Xcode: Fix PCH support with Swift & C++

Previously, when a mixed language target ends up with `Swift` as the
`LINKER_LANGUAGE`, the PCH file was not set for the target at all.

Fixes: #21224

4 files changed, 29 insertions, 0 deletions

diff --git a/Tests/SwiftMixPCH/CMain.c b/Tests/SwiftMixPCH/CMain.c
new file mode 100644
index 0000000..4cd78e6
--- /dev/null
+++ b/Tests/SwiftMixPCH/CMain.c
@@ -0,0 +1,9 @@
+#ifndef PCH_VALUE
+#  error "PCH_VALUE not defined"
+#endif
+
+int main(void)
+{
+  const int value = PCH_VALUE;
+  return value == 42 ? 0 : 1;
+}
diff --git a/Tests/SwiftMixPCH/CMakeLists.txt b/Tests/SwiftMixPCH/CMakeLists.txt
new file mode 100644
index 0000000..d5704f1
--- /dev/null
+++ b/Tests/SwiftMixPCH/CMakeLists.txt
@@ -0,0 +1,15 @@
+cmake_minimum_required(VERSION 3.15)
+if(POLICY CMP0157)
+  cmake_policy(SET CMP0157 NEW)
+endif()
+
+project(SwiftMixPCH C Swift)
+
+# Swift on Windows only provides a release runtime.
+set(CMAKE_MSVC_RUNTIME_LIBRARY MultiThreadedDLL)
+
+add_executable(SwiftMixPCH CMain.c SwiftFunc.swift)
+target_precompile_headers(SwiftMixPCH PRIVATE pch.h)
+
+# We don't want swift to emit main()
+target_compile_options(SwiftMixPCH PRIVATE "$<$<COMPILE_LANGUAGE:Swift>:-parse-as-library>")
diff --git a/Tests/SwiftMixPCH/SwiftFunc.swift b/Tests/SwiftMixPCH/SwiftFunc.swift
new file mode 100644
index 0000000..d49c36f
--- /dev/null
+++ b/Tests/SwiftMixPCH/SwiftFunc.swift
@@ -0,0 +1,4 @@
+
+func SwiftFunc() -> Int32 {
+    return 0;
+}
diff --git a/Tests/SwiftMixPCH/pch.h b/Tests/SwiftMixPCH/pch.h
new file mode 100644
index 0000000..6de0669
--- /dev/null
+++ b/Tests/SwiftMixPCH/pch.h
@@ -0,0 +1 @@
+#define PCH_VALUE 42