nil as Object+ as Int32 causes Bug: trying to downcast Int32 <- Object+

[Veedrac]

nil as Object+ as Int32

gives

Bug: trying to downcast Int32 <- Object+
[5698614] ???
[9665895] ???
[9753974] ???
[9538525] ???
[8301014] ???
[12725667] ???
[5696909] ???
[12660264] main +40
[139740445013776] __libc_start_main +240
[5673001] _start +41
[0] ???

Error: you've found a bug in the Crystal compiler. Please open an issue, including source code that will allow us to reproduce the bug: https://github.com/crystal-lang/crystal/issues

However,

puts typeof(nil as Object+ as Int32)

correctly gives Int32.

FWIW, 1 as Object+ as Int32 also errors in this way.

[Veedrac]

Other problems with as Object+:

• (1 as Object+) == 1 causes Invalid memory access (signal 11) at address 0x7ffcfdcc3ed0 at runtime. So does (1 as Object+).itself, impressively.
• 1 == (1 as Object+) causes Bug: trying to downcast Int8 <- Object+.
• (1 as Object+) == (1 as Object+) goes into an infinite loop.
• (1 as Object+).hash gives no overload matches '(Pointer(Void), Pointer(Void) -> LibUnwind::ReasonCode)#hash', which may or may not be a bug.
• (1 as Object+).to_s fails compiling when instantiating Int#abs() with undefined method '-' for Int, which seems wrong.
• puts typeof(0 as Object+) crashes.
• typeof((raise "") as Object+) gives Object+, not NoReturn. The behaviour of NoReturn with other casts suggests that is wrong.

[refi64]

I think the TYPE+ types are internal compiler stuff that's not meant for you to actually use.

[asterite]

@kirbyfan64 is right here. The + notation is only available because in some cases the compiler wasn't behaving right and having + to check if it fixes the problem really helped. In one of the next releases we will remove this from the language (and it's not even documented).

[asterite]

(I'll still keep this issue open because it triggers a bug and shouldn't be allowed)

[Veedrac]

puts typeof(nil as Object) also throws Invalid memory access (signal 11) at address 0x7fffc2a9edb0. Is this a separate problem?

[refi64]

@Veedrac Looks like a recursion issue:

...
#46 0x0000000000e9062e in lookup_matches_checking_expansion ()
    at /media/ryan/stuff/crystal/src/compiler/crystal/semantic/call.cr:311
#47 0x0000000000e87b4a in lookup_matches_in_type ()
    at /media/ryan/stuff/crystal/src/compiler/crystal/semantic/call.cr:222
#48 0x0000000000e8784e in lookup_matches_in ()
    at /media/ryan/stuff/crystal/src/compiler/crystal/semantic/call.cr:192
#49 0x0000000000ea1690 in lookup_matches_in ()
    at /media/ryan/stuff/crystal/src/compiler/crystal/semantic/call.cr:191
#50 0x0000000000e62a94 in lookup_matches_without_splat ()
    at /media/ryan/stuff/crystal/src/compiler/crystal/semantic/call.cr:137
#51 0x0000000000e6268b in lookup_matches ()
    at /media/ryan/stuff/crystal/src/compiler/crystal/semantic/call.cr:111
#52 0x0000000000e45ace in recalculate ()
    at /media/ryan/stuff/crystal/src/compiler/crystal/semantic/call.cr:80
---Type <return> to continue, or q <return> to quit---
#53 0x0000000000e4543e in on_new_subclass ()
    at /media/ryan/stuff/crystal/src/compiler/crystal/semantic/call.cr:607
#54 0x0000000001278bd3 in notify_subclass_added ()
    at /media/ryan/stuff/crystal/src/compiler/crystal/types.cr:792
#55 0x000000000128161d in add_subclass ()
    at /media/ryan/stuff/crystal/src/compiler/crystal/types.cr:805
#56 0x0000000000f5051c in force_add_subclass ()
    at /media/ryan/stuff/crystal/src/compiler/crystal/types.cr:988
#57 0x0000000000f50fe1 in initialize ()
    at /media/ryan/stuff/crystal/src/compiler/crystal/types.cr:984
#58 0x0000000000f50e46 in *Crystal::ClassType@Crystal::ClassType#initialize<Crystal::MetaclassType, Crystal::Program, Crystal::Program, String, Crystal::Type+>:Nil () at /media/ryan/stuff/crystal/src/compiler/crystal/types.cr:2521
#59 0x0000000000f50a7d in initialize ()
    at /media/ryan/stuff/crystal/src/compiler/crystal/types.cr:2520
#60 0x0000000000f50625 in *Crystal::MetaclassType::new<Crystal::Program, Crystal::Type+, Nil, Nil>:Crystal::MetaclassType ()
    at /media/ryan/stuff/crystal/src/compiler/crystal/types.cr:2529
#61 0x0000000000f5059d in *Crystal::MetaclassType::new<Crystal::Program, Crystal::Type+>:Crystal::MetaclassType ()
    at /media/ryan/stuff/crystal/src/compiler/crystal/types.cr:2529
#62 0x0000000000adc531 in metaclass ()
    at /media/ryan/stuff/crystal/src/compiler/crystal/types.cr:21
---Type <return> to continue, or q <return> to quit---
#63 0x0000000000f528ca in virtual_type ()
    at /media/ryan/stuff/crystal/src/compiler/crystal/types.cr:2547
#64 0x0000000000b0b8ee in lookup_matches ()
    at /media/ryan/stuff/crystal/src/compiler/crystal/semantic/method_lookup.cr:234
#65 0x0000000000b0a3e9 in *Crystal::VirtualMetaclassType@Crystal::VirtualTypeLookup#lookup_matches<Crystal::VirtualMetaclassType, Crystal::CallSignature>:Crystal::Matches () at /media/ryan/stuff/crystal/src/compiler/crystal/types.cr:718
#66 0x0000000000e90c88 in lookup_matches_with_signature ()
    at /media/ryan/stuff/crystal/src/compiler/crystal/semantic/call.cr:334
#67 0x0000000000e9062e in lookup_matches_checking_expansion ()
    at /media/ryan/stuff/crystal/src/compiler/crystal/semantic/call.cr:311
#68 0x0000000000e87b4a in lookup_matches_in_type ()
... (stack trace repeats here again)

[asterite]

I just removed the + syntax, and also made sure a compile error happens when trying to cast something to Object (and to Reference, which is similar). These in the future will probably work.