Type checker does not detect a signature mismatch

[FriedrichGretz]

Bug description

Consider the source code below. The function expectCallback needs another function as its argument to produce a number. If we use callback this works as expected.

However, if (by mistake) we use a method we'd expect the compiler to detect a signature mismatch because methods implicitly have an extra this parameter. This is not detected. The code below compiles without issues.

Only during runtime we see the expected problem:

RuntimeError: null function or function signature mismatch
    at assembly/index/expectCallback (wasm://wasm/ca122872:wasm-function[50]:0xfee)

Steps to reproduce

function callback(a: i32): i32 {
  return a + 3
}

class C {
  callback(a: i32): i32 {
    return a + 3
  }  
}

function expectCallback(c: ((arg0:i32) => i32)): i32 {
  return c(4)
}

export function fut(): i32 {
  //return expectCallback(callback)
  const cl = new C()
  return expectCallback(cl.callback)
}

AssemblyScript version

0.27.5