[SyntaxParse] Don't record tokens while skipping

Author: rintaro

include/swift/Parse/SyntaxParsingContext.h

@@ -355,7 +355,9 @@ class alignas(1 << SyntaxAlignInBits) SyntaxParsingContext {
 
   void setShouldDefer(bool Value = true) { ShouldDefer = Value; }
 
-  bool shouldDefer() const { return ShouldDefer || IsBacktracking; }
+  bool shouldDefer() const {
+    return ShouldDefer || IsBacktracking || Mode == AccumulationMode::Discard;
+  }
 
   /// Explicitly finalizing syntax tree creation.
   /// This function will be called during the destroying of a root syntax

lib/Parse/ParseDecl.cpp

@@ -2706,6 +2706,8 @@ bool Parser::isStartOfDecl() {
 void Parser::consumeDecl(ParserPosition BeginParserPosition,
                          ParseDeclOptions Flags,
                          bool IsTopLevel) {
+  SyntaxParsingContext Discarding(SyntaxContext);
+  Discarding.setDiscard();
   SourceLoc CurrentLoc = Tok.getLoc();
 
   SourceLoc EndLoc = PreviousLoc;

lib/Parse/ParseStmt.cpp

@@ -249,6 +249,8 @@ bool Parser::isTerminatorForBraceItemListKind(BraceItemListKind Kind,
 
 void Parser::consumeTopLevelDecl(ParserPosition BeginParserPosition,
                                  TopLevelCodeDecl *TLCD) {
+  SyntaxParsingContext Discarding(SyntaxContext);
+  Discarding.setDiscard();
   SourceLoc EndLoc = PreviousLoc;
   backtrackToPosition(BeginParserPosition);
   SourceLoc BeginLoc = Tok.getLoc();