Sema: Don't complain about internal type aliases referenced from @inlinable functions in Swift < 4.2

Author: slavapestov

lib/Sema/ResilienceDiagnostics.cpp

@@ -129,9 +129,12 @@ bool TypeChecker::diagnoseInlinableDeclRef(SourceLoc loc,
   DowngradeToWarning downgradeToWarning = DowngradeToWarning::No;
 
   // Swift 4.2 did not perform any checks for type aliases.
-  if (!Context.isSwiftVersionAtLeast(5) &&
-      isa<TypeAliasDecl>(D))
-    downgradeToWarning = DowngradeToWarning::Yes;
+  if (isa<TypeAliasDecl>(D)) {
+    if (!Context.isSwiftVersionAtLeast(4, 2))
+      return false;
+    if (!Context.isSwiftVersionAtLeast(5))
+      downgradeToWarning = DowngradeToWarning::Yes;
+  }
 
   auto diagID = diag::resilience_decl_unavailable;
   if (downgradeToWarning == DowngradeToWarning::Yes)

test/Compatibility/attr_inlinable_typealias_swift4.swift

@@ -0,0 +1,21 @@
+// RUN: %target-typecheck-verify-swift -swift-version 4
+
+// No diagnostics at all in Swift 4.0 mode.
+
+private typealias PrivateAlias = Int
+
+internal typealias InternalAlias = Int
+
+@usableFromInline typealias UsableFromInlineAlias = Int
+
+public typealias PublicAlias = Int
+
+@inlinable public func f() {
+  _ = PrivateAlias.self
+
+  _ = InternalAlias.self
+
+  _ = UsableFromInlineAlias.self
+
+  _ = PublicAlias.self
+}

test/Compatibility/attr_inlinable_typealias.swift renamed to test/Compatibility/attr_inlinable_typealias_swift42.swift

@@ -1,4 +1,6 @@
-// RUN: %target-typecheck-verify-swift -swift-version 4
+// RUN: %target-typecheck-verify-swift -swift-version 4.2
+
+// Only warnings in Swift 4.2 mode.
 
 private typealias PrivateAlias = Int
 // expected-note@-1 {{type alias 'PrivateAlias' is not '@usableFromInline' or public}}