0.706

Hey everyone! We've been hard at work fixing bugs and improving native codegen. Enjoy!

Analysis

• Rename the class tag to extern in type functions

• Fix #2204

• Rework type unification in terms of subtyping.

  This uses the new solver's understanding of subtyping to drive unification for
  some internal callsites. This is a broad change that should result in more
  consistent inference. For example:

  local function sum<T>(x: T, y: T, z: (T, T) -> T) return z(x, y) end
  local function sumrec(f: typeof(sum))
      return sum(2, 3, function<X>(g: X, h: X): add<X, X> return g + h end)
  end
  -- Prior we would claim that `b` is of type `add<X, X> | number`: not good!
  -- We now correctly claim that it is of type `number` thanks to bug fixes
  -- made to subtyping that did not make their way to the unifier.
  local b = sumrec(sum)

Native Codegen

• Improve vector handling in binary operations
• Fix missed optimization causing an assertion failure
• Propagate loads of STORE_VECTOR components produced by UINT_TO_FLOAT
• Constant-fold new operand of CHECK_BUFFER_LEN
• For register load-store propagation, use the second operand only for LOAD_FLOAT
• TValue store cannot be removed when it's partially over-written
• Rework equality and ordering comparisons to fix issues and be more type aware
• Migrate Luau NCG IrInst operands representation to SmallVector

Runtime

• Fix 64-bit countrz to build on 32 bit Windows.
• Remap Luau local debug and type information after performing jump expansion
• Add support for building Luau as a shared library
• Luau should be able to make fastcalls even if library name is obscured by a local polyfill

OSS Contributions

• Track type spans in ToStringResult to support decomposition #2163
• Expose luaL_traceback from Lua C API #2167

Internal Contributors

Co-authored-by: Ariel Weiss arielweiss@roblox.com
Co-authored-by: Hunter Goldstein hgoldstein@roblox.com
Co-authored-by: Ilya Rezvov irezvov@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: 0.705...0.706