Syntax: synthesize right brace tokens if they are missing from nominal type decls.

Author: nkcsgexi

lib/Parse/ParseDecl.cpp

@@ -3507,7 +3507,10 @@ bool Parser::parseDeclList(SourceLoc LBLoc, SourceLoc &RBLoc,
       }
     }
   }
-  parseMatchingToken(tok::r_brace, RBLoc, ErrorDiag, LBLoc);
+  if (parseMatchingToken(tok::r_brace, RBLoc, ErrorDiag, LBLoc)) {
+    // Synthesize an r_brace syntax node if the token is absent
+    SyntaxContext->synthesize(tok::r_brace, RBLoc);
+  }
 
   // Increase counter.
   if (auto *stat = Context.Stats) {

test/Syntax/Outputs/round_trip_invalid.swift.withkinds

@@ -13,4 +13,10 @@ let <PatternBinding><IdentifierPattern>strings</IdentifierPattern><TypeAnnotatio
 
 // Function body without closing brace token.
 func foo<FunctionSignature><ParameterClause>() </ParameterClause></FunctionSignature><CodeBlock>{<VariableDecl>
-  var <PatternBinding><IdentifierPattern>a </IdentifierPattern><InitializerClause>= <IntegerLiteralExpr>2</IntegerLiteralExpr></InitializerClause></PatternBinding></VariableDecl></CodeBlock></FunctionDecl>
+  var <PatternBinding><IdentifierPattern>a </IdentifierPattern><InitializerClause>= <IntegerLiteralExpr>2</IntegerLiteralExpr></InitializerClause></PatternBinding></VariableDecl><ClassDecl>
+
+class C <MemberDeclBlock>{<MemberDeclListItem><StructDecl>
+struct S <MemberDeclBlock>{<MemberDeclListItem><EnumDecl>
+enum E <MemberDeclBlock>{<MemberDeclListItem><ProtocolDecl>
+protocol P <MemberDeclBlock>{<MemberDeclListItem><ExtensionDecl>
+extension <SimpleTypeIdentifier>P </SimpleTypeIdentifier><MemberDeclBlock>{</MemberDeclBlock></ExtensionDecl></MemberDeclListItem></MemberDeclBlock></ProtocolDecl></MemberDeclListItem></MemberDeclBlock></EnumDecl></MemberDeclListItem></MemberDeclBlock></StructDecl></MemberDeclListItem></MemberDeclBlock></ClassDecl></CodeBlock></FunctionDecl>

test/Syntax/round_trip_invalid.swift

@@ -14,3 +14,9 @@ let strings: [Strin[g]?
 // Function body without closing brace token.
 func foo() {
   var a = 2
+
+class C {
+struct S {
+enum E {
+protocol P {
+extension P {

utils/gyb_syntax_support/DeclNodes.py

@@ -282,7 +282,7 @@
          element='MemberDeclListItem'),
 
     # member-decl = decl ';'?
-    Node('MemberDeclListItem', kind='Syntax',
+    Node('MemberDeclListItem', kind='Syntax', omit_when_empty=True,
          description='''
          A member declaration of a type consisting of a declaration and an \
          optional semicolon;