[AST] Fix an assertion violation in FieldDecl::getParent.
Summary:
FieldDecl::getParent assumes that the FiledDecl::getDeclContext returns a
RecordDecl, this is true for C/C++, but not for ObjCIvarDecl:
The Decls hierarchy is like following
FieldDecl <-- ObjCIvarDecl
DeclContext <-- ObjCContainerDecl <-- ObjCInterfaceDecl
^
|----- TagDecl <-- RecordDecl
calling getParent() on ObjCIvarDecl will:
1. invoke getDeclContext(), which returns a DeclContext*, which points to an ObjCInterfaceDecl;
2. then downcast the "DeclContext" pointer to a RecordDecl*, and we will hit
the "is_a<RecordDecl>" assertion in llvm::cast (undefined behavior
in release build without assertion enabled);
Fixes https://github.com/clangd/clangd/issues/369
Reviewers: sammccall
Reviewed By: sammccall
Subscribers: rsmith, jkorous, arphaman, kadircet, usaxena95, cfe-commits
Tags: #clang
Differential Revision: https://reviews.llvm.org/D79627