General

Expose an optional get_alias API as an alternative to get_config in Luau.Require and Luau.RequireNavigator.
Improve the Luau CLI's virtual filesystem implementation to fix bugs related to init.luau. Fixes #1816

New Type Solver

Avoid double reporting errors when erroneous arguments are provided to type functions.
Fix some instances of unresovable cyclic type functions in loops by only considering the first loop cycles. This results in some type inference inaccuracies when the type of a variable in loop through multiple iterations. Fixes #1413.
Better generalize free types that have meaningful lower and upper bounds, especially for table indexers.
Report more specific errors when assigning or returning table literal types, instead of citing the entire table type.
Inference for functions with generic type packs is greatly improved.
Fix some internal compiler exceptions when using type-stating functions like table.freeze in if _ then _ else _ expressions and short circuiting binary operations.
More consistently simplify unions of primitive types, especially in array-like and dictionary-like tables.

Fix a crash when type checking an erroneous type alias containing typeof with a type assertion expression, as in:

type MyTable = {}
-- This will error at type checking time as it's a duplicate
type MyTable = typeof(setmetatable(SomeTable :: {}, SomeMetaTable));

Fix a crash when inferring the type of an index expression where the indexee is invalid (e.g. nil).

Runtime

Avoid throwing an exception from luau_load if we run out of memory.
Type functions are no longer compiled and included in bytecode. Fixes #1817.
Fix some instances of Luau C API functions reading invalid debug information (generally when the first or last instruction of a block was being inspected). Fixes #1369.
Avoid potential signed integer overflow when doing bounds checks on tables.
Support 16 byte aligned userdata objects when system allocation alignment is also 16 bytes.
Fix memory leaks in Luau.Require when using VM build with no exceptions. Fixes #1827.

Internal Contributors

Co-authored-by: Andy Friesen afriesen@roblox.com
Co-authored-by: Ariel Weiss aaronweiss@roblox.com
Co-authored-by: Hunter Goldstein hgoldstein@roblox.com
Co-authored-by: James McNellis jmcnellis@roblox.com
Co-authored-by: Sora Kanosue skanosue@roblox.com
Co-authored-by: Talha Pathan tpathan@roblox.com
Co-authored-by: Varun Saini vsaini@roblox.com
Co-authored-by: Vyacheslav Egorov vegorov@roblox.com

General Changes

Remove a static_assert that prevented Luau from building on 32-bit targets.
Fix proxyrequire (see #1804)
Replace contents API with new loadname API in Luau.Require
Store the positions of : symbols in the CST.
Fix a minor bug in the new incremental autocomplete engine: Properly suggest else and elseif if the cursor is currently within an if block.

New Type Solver

Allow generics to be substituted for negation types when performing subtype tests
Crash fixes
Surface subtyping errors more consistently.
Avoid creating double-negation types (like ~~(false?)) when generating constraints.

Internal Contributors

Co-authored-by: Andy Friesen afriesen@roblox.com
Co-authored-by: Ariel Weiss aaronweiss@roblox.com
Co-authored-by: Aviral Goel agoel@roblox.com
Co-authored-by: Hunter Goldstein hgoldstein@roblox.com
Co-authored-by: Sora Kanosue skanosue@roblox.com
Co-authored-by: Talha Pathan tpathan@roblox.com
Co-authored-by: Varun Saini vsaini@roblox.com
Co-authored-by: Vighnesh Vijay vvijay@roblox.com
Co-authored-by: Vyacheslav Egorov vegorov@roblox.com

Full Changelog: 0.672...0.673

What's Changed?

Hi there, folks! It's been another busy week in the type mines, trying to bring you all the very best type inference system we can. We've got a bunch of updates to large pain points across the new type solver, and our next big update (currently under a debug flag) improving type generalization is finally nearing completion (and should hopefully eliminate quite a lot of "type solver failed to complete" errors). We've also continued polishing both the CST Parser and the Luau.Require library we introduced a few releases ago based on user feedback and bug reports, and we're really happy with how they're turning out.

Parser

Fixes a bug in the CST tooling where the spacing on return type annotations for functions was not being printed correctly.
Resolves some issues with the JSON encoding of AstGenericType and AstGenericTypePack

Runtime

Implements support for yielding requires in Luau.Require library.
Improves the error messages for require-by-string to include the chunk name that was problematic where possible and the overall require path that failed to be required.
Fixes a bug that prevented the use of require within C functions and pcall.
Adds an API to support selectively removing chunks from the require cache in Luau.Require
Adds an API to support clearing the entire require cache in Luau.Require

New Type Solver

Fixes a crash in the new non-strict mode when visiting function return types in incomplete ASTs (e.g. during editing).
Improves type simplification to support intersections of tables with extern types, resolving one of the causes of frequent refinements unexpectedly leading to never.
Improves type inference to better understand diverging branches in functions, reducing false negatives where the type system fails to learn that a binding must now always be initialized.
Fixes a typo in the type definitions for user-defined function types where the intersection tag was misspelled.
Improves the overall accuracy of free type tracking during constraint solving, leading to better inference results overall.
Implements types.optional as a new library function for user-defined type functions to make it easier to union a type with nil.
Resolves a number of bugs caused by local type inference expanding the domain of upvalues

Internal Contributors

Co-authored-by: Andy Friesen afriesen@roblox.com
Co-authored-by: Ariel Weiss aaronweiss@roblox.com
Co-authored-by: Hunter Goldstein hgoldstein@roblox.com
Co-authored-by: Talha Pathan tpathan@roblox.com
Co-authored-by: Varun Saini vsaini@roblox.com
Co-authored-by: Vighnesh Vijay vvijay@roblox.com

Full Changelog: 0.671...0.672

What's Changed

Internally rename ClassType to ExternType. In definition files, the syntax to define these types has changed to declare extern type Foo with prop: type end
Add luarequire_registermodule to Luau.Require
Support yieldable Luau C functions calling other functions
Store return types as AstTypePack* on Ast nodes

New Solver

Improve the logic that determines constraint dispatch ordering
Fix a crash in the type solver that arose when using multi-return functions with string.format
Fix #1736
Initial steps toward rethinking function generalization:
- Instead of generalizing every type in a function all at once, we will instead generalize individual type variables once their bounds have been fully resolved. This will make it possible to properly interleave type function reduction and generalization.
Magic functions are no longer considered magical in cases where they are not explicitly called by the code.
- The most prominent example of this is in for..in loops where the function call is part of the desugaring process.
- Almost all magic functions work by directly inspecting the AST, so they can't work without an AST fragment anyway.
- Further, none of the magic functions we have are usefully used in this way.

Full Changelog: 0.670...0.671

Co-authored-by: Andy Friesen afriesen@roblox.com
Co-authored-by: Ariel Weiss aaronweiss@roblox.com
Co-authored-by: Hunter Goldstein hgoldstein@roblox.com
Co-authored-by: Sora Kanosue skanosue@roblox.com
Co-authored-by: Talha Pathan tpathan@roblox.com
Co-authored-by: Varun Saini vsaini@roblox.com
Co-authored-by: Vighnesh Vijay vvijay@roblox.com
Co-authored-by: Vyacheslav Egorov vegorov@roblox.com

@MaidenlessUsr

What's Changed

This week has been focused primarily on bugfixes, with a ton of usability improvements to the new solver, fragment autocomplete, and the concrete syntax tree project.

Community Contributions

Update Arch Linux installation instructions by @MaidenlessUsr in #1774

Runtime

Fix an assertion caused by failing to allocate native code pages.
Expose a lua_pushrequire function, which performs the same initialization steps as luaopen_require but does not register require globally. This lets users create specialized, custom requires.

New Solver

Fix a bug in simplification of types caused by combinatorial explosion of intersection and union types.
Fix a memory leak in fragment autocomplete
Improve the isolation of modules in fragment autocomplete
Throw errors when users define a type function with the name typeof
Continue to narrow intersection types which might be never.
Major rework of generalization continues - we are blazing a new path with eager + non-reentrant generalization and actively working to make these more performant and less error prone.
Improve the ability of and/or type functions to reduce, even when their arguments are generic.
Report arity mismatches for undersaturated calls with unknown parameters

New Non-Strict

Extends the new non-strict mode to report unknown symbols in types

Old Solver

Fix a crash caused by excessive stack usage during typechecking

Misc

Improvements to Concrete Syntax Tree location tracking for string table props.
Do not store file extensions in module chunknames [Luau CLI] by @vrn-sn in #1772

Full Changelog: `0.669...0.670`

Co-authored-by: Andy Friesen afriesen@roblox.com
Co-authored-by: Ariel Weiss aaronweiss@roblox.com
Co-authored-by: Aviral Goel agoel@roblox.com
Co-authored-by: Hunter Goldstein hgoldstein@roblox.com
Co-authored-by: Sora Kanosue skanosue@roblox.com
Co-authored-by: Talha Pathan tpathan@roblox.com
Co-authored-by: Varun Saini vsaini@roblox.com
Co-authored-by: Vighnesh Vijay vvijay@roblox.com
Co-authored-by: Vyacheslav Egorov vegorov@roblox.com

What's Changed

General

We updated Luau's license year to 2025!
We fixed a bug where large amounts of errors were being printed when deep intersections of unions error.

Require-by-String

This release introduces the Luau.Require library, which exposes the runtime semantics of require-by-string, including support for the new @self alias described in this RFC.

The library operates on a virtualized filesystem, allowing consumers to specify navigation rules without assuming a filesystem context. Documentation in Require.h explains how to enable the library, and the setupState function in Repl.cpp demonstrates how we've integrated it into the luau CLI tool. Note that the interface in Require.h is written in C, which enables any application written in a language with a C foreign-function interface to link against this library and enable require-by-string. This makes it straightforward for any application embedding Luau to support require-by-string, provided that it defines or operates within an environment resembling a virtual filesystem.

The core navigation semantics of require-by-string have additionally been pulled into the Luau.RequireNavigator library. While Luau.Require internally depends on Luau.RequireNavigator, the latter does not depend on the Luau VM. This library provides an interface for inspecting require-by-string's navigation behavior and therefore serves as a useful dependency for static tooling. Documentation for Luau.RequireNavigator is available in RequireNavigator.h.

Autocomplete

We fixed a memory leak in fragment autocomplete!

New Solver And Old Solver

We've found a infinite iteration error over a type pack. We added a way to detect this error and throw an InternalCompileError instead.
We fix table.freeze not accounting for the first argument not getting type stated. We fall back to regular inference instead.
We fix a crash in the old solver with length_error.
We fix a crash in the new solver stemming from generalization reentrancy. Now we correctly generalize interior free types that do not appear in a function signature.
We fix a nil refinement. (Fixes #1687 and #1451)

Internal Contributors

Co-authored-by: Andy Friesen afriesen@roblox.com
Co-authored-by: Hunter Goldstein hgoldstein@roblox.com
Co-authored-by: Talha Pathan tpathan@roblox.com
Co-authored-by: Varun Saini vsaini@roblox.com
Co-authored-by: Vighnesh Vijay vvijay@roblox.com
Co-authored-by: Vyacheslav Egorov vegorov@roblox.com

Full Changelog: 0.668...0.669

New Type Solver

Update resolved types for singleton unions and intersections to avoid crashing when type checking type assertions.
Generalize free return type pack of a function type inferred at call site to ensure that the free type does not leak to another module.
Fix crash from cyclic indexers by reducing if possible or producing an error otherwise.
Fix handling of irreducible type functions to prevent type inference from failing.
Fix handling of recursive metatables to avoid infinite recursion.

New and Old Type Solver

Fix accidental capture of all exceptions in multi-threaded typechecking by converting all typechecking exceptions to InternalCompilerError and only capturing those.

Fragment Autocomplete

Add a block based diff algorithm based on class index and span for re-typechecking. This reduces the granularity of fragment autocomplete to avoid flakiness when the fragment does not have enough type information.
Fix bugs arising from incorrect scope selection for autocompletion.

Roundtrippable AST

Store type alias location in TypeFun class to ensure it is accessible for exported types as part of the public interface.

Build System

Bump minimum supported CMake version to 3.10 since GitHub is phasing out the currently supported minimum version 3.0, released 11 years ago.
Fix compilation when HARDSTACKTESTS is enabled.

Miscellaneous

Flag removals and cleanup of unused code.

Internal Contributors

Co-authored-by: Andy Friesen afriesen@roblox.com
Co-authored-by: Ariel Weiss aaronweiss@roblox.com
Co-authored-by: Hunter Goldstein hgoldstein@roblox.com
Co-authored-by: Talha Pathan tpathan@roblox.com
Co-authored-by: Vighnesh Vijay vvijay@roblox.com
Co-authored-by: Vyacheslav Egorov vegorov@roblox.com

External Contributors

Thanks to @grh-official for PR #1759

Full Changelog: 0.667...0.668

@vvatheus

After a very auspicious release last week, we have a new bevy of changes for you!

What's Changed

Deprecated Attribute

This release includes an implementation of the @deprecated attribute proposed in this RFC. It relies on the new type solver to propagate deprecation information from function and method AST nodes to the corresponding type objects. These objects are queried by a linter pass when it encounters local, global, or indexed variables, to issue deprecation warnings. Uses of deprecated functions and methods in recursion are ignored. To support deprecation of class methods, the parser has been extended to allow attribute declarations on class methods. The implementation does not support parameters, so it is not currently possible for users to customize deprecation messages.

General

Add a limit for normalization 8000 of function types.

New Type Solver

Fix type checker to accept numbers as concat operands (Fixes #1671).
Fix user-defined type functions failing when used inside type aliases/nested calls (Fixes #1738, Fixes #1679).
Improve constraint generation for overloaded functions (in part thanks to @vvatheus in #1694).
Improve type inference for indexers on table literals, especially when passing table literals directly as a function call argument.
Equate regular error type and intersection with a negation of an error type.
Avoid swapping types in 2-part union when RHS is optional.
Use simplification when doing ~nil refinements.
len<> now works on metatables without __len function.

AST

Retain source information for AstTypeUnion and AstTypeIntersection.

Transpiler

Print attributes on functions.

Parser

Allow types in indexers to begin with string literals by @jackdotink in #1750.

Autocomplete

Evaluate user-defined type functions in ill-formed source code to provide autocomplete.
Fix the start location of functions that have attributes.
Implement better fragment selection.

New Contributors

@vvatheus made their first contribution in #1694

Internal Contributors

Co-authored-by: Andy Friesen afriesen@roblox.com
Co-authored-by: Ariel Weiss aaronweiss@roblox.com
Co-authored-by: Aviral Goel agoel@roblox.com
Co-authored-by: Hunter Goldstein hgoldstein@roblox.com
Co-authored-by: Sora Kanosue skanosue@roblox.com
Co-authored-by: Talha Pathan tpathan@roblox.com
Co-authored-by: Varun Saini vsaini@roblox.com
Co-authored-by: Vighnesh Vijay vvijay@roblox.com
Co-authored-by: Vyacheslav Egorov vegorov@roblox.com

Full Changelog: 0.666...0.667

Another week, another release. Happy spring! 🌷

What's Changed

New Type Solver

Add typechecking and autocomplete support for user-defined type
functions!
Improve the display of type paths, making type mismatch errors far
more human-readable.
Enhance various aspects of the index type function: support function
type metamethods, fix crashes involving cyclic metatables, and forward
any types through the type function.
Fix incorrect subtyping results involving the buffer type.
Fix crashes related to typechecking anonymous functions in nonstrict
mode.

AST

Retain source information for type packs, functions, and type
functions.
Introduce AstTypeOptional to differentiate T? from T | nil in
the AST.
Prevent the transpiler from advancing before tokens when the AST has
errors.

Autocomplete

Introduce demand-based cloning and better module isolation for
fragment autocomplete, leading to a substantial speedup in performance.
Guard against recursive unions in autocompleteProps.

Internal Contributors

Co-authored-by: Andy Friesen afriesen@roblox.com
Co-authored-by: Ariel Weiss aaronweiss@roblox.com
Co-authored-by: Hunter Goldstein hgoldstein@roblox.com
Co-authored-by: Talha Pathan tpathan@roblox.com
Co-authored-by: Vighnesh Vijay vvijay@roblox.com
Co-authored-by: Vyacheslav Egorov vegorov@roblox.com

Full Changelog: 0.665...0.666

Hello all! Another week, another Luau release!

Change to `lua_setuserdatametatable`

This release fixes #1710: lua_setuserdatametatable is being changed so that it only operates on the top of the stack: the idx parameter is being removed. Prior to this, lua_setuserdatametable would set the metatable of the value in the stack at idx, but always pop the top of the stack. The old behavior is available in this release as lua_setuserdatametatable_DEPRECATED.

What's changed?

This release exposes a generalized implementation of require-by-string's autocomplete logic. FileResolver can now be optionally constructed with a RequireSuggester, which provides an interface for converting a given module to a RequireNode. Consumers of this new API implement a RequireNode to define how modules are represented in their embedded context, and the new API manages the logic specific to require-by-string, including providing suggestions for require aliases. This enhancement moves toward integrating require-by-string's semantics into the language itself, rather than merely providing a specification for community members to implement themselves.

New Type Solver

Fixed a source of potential Luau::follow detected a Type cycle internal compiler exceptions when assigning a global to itself.
Fixed an issue whereby *no-refine* (a type which should not be visible at the end of type checking) was not being properly elided, causing inference of class-like tables to become unreadable / induce crashes in autocomplete.
Fixed a case of incomplete constraint solving when performing basic math in a loop

Fragment Autocomplete

Fixed several crashes related to not properly filling in scope information for the fragments
Fixed a source of memory corruption by isolating the return type of a fragment when it is type checked.
Improved performance by opting not to clone persistent types for the fragment (e.g.: built in types)

Full Changelog: 0.664...0.665

Internal Contributors

Co-authored-by: Andy Friesen afriesen@roblox.com
Co-authored-by: Hunter Goldstein hgoldstein@roblox.com
Co-authored-by: Talha Pathan tpathan@roblox.com
Co-authored-by: Varun Saini vsaini@roblox.com
Co-authored-by: Vighnesh Vijay vvijay@roblox.com
Co-authored-by: Vyacheslav Egorov vegorov@roblox.com

Releases: luau-lang/luau

0.674

General

New Type Solver

Runtime

Internal Contributors

0.673

General Changes

New Type Solver

Internal Contributors

0.672

What's Changed?

Parser

Runtime

New Type Solver

Internal Contributors

0.671

What's Changed

New Solver

0.670

What's Changed

Community Contributions

Runtime

New Solver

New Non-Strict

Old Solver

Misc

Full Changelog: 0.669...0.670

Contributors

0.669

What's Changed

General

Require-by-String

Autocomplete

New Solver And Old Solver

Internal Contributors

0.668

New Type Solver

New and Old Type Solver

Fragment Autocomplete

Roundtrippable AST

Build System

Miscellaneous

Internal Contributors

External Contributors

0.667

What's Changed

Deprecated Attribute

General

New Type Solver

AST

Transpiler

Parser

Autocomplete

New Contributors

Internal Contributors

Contributors

0.666

What's Changed

New Type Solver

AST

Autocomplete

Internal Contributors

0.665

Change to lua_setuserdatametatable

What's changed?

New Type Solver

Fragment Autocomplete

Internal Contributors

Full Changelog: `0.669...0.670`

Change to `lua_setuserdatametatable`