Compiler bug in Array#unshift

[mcarpenter]

Description

I have a table (matrix, 2D array) of type Array(Array(Int32 | String)). If I #unshift a row of type Array(String) onto it then the compiler crashes with Function return type does not match operand type of return inst!. Running 0.35.1 from the official PPA (Ubuntu repo) on Ubuntu 18.

The error appears to be related to the union type: it goes away with Array(Array(String)) at least. Other methods (<<, +) seem to be okay.

Reproducer

foo.cr:

table = [["x", 1]]
header = [] of String
table.unshift(header)

$ crystal foo.cr
Module validation failed: Function return type does not match operand type of return inst!
  ret i32* %1, !dbg !69
 %"Array(Int32 | String)"* (Exception)
  from ../../../../../crystal/src/int.cr:1091:11 in 'finish'
  from ../../../../../crystal/src/compiler/crystal/codegen/codegen.cr:69:7 in 'codegen'
  from ../../../../../crystal/src/compiler/crystal/compiler.cr:172:16 in 'compile'
  from ../../../../../crystal/src/compiler/crystal/command.cr:209:5 in 'run_command'
  from ../../../../../crystal/src/compiler/crystal/command.cr:116:7 in 'run'
  from ../../../../../crystal/src/compiler/crystal.cr:11:1 in '__crystal_main'
  from ../../../../../crystal/src/crystal/main.cr:105:5 in 'main'
  from src/env/__libc_start_main.c:94:2 in 'libc_start_main_stage2'
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

Version and platform information

$ crystal --version
Crystal 0.35.1 [5999ae29b] (2020-06-19)

LLVM: 8.0.0
Default target: x86_64-unknown-linux-gnu
$ cat /etc/lsb-release 
DISTRIB_ID=Ubuntu
DISTRIB_RELEASE=18.04
DISTRIB_CODENAME=bionic
DISTRIB_DESCRIPTION="Ubuntu 18.04.5 LTS"
$ uname -a 
Linux juliet 4.15.0-128-lowlatency #131-Ubuntu SMP PREEMPT Wed Dec 9 08:07:00 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux

[Sija]

Same here on macOS (10.14.6):

Module validation failed: Function return type does not match operand type of return inst!
  ret i32* %1, !dbg !71
 %"Array(Int32 | String)"* (Exception)
  from src/llvm/module.cr:80:9 in 'verify'
  from src/compiler/crystal/codegen/codegen.cr:369:9 in 'finish'
  from src/compiler/crystal/codegen/codegen.cr:69:7 in 'codegen'
  from src/compiler/crystal/codegen/codegen.cr:65:5 in 'codegen:debug:single_module'
  from src/compiler/crystal/progress_tracker.cr:22:7 in 'codegen'
  from src/compiler/crystal/compiler.cr:172:16 in 'compile'
  from src/compiler/crystal/command/eval.cr:29:14 in 'eval'
  from src/compiler/crystal/command.cr:97:7 in 'run'
  from src/compiler/crystal/command.cr:49:5 in 'run'
  from src/compiler/crystal/command.cr:48:3 in 'run'
  from src/compiler/crystal.cr:11:1 in '__crystal_main'
  from src/crystal/main.cr:105:5 in 'main_user_code'
  from src/crystal/main.cr:91:7 in 'main'
  from src/crystal/main.cr:114:3 in 'main'
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

crystal --version:

Crystal 1.0.0-dev [7d9bbdd6e] (2021-01-06)

LLVM: 11.0.0
Default target: x86_64-apple-macosx

[asterite]

Reduced:

class Gen(T)
end

ptr = Pointer(Gen(Int32 | Char)).malloc(1_u64)
ptr.value = Gen(Int32).new

The above shouldn't compile. It's the same with every generic type. I think for Pointer specially we need to match generic in an invariant way.

[mcarpenter]

Hi, thanks for the quick response and detailed explanation.

For others that may stumble on this: I tried a few workarounds and found that I can nudge the compiler in the right direction.

I aimed to do:

header : Array(String|Int32) = %w{Name Size} # Error: type must be Array(String | Int32), not Array(String)

Instead:

header : Array(String|Int32) = ["Name", "Size"] # Error: type must be Array(String | Int32), not Array(String)
header : Array(String|Int32) = ["Name", Int32.new(5)] # OK (but not useful for me)
header : Array(String|Int32) = ["Name", "Size"].as(Array(String|Int32)) # Error: can't cast Array(String) to Array(String | Int32)
header : Array(String|Int32) = ["Name".as(String|Int32), "Size"] # OK
header : Array(String|Int32) = [] of (String|Int32) << "Name" << "Size" # OK
header : Array(String|Int32) = [] of (String|Int32) + %w{Name Size} # OK
header = [] of (String|Int32) + %w{Name Size} # OK

[Blacksmoke16]

@mcarpenter You should just be able to do header : Array(String|Int32) = ["Name", "Size"] of String | Int32.

[mcarpenter]

I can drop the type restriction too:

header = ["Name", "Size"] of String|Int32

Kind of a shame that doesn't work with %w{} but it's certainly nicer than what I had. Thanks!