Xcode: Add option to set Swift language version

Create a new CMAKE_Swift_LANGUAGE_VERSION variable to specify the
SWIFT_VERSION attribute in a generated Xcode project.  Ideally this
would be a `<LANG>_STANDARD` property but since Swift support is
very minimal we should reserve that property for more complete
treatment later.

Issue: #16326

1 files changed, 7 insertions, 1 deletions

diff --git a/Source/cmGlobalXCodeGenerator.cxx b/Source/cmGlobalXCodeGenerator.cxx
index 42d97db..0d5de06 100644
--- a/Source/cmGlobalXCodeGenerator.cxx
+++ b/Source/cmGlobalXCodeGenerator.cxx
@@ -2997,7 +2997,13 @@ bool cmGlobalXCodeGenerator::CreateXCodeObjects(
                                 this->CreateString(this->GeneratorToolset));
   }
   if (this->GetLanguageEnabled("Swift")) {
-    buildSettings->AddAttribute("SWIFT_VERSION", this->CreateString("2.3"));
+    std::string swiftVersion = "2.3";
+    if (const char* vers = this->CurrentMakefile->GetDefinition(
+          "CMAKE_Swift_LANGUAGE_VERSION")) {
+      swiftVersion = vers;
+    }
+    buildSettings->AddAttribute("SWIFT_VERSION",
+                                this->CreateString(swiftVersion));
   }
 
   std::string symroot = root->GetCurrentBinaryDirectory();