Add FFlag

Analysis/src/ConstraintGraphBuilder.cpp

@@ -21,6 +21,7 @@
 
 LUAU_FASTINT(LuauCheckRecursionLimit);
 LUAU_FASTFLAG(DebugLuauMagicTypes);
+LUAU_FASTFLAG(LuauParseDeclareClassIndexer);
 
 namespace Luau
 {
@@ -1151,7 +1152,7 @@ ControlFlow ConstraintGraphBuilder::visit(const ScopePtr& scope, AstStatDeclareC
 
     scope->exportedTypeBindings[className] = TypeFun{{}, classTy};
 
-    if (declaredClass->indexer)
+    if (FFlag::LuauParseDeclareClassIndexer && declaredClass->indexer)
     {
         // TODO: Recursion limit.
         ctv->indexer = TableIndexer{

Analysis/src/TypeAttach.cpp

@@ -13,6 +13,8 @@
 
 #include <string>
 
+LUAU_FASTFLAG(LuauParseDeclareClassIndexer);
+
 static char* allocateString(Luau::Allocator& allocator, std::string_view contents)
 {
     char* result = (char*)allocator.allocate(contents.size() + 1);
@@ -228,7 +230,7 @@ public:
         }
 
         AstTableIndexer* indexer = nullptr;
-        if (ctv.indexer)
+        if (FFlag::LuauParseDeclareClassIndexer && ctv.indexer)
         {
             RecursionCounter counter(&count);
 

Analysis/src/TypeInfer.cpp

@@ -41,6 +41,7 @@ LUAU_FASTFLAGVARIABLE(LuauTypecheckTypeguards, false)
 LUAU_FASTFLAGVARIABLE(LuauTinyControlFlowAnalysis, false)
 LUAU_FASTFLAGVARIABLE(LuauTypecheckClassTypeIndexers, false)
 LUAU_FASTFLAGVARIABLE(LuauAlwaysCommitInferencesOfFunctionCalls, false)
+LUAU_FASTFLAG(LuauParseDeclareClassIndexer)
 
 namespace Luau
 {
@@ -1757,7 +1758,7 @@ ControlFlow TypeChecker::check(const ScopePtr& scope, const AstStatDeclareClass&
     if (!ctv->metatable)
         ice("No metatable for declared class");
 
-    if (const auto& indexer = declaredClass.indexer)
+    if (const auto& indexer = declaredClass.indexer; FFlag::LuauParseDeclareClassIndexer && indexer)
         ctv->indexer = TableIndexer(resolveType(scope, *indexer->indexType), resolveType(scope, *indexer->resultType));
 
     TableType* metatable = getMutable<TableType>(*ctv->metatable);

Ast/src/Parser.cpp

@@ -13,6 +13,7 @@
 // See docs/SyntaxChanges.md for an explanation.
 LUAU_FASTINTVARIABLE(LuauRecursionLimit, 1000)
 LUAU_FASTINTVARIABLE(LuauParseErrorLimit, 100)
+LUAU_FASTFLAGVARIABLE(LuauParseDeclareClassIndexer, false)
 
 #define ERROR_INVALID_INTERP_DOUBLE_BRACE "Double braces are not permitted within interpolated strings. Did you mean '\\{'?"
 
@@ -886,7 +887,8 @@ AstStat* Parser::parseDeclaration(const Location& start)
             {
                 props.push_back(parseDeclaredClassMethod());
             }
-            else if (lexer.current().type == '[' && (lexer.lookahead().type == Lexeme::RawString || lexer.lookahead().type == Lexeme::QuotedString))
+            else if (lexer.current().type == '[' && (!FFlag::LuauParseDeclareClassIndexer || lexer.lookahead().type == Lexeme::RawString ||
+                                                        lexer.lookahead().type == Lexeme::QuotedString))
             {
                 const Lexeme begin = lexer.current();
                 nextLexeme(); // [
@@ -905,7 +907,7 @@ AstStat* Parser::parseDeclaration(const Location& start)
                 else
                     report(begin.location, "String literal contains malformed escape sequence");
             }
-            else if (lexer.current().type == '[')
+            else if (lexer.current().type == '[' && FFlag::LuauParseDeclareClassIndexer)
             {
                 if (indexer)
                 {

tests/Parser.test.cpp

@@ -1886,6 +1886,8 @@ TEST_CASE_FIXTURE(Fixture, "class_method_properties")
 
 TEST_CASE_FIXTURE(Fixture, "class_indexer")
 {
+    ScopedFastFlag LuauParseDeclareClassIndexer("LuauParseDeclareClassIndexer", true);
+
     AstStatBlock* stat = parseEx(R"(
         declare class Foo
             prop: boolean

tests/TypeInfer.definitions.test.cpp

@@ -397,6 +397,7 @@ TEST_CASE_FIXTURE(Fixture, "class_definition_string_props")
 
 TEST_CASE_FIXTURE(Fixture, "class_definition_indexer")
 {
+    ScopedFastFlag LuauParseDeclareClassIndexer("LuauParseDeclareClassIndexer", true);
     ScopedFastFlag LuauTypecheckClassTypeIndexers("LuauTypecheckClassTypeIndexers", true);
 
     loadDefinition(R"(