[Parse] Upgrade operator_static_in_protocol to Swift 4 error.

Part of rdar://problem/28961650 .

Author: huonw

include/swift/AST/DiagnosticsParse.def

@@ -320,9 +320,12 @@ ERROR(static_func_decl_global_scope,none,
       (StaticSpellingKind))
 ERROR(func_decl_expected_arrow,none,
       "expected '->' after function parameter tuple", ())
-WARNING(operator_static_in_protocol,none,
+WARNING(swift3_operator_static_in_protocol,none,
         "operator '%0' declared in protocol must be 'static'",
         (StringRef))
+ERROR(operator_static_in_protocol,none,
+      "operator '%0' declared in protocol must be 'static'",
+      (StringRef))
 
 // Enum
 ERROR(expected_lbrace_enum,PointsToFirstBadToken,

lib/Parse/ParseDecl.cpp

@@ -4719,11 +4719,15 @@ Parser::parseDeclFunc(SourceLoc StaticLoc, StaticSpellingKind StaticSpelling,
     // Within a protocol, recover from a missing 'static'.
     if (Flags & PD_InProtocol) {
       switch (StaticSpelling) {
-      case StaticSpellingKind::None:
-        diagnose(NameLoc, diag::operator_static_in_protocol, SimpleName.str())
-          .fixItInsert(FuncLoc, "static ");
+      case StaticSpellingKind::None: {
+        auto Message = Context.isSwiftVersion3()
+                           ? diag::swift3_operator_static_in_protocol
+                           : diag::operator_static_in_protocol;
+        diagnose(NameLoc, Message, SimpleName.str())
+            .fixItInsert(FuncLoc, "static ");
         StaticSpelling = StaticSpellingKind::KeywordStatic;
         break;
+      }
 
       case StaticSpellingKind::KeywordStatic:
         // Okay, this is correct.

test/SILOptimizer/devirt_static_witness_method.sil

@@ -6,7 +6,7 @@ import Swift
 import SwiftShims
 
 protocol CanAdd {
-  func +(lhs: Self, rhs: Self) -> Self
+  static func +(lhs: Self, rhs: Self) -> Self
 }
 
 extension Int64 : CanAdd {

test/Serialization/Inputs/has_xref.swift

@@ -10,7 +10,7 @@ public func numericArray(_ x: IntSlice) {}
 
 
 public protocol ExtraIncrementable {
-  prefix func +++(base: inout Self)
+  static prefix func +++(base: inout Self)
 }
 
 extension SpecialInt : ExtraIncrementable {}