Eliminates extraneous newlines between top-level Objective-C declarations in `-emit-objc-header` headers. Specifically, there should now always be exactly one—no more, no less—empty line between `@end` and whatever follows it.
Besides being more aesthetically pleasing, this eliminates ordering-dependent behavior where PrintAsClang would print an extra newline when visiting an empty extension, which meant that the order in which empty and non-empty extensions were visited during printing could result in whitespace differences in the compiler output. Printing the blank line is now conditional on whether `tell()` indicates that characters were actually written to the output.
Fixes rdar://143533893.
Consider the case of a toolchain that includes clang is being used to
compile Swift. With the current ordering, the header will be found
relative to that toolchain, which could be out of date as compared to
tip. This is the case today if eg. a 5.7 toolchain is used to build
main/5.9 as the shim header is missing a definition.
Each emitted declaration is annotated with the external_source_symbol with its own USR, to allow Clang's indexer to recognize this declaration as a Swift declaration with a specific USR
The _SwiftCxxInteroperability.h is too tightly coupled to the compiler right now and should not be shipped with the standard library. In the future it could be moved back to the standard library.
non-throwing functions.
Activating swift-functions-errors tests
Inserting macros and additional parameters in C and C++ functions following the pattern to lowering to LLVM IR.
This change removes the -emit-cxx-header option, and adds a new -emit-clang-header-path option instead. It's aliased to -emit-objc-header-path for now, but in the future, -emit-objc-header-path will alias to it. After this change Swift can start emitting a single header file that can be expose declarations to C, Objective-C, or C++. For now C++ interface is generated (for all public decls) only when -enable-cxx-interop flag is passed, but that behavior will change once attribute is supported.
We will place tests that test the semantics and runtime of the generated
C++ code into Interop/SwiftToCxx. PrintCxx test directory will only be
used to test high level flow without concerning itself about the C++ semantics.
