Swift: disallow WIN32_EXECUTABLE properties

Currently, the compiler does not synthesize the correct entry point for
the application and passing the subsystem flag does not work the same
way with the Swift linker language.  Add a check to prevent the
application of `WIN32_EXECUTABLE` to Swift executables until they can be
properly supported.  This will prevent the need for a future policy
change.

Closes: #19325

5 files changed, 12 insertions, 1 deletions

diff --git a/Tests/RunCMake/Swift/E.swift b/Tests/RunCMake/Swift/E.swift
new file mode 100644
index 0000000..a415467
--- /dev/null
+++ b/Tests/RunCMake/Swift/E.swift
@@ -0,0 +1,2 @@
+func f() {
+}
diff --git a/Tests/RunCMake/Swift/RunCMakeTest.cmake b/Tests/RunCMake/Swift/RunCMakeTest.cmake
index de99042..4817045 100644
--- a/Tests/RunCMake/Swift/RunCMakeTest.cmake
+++ b/Tests/RunCMake/Swift/RunCMakeTest.cmake
@@ -6,7 +6,7 @@ if(RunCMake_GENERATOR STREQUAL Xcode)
   endif()
 elseif(RunCMake_GENERATOR STREQUAL Ninja)
   if(CMAKE_Swift_COMPILER)
-    # Add Ninja-specific Swift tests here.
+    run_cmake(Win32ExecutableDisallowed)
   endif()
 else()
   run_cmake(NotSupported)
diff --git a/Tests/RunCMake/Swift/Win32ExecutableDisallowed-result.txt b/Tests/RunCMake/Swift/Win32ExecutableDisallowed-result.txt
new file mode 100644
index 0000000..d00491f
--- /dev/null
+++ b/Tests/RunCMake/Swift/Win32ExecutableDisallowed-result.txt
@@ -0,0 +1 @@
+1
diff --git a/Tests/RunCMake/Swift/Win32ExecutableDisallowed-stderr.txt b/Tests/RunCMake/Swift/Win32ExecutableDisallowed-stderr.txt
new file mode 100644
index 0000000..d78101a
--- /dev/null
+++ b/Tests/RunCMake/Swift/Win32ExecutableDisallowed-stderr.txt
@@ -0,0 +1,4 @@
+^CMake Error at Win32ExecutableDisallowed.cmake:[0-9]+ \(add_executable\):
+  WIN32_EXECUTABLE property is not supported on Swift executables
+Call Stack \(most recent call first\):
+  CMakeLists.txt:[0-9]+ \(include\)
diff --git a/Tests/RunCMake/Swift/Win32ExecutableDisallowed.cmake b/Tests/RunCMake/Swift/Win32ExecutableDisallowed.cmake
new file mode 100644
index 0000000..02d5447
--- /dev/null
+++ b/Tests/RunCMake/Swift/Win32ExecutableDisallowed.cmake
@@ -0,0 +1,4 @@
+enable_language(Swift)
+add_executable(E E.swift)
+set_target_properties(E PROPERTIES
+  WIN32_EXECUTABLE TRUE)