clang/lib/Sema/SemaTemplate.cpp
    A clang/test/C/C2x/n2350.c
    M clang/test/C/drs/dr4xx.c
    M clang/test/CXX/drs/dr4xx.cpp
    M clang/test/Parser/declarators.c
    M clang/test/SemaCXX/offsetof.cpp

  Log Message:
  -----------
  Diagnose extensions in 'offsetof'

https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2350.htm made very
clear that it is an UB having type definitions with in offsetof.
Clang supports defining a type as the first argument as a conforming
extension due to how many projects use the construct in C99 and earlier
to calculate the alignment of a type. GCC also supports defining a type
as the first argument.

This adds extension warnings and documentation for the functionality
Clang explicitly supports.

Fixes #57065

Co-authored-by: Yingchi Long <i at lyc.dev>
Co-authored-by: Aaron Ballman <aaron at aaronballman.com>