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

Source/cmGlobalGenerator.cxx

@@ -331,6 +331,37 @@ bool cmGlobalGenerator::CheckTargetsForMissingSources() const
   return failed;
 }
 
+bool cmGlobalGenerator::CheckTargetsForType() const
+{
+  if (!this->GetLanguageEnabled("Swift")) {
+    return false;
+  }
+  bool failed = false;
+  for (cmLocalGenerator* generator : this->LocalGenerators) {
+    for (cmGeneratorTarget* target : generator->GetGeneratorTargets()) {
+      std::vector<std::string> configs;
+      target->Makefile->GetConfigurations(configs);
+      if (configs.empty()) {
+        configs.emplace_back();
+      }
+
+      for (std::string const& config : configs) {
+        if (target->GetLinkerLanguage(config) == "Swift") {
+          if (target->GetPropertyAsBool("WIN32_EXECUTABLE")) {
+            this->GetCMakeInstance()->IssueMessage(
+              MessageType::FATAL_ERROR,
+              "WIN32_EXECUTABLE property is not supported on Swift "
+              "executables",
+              target->GetBacktrace());
+            failed = true;
+          }
+        }
+      }
+    }
+  }
+  return failed;
+}
+
 bool cmGlobalGenerator::IsExportedTargetsFile(
   const std::string& filename) const
 {
@@ -1414,6 +1445,10 @@ bool cmGlobalGenerator::Compute()
     return false;
   }
 
+  if (this->CheckTargetsForType()) {
+    return false;
+  }
+
   for (cmLocalGenerator* localGen : this->LocalGenerators) {
     localGen->ComputeHomeRelativeOutputPath();
   }

Source/cmGlobalGenerator.h

@@ -609,6 +609,7 @@ private:
   virtual void ForceLinkerLanguages();
 
   bool CheckTargetsForMissingSources() const;
+  bool CheckTargetsForType() const;
 
   void CreateLocalGenerators();
 

Tests/RunCMake/Swift/E.swift

@@ -0,0 +1,2 @@
+func f() {
+}

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)

Tests/RunCMake/Swift/Win32ExecutableDisallowed-result.txt

@@ -0,0 +1 @@
+1

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]+ \(include\)

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)