Implement optional chaining

This change implements optional chaining (https://github.com/tc39/proposal-optional-chaining) by adding a new type of optional lookup with an offset to the end of a chain.
If `undefined` or `null` is encountered during an access marked as optional, we jump to that end offset.

Features:
- Full support for all kinds of optional chain
- With some codegen overhead but zero overhead during normal non-optional FieldMemberExpression resolution
- Properly retains this contexts and does not need to resolve anything twice (this has been an issue previously)
- No extra AST structures, just flags for existing ones

[ChangeLog][QtQml] Added support for optional chaining (https://github.com/tc39/proposal-optional-chaining)

Fixes: QTBUG-77926
Change-Id: I9a41cdc4ca272066c79c72b9b22206498a546843
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>

1 files changed, 3 insertions, 3 deletions

diff --git a/tools/qmlformat/dumpastvisitor.cpp b/tools/qmlformat/dumpastvisitor.cpp
index 04967ed0af..baf6651b20 100644
--- a/tools/qmlformat/dumpastvisitor.cpp
+++ b/tools/qmlformat/dumpastvisitor.cpp
@@ -405,14 +405,14 @@ QString DumpAstVisitor::parseExpression(ExpressionNode *expression)
         if (fieldMemberExpr->base->kind == Node::Kind_NumericLiteral)
             result = "(" + result + ")";
 
-        result += "." + fieldMemberExpr->name.toString();
+        result += (fieldMemberExpr->isOptional ? "?." : ".") + fieldMemberExpr->name.toString();
 
         return result;
     }
     case Node::Kind_ArrayMemberExpression: {
         auto *arrayMemberExpr = cast<ArrayMemberExpression *>(expression);
         return parseExpression(arrayMemberExpr->base)
-                + "[" + parseExpression(arrayMemberExpr->expression) + "]";
+                + (arrayMemberExpr->isOptional ? "?." : "") + "[" + parseExpression(arrayMemberExpr->expression) + "]";
     }
     case Node::Kind_NestedExpression:
         return "("+parseExpression(cast<NestedExpression *>(expression)->expression)+")";
@@ -458,7 +458,7 @@ QString DumpAstVisitor::parseExpression(ExpressionNode *expression)
     case Node::Kind_CallExpression: {
         auto *callExpr = cast<CallExpression *>(expression);
 
-        return parseExpression(callExpr->base) + "(" + parseArgumentList(callExpr->arguments) + ")";
+        return parseExpression(callExpr->base) + (callExpr->isOptional ? "?." : "") + "(" + parseArgumentList(callExpr->arguments) + ")";
     }
     case Node::Kind_NewExpression:
         return "new "+parseExpression(cast<NewExpression *>(expression)->expression);