[Parser] Correct a fixit to preserve the trailing content after replacing Protocol<A, B>. rdar://27992964

When migrating, we found our fixit to replace the old protocol composition syntax, namely "Protocol<A, B>",
to the new syntax, "A & B", does not preserve the trailing content after '>'. For instance, we replace "Protocol<A, B>?"
with "A & B". This patch fixes the issue by inserting whatever after '>' in the old syntax to the new
replacement string. I consider this as a hack; the root-cause fix should be in the lexer to smartly separate
'>' and '?' as two tokens instead of one.

Author: nkcsgexi

lib/Parse/ParseType.cpp

@@ -450,7 +450,7 @@ ParserResult<TypeRepr> Parser::parseTypeIdentifierOrTypeComposition() {
       // Skip until we hit the '>'.
       RAngleLoc = skipUntilGreaterInTypeList(/*protocolComposition=*/true);
     }
-    
+
     auto composition = ProtocolCompositionTypeRepr::create(
       Context, Protocols, ProtocolLoc, {LAngleLoc, RAngleLoc});
 
@@ -470,6 +470,16 @@ ParserResult<TypeRepr> Parser::parseTypeIdentifierOrTypeComposition() {
         replacement += extractText(*Begin);
       }
 
+      // Copy trailing content after '>' to the replacement string.
+      // FIXME: lexer should smartly separate '>' and trailing contents like '?'.
+      StringRef TrailingContent = L->getTokenAt(RAngleLoc).getRange().str().
+        substr(1);
+      if (!TrailingContent.empty()) {
+        replacement.insert(replacement.begin(), '(');
+        replacement += ")";
+        replacement += TrailingContent;
+      }
+
       // Replace 'protocol<T1, T2>' with 'T1 & T2'
       diagnose(ProtocolLoc,
         Protocols.size() > 1 ? diag::deprecated_protocol_composition

test/FixCode/fixits-apply.swift

@@ -270,3 +270,8 @@ func testBoolValue(a : BoolFoo) {
   guard a {}
   if a as BoolFoo {}
 }
+
+protocol P1 {}
+protocol P2 {}
+var a : protocol<P1, P2>?
+var a2 : protocol<P1>= 17

test/FixCode/fixits-apply.swift.result

@@ -273,3 +273,8 @@ func testBoolValue(a : BoolFoo) {
   guard a.boolValue {}
   if (a as BoolFoo).boolValue {}
 }
+
+protocol P1 {}
+protocol P2 {}
+var a : (P1 & P2)?
+var a2 : (P1)= 17 as! P1

test/type/protocol_composition.swift

@@ -48,7 +48,7 @@ func testEquality() {
   let x4 : (_ : P2) -> ()
   x3 = x4
   _ = x3
-  
+
   // Empty protocol-conformance types are empty.
   let x5 : (_ : Any) -> ()
   let x6 : (_ : Any2) -> ()
@@ -123,7 +123,7 @@ func testConversion() {
 }
 
 // Test the parser's splitting of >= into > and =.
-var x : protocol<P5>= 17 // expected-warning {{'protocol<...>' composition syntax is deprecated and not needed here}} {{9-22=P5}}
+var x : protocol<P5>= 17 // expected-warning {{'protocol<...>' composition syntax is deprecated and not needed here}} {{9-22=(P5)=}}
 
 typealias A = protocol<> // expected-warning {{'protocol<>' syntax is deprecated; use 'Any' instead}} {{15-25=Any}}
 typealias B1 = protocol<P1,P2> // expected-warning {{'protocol<...>' composition syntax is deprecated; join the protocols using '&'}} {{16-31=P1 & P2}}