[all-commits] [llvm/llvm-project] 92a09c: [clang][nullability] allow _Nonnull etc on nullabl...

[Sam McCall via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 92a09c0165b87032e1bd05020a78ed845cf35661
      https://github.com/llvm/llvm-project/commit/92a09c0165b87032e1bd05020a78ed845cf35661
  Author: Sam McCall <sam.mccall at gmail.com>
  Date:   2024-03-14 (Thu, 14 Mar 2024)

  Changed paths:
    M clang/docs/ReleaseNotes.rst
    M clang/include/clang/Basic/Attr.td
    M clang/include/clang/Basic/AttrDocs.td
    M clang/include/clang/Basic/Features.def
    M clang/include/clang/Parse/Parser.h
    M clang/include/clang/Sema/Sema.h
    M clang/lib/AST/Type.cpp
    M clang/lib/CodeGen/CGCall.cpp
    M clang/lib/CodeGen/CodeGenFunction.cpp
    M clang/lib/Parse/ParseDeclCXX.cpp
    M clang/lib/Sema/SemaAttr.cpp
    M clang/lib/Sema/SemaChecking.cpp
    M clang/lib/Sema/SemaDecl.cpp
    M clang/lib/Sema/SemaDeclAttr.cpp
    M clang/lib/Sema/SemaInit.cpp
    M clang/lib/Sema/SemaOverload.cpp
    M clang/lib/Sema/SemaTemplate.cpp
    M clang/lib/Sema/SemaType.cpp
    M clang/test/Sema/nullability.c
    M clang/test/SemaCXX/nullability.cpp

  Log Message:
  -----------
  [clang][nullability] allow _Nonnull etc on nullable class types (#82705)

This enables clang and external nullability checkers to make use of
these annotations on nullable C++ class types like unique_ptr.

These types are recognized by the presence of the _Nullable attribute.
Nullable standard library types implicitly receive this attribute.

Existing static warnings for raw pointers are extended to smart
pointers:

- nullptr used as return value or argument for non-null functions
  (`-Wnonnull`)
- assigning or initializing nonnull variables with nullable values
  (`-Wnullable-to-nonnull-conversion`)

It doesn't implicitly add these attributes based on the assume_nonnull
pragma, nor warn on missing attributes where the pragma would apply
them.
I'm not confident that the pragma's current behavior will work well for
C++ (where type-based metaprogramming is much more common than C/ObjC).
We'd like to revisit this once we have more implementation experience.

Support can be detected as `__has_feature(nullability_on_classes)`.
This is needed for back-compatibility, as previously clang would issue a
hard error when _Nullable appears on a smart pointer.

UBSan's `-fsanitize=nullability` will not check smart-pointer types.
It can be made to do so by synthesizing calls to `operator bool`, but
that's left for future work.

Discussion:
https://discourse.llvm.org/t/rfc-allowing-nonnull-etc-on-smart-pointers/77201/26



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