teal-language/tl

internals: remove duplicate entries from interface_list

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#1,018 opened on Jul 17, 2025

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good first issue

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Description

Reported by @upedd :

One quick question about Teal, when dealing with complex interface hierarchies, sometimes there are duplicate entries in the interface_list of a record type. Is this the expected behavior? See example:

local interface A 
end

local interface B is A
end

local interface C is A
end

-- interface_list of D is now {B, A, C, A} 
local record D is B, C
end

My reply:

it should not hurt in practice, but we should clean it up. The order does matter since that is how conflicts are handled, but basically we should be able to ignore duplicate entries, so {B, A, C} would be the correct list in that case. I'll file an issue to remind myself to clean it up.

Contributor guide

Research direction
Examine how interface list is constructed in the type checker and add deduplication logic while preserving order.
Tech stack
lua
Domain
backend
Issue type
Refactor
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
2
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
Lua
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
75