Merge pull request #708 from slavapestov/unavailable-enum-case-warning-5.5

Pass -warn-on-potentially-unavailable-enum-case frontend flag when building a module [5.5]

Author: slavapestov

Sources/SwiftDriver/Driver/Driver.swift

@@ -329,6 +329,20 @@ public struct Driver {
       .appending(component: "Frameworks")
   } ()
 
+  public func isFrontendArgSupported(_ opt: Option) -> Bool {
+    var current = opt.spelling
+    while(true) {
+      if supportedFrontendFlags.contains(current) {
+        return true
+      }
+      if current.starts(with: "-") {
+        current = String(current.dropFirst())
+      } else {
+        return false
+      }
+    }
+  }
+
   /// Handler for emitting diagnostics to stderr.
   public static let stderrDiagnosticsHandler: DiagnosticsEngine.DiagnosticsHandler = { diagnostic in
     stdErrQueue.sync {

Sources/SwiftDriver/Jobs/FrontendJobHelpers.swift

@@ -85,6 +85,15 @@ extension Driver {
       commandLine.appendFlag("-aarch64-use-tbi")
     }
 
+    // Potentially unavailable enum cases are downgraded to a warning when building a
+    // swiftmodule, to allow building a module (or module interface) for an older
+    // deployment target than the framework itself.
+    if isFrontendArgSupported(.warnOnPotentiallyUnavailableEnumCase) {
+      if compilerOutputType == .swiftModule {
+        commandLine.appendFlag(.warnOnPotentiallyUnavailableEnumCase)
+      }
+    }
+
     // Enable or disable ObjC interop appropriately for the platform
     if targetTriple.isDarwin {
       commandLine.appendFlag(.enableObjcInterop)

Sources/SwiftOptions/Options.swift

@@ -510,6 +510,7 @@ extension Option {
   public static let warnLongExpressionTypeChecking: Option = Option("-warn-long-expression-type-checking", .separate, attributes: [.helpHidden, .frontend, .noDriver], metaVar: "<n>", helpText: "Warns when type-checking a function takes longer than <n> ms")
   public static let warnLongFunctionBodiesEQ: Option = Option("-warn-long-function-bodies=", .joined, alias: Option.warnLongFunctionBodies, attributes: [.helpHidden, .frontend, .noDriver])
   public static let warnLongFunctionBodies: Option = Option("-warn-long-function-bodies", .separate, attributes: [.helpHidden, .frontend, .noDriver], metaVar: "<n>", helpText: "Warns when type-checking a function takes longer than <n> ms")
+  public static let warnOnPotentiallyUnavailableEnumCase: Option = Option("-warn-on-potentially-unavailable-enum-case", .flag, attributes: [.helpHidden, .frontend, .noDriver], helpText: "Downgrade potential unavailability of enum case to a warning")
   public static let warnSwift3ObjcInferenceComplete: Option = Option("-warn-swift3-objc-inference-complete", .flag, attributes: [.frontend, .doesNotAffectIncrementalBuild], helpText: "Warn about deprecated @objc inference in Swift 3 for every declaration that will no longer be inferred as @objc in Swift 4")
   public static let warnSwift3ObjcInferenceMinimal: Option = Option("-warn-swift3-objc-inference-minimal", .flag, attributes: [.frontend, .doesNotAffectIncrementalBuild], helpText: "Warn about deprecated @objc inference in Swift 3 based on direct uses of the Objective-C entrypoint")
   public static let warnSwift3ObjcInference: Option = Option("-warn-swift3-objc-inference", .flag, alias: Option.warnSwift3ObjcInferenceComplete, attributes: [.helpHidden, .frontend, .doesNotAffectIncrementalBuild])