Type identifying where clause doesn't work when concrete type is provided as a generic argument

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Description

local interface IFoo
   get_type: function(self): string
end

local record Foo is IFoo where self:get_type() == "foo"
end

function Foo:get_type():string
   return "foo"
end

function Foo.new():Foo
   return setmetatable({}, { __index = Foo })
end

local function create_foo():IFoo
   return Foo.new()
end

local function process_foo<T>(foo:IFoo):T
   -- This works:
   -- return foo as T

   -- This does not:
   -- Does not compile due to errors:
   -- "cannot resolve a type for foo here"
   -- "foo (of type IFoo) can never be a T"
   assert(foo is T)
   return foo
end

local foo1 = create_foo()
local _foo2:Foo = process_foo(foo1)

assert(foo1 is Foo) -- this works fine

Contributor guide

Research direction

Investigate how the Teal compiler resolves generic type arguments and where clauses. Focus on the type checking logic for 'is' operations and assertion statements. Look for test cases related to type narrowing with generics.

Tech stack

lua

Domain

compilers

Issue type

Bug

DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.

3

Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.

1-3 hours

Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.

Active

ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.

Clear

Prerequisites

LuaType system concepts

Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.

40