[libSyntax] Omit unknown nodes if they do not have any children

Author: ahoppen

include/swift/Syntax/SyntaxKind.h.gyb

@@ -71,11 +71,11 @@ bool isTokenKind(SyntaxKind Kind);
 
 bool isUnknownKind(SyntaxKind Kind);
 
-bool shallBeOmittedWhenNoChildren(SyntaxKind Kind);
-
 SyntaxKind getUnknownKind(SyntaxKind Kind);
 } // end namespace syntax
 
+bool parserShallOmitWhenNoChildren(syntax::SyntaxKind Kind);
+
 namespace json {
 
 /// Serialization traits for SyntaxKind.

lib/Parse/SyntaxParsingContext.cpp

@@ -113,6 +113,9 @@ RC<RawSyntax> SyntaxParsingContext::bridgeAs(SyntaxContextKind Kind,
       break;
     }
     return RawNode;
+  } else if (Parts.empty()) {
+    // Just omit the unknown node if it does not have any children
+    return nullptr;
   } else {
     SyntaxKind UnknownKind;
     switch (Kind) {
@@ -171,7 +174,7 @@ void SyntaxParsingContext::addSyntax(Syntax Node) {
 
 void SyntaxParsingContext::createNodeInPlace(SyntaxKind Kind, size_t N) {
   if (N == 0) {
-    if (!shallBeOmittedWhenNoChildren(Kind))
+    if (!parserShallOmitWhenNoChildren(Kind))
       Storage.push_back(createSyntaxAs(Kind, {}));
     return;
   }
@@ -387,7 +390,9 @@ SyntaxParsingContext::~SyntaxParsingContext() {
   case AccumulationMode::CoerceKind: {
     assert(!isRoot());
     if (Storage.size() == Offset) {
-      Storage.push_back(bridgeAs(CtxtKind, {}));
+      if (auto BridgedNode = bridgeAs(CtxtKind, {})) {
+        Storage.push_back(BridgedNode);
+      }
     } else {
       auto I = Storage.begin() + Offset;
       *I = bridgeAs(CtxtKind, getParts());

lib/Syntax/SyntaxKind.cpp.gyb

@@ -44,6 +44,19 @@ StringRef getTokenText(tok kind) {
   return text;
 }
 
+bool parserShallOmitWhenNoChildren(syntax::SyntaxKind Kind) {
+  switch(Kind) {
+%   for node in SYNTAX_NODES:
+%     if node.shall_be_omitted_when_empty():
+  case syntax::SyntaxKind::${node.syntax_kind}:
+%     end
+%   end
+    return true;
+  default:
+    return false;
+  }
+}
+
 namespace syntax {
 
 void dumpSyntaxKind(llvm::raw_ostream &os, const SyntaxKind kind) {
@@ -109,19 +122,6 @@ bool isUnknownKind(SyntaxKind Kind) {
          Kind == SyntaxKind::UnknownPattern;
 }
 
-bool shallBeOmittedWhenNoChildren(SyntaxKind Kind) {
-  switch(Kind) {
-%   for node in SYNTAX_NODES:
-%     if node.shall_be_omitted_when_empty():
-  case SyntaxKind::${node.syntax_kind}:
-%     end
-%   end
-    return true;
-  default:
-    return false;
-  }
-}
-
 SyntaxKind getUnknownKind(SyntaxKind Kind) {
   if (isExprKind(Kind))
     return SyntaxKind::UnknownExpr;