[BUG] Type checker is failing to compare two function types

[sibarras]

Bug description

A struct with a parametrized type, who is also the return type of a function parameter (or argument) is not making the compiler happy. No matter if the function signature is exactly what is needed.

Steps to reproduce

• Include relevant code snippet or link to code that did not work as expected.

# Needs a function as a parameter
struct Foo[T: AnyType, f1: fn () -> T]:
    alias one_generator = f1

# Needs a function as an argument
struct Bar[T: AnyType]:
    var one_generator: fn () -> T

    fn __init__(inout self, f1: fn () -> T):
        self.one_generator = f1

# function to be passed
fn returns_one() -> Int:
    return 1


fn main() -> None:
    var foo = Foo[Int, returns_one]
    # error: 'Foo' parameter #1 has 'fn() -> Int' type, but value has type 'fn() -> Int'
    var bar = Bar[Int](returns_one)
    # error: invalid initialization: argument #1 cannot be converted from 'fn() -> Int' to 'fn() -> Int'

The problem goes away if I specify the return type to be a an Int instead of the type T. But this is not generic.

struct Foo[T: AnyType, f1: fn () -> Int]:
    alias one_generator = f1


struct Bar[T: AnyType]:
    var one_generator: fn () -> Int

    fn __init__(inout self, f1: fn () -> Int):
        self.one_generator = f1


fn returns_one() -> Int:
    return 1


fn main() -> None:
    alias foo = Foo[Int, returns_one]
    _ = Bar[Int](returns_one)

But this is not generic :(

System information

- What OS did you do install Mojo on ?
╭──────────────────┬─────────────────────────────────────╮
│ kernel-name      │ Linux                               │
│ kernel-release   │ 5.15.153.1-microsoft-standard-WSL2  │
│ kernel-version   │ #1 SMP Fri Mar 29 23:14:13 UTC 2024 │
│ machine          │ x86_64                              │
│ operating-system │ GNU/Linux                           │
╰──────────────────┴─────────────────────────────────────╯
- Provide version information for Mojo by pasting the output of `mojo -v`
mojo 2024.7.2505 (defedaa4)
- Provide Modular CLI version by pasting the output of `modular -v`
modular 0.8.0 (39a426b5)

[soraros]

Duplicate of #1631.