Build in Swift 6 mode using CMake

The CMake build should only be run when building an entire toolchain, which means that we are guaranteed to have a Swift 6 compiler at hand and can unconditionally enable Swift 6 mode.

Author: ahoppen

Sources/CMakeLists.txt

@@ -1,4 +1,6 @@
 add_compile_options("$<$<COMPILE_LANGUAGE:Swift>:SHELL:-package-name SourceKitLSP>")
+add_compile_options("$<$<COMPILE_LANGUAGE:Swift>:SHELL:-DRESILIENT_LIBRARIES>")
+add_compile_options("$<$<COMPILE_LANGUAGE:Swift>:SHELL:-swift-version 6>")
 add_subdirectory(BuildServerProtocol)
 add_subdirectory(BuildSystemIntegration)
 add_subdirectory(CAtomics)

Sources/SourceKitLSP/Swift/CodeActions/ConvertIntegerLiteral.swift

@@ -51,6 +51,10 @@ struct ConvertIntegerLiteral: SyntaxCodeActionProvider {
         prefix = "0x"
       case .decimal:
         prefix = ""
+      #if RESILIENT_LIBRARIES
+      @unknown default:
+        fatalError("Unknown case")
+      #endif
       }
 
       let convertedValue: ExprSyntax =

Sources/SourceKitLSP/Swift/Diagnostic.swift

@@ -423,6 +423,10 @@ fileprivate extension SwiftDiagnostics.DiagnosticSeverity {
     case .warning: return .warning
     case .note: return .information
     case .remark: return .hint
+    #if RESILIENT_LIBRARIES
+    @unknown default:
+      fatalError("Unknown case")
+    #endif
     }
   }
 }