Arbitraries.GenForType does not support arrays

[Wessie]

passing an array type to GenForType returns nil, and this only panics once the properties are actually ran so it isn't obvious what the issue is, it produces the following stack trace:

! roundtrip: Error on property evaluation after 0 passed tests: Check
   paniced: runtime error: invalid memory address or nil pointer dereference
goroutine 19 [running]:
runtime/debug.Stack()
        /usr/local/go/src/runtime/debug/stack.go:24 +0x5e
github.com/leanovate/gopter/prop.ForAll.SaveProp.func3.1()
        /home/wessie/go/pkg/mod/github.com/leanovate/[email protected]/prop.go:20 +0x6b
panic({0x6c7ec0?, 0x96c6a0?})
        /usr/local/go/src/runtime/panic.go:914 +0x21f
github.com/leanovate/gopter/prop.ForAll.func1(0xc0000be2e0)
        /home/wessie/go/pkg/mod/github.com/leanovate/[email protected]/prop/forall.go:33 +0xc7
github.com/leanovate/gopter/prop.ForAll.SaveProp.func3(0x7fc1b4964b98?)
        /home/wessie/go/pkg/mod/github.com/leanovate/[email protected]/prop.go:25 +0x5b
github.com/leanovate/gopter.Prop.Check.func1(0x0, 0xc000090580)
        /home/wessie/go/pkg/mod/github.com/leanovate/[email protected]/prop.go:53 +0x132
github.com/leanovate/gopter.(*runner).runWorkers(0xc000094f90)
        /home/wessie/go/pkg/mod/github.com/leanovate/[email protected]/runner.go:49 +0x1cd
github.com/leanovate/gopter.Prop.Check(0xc000090560, 0xc0000f0b80)
        /home/wessie/go/pkg/mod/github.com/leanovate/[email protected]/prop.go:112 +0x1be
github.com/leanovate/gopter.(*Properties).Run(0xc0000d9f38, {0x78f100, 0xc0000be2a0})
        /home/wessie/go/pkg/mod/github.com/leanovate/[email protected]/properties.go:37 +0xa9
github.com/leanovate/gopter.(*Properties).TestingRun(0xc0000d9f38, 0xc000084ea0, {0x0, 0x0, 0x6b14a0?})
        /home/wessie/go/pkg/mod/github.com/leanovate/[email protected]/properties.go:56 +0xfc

GenForType should probably panic if there is an unsupported type

[untoldwind]

Can you provide a short example to reproduce this?

[Wessie]

a := arbitrary.DefaultArbitraries()
gen := a.GenForType(reflect.TypeOf([20]byte{}))
fmt.Println(gen)

will print <nil> https://go.dev/play/p/1_Mxhuc5GKl

[untoldwind]

Can you check if the current master branch fixes your problem?

[Wessie]

Yes, this fixes array support, but it would still be a nice quality of life change if passing an unsupported type to GenForType actually panicked with a reasonable message indicating such.

Also there is a typo in the array_shink.go filename

[Wessie]

I'm sorry, it seems panicking on unsupported types is a breaking change.

Since struct types ignore unsupported fields it means anyone generating structs with unsupported fields now gets a panic instead.

It's fine for the map/slice/array versions but structs explicitly ignore fields https://github.com/leanovate/gopter/blob/master/arbitrary/gen_for_kind.go#L331 if GenForType returns nil.

Sorry for the shortsightedness, maybe we can move the check into Arbitraries.ForAll instead.

[untoldwind]

Removed the panic for now, have to dig a bit deeper into the ForAll