[libSyntax] Change OpaqueSyntaxNode to be a const void *

The data of an OpaqueSyntaxNode should never be modified. Also, this
allows us to get rid of two const_casts.

Author: ahoppen

include/swift/Parse/ParsedRawSyntaxNode.h

@@ -22,7 +22,7 @@
 
 namespace swift {
 
-typedef void *OpaqueSyntaxNode;
+typedef const void *OpaqueSyntaxNode;
 class SyntaxParsingContext;
 
 /// Represents a raw syntax node formed by the parser.

include/swift/Parse/SyntaxParseActions.h

@@ -33,7 +33,7 @@ class SourceFileSyntax;
 enum class SyntaxKind;
 }
 
-typedef void *OpaqueSyntaxNode;
+typedef const void *OpaqueSyntaxNode;
 
 class SyntaxParseActions {
   virtual void _anchor();

include/swift/Subsystems.h

@@ -53,7 +53,7 @@ namespace swift {
   class IRGenOptions;
   class LangOptions;
   class ModuleDecl;
-  typedef void *OpaqueSyntaxNode;
+  typedef const void *OpaqueSyntaxNode;
   class Parser;
   class SerializationOptions;
   class SILOptions;

lib/SyntaxParse/SyntaxTreeCreator.cpp

@@ -130,13 +130,13 @@ OpaqueSyntaxNode SyntaxTreeCreator::recordToken(tok tokenKind,
   auto raw =
       TokenCache->getToken(Arena, tokenKind, range.getByteLength(), tokenText,
                            leadingTriviaText, trailingTriviaText);
-  return static_cast<OpaqueSyntaxNode>(const_cast<RawSyntax *>(raw));
+  return static_cast<OpaqueSyntaxNode>(raw);
 }
 
 OpaqueSyntaxNode
 SyntaxTreeCreator::recordMissingToken(tok kind, SourceLoc loc) {
   auto raw = RawSyntax::missing(kind, getTokenText(kind), Arena);
-  return static_cast<OpaqueSyntaxNode>(const_cast<RawSyntax *>(raw));
+  return static_cast<OpaqueSyntaxNode>(raw);
 }
 
 OpaqueSyntaxNode
@@ -151,7 +151,7 @@ SyntaxTreeCreator::recordRawSyntax(syntax::SyntaxKind kind,
   size_t TextLength = range.isValid() ? range.getByteLength() : 0;
   auto raw =
       RawSyntax::make(kind, parts, TextLength, SourcePresence::Present, Arena);
-  return static_cast<OpaqueSyntaxNode>(const_cast<RawSyntax *>(raw));
+  return static_cast<OpaqueSyntaxNode>(raw);
 }
 
 std::pair<size_t, OpaqueSyntaxNode>
@@ -163,7 +163,7 @@ SyntaxTreeCreator::lookupNode(size_t lexerOffset, syntax::SyntaxKind kind) {
     return {0, nullptr};
   const RawSyntax *raw = cacheLookup->getRaw();
   size_t length = raw->getTextLength();
-  return {length, static_cast<OpaqueSyntaxNode>(const_cast<RawSyntax *>(raw))};
+  return {length, static_cast<OpaqueSyntaxNode>(raw)};
 }
 
 void SyntaxTreeCreator::discardRecordedNode(OpaqueSyntaxNode opaqueN) {

tools/libSwiftSyntaxParser/libSwiftSyntaxParser.cpp

@@ -183,7 +183,8 @@ class CLibParseActions : public SyntaxParseActions {
     auto numValue = serialization::getNumericValue(kind);
     node.kind = numValue;
     assert(node.kind == numValue && "syntax kind value is too large");
-    node.layout_data.nodes = elements.data();
+    node.layout_data.nodes =
+        const_cast<const swiftparse_client_node_t *>(elements.data());
     node.layout_data.nodes_count = elements.size();
     makeCRange(node.range, range);
     node.present = true;
@@ -302,7 +303,7 @@ swiftparse_client_node_t SynParser::parse(const char *source) {
     pConsumer = std::make_unique<SynParserDiagConsumer>(*this, bufID);
     PU.getDiagnosticEngine().addConsumer(*pConsumer);
   }
-  return PU.parse();
+  return const_cast<swiftparse_client_node_t>(PU.parse());
 }
 }
 //===--- C API ------------------------------------------------------------===//