0.512

Analysis changes

• Improve refinement support for unions, in particular it's now possible to implement tagged unions as a union of tables where individual branches use a string literal type for one of the fields.
• Fix string.split type information

Runtime changes

• Optimize select(_, ...) to run in constant time (~2.7x faster on VariadicSelect benchmark)
• Improve debug line information for multi-line assignments
• Improve compilation of table literals when table keys are constant expressions/variables
• Use forward GC barrier for setmetatable which slightly accelerates GC progress

CLI changes

• Repl now uses _PRETTYPRINT if available to print expression values instead of print

Community contributions

• luau-analyze: Add support for reading source code from stdin by @vladmarica in #325

0.511

Analysis changes

• TableOperations lint now includes a warning for table.create(N, {}) (which is likely a mistake since the table is shared by all entries)
• Type checker now type checks #v when v is a union
• Parser now rejects sources that consists of a single unfinished long comment (fixes #312)

Runtime changes

• Work around significant MSVC 2022 performance regression, bringing it more or less in line with MSVC 2019
• Compiler now predicts array size for newly allocated tables when the table is filled in a short loop
• Small improvements in compilation throughput (~2% faster)
• Implement paged sweeper for GC which improves sweep throughput 2-3x and reduces memory consumption by 8 bytes per object (once it is stabilized we will see additional 8 bytes per object of savings)

CLI changes

• Improve Repl Tab completion
• Repl now supports -i (interactive mode to run code in context of a script's environment) and -On (to control optimization flags)

Community contributions

• Fix some mistakes in the documentation by @Halalaluyafail3 in #314
• Improve Grammar documentation by @JohnnyMorganz in #315
• Update copyright years. by @SnowyShiro in #323

0.510

Analysis changes

• Implement support for default generic arguments (RFC #61)
• Table literals are now unsealed by default, allowing more correct programs to type check in strict mode (RFC #276)
• Improve type checking in certain contexts when the target type is known
• Type checking now allows for different types in different branches of if-then-else expression, and returns a union of all types
• Type checking large module graphs now consumes less memory
• Fix type checking crashes with recursive metatables

Community contributions

• MSVC warning C4244 fixes by @rafabr34 in #308
• Update compatibility.md to mark coroutine.close as supported by @metatablecat in #309

0.509

Analysis changes

• Rework transaction log used for type checking which should result in more robust type checking internals with fewer bugs
• Improve refinement of complex expressions to propagate types through lookup chains like foo and foo.bar and foo.bar.baz
• Reduce the amount of memory consumed by type checker on large module graphs
• Type checker now errors on attempts to change the type of imported module fields
• The return type of newproxy is now any (#296)
• Fix error locations for type errors in string.format arguments

Runtime changes

• Make tonumber(x) ~2x faster by avoiding reparsing string arguments
• Implement new number printing algorithm (Schubfach) which makes tostring(number) produce precise (round-trippable) and short decimal output up to 10x faster
• Fix lua_Debug::linedefined to point to the line with the function definition instead of the first statement (#265)

CLI changes

• Fix minor bugs in Tab completion in Repl
• Repl now saves/restores command history in ~/.luau_history

Community contributions

• Add CodeMirror Editor for Web demo by @MathematicalDessert in #228

0.507

Analysis changes

• Type ascription (::) now permits casts between related types in both directions, allowing to refine or loosen the type (RFC #56)
• Fix type definition for tonumber to return number? since the input string isn't guaranteed to contain a valid number
• Fix type refinements for field access via []
• Many stability fixes for type checker
• Provide extra information in error messages for type mismatches in more cases
• Improve performance of type checking for large unions when union members are string literals

Runtime changes

• Fix some C APIs like lua_equal or lua_getfield triggering GC assertions in presence of metatables
• Add lua_getcoverage API for code coverage collection
• Improve performance of truthiness checks in some cases, particularly on Apple M1, resulting in 10-25% perf gains on qsort benchmark depending on the CPU/compiler
• Fix support for little-endian systems; IBM s390x here we go!

CLI changes

• Add coverage reporting support to Repl (--coverage command line argument)
• Add shebang support by @Rerumu in #149
• Work around code signing issues during Makefile builds on macOS

Community contributions

• Fix Json Encoding for AstArray by @xgladius in #279
• Add Grammar documentation by @JohnnyMorganz in #266

0.506

Changes

• Fix some cases where type checking would overflow the native stack
• Improve autocomplete behavior when assigning a partially written function call (not currently exposed through command line tools)
• Improve autocomplete type inference feedback for some expressions where previously the type would not be known
• Improve quantification performance during type checking for large types
• Improve type checking for table literals when the expected type of the table is known because of a type annotation
• Fix type checking errors in cases where required module has errors in the resulting type
• Fix debug line information for multi-line chained call sequences (#255)
• lua_ref can no longer be used with LUA_REGISTRYINDEX to prevent mistakes when migrating Lua FFI (#247)
• Fix assertions and possible crashes when executing script code indirectly via metatable dispatch from lua_equal/lua_lessthan/lua_getfield/etc. (#259)
• Fix flamegraph scripts to run under Python 2

Community contributions

• Add luaL_checkboolean and luaL_optboolean by @MathematicalDessert in #221
• Expand vectors to 4 components using compile time switch by @petrihakkinen in #214
• Removed LUALIB_API from source file method bodies by @KaleidoDeer in #235
• Add LUA_GCCOUNTB option for lua_gc by @petrihakkinen in #254
• Fix luaL_sandbox leaving a value on the stack by @petrihakkinen in #253
• Allow reconfiguring VM defaults via build defines by @kunitoki in #260
• Fix luau_load 'env' to work with absolute stack index & add lua_absindex by @petrihakkinen in #263
• Add lua_isvector, luaL_checkvector and luaL_optvector by @petrihakkinen in #261

Breaking changes

This release introduces a small breaking change in lua.h (only relevant for embedders) to improve compatibility with Lua/LuaJIT:

• lua_newuserdata now takes 2 arguments; lua_newuserdatatagged should be used if the third argument was non-0.

0.505

Changes

• Improve error recovery during type checking
• Initial (not fully complete) implementation for singleton types (RFC #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 #88)

Community Contributions

• fix unable to find library -lpthread by @leleliu008 in #203

Breaking changes

This release introduces small breaking changes in lua.h (only relevant for embedders):

• 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.

0.504

Changes

• Type mismatch errors now show detailed information for compound types, highlighting the mismatching component
• Fix string.pack bug on ARM when packing negative numbers using unsigned formats (#171)
• Implement bit32.countlz/countrz (RFC #89)
• Minor compiler throughput optimization (~2% faster compilation)
• Improve transpiler behavior for edge cases and better test coverage (not exposed through CLI at the moment)
• Improve error recovery when parsing invalid assignments
• Build fixes for fuzzing targets
• Add lua_getthreaddata/lua_setthreaddata to be able to associate custom data with coroutines

Community contributions

• Fold length operations when argument is a constant string by @bmcq-0 in #141
• Look for .luau before .lua in REPL & Analyze (#97) by @Kittenz in #124
• Fix CLI analysis reporting wrong file names by @Rerumu in #146
• Add userdata to lua_Callbacks by @LoganDark in #168
• Don't allow registry to be set to readonly by @LoganDark in #184
• Remove Roblox-specific mutable globals by @LoganDark in #185
• Save bytecode to file through CLI by @NotDSF in #170
• Feature: Web REPL using Emscripten by @MathematicalDessert in #138
• Fixes IFTODT error while compiling from an android device by @ThePotato97 in #199

0.503

Changes

• Support for time tracing for analysis/compiler (not currently exposed through CLI)
• Support for type pack arguments in type aliases (RFC: Type alias type packs #83)
• Basic support for require(path) in luau-analyze
• Add a lint warning for table.move with 0 index as part of TableOperation lint
• Remove last STL dependency from Luau.VM
• Minor VS2022 performance tuning
• Major optimizations to type checking performance on complex programs/types (up to two orders of magnitude speedup for programs
  involving huge tagged unions)
• Fix a few issues encountered by UBSAN
• Fix gcc-11 test builds
• Fix a rare corner case where luau_load wouldn't wake inactive threads which could result in a use-after-free due to GC

Community contributions

• Fix CLI abort when non lua string passed to error by @grant-h in #114
• Removes MismatchedCount argument swapping workaround by @cipharius in #103
• Spelling fixes by @jsoref in #119

0.501

First open-source release 🎉