These are still disabled by default, but will work in ObjC code if you
enable the `-import-insertions` flag.
Completion requires ASTSignals to be available; before ASTSignals are
available, we will always use #include. Once they are available, the
behavior varies as follows:
- For source files, use #import if the ObjC language flag is enabled
- For header files:
- If the ObjC language flag is disabled, use #include
- If the header file contains any #imports, use #import
- If the header file references any ObjC decls, use #import
- Otherwise, use #include
IncludeFixer support is similar, but it does not rely upon ASTSignals,
instead it does the above checks excluding the scan for ObjC symbols.
Differential Revision: https://reviews.llvm.org/D139458
Many useful signals can be derived from a valid AST which is regularly updated by
the ASTWorker. `runWithPreamble` does not have access to the ParsedAST
but it can be provided access to some signals derived from a (possibly
stale) AST.
Differential Revision: https://reviews.llvm.org/D94424
