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, 4 insertions, 0 deletions

diff --git a/src/qml/parser/qqmljsast_p.h b/src/qml/parser/qqmljsast_p.h
index 6836579209..d32595429e 100644
--- a/src/qml/parser/qqmljsast_p.h
+++ b/src/qml/parser/qqmljsast_p.h
@@ -460,6 +460,7 @@ public:
     ExpressionNode() {}
 
     ExpressionNode *expressionCast() override;
+    bool containsOptionalChain() const;
 
     AST::FormalParameterList *reparseAsFormalParameterList(MemoryPool *pool);
 
@@ -1198,6 +1199,7 @@ public:
     ExpressionNode *expression;
     SourceLocation lbracketToken;
     SourceLocation rbracketToken;
+    bool isOptional = false;
 };
 
 class QML_PARSER_EXPORT FieldMemberExpression: public LeftHandSideExpression
@@ -1222,6 +1224,7 @@ public:
     QStringView name;
     SourceLocation dotToken;
     SourceLocation identifierToken;
+    bool isOptional = false;
 };
 
 class QML_PARSER_EXPORT TaggedTemplate : public LeftHandSideExpression
@@ -1314,6 +1317,7 @@ public:
     ArgumentList *arguments;
     SourceLocation lparenToken;
     SourceLocation rparenToken;
+    bool isOptional = false;
 };
 
 class QML_PARSER_EXPORT ArgumentList: public Node