Declaring a u16 function breaks the % operation

[certik]

Minimal example:

from lpython import i16, i32

def f():
    i: i32 = 5
    print(i16(i % 1023))

def u16(x: i16) -> i32:
    if x >= i16(0):
        return i32(x)
    else:
        return i32(x) + 65536

This gives:

$ lpython a.py 
warning: The module 'lpython_builtin' located in /Users/ondrej/repos/lpython/src/bin/../runtime/lpython_builtin.py cannot be loaded
 --> a.py:5:15
  |
5 |     print(i16(i % 1023))
  |               ^^^^^^^^ imported here

semantic error: Unsupported type annotation: u16
   --> /Users/ondrej/repos/lpython/src/bin/../runtime/lpython_builtin.py:504:26
    |
504 | def _lpython_floordiv(a: u16, b: u16) -> u16:
    |                          ^^^ 

The issue is likely here:

    ASR::ttype_t* get_type_from_var_annotation(std::string var_annotation,
        const Location& loc, Vec<ASR::dimension_t>& dims,
        AST::expr_t** m_args=nullptr, size_t n_args=0,
        bool raise_error=true, ASR::abiType abi=ASR::abiType::Source,
        bool is_argument=false) {
        ASR::ttype_t* type = nullptr;
        ASR::symbol_t *s = current_scope->resolve_symbol(var_annotation);
        if (s) {
            if (ASR::is_a<ASR::Variable_t>(*s)) {
...

Where it finds s as a "user" function. However this function was declared below and in the main module, not the built-in module, so unless the module is inlined, this shouldn't happen.

Finally, the error message should point to the user defined function and say that it can't be used for annotation.

[ubaidsk]

Since #2049 we were using the same Translation_Unit_t/global_scope across modules. The symbols defined in the main_module get added to the Translation_Unit_t/global_scope. Due to this, other modules are able to access the symbols defined in the main_module (as the global_scope is shared with them). I think, therefore, the error described in this issue occurs.

I fixed this issue in #2161 by processing/forming the main_module as a Module_t (and embedding it inside the Translation_Unit_t. This way the symbols defined in the main_module are not added to the global scope (but instead to the module scope) and thus are not accessible by other modules.

[certik]

@Shaikh-Ubaid awesome, great job!

I think this is a cleaner solution.