Report incorrect types of return values and function arguments

[hazzus]

Code Example

function f() : int {
  return "hello";
}

function g(array $x) {}

g(1);

Actual Behavior

No warnings

Expected Behavior

Warning about return "hello", where "hello" doesn't match int return type of f
Warning about g(1), where 1 doesn't match array argument type of g

PHP7 actually fails stage of execution of such code with uncaught TypeError. But with some exceptions:

function u(string $x) {}

u(1)

It's executable without errors, but semantically may be not right

[i582]

Will be tracked further in #1123.