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Prevent fatal compiler error with unboxing code and GADTs#1578

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mshinwell merged 3 commits intooxcaml:mainfrom
Ekdohibs:fix-unboxing-crash
Jul 25, 2023
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Prevent fatal compiler error with unboxing code and GADTs#1578
mshinwell merged 3 commits intooxcaml:mainfrom
Ekdohibs:fix-unboxing-crash

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@Ekdohibs Ekdohibs commented Jul 19, 2023

This prevents a crash on this example:

type foo =
  | A of float
  | B of int

type bar = Other

type 'a t =
  | Foo : foo -> foo t
  | Bar : bar t


let f (type a) : a t -> a = function
  | Foo x -> x
  | Bar -> Other


let baz p x z =
  let a =
    if p then (f x)
    else B z
  in
  Sys.opaque_identity a

I think we could also rewrite the code to Invalid in this case, but I'm not sure how to do that.

@Ekdohibs Ekdohibs requested review from Gbury and chambart as code owners July 19, 2023 17:03
@mshinwell mshinwell added bug Something isn't working flambda2 Prerequisite for, or part of, flambda2 labels Jul 24, 2023
@mshinwell mshinwell changed the title Prevent crash with unboxing code and GADTs Prevent fatal compiler error with unboxing code and GADTs Jul 24, 2023
chambart
chambart approved these changes Jul 24, 2023
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I tried to think about potential problems since this might be a bit tricky. But this seems sound.

It would be possible to produce invalid in that case, but it is probably too much work for quite a small benefit.

chambart
chambart reviewed Jul 24, 2023
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@Ekdohibs Ekdohibs requested a review from lukemaurer as a code owner July 25, 2023 09:13
@mshinwell mshinwell merged commit 83fa0b2 into oxcaml:main Jul 25, 2023
@Gbury Gbury mentioned this pull request Aug 1, 2023
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@chambart chambart chambart approved these changes

@mshinwell mshinwell mshinwell approved these changes

@Gbury Gbury Awaiting requested review from Gbury

@lukemaurer lukemaurer Awaiting requested review from lukemaurer

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3 participants

@Ekdohibs @mshinwell @chambart