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Fatal error when unifying an intersection type with a bool due to "=" or pattern-matching with true or false #7937

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vicuna opened this issue Mar 5, 2019 · 4 comments

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@vicuna
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commented Mar 5, 2019

Original bug ID: 7937
Reporter: georges.duperon
Assigned to: @Octachron
Status: resolved (set by @Octachron on 2019-03-07T11:09:56Z)
Resolution: fixed
Priority: normal
Severity: crash
Platform: Linux
OS: Debian
OS Version: Debian 9
Version: 4.07.0
Fixed in version: 4.09.0+dev
Category: typing
Monitored by: @nojb @gasche

Bug description

Fatal error: exception Ctype.Unify(_)

Triggered by this minimized version (credits go to Paul Laforgue):

type 'a fb = 'a constraint 'a = [< `K of int & 'a];;
let g : 'a. 'a fb -> bool = fun v -> v = true;;

More verbose version:

type ('a, 'select) fb = 'a constraint 'select = [< L of int & 'a | R of bool & 'a ];;
let g : 'a 'select . ('a, 'select) fb -> bool = fun v -> v = true;;

Steps to reproduce

$ cat oops.ml
type 'a fb = 'a constraint 'a = [< `K of int & 'a];;
let g : 'a. 'a fb -> bool = fun v -> v = true;;
$ ocamlc -i oops.ml
Fatal error: exception Ctype.Unify(_)

@vicuna

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commented Mar 5, 2019

Comment author: @gasche

I just tried, the same testcase still fails on trunk ( 4.09.0+dev0-2019-01-18 ).

@vicuna

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commented Mar 5, 2019

Comment author: @trefis

And the failure goes back at least to 4.02, so I'd guess it's been here "forever".

@vicuna

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commented Mar 5, 2019

Comment author: @Octachron

This was introduced in 4.01 with variants and record disambiguation: #2287 .

@vicuna

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commented Mar 7, 2019

Comment author: @Octachron

This uncaught exception is fixed in 4.09 by the PR above. Thanks for the report!

@vicuna vicuna closed this Mar 7, 2019
@vicuna vicuna added the typing label Mar 14, 2019
@vicuna vicuna added the bug label Mar 20, 2019
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