Merge pull request #5217 from milseman/3_0_escaping

[3.0 compat] Don't diagnose @escaping var-arg closures.

Author: ematejska

lib/Sema/TypeCheckType.cpp

@@ -2002,8 +2002,16 @@ Type TypeResolver::resolveAttributedType(TypeAttributes &attrs,
   // Handle @escaping
   if (hasFunctionAttr && ty->is<FunctionType>()) {
     if (attrs.has(TAK_escaping)) {
+      // For compatibility with 3.0, we don't emit an error if it appears on a
+      // variadic argument list.
+      //
+      // FIXME: Version-gate on Swift language version 3, as we don't want its
+      // presence to confuse users.
+      bool skipDiagnostic = isVariadicFunctionParam;
+
       // The attribute is meaningless except on parameter types.
-      if (!isFunctionParam) {
+      bool shouldDiagnose = !isFunctionParam && !skipDiagnostic;
+      if (shouldDiagnose) {
         auto &SM = TC.Context.SourceMgr;
         auto loc = attrs.getLoc(TAK_escaping);
         auto attrRange = SourceRange(

test/attr/attr_escaping.swift

@@ -139,6 +139,11 @@ func takesVarargsOfFunctions(fns: () -> ()...) {
   }
 }
 
+// This is allowed, in order to keep source compat with Swift version 3.0.
+//
+// FIXME: version-gate on Swift version 3
+func takesVarargsOfFunctionsExplicitEscaping(fns: @escaping () -> ()...) {}
+
 func takesNoEscapeFunction(fn: () -> ()) { // expected-note {{parameter 'fn' is implicitly non-escaping}}
   takesVarargsOfFunctions(fns: fn) // expected-error {{passing non-escaping parameter 'fn' to function expecting an @escaping closure}}
 }