fix <rdar://21712891> Swift Compiler bug: String subscripts with range should require closing bracket.

This is a parser bug causing us to accept invalid code.

Author: lattner

lib/Parse/Parser.cpp

@@ -615,7 +615,7 @@ Parser::parseList(tok RightK, SourceLoc LeftLoc, SourceLoc &RightLoc,
     // If the lexer stopped with an EOF token whose spelling is ")", then this
     // is actually the tuple that is a string literal interpolation context.
     // Just accept the ")" and build the tuple as we usually do.
-    if (Tok.is(tok::eof) && Tok.getText() == ")") {
+    if (Tok.is(tok::eof) && Tok.getText() == ")" && RightK == tok::r_paren) {
       RightLoc = Tok.getLoc();
       return Status;
     }

test/Parse/recovery.swift

@@ -710,4 +710,10 @@ infix operator · {  // expected-error {{'·' is considered to be an identifier,
   associativity none precedence 150
 }
 
+// <rdar://problem/21712891> Swift Compiler bug: String subscripts with range should require closing bracket.
+func r21712891(s : String) -> String {
+  let a = s.startIndex..<s.startIndex
+  // The specific errors produced don't actually matter, but we need to reject this.
+  return "\(s[a)"  // expected-error 3 {{}}
+}