[Parse] Improve diagnostic for deprecated protocol<...> syntax (#3631)

* Don't emit deprecated warnings for incomplete protocol<...>.
  E.g: `func fn(x: protocol<P) {}`
* Different message for single protocol compostion.
  E.g: `typealias MyError = protocol<Error>`

Author: rintaro

include/swift/AST/DiagnosticsParse.def

@@ -655,6 +655,8 @@ ERROR(disallowed_protocol_composition,PointsToFirstBadToken,
 
 WARNING(deprecated_protocol_composition,none,
         "'protocol<...>' composition syntax is deprecated; join the protocols using '&'", ())
+WARNING(deprecated_protocol_composition_single,none,
+        "'protocol<...>' composition syntax is deprecated and not needed here", ())
 WARNING(deprecated_any_composition,none,
         "'protocol<>' syntax is deprecated; use 'Any' instead", ())
 

lib/Parse/ParseType.cpp

@@ -458,17 +458,23 @@ ParserResult<TypeRepr> Parser::parseTypeIdentifierOrTypeComposition() {
       RAngleLoc = skipUntilGreaterInTypeList(/*protocolComposition=*/true);
     }
 
-    // Replace 'protocol<T1, T2>' with 'T1 & T2'
-    auto Diag = diagnose(ProtocolLoc, diag::deprecated_protocol_composition);
     auto composition = ProtocolCompositionTypeRepr::create(
       Context, Protocols, ProtocolLoc, {LAngleLoc, RAngleLoc});
 
-    Diag.highlight({ProtocolLoc, RAngleLoc});
-    for (auto Comma : Commas)          // remove commas and '<'
-      Diag.fixItReplace(Comma, " &");
-    Diag
-      .fixItRemove({ProtocolLoc, LAngleLoc}) // remove 'protocol<'
-      .fixItRemove(RAngleLoc); // remove '>'
+    if (Status.isSuccess()) {
+      // Only if we have complete protocol<...> construct, diagnose deprecated.
+      auto Diag = diagnose(ProtocolLoc,
+        Commas.size() > 0 ? diag::deprecated_protocol_composition
+                          : diag::deprecated_protocol_composition_single);
+      Diag.highlight({ProtocolLoc, RAngleLoc});
+
+      // Replace 'protocol<T1, T2>' with 'T1 & T2'
+      for (auto Comma : Commas)          // remove commas and '<'
+        Diag.fixItReplace(Comma, " &");
+      Diag
+        .fixItRemove({ProtocolLoc, LAngleLoc}) // remove 'protocol<'
+        .fixItRemove(RAngleLoc); // remove '>'
+    }
 
     return makeParserResult(Status, composition);
   }

test/Parse/recovery.swift

@@ -281,7 +281,7 @@ struct ErrorTypeInVarDecl7 {
 }
 
 struct ErrorTypeInVarDecl8 {
-  var v1 : protocol<FooProtocol // expected-error {{expected '>' to complete protocol composition type}} expected-note {{to match this opening '<'}} expected-warning{{'protocol<...>' composition syntax is deprecated; join the protocols using '&'}}
+  var v1 : protocol<FooProtocol // expected-error {{expected '>' to complete protocol composition type}} expected-note {{to match this opening '<'}}
   var v2 : Int
 }
 
@@ -291,25 +291,22 @@ struct ErrorTypeInVarDecl9 {
 }
 
 struct ErrorTypeInVarDecl10 {
-  var v1 : protocol<FooProtocol // expected-error {{expected '>' to complete protocol composition type}} expected-note {{to match this opening '<'}} expected-warning {{'protocol<...>' composition syntax is deprecated; join the protocols using '&'}}
+  var v1 : protocol<FooProtocol // expected-error {{expected '>' to complete protocol composition type}} expected-note {{to match this opening '<'}}
   var v2 : Int
 }
 
 struct ErrorTypeInVarDecl11 {
-  var v1 : protocol<FooProtocol, // expected-error {{expected identifier for type name}} expected-warning {{'protocol<...>' composition syntax is deprecated; join the protocols using '&'}}
+  var v1 : protocol<FooProtocol, // expected-error {{expected identifier for type name}}
   var v2 : Int
 }
 
 func ErrorTypeInPattern1(_: protocol<) { } // expected-error {{expected identifier for type name}}
-                                           // expected-warning @-1 {{'protocol<...>' composition syntax is deprecated; join the protocols using '&'}}
-func ErrorTypeInPattern2(_: protocol<F) { } // expected-warning {{'protocol<...>' composition syntax is deprecated; join the protocols using '&'}}
-                                            // expected-error@-1 {{expected '>' to complete protocol composition type}}
-                                            // expected-note@-2 {{to match this opening '<'}}
-                                            // expected-error@-3 {{use of undeclared type 'F'}}
+func ErrorTypeInPattern2(_: protocol<F) { } // expected-error {{expected '>' to complete protocol composition type}}
+                                            // expected-note@-1 {{to match this opening '<'}}
+                                            // expected-error@-2 {{use of undeclared type 'F'}}
 
 func ErrorTypeInPattern3(_: protocol<F,) { } // expected-error {{expected identifier for type name}}
                                              // expected-error@-1 {{use of undeclared type 'F'}}
-                                             // expected-warning@-2 {{'protocol<...>' composition syntax is deprecated; join the protocols using '&'}}
 
 struct ErrorTypeInVarDecl12 {
   var v1 : FooProtocol & // expected-error{{expected identifier for type name}}

test/expr/expressions.swift

@@ -230,7 +230,7 @@ func test_lambda() {
 
 func test_lambda2() {
   { () -> protocol<Int> in
-    // expected-warning @-1 {{'protocol<...>' composition syntax is deprecated; join the protocols using '&'}}
+    // expected-warning @-1 {{'protocol<...>' composition syntax is deprecated and not needed here}} {{11-20=}} {{23-24=}}
     // expected-error @-2 {{non-protocol type 'Int' cannot be used within a protocol composition}}
     // expected-warning @-3 {{result of call is unused}}
     return 1

test/type/protocol_composition.swift

@@ -111,22 +111,21 @@ func testConversion() {
   accept_manyPrintable(sp)
 
   // Conversions among existential types.
-  var x2 : protocol<SuperREPLPrintable, FooProtocol> // expected-warning {{'protocol<...>' composition syntax is deprecated; join the protocols using '&'}}
+  var x2 : protocol<SuperREPLPrintable, FooProtocol> // expected-warning {{'protocol<...>' composition syntax is deprecated; join the protocols using '&'}} {{12-21=}} {{39-40= &}} {{52-53=}}
   x2 = x // expected-error{{value of type 'FooProtocol & REPLPrintable' does not conform to 'FooProtocol & SuperREPLPrintable' in assignment}}
   x = x2
 
   // Subtyping
   var _ : () -> FooProtocol & SuperREPLPrintable = return_superPrintable
 
   // FIXME: closures make ABI conversions explicit. rdar://problem/19517003
-  var _ : () -> protocol<FooProtocol, REPLPrintable> = { return_superPrintable() } // expected-warning {{'protocol<...>' composition syntax is deprecated; join the protocols using '&'}}
+  var _ : () -> protocol<FooProtocol, REPLPrintable> = { return_superPrintable() } // expected-warning {{'protocol<...>' composition syntax is deprecated; join the protocols using '&'}} {{17-26=}} {{37-38= &}} {{52-53=}}
 }
 
 // Test the parser's splitting of >= into > and =.
-var x : protocol<P5>= 17 // expected-warning {{'protocol<...>' composition syntax is deprecated; join the protocols using '&'}}
+var x : protocol<P5>= 17 // expected-warning {{'protocol<...>' composition syntax is deprecated and not needed here}} {{9-18=}} {{20-22=}}
 
 typealias A = protocol<> // expected-warning {{'protocol<>' syntax is deprecated; use 'Any' instead}} {{15-25=Any}}
 typealias B = protocol<P1, P2> // expected-warning {{'protocol<...>' composition syntax is deprecated; join the protocols using '&'}} {{15-24=}} {{26-27= &}} {{30-31=}}
 
-
-
+typealias C = protocol<P1> // expected-warning {{'protocol<...>' composition syntax is deprecated and not needed here}} {{15-24=}} {{26-27=}}