fix <rdar://problem/23952125> QoI: Subscript in protocol with missing {}, better diagnostic please

we used to say:
error: expected '{' for subscripting

we now say:

error: subscript in protocol must have explicit { get } or { get set } specifier

and produce a fixit to insert { get set }

Author: lattner

include/swift/AST/DiagnosticsParse.def

@@ -329,7 +329,11 @@ ERROR(expected_arrow_subscript,decl_parsing,PointsToFirstBadToken,
 ERROR(expected_type_subscript,type_parsing,PointsToFirstBadToken,
       "expected subscripting element type", ())
 ERROR(expected_lbrace_subscript,decl_parsing,PointsToFirstBadToken,
-      "expected '{' for subscripting", ())
+      "expected '{' in subscript to specify getter and setter implementation",
+      ())
+ERROR(expected_lbrace_subscript_protocol,decl_parsing,PointsToFirstBadToken,
+      "subscript in protocol must have explicit { get } or "
+      "{ get set } specifier", ())
 ERROR(subscript_without_get,decl_parsing,none,
       "subscript declarations must have a getter", ())
 ERROR(subscript_static,decl_parsing,none,

lib/Parse/ParseDecl.cpp

@@ -4840,7 +4840,11 @@ ParserStatus Parser::parseDeclSubscript(ParseDeclOptions Flags,
   if (Tok.isNot(tok::l_brace))  {
     // Subscript declarations must always have at least a getter, so they need
     // to be followed by a {.
-    diagnose(Tok, diag::expected_lbrace_subscript);
+    if (Flags.contains(PD_InProtocol))
+      diagnose(Tok, diag::expected_lbrace_subscript_protocol)
+        .fixItInsertAfter(ElementTy.get()->getEndLoc(), " { get set }");
+    else
+      diagnose(Tok, diag::expected_lbrace_subscript);
     Status.setIsParseError();
   } else {
     if (parseGetSet(Flags, Indices.get(), ElementTy.get(),

test/Parse/subscripting.swift

@@ -127,7 +127,7 @@ struct A4 {
 }
 
 struct A5 {
-  subscript(i : Int) -> Int // expected-error {{expected '{' for subscripting}}
+  subscript(i : Int) -> Int // expected-error {{expected '{' in subscript to specify getter and setter implementation}}
 }
 
 struct A6 {
@@ -155,7 +155,7 @@ struct A7b {
 }
 
 struct A8 {
-  subscript(i : Int) -> Int // expected-error{{expected '{' for subscripting}}
+  subscript(i : Int) -> Int // expected-error{{expected '{' in subscript to specify getter and setter implementation}}
     get { // expected-error{{expected declaration}}
       return stored
     }

test/decl/subscript/subscripting.swift

@@ -272,3 +272,14 @@ class Foo {
     }
 }
 
+// <rdar://problem/23952125> QoI: Subscript in protocol with missing {}, better diagnostic please
+protocol r23952125 {
+  typealias ItemType
+  var count: Int { get }
+  subscript(index: Int) -> ItemType  // expected-error {{subscript in protocol must have explicit { get } or { get set } specifier}} {{36-36= { get set \}}}
+  
+  var c : Int // expected-error {{property in protocol must have explicit { get } or { get set } specifier}}
+}
+
+
+