Sync to upstream/release/505 (#216)

- Improve error recovery during type checking
- Initial (not fully complete) implementation for singleton types (RFC RFC: Singleton types #37)
- Implement a C-friendly interface for compiler (luacode.h)
- Remove C++ features from lua.h (removed default arguments from luau_load and lua_pushcfunction)
- Fix lua_breakpoint behavior when enabled=false
- Implement coroutine.close (RFC RFC: coroutine.close #88)

Note, this introduces small breaking changes in lua.h:

- luau_load env argument is now required, pass an extra 0
- lua_pushcfunction now must be called with 3 arguments; if you were calling it with 2 arguments, pass an extra NULL; if you were calling it with 4, use lua_pushcclosure.

These changes are necessary to make sure lua.h can be used from pure C - the future release will make it possible by adding an option to luaconf.h to change function name mangling to be C-compatible. We don't anticipate breaking the FFI interface in the future, but this change was necessary to restore C compatibility.

Closes #121
Fixes #213

Analysis/include/Luau/Documentation.h

@@ -12,10 +12,17 @@ namespace Luau
 struct FunctionDocumentation;
 struct TableDocumentation;
 struct OverloadedFunctionDocumentation;
+struct BasicDocumentation;
 
-using Documentation = Luau::Variant<std::string, FunctionDocumentation, TableDocumentation, OverloadedFunctionDocumentation>;
+using Documentation = Luau::Variant<BasicDocumentation, FunctionDocumentation, TableDocumentation, OverloadedFunctionDocumentation>;
 using DocumentationSymbol = std::string;
 
+struct BasicDocumentation
+{
+    std::string documentation;
+    std::string learnMoreLink;
+};
+
 struct FunctionParameterDocumentation
 {
     std::string name;
@@ -29,6 +36,7 @@ struct FunctionDocumentation
     std::string documentation;
     std::vector<FunctionParameterDocumentation> parameters;
     std::vector<DocumentationSymbol> returns;
+    std::string learnMoreLink;
 };
 
 struct OverloadedFunctionDocumentation
@@ -43,6 +51,7 @@ struct TableDocumentation
 {
     std::string documentation;
     Luau::DenseHashMap<std::string, DocumentationSymbol> keys;
+    std::string learnMoreLink;
 };
 
 using DocumentationDatabase = Luau::DenseHashMap<DocumentationSymbol, Documentation>;

Analysis/include/Luau/ToString.h

@@ -23,10 +23,11 @@ struct ToStringNameMap
 
 struct ToStringOptions
 {
-    bool exhaustive = false;            // If true, we produce complete output rather than comprehensible output
-    bool useLineBreaks = false;         // If true, we insert new lines to separate long results such as table entries/metatable.
-    bool functionTypeArguments = false; // If true, output function type argument names when they are available
-    bool hideTableKind = false;         // If true, all tables will be surrounded with plain '{}'
+    bool exhaustive = false;                      // If true, we produce complete output rather than comprehensible output
+    bool useLineBreaks = false;                   // If true, we insert new lines to separate long results such as table entries/metatable.
+    bool functionTypeArguments = false;           // If true, output function type argument names when they are available
+    bool hideTableKind = false;                   // If true, all tables will be surrounded with plain '{}'
+    bool hideNamedFunctionTypeParameters = false; // If true, type parameters of functions will be hidden at top-level.
     size_t maxTableLength = size_t(FInt::LuauTableTypeMaximumStringifierLength); // Only applied to TableTypeVars
     size_t maxTypeLength = size_t(FInt::LuauTypeMaximumStringifierLength);
     std::optional<ToStringNameMap> nameMap;
@@ -64,6 +65,8 @@ inline std::string toString(TypePackId ty)
 std::string toString(const TypeVar& tv, const ToStringOptions& opts = {});
 std::string toString(const TypePackVar& tp, const ToStringOptions& opts = {});
 
+std::string toStringNamedFunction(const std::string& prefix, const FunctionTypeVar& ftv, ToStringOptions opts = {});
+
 // It could be useful to see the text representation of a type during a debugging session instead of exploring the content of the class
 // These functions will dump the type to stdout and can be evaluated in Watch/Immediate windows or as gdb/lldb expression
 void dump(TypeId ty);

Analysis/include/Luau/TypeInfer.h

@@ -175,10 +175,10 @@ struct TypeChecker
     std::vector<std::optional<TypeId>> getExpectedTypesForCall(const std::vector<TypeId>& overloads, size_t argumentCount, bool selfCall);
     std::optional<ExprResult<TypePackId>> checkCallOverload(const ScopePtr& scope, const AstExprCall& expr, TypeId fn, TypePackId retPack,
         TypePackId argPack, TypePack* args, const std::vector<Location>& argLocations, const ExprResult<TypePackId>& argListResult,
-        std::vector<TypeId>& overloadsThatMatchArgCount, std::vector<OverloadErrorEntry>& errors);
+        std::vector<TypeId>& overloadsThatMatchArgCount, std::vector<TypeId>& overloadsThatDont, std::vector<OverloadErrorEntry>& errors);
     bool handleSelfCallMismatch(const ScopePtr& scope, const AstExprCall& expr, TypePack* args, const std::vector<Location>& argLocations,
         const std::vector<OverloadErrorEntry>& errors);
-    ExprResult<TypePackId> reportOverloadResolutionError(const ScopePtr& scope, const AstExprCall& expr, TypePackId retPack, TypePackId argPack,
+    void reportOverloadResolutionError(const ScopePtr& scope, const AstExprCall& expr, TypePackId retPack, TypePackId argPack,
         const std::vector<Location>& argLocations, const std::vector<TypeId>& overloads, const std::vector<TypeId>& overloadsThatMatchArgCount,
         const std::vector<OverloadErrorEntry>& errors);
 
@@ -282,6 +282,14 @@ struct TypeChecker
     // Wrapper for merge(l, r, toUnion) but without the lambda junk.
     void merge(RefinementMap& l, const RefinementMap& r);
 
+    // Produce an "emergency backup type" for recovery from type errors.
+    // This comes in two flavours, depening on whether or not we can make a good guess
+    // for an error recovery type.
+    TypeId errorRecoveryType(TypeId guess);
+    TypePackId errorRecoveryTypePack(TypePackId guess);
+    TypeId errorRecoveryType(const ScopePtr& scope);
+    TypePackId errorRecoveryTypePack(const ScopePtr& scope);
+
 private:
     void prepareErrorsForDisplay(ErrorVec& errVec);
     void diagnoseMissingTableKey(UnknownProperty* utk, TypeErrorData& data);
@@ -297,6 +305,10 @@ struct TypeChecker
     TypeId freshType(const ScopePtr& scope);
     TypeId freshType(TypeLevel level);
 
+    // Produce a new singleton type var.
+    TypeId singletonType(bool value);
+    TypeId singletonType(std::string value);
+
     // Returns nullopt if the predicate filters down the TypeId to 0 options.
     std::optional<TypeId> filterMap(TypeId type, TypeIdPredicate predicate);
 
@@ -330,8 +342,8 @@ struct TypeChecker
         const std::vector<TypePackId>& typePackParams, const Location& location);
 
     // Note: `scope` must be a fresh scope.
-    std::pair<std::vector<TypeId>, std::vector<TypePackId>> createGenericTypes(
-        const ScopePtr& scope, std::optional<TypeLevel> levelOpt, const AstNode& node, const AstArray<AstName>& genericNames, const AstArray<AstName>& genericPackNames);
+    std::pair<std::vector<TypeId>, std::vector<TypePackId>> createGenericTypes(const ScopePtr& scope, std::optional<TypeLevel> levelOpt,
+        const AstNode& node, const AstArray<AstName>& genericNames, const AstArray<AstName>& genericPackNames);
 
 public:
     ErrorVec resolve(const PredicateVec& predicates, const ScopePtr& scope, bool sense);
@@ -347,7 +359,6 @@ struct TypeChecker
     void resolve(const OrPredicate& orP, ErrorVec& errVec, RefinementMap& refis, const ScopePtr& scope, bool sense);
     void resolve(const IsAPredicate& isaP, ErrorVec& errVec, RefinementMap& refis, const ScopePtr& scope, bool sense);
     void resolve(const TypeGuardPredicate& typeguardP, ErrorVec& errVec, RefinementMap& refis, const ScopePtr& scope, bool sense);
-    void DEPRECATED_resolve(const TypeGuardPredicate& typeguardP, ErrorVec& errVec, RefinementMap& refis, const ScopePtr& scope, bool sense);
     void resolve(const EqPredicate& eqP, ErrorVec& errVec, RefinementMap& refis, const ScopePtr& scope, bool sense);
 
     bool isNonstrictMode() const;
@@ -387,12 +398,9 @@ struct TypeChecker
     const TypeId booleanType;
     const TypeId threadType;
     const TypeId anyType;
-
-    const TypeId errorType;
     const TypeId optionalNumberType;
 
     const TypePackId anyTypePack;
-    const TypePackId errorTypePack;
 
 private:
     int checkRecursionCount = 0;

Analysis/include/Luau/TypeVar.h

@@ -108,6 +108,79 @@ struct PrimitiveTypeVar
     }
 };
 
+// Singleton types https://github.com/Roblox/luau/blob/master/rfcs/syntax-singleton-types.md
+// Types for true and false
+struct BoolSingleton
+{
+    bool value;
+
+    bool operator==(const BoolSingleton& rhs) const
+    {
+        return value == rhs.value;
+    }
+
+    bool operator!=(const BoolSingleton& rhs) const
+    {
+        return !(*this == rhs);
+    }
+};
+
+// Types for "foo", "bar" etc.
+struct StringSingleton
+{
+    std::string value;
+
+    bool operator==(const StringSingleton& rhs) const
+    {
+        return value == rhs.value;
+    }
+
+    bool operator!=(const StringSingleton& rhs) const
+    {
+        return !(*this == rhs);
+    }
+};
+
+// No type for float singletons, partly because === isn't any equalivalence on floats
+// (NaN != NaN).
+
+using SingletonVariant = Luau::Variant<BoolSingleton, StringSingleton>;
+
+struct SingletonTypeVar
+{
+    explicit SingletonTypeVar(const SingletonVariant& variant)
+        : variant(variant)
+    {
+    }
+
+    explicit SingletonTypeVar(SingletonVariant&& variant)
+        : variant(std::move(variant))
+    {
+    }
+
+    // Default operator== is C++20.
+    bool operator==(const SingletonTypeVar& rhs) const
+    {
+        return variant == rhs.variant;
+    }
+
+    bool operator!=(const SingletonTypeVar& rhs) const
+    {
+        return !(*this == rhs);
+    }
+
+    SingletonVariant variant;
+};
+
+template<typename T>
+const T* get(const SingletonTypeVar* stv)
+{
+    if (stv)
+        return get_if<T>(&stv->variant);
+    else
+        return nullptr;
+}
+
 struct FunctionArgument
 {
     Name name;
@@ -332,8 +405,8 @@ struct LazyTypeVar
 
 using ErrorTypeVar = Unifiable::Error;
 
-using TypeVariant = Unifiable::Variant<TypeId, PrimitiveTypeVar, FunctionTypeVar, TableTypeVar, MetatableTypeVar, ClassTypeVar, AnyTypeVar,
-    UnionTypeVar, IntersectionTypeVar, LazyTypeVar>;
+using TypeVariant = Unifiable::Variant<TypeId, PrimitiveTypeVar, SingletonTypeVar, FunctionTypeVar, TableTypeVar, MetatableTypeVar, ClassTypeVar,
+    AnyTypeVar, UnionTypeVar, IntersectionTypeVar, LazyTypeVar>;
 
 struct TypeVar final
 {
@@ -410,6 +483,9 @@ bool isGeneric(const TypeId ty);
 // Checks if a type may be instantiated to one containing generic type binders
 bool maybeGeneric(const TypeId ty);
 
+// Checks if a type is of the form T1|...|Tn where one of the Ti is a singleton
+bool maybeSingleton(TypeId ty);
+
 struct SingletonTypes
 {
     const TypeId nilType;
@@ -418,16 +494,19 @@ struct SingletonTypes
     const TypeId booleanType;
     const TypeId threadType;
     const TypeId anyType;
-    const TypeId errorType;
     const TypeId optionalNumberType;
 
     const TypePackId anyTypePack;
-    const TypePackId errorTypePack;
 
     SingletonTypes();
     SingletonTypes(const SingletonTypes&) = delete;
     void operator=(const SingletonTypes&) = delete;
 
+    TypeId errorRecoveryType(TypeId guess);
+    TypePackId errorRecoveryTypePack(TypePackId guess);
+    TypeId errorRecoveryType();
+    TypePackId errorRecoveryTypePack();
+
 private:
     std::unique_ptr<struct TypeArena> arena;
     TypeId makeStringMetatable();

Analysis/include/Luau/Unifiable.h

@@ -105,6 +105,8 @@ struct Generic
 
 struct Error
 {
+    // This constructor has to be public, since it's used in TypeVar and TypePack,
+    // but shouldn't be called directly. Please use errorRecoveryType() instead.
     Error();
 
     int index;

Analysis/include/Luau/Unifier.h

@@ -65,6 +65,7 @@ struct Unifier
 private:
     void tryUnify_(TypeId superTy, TypeId subTy, bool isFunctionCall = false, bool isIntersection = false);
     void tryUnifyPrimitives(TypeId superTy, TypeId subTy);
+    void tryUnifySingletons(TypeId superTy, TypeId subTy);
     void tryUnifyFunctions(TypeId superTy, TypeId subTy, bool isFunctionCall = false);
     void tryUnifyTables(TypeId left, TypeId right, bool isIntersection = false);
     void DEPRECATED_tryUnifyTables(TypeId left, TypeId right, bool isIntersection = false);

Analysis/src/Autocomplete.cpp

@@ -14,6 +14,7 @@
 
 LUAU_FASTFLAGVARIABLE(ElseElseIfCompletionImprovements, false);
 LUAU_FASTFLAG(LuauIfElseExpressionAnalysisSupport)
+LUAU_FASTFLAGVARIABLE(LuauAutocompleteAvoidMutation, false);
 
 static const std::unordered_set<std::string> kStatementStartingKeywords = {
     "while", "if", "local", "repeat", "function", "do", "for", "return", "break", "continue", "type", "export"};
@@ -198,11 +199,24 @@ static TypeCorrectKind checkTypeCorrectKind(const Module& module, TypeArena* typ
         UnifierSharedState unifierState(&iceReporter);
         Unifier unifier(typeArena, Mode::Strict, module.getModuleScope(), Location(), Variance::Covariant, unifierState);
 
-        unifier.tryUnify(expectedType, actualType);
+        if (FFlag::LuauAutocompleteAvoidMutation)
+        {
+            SeenTypes seenTypes;
+            SeenTypePacks seenTypePacks;
+            expectedType = clone(expectedType, *typeArena, seenTypes, seenTypePacks, nullptr);
+            actualType = clone(actualType, *typeArena, seenTypes, seenTypePacks, nullptr);
+
+            auto errors = unifier.canUnify(expectedType, actualType);
+            return errors.empty();
+        }
+        else
+        {
+            unifier.tryUnify(expectedType, actualType);
 
-        bool ok = unifier.errors.empty();
-        unifier.log.rollback();
-        return ok;
+            bool ok = unifier.errors.empty();
+            unifier.log.rollback();
+            return ok;
+        }
     };
 
     auto expr = node->asExpr();
@@ -1496,11 +1510,9 @@ AutocompleteResult autocomplete(Frontend& frontend, const ModuleName& moduleName
     if (!sourceModule)
         return {};
 
-    TypeChecker& typeChecker =
-        (frontend.options.typecheckTwice ? frontend.typeCheckerForAutocomplete : frontend.typeChecker);
-    ModulePtr module =
-        (frontend.options.typecheckTwice ? frontend.moduleResolverForAutocomplete.getModule(moduleName)
-                                         : frontend.moduleResolver.getModule(moduleName));
+    TypeChecker& typeChecker = (frontend.options.typecheckTwice ? frontend.typeCheckerForAutocomplete : frontend.typeChecker);
+    ModulePtr module = (frontend.options.typecheckTwice ? frontend.moduleResolverForAutocomplete.getModule(moduleName)
+                                                        : frontend.moduleResolver.getModule(moduleName));
 
     if (!module)
         return {};
@@ -1527,8 +1539,7 @@ OwningAutocompleteResult autocompleteSource(Frontend& frontend, std::string_view
     sourceModule->mode = Mode::Strict;
     sourceModule->commentLocations = std::move(result.commentLocations);
 
-    TypeChecker& typeChecker =
-        (frontend.options.typecheckTwice ? frontend.typeCheckerForAutocomplete : frontend.typeChecker);
+    TypeChecker& typeChecker = (frontend.options.typecheckTwice ? frontend.typeCheckerForAutocomplete : frontend.typeChecker);
 
     ModulePtr module = typeChecker.check(*sourceModule, Mode::Strict);
 

Analysis/src/EmbeddedBuiltinDefinitions.cpp

@@ -153,6 +153,7 @@ declare function gcinfo(): number
                 wrap: <A..., R...>((A...) -> R...) -> any,
                 yield: <A..., R...>(A...) -> R...,
                 isyieldable: () -> boolean,
+                close: (thread) -> (boolean, any?)
             }
 
             declare table: {

Analysis/src/Error.cpp

@@ -180,13 +180,13 @@ struct ErrorConverter
         switch (e.context)
         {
         case CountMismatch::Return:
-            return "Expected to return " + std::to_string(e.expected) + " value" + expectedS + ", but " +
-                   std::to_string(e.actual) + " " + actualVerb + " returned here";
+            return "Expected to return " + std::to_string(e.expected) + " value" + expectedS + ", but " + std::to_string(e.actual) + " " +
+                   actualVerb + " returned here";
         case CountMismatch::Result:
             // It is alright if right hand side produces more values than the
             // left hand side accepts. In this context consider only the opposite case.
-            return "Function only returns " + std::to_string(e.expected) + " value" + expectedS + ". " +
-                   std::to_string(e.actual) + " are required here";
+            return "Function only returns " + std::to_string(e.expected) + " value" + expectedS + ". " + std::to_string(e.actual) +
+                   " are required here";
         case CountMismatch::Arg:
             if (FFlag::LuauTypeAliasPacks)
                 return "Argument count mismatch. Function " + wrongNumberOfArgsString(e.expected, e.actual);

Analysis/src/Frontend.cpp

@@ -22,7 +22,6 @@ LUAU_FASTFLAGVARIABLE(LuauResolveModuleNameWithoutACurrentModule, false)
 LUAU_FASTFLAG(LuauTraceRequireLookupChild)
 LUAU_FASTFLAGVARIABLE(LuauPersistDefinitionFileTypes, false)
 LUAU_FASTFLAG(LuauNewRequireTrace2)
-LUAU_FASTFLAGVARIABLE(LuauClearScopes, false)
 
 namespace Luau
 {
@@ -458,8 +457,7 @@ CheckResult Frontend::check(const ModuleName& name)
             module->astTypes.clear();
             module->astExpectedTypes.clear();
             module->astOriginalCallTypes.clear();
-            if (FFlag::LuauClearScopes)
-                module->scopes.resize(1);
+            module->scopes.resize(1);
         }
 
         if (mode != Mode::NoCheck)