Explicitly returning a lib struct or tuple inside a `fun` results in a codegen error

[BlobCodes]

Bug Report

Any code explicitly returning a lib struct or a tuple inside a fun results in a codegen error.

Here's an example (also works with empty prelude):

lib LibFoo
  struct Bar
    value : Int32
  end
end

fun foo : LibFoo::Bar
  return LibFoo::Bar.new
end

This results in the following compilation error:

Module validation failed: Function return type does not match operand type of return inst!
  ret %"struct.LibFoo::Bar" %2, !dbg !668
 { i64 } (Exception)
  from /crystal/src/string.cr:5488:31 in 'codegen'
  from /crystal/src/compiler/crystal/compiler.cr:195:16 in 'compile:combine_rpath'
  from /crystal/src/compiler/crystal/compiler.cr:188:56 in 'compile:combine_rpath'
  from /crystal/src/compiler/crystal/command/eval.cr:30:5 in 'eval'
  from /crystal/src/compiler/crystal/command.cr:125:12 in 'run'
  from /crystal/src/compiler/crystal.cr:11:1 in '__crystal_main'
  from /crystal/src/crystal/main.cr:129:5 in 'main'
  from src/env/__libc_start_main.c:95:2 in 'libc_start_main_stage2'

---

Another example:

fun foo : {Int32}
  return {0}
end

..which results in this error:

Module validation failed: Function return type does not match operand type of return inst!
  ret %"Tuple(Int32)" %2, !dbg !668
 { i64 } (Exception)
  from /crystal/src/string.cr:5488:31 in 'codegen'
  from /crystal/src/compiler/crystal/compiler.cr:195:16 in 'compile:combine_rpath'
  from /crystal/src/compiler/crystal/compiler.cr:188:56 in 'compile:combine_rpath'
  from /crystal/src/compiler/crystal/command/eval.cr:30:5 in 'eval'
  from /crystal/src/compiler/crystal/command.cr:125:12 in 'run'
  from /crystal/src/compiler/crystal.cr:11:1 in '__crystal_main'
  from /crystal/src/crystal/main.cr:129:5 in 'main'
  from src/env/__libc_start_main.c:95:2 in 'libc_start_main_stage2'

System information

$ crystal -v
Crystal 1.11.2 [fda656c71] (2024-01-18)

LLVM: 15.0.7
Default target: x86_64-unknown-linux-gnu