There seems to be something wrong with unsafePartial

[i-am-the-slime]

I was trying to compile purescript-unicode. I had to add some FFI and that was fine. However I got weird errors when it got to compiling/running this piece of code:

bsearch ∷ ∀ a . a -> Array a -> Int -> (a -> a -> Ordering) -> Maybe a
bsearch a array size compare = go 0 size
    where
    go i k | i > k = Nothing
           | otherwise = let j = floor (toNumber (i + k) / 2.0)
                             b = unsafePartial (Array.unsafeIndex array j)
                         in case compare a b of
                              EQ -> Just b
                              GT -> go (j + 1) k
                              _  -> go i (j - 1)

The error being:

build project.localhost/purescript-native/output/Main: cannot load project.localhost/purescript-native/output/array: cannot find module providing package project.localhost/purescript-native/output/array

If I rename the variable to anything other than array the error now complains about the new name, e.g.:

build project.localhost/purescript-native/output/Main: cannot load project.localhost/purescript-native/output/otherName: cannot find module providing package project.localhost/purescript-native/output/otherName

The beginning of Data_Char_Unicode_Internal.purs is this:

// Code generated by psgo. DO NOT EDIT.

package Data_Char_Unicode_Internal

import . "github.com/purescript-native/go-runtime"

import (
    "project.localhost/purescript-native/output/Data.Show"
    "project.localhost/purescript-native/output/Data.Maybe"
    "project.localhost/purescript-native/output/Data.Boolean"
    "project.localhost/purescript-native/output/Data.Int"
    "project.localhost/purescript-native/output/otherName"
    "project.localhost/purescript-native/output/Data.Ordering"
    "project.localhost/purescript-native/output/Data.Array"
    "project.localhost/purescript-native/output/Data.Eq"
    "project.localhost/purescript-native/output/Data.Functor"
)

Note the suspicious

    "project.localhost/purescript-native/output/otherName"

When I change the code to not use unsafeIndex but this:

b = fromMaybe' (\_ -> unsafeCrashWith "Array index out of bounds") (Array.index otherName j)

the build succeeds.

I don't know what this might be but I'm hopeful you might know!

[andyarvanitis]

Yeah, I'm able to reproduce it and see the bad codegen. It looks like a simple bug in the unsafeIndex inliner that's easy to fix. I'll have a closer look in a bit.

[andyarvanitis]

I've finished testing the fix, and it's checked in as well as in the "2019-12-03" binary release.

Also let me know if you see a "missing function 'Index'" error (it would be at the go build stage). If you do, see if doing

$ go mod tidy && go clean -modcache

fixes it. Thanks for trying it and for the bug report.

[i-am-the-slime]

I will probably try tomorrow!

[i-am-the-slime]

I think this worked.