[llvm-bugs] [Bug 46248] New: `-fmodules-local-submodule-visibility` does not work correctly with Objective-C

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=46248

            Bug ID: 46248
           Summary: `-fmodules-local-submodule-visibility` does not work
                    correctly with Objective-C
           Product: clang
           Version: trunk
          Hardware: All
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Frontend
          Assignee: unassignedclangbugs at nondot.org
          Reporter: mboehme at google.com
                CC: llvm-bugs at lists.llvm.org, neeilans at live.com,
                    richard-llvm at metafoo.co.uk

Multiple places in AST/DeclObjC.{h,cpp} and Sema/SemaDeclObjC.cpp use
Decl::isHidden() instead of Sema::isVisible().

These two methods are equivalent only if -fmodules-local-submodule-visibility
is not turned on.

If -fmodules-local-submodule-visibility is turned on, Decl::isHidden() can
return true for declarations that have been made visible by importing the
(sub)module that owns them. (See also the FIXME in the comment for
Decl::isHidden().) As a result, the Objective-C code using Decl::isHidden()
will falsely assume that such declarations are hidden when in fact they are
visible.

For examples of how this causes wrong behavior, witness how adding the
-fmodules-local-submodule-visibility option to tests objc-categories.m,
objc-category-2.m and objc-category-3.m in test/Modules causes these tests to
fail.

Fixing this in Sema/SemaDeclObjC.cpp is easy, as Decl::isHidden() can simply be
replaced by Sema::isVisible().

Fixing this in AST/DeclObjC.{h,cpp} is more difficult as AST is not allowed to
depend on Sema. As a result, the functions in question and all of their callers
need to be moved to Sema. From what I have seen, this is a non-trivial
undertaking.

For more context, see also description on this change:
https://github.com/llvm/llvm-project/commit/90dc5254725e32c0fab65213c554b689a2a0bbbf

Also note this in-review change, which changes the name of Decl::isHidden() to
more accurately reflect what it does:
https://reviews.llvm.org/D81392

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