swift: Pass C++ base compile options to swiftc

Author: dblsaiko

docs/markdown/snippets/swift-pass-c-compiler-options.md

@@ -1,8 +1,9 @@
 ## Swift compiler receives select C family compiler options
 
-Meson now passes select few C family (C/Obj-C) compiler options to the
-Swift compiler, notably *-std=*, in order to improve the compatibility
-of C code as interpreted by the C compiler and the Swift compiler.
+Meson now passes select few C family (C/C++/Obj-C/Obj-C++) compiler
+options to the Swift compiler, notably *-std=*, in order to improve
+the compatibility of C code as interpreted by the C compiler and the
+Swift compiler.
 
 NB: This does not include any of the options set in the target's
 c_flags.

mesonbuild/compilers/swift.py

@@ -140,7 +140,11 @@ def get_option_std_args(self, target: build.BuildTarget, env: Environment, subpr
             args += ['-swift-version', std]
 
         # Pass C compiler -std=... arg to swiftc
-        c_lang = first(['objc', 'c'], lambda x: x in target.compilers)
+        c_langs = ['objc', 'c']
+        if target.uses_swift_cpp_interop():
+            c_langs = ['objcpp', 'cpp', *c_langs]
+
+        c_lang = first(c_langs, lambda x: x in target.compilers)
         if c_lang is not None:
             cc = target.compilers[c_lang]
             args.extend(arg for c_arg in cc.get_option_std_args(target, env, subproject) for arg in ['-Xcc', c_arg])