From 2d4852907318d5fdd0cf3c30e671da861fe96ff1 Mon Sep 17 00:00:00 2001
From: davidot <davidot@serenityos.org>
Date: Mon, 18 Oct 2021 23:32:47 +0200
Subject: [PATCH] LibJS: Implement private identifiers in optional chains

---
 Userland/Libraries/LibJS/AST.cpp    | 11 +++++++++++
 Userland/Libraries/LibJS/AST.h      |  6 +++++-
 Userland/Libraries/LibJS/Parser.cpp | 20 +++++++++++++++++++-
 3 files changed, 35 insertions(+), 2 deletions(-)

diff --git a/Userland/Libraries/LibJS/AST.cpp b/Userland/Libraries/LibJS/AST.cpp
index 009065051c..a715fa384b 100644
--- a/Userland/Libraries/LibJS/AST.cpp
+++ b/Userland/Libraries/LibJS/AST.cpp
@@ -2704,6 +2704,11 @@ void OptionalChain::dump(int indent) const
                 print_indent(indent + 1);
                 outln("MemberReference({})", ref.mode == Mode::Optional ? "Optional" : "Not Optional");
                 ref.identifier->dump(indent + 2);
+            },
+            [&](PrivateMemberReference const& ref) {
+                print_indent(indent + 1);
+                outln("PrivateMemberReference({})", ref.mode == Mode::Optional ? "Optional" : "Not Optional");
+                ref.private_identifier->dump(indent + 2);
             });
     }
 }
@@ -2738,6 +2743,12 @@ Optional<OptionalChain::ReferenceAndValue> OptionalChain::to_reference_and_value
                     create_ast_node<SyntheticReferenceExpression>(source_range(), *base_reference, base),
                     ref.identifier,
                     false);
+            },
+            [&](PrivateMemberReference const& ref) -> NonnullRefPtr<Expression> {
+                return create_ast_node<MemberExpression>(source_range(),
+                    create_ast_node<SyntheticReferenceExpression>(source_range(), *base_reference, base),
+                    ref.private_identifier,
+                    false);
             });
         if (is<CallExpression>(*expression)) {
             base_reference = JS::Reference {};
diff --git a/Userland/Libraries/LibJS/AST.h b/Userland/Libraries/LibJS/AST.h
index 88ef640da4..6b8b46bd9a 100644
--- a/Userland/Libraries/LibJS/AST.h
+++ b/Userland/Libraries/LibJS/AST.h
@@ -1590,8 +1590,12 @@ public:
         NonnullRefPtr<Identifier> identifier;
         Mode mode;
     };
+    struct PrivateMemberReference {
+        NonnullRefPtr<PrivateIdentifier> private_identifier;
+        Mode mode;
+    };
 
-    using Reference = Variant<Call, ComputedReference, MemberReference>;
+    using Reference = Variant<Call, ComputedReference, MemberReference, PrivateMemberReference>;
 
     OptionalChain(SourceRange source_range, NonnullRefPtr<Expression> base, Vector<Reference> references)
         : Expression(source_range)
diff --git a/Userland/Libraries/LibJS/Parser.cpp b/Userland/Libraries/LibJS/Parser.cpp
index 787fc3ff90..0bfdefb1ed 100644
--- a/Userland/Libraries/LibJS/Parser.cpp
+++ b/Userland/Libraries/LibJS/Parser.cpp
@@ -2696,6 +2696,17 @@ NonnullRefPtr<OptionalChain> Parser::parse_optional_chain(NonnullRefPtr<Expressi
                 chain.append(OptionalChain::ComputedReference { parse_expression(0), OptionalChain::Mode::Optional });
                 consume(TokenType::BracketClose);
                 break;
+            case TokenType::PrivateIdentifier: {
+                if (!is_private_identifier_valid())
+                    syntax_error(String::formatted("Reference to undeclared private field or method '{}'", m_state.current_token.value()));
+
+                auto start = position();
+                auto private_identifier = consume();
+                chain.append(OptionalChain::PrivateMemberReference {
+                    create_ast_node<PrivateIdentifier>({ m_state.current_token.filename(), start, position() }, private_identifier.value()),
+                    OptionalChain::Mode::Optional });
+                break;
+            }
             case TokenType::TemplateLiteralStart:
                 // 13.3.1.1 - Static Semantics: Early Errors
                 // OptionalChain :
@@ -2721,7 +2732,14 @@ NonnullRefPtr<OptionalChain> Parser::parse_optional_chain(NonnullRefPtr<Expressi
             chain.append(OptionalChain::Call { parse_arguments(), OptionalChain::Mode::NotOptional });
         } else if (match(TokenType::Period)) {
             consume();
-            if (match_identifier_name()) {
+            if (match(TokenType::PrivateIdentifier)) {
+                auto start = position();
+                auto private_identifier = consume();
+                chain.append(OptionalChain::PrivateMemberReference {
+                    create_ast_node<PrivateIdentifier>({ m_state.current_token.filename(), start, position() }, private_identifier.value()),
+                    OptionalChain::Mode::NotOptional,
+                });
+            } else if (match_identifier_name()) {
                 auto start = position();
                 auto identifier = consume();
                 chain.append(OptionalChain::MemberReference {