[Parse] Remove 'ParserDiagnostics' experimental feature

Now that we have ParserASTGen mode which includes the swift-syntax
parser diagnostics.

Author: rintaro

include/swift/AST/ASTBridging.h

@@ -1375,6 +1375,12 @@ BridgedPackExpansionExpr_createParsed(BridgedASTContext cContext,
                                       BridgedSourceLoc cRepeatLoc,
                                       BridgedExpr cPatternExpr);
 
+SWIFT_NAME("BridgedParenExpr.createParsed(_:leftParenLoc:expr:rightParenLoc:)")
+BridgedParenExpr BridgedParenExpr_createParsed(BridgedASTContext cContext,
+                                               BridgedSourceLoc cLParen,
+                                               BridgedExpr cExpr,
+                                               BridgedSourceLoc cRParen);
+
 SWIFT_NAME("BridgedPostfixUnaryExpr.createParsed(_:operator:operand:)")
 BridgedPostfixUnaryExpr
 BridgedPostfixUnaryExpr_createParsed(BridgedASTContext cContext,

include/swift/Basic/Features.def

@@ -300,11 +300,6 @@ EXPERIMENTAL_FEATURE(ParserRoundTrip, false)
 /// Swift parser.
 EXPERIMENTAL_FEATURE(ParserValidation, false)
 
-/// Whether to emit diagnostics from the new parser first, and only emit
-/// diagnostics from the existing parser when there are none from the new
-/// parser.
-EXPERIMENTAL_FEATURE(ParserDiagnostics, false)
-
 /// Enables implicit some while also enabling existential `any`
 EXPERIMENTAL_FEATURE(ImplicitSome, false)
 

lib/AST/Bridging/ExprBridging.cpp

@@ -383,6 +383,14 @@ BridgedRegexLiteralExpr_createParsed(BridgedASTContext cContext,
                                         cRegexText.unbridged());
 }
 
+BridgedParenExpr BridgedParenExpr_createParsed(BridgedASTContext cContext,
+                                               BridgedSourceLoc cLParen,
+                                               BridgedExpr cExpr,
+                                               BridgedSourceLoc cRParen) {
+  ASTContext &context = cContext.unbridged();
+  return new (context)
+      ParenExpr(cLParen.unbridged(), cExpr.unbridged(), cRParen.unbridged());
+}
 BridgedSequenceExpr BridgedSequenceExpr_createParsed(BridgedASTContext cContext,
                                                      BridgedArrayRef exprs) {
   return SequenceExpr::create(cContext.unbridged(), exprs.unbridged<Expr *>());

lib/ASTGen/Sources/ASTGen/Exprs.swift

@@ -172,7 +172,7 @@ extension ASTGenVisitor {
     case .tryExpr(let node):
       return self.generate(tryExpr: node)
     case .tupleExpr(let node):
-      return self.generate(tupleExpr: node).asExpr
+      return self.generate(tupleExpr: node)
     case .typeExpr(let node):
       return self.generate(typeExpr: node).asExpr
     case .unresolvedAsExpr:
@@ -890,7 +890,19 @@ extension ASTGenVisitor {
     }
   }
 
-  func generate(tupleExpr node: TupleExprSyntax) -> BridgedTupleExpr {
+  func generate(tupleExpr node: TupleExprSyntax) -> BridgedExpr {
+    if node.elements.count == 1,
+       let first = node.elements.first,
+       first.label == nil,
+       !first.expression.is(PackExpansionExprSyntax.self) {
+      return BridgedParenExpr.createParsed(
+        self.ctx,
+        leftParenLoc: self.generateSourceLoc(node.leftParen),
+        expr: self.generate(expr: node.elements.first!.expression),
+        rightParenLoc: self.generateSourceLoc(node.rightParen)
+      ).asExpr
+    }
+
     let expressions = node.elements.lazy.map {
       self.generate(expr: $0.expression)
     }
@@ -912,7 +924,7 @@ extension ASTGenVisitor {
       labels: labels.bridgedArray(in: self),
       labelLocs: labelLocations.bridgedArray(in: self),
       rightParenLoc: self.generateSourceLoc(node.rightParen)
-    )
+    ).asExpr
   }
 
   func generate(typeExpr node: TypeExprSyntax) -> BridgedTypeExpr {

test/ASTGen/diagnostics.swift

@@ -28,3 +28,7 @@ func testEditorPlaceholder() -> Int {
   foo(<#T##x: String##String#>) // expected-error {{editor placeholder in source file}})
   return <#T##Int#> // expected-error {{editor placeholder in source file}}
 }
+
+_ = [(Int) -> async throws Int]()
+// expected-error@-1{{'async throws' must precede '->'}}
+// expected-note@-2{{move 'async throws' in front of '->'}}{{15-21=}} {{21-28=}} {{20-21= }} {{12-12=async }} {{12-12=throws }}