[stdlib] Fix allow immutable UnsafePointer and adjust .unsafe_ptr() methods

[martinvuyk]

Fix allow immutable UnsafePointer and adjust .unsafe_ptr() methods. Fixes MSTDL-956

[martinvuyk]

@JoeLoser All the tests are passing but the packaging of test_utils is giving problems, the linker keeps grabbing nightly stdlib even though the script sets MODULAR_MOJO_NIGHTLY_IMPORT_PATH=$BUILD_DIR and I've also tried adding mojo package "${TEST_UTILS_PATH}" -I ${BUILD_DIR}.

[JoeLoser]

This is so exciting to see coming together! I appreciate you tackling this! 🎉

[JoeLoser]

Question Can you help me understand why this is needed? You should be able to directly access the is_mutable from the call sites without any issues.

[martinvuyk]

Not on type signatures where all you have is __origin_of() and you want to extract the mutability of that:

    @staticmethod
    @always_inline("nodebug")
    fn address_of(
        ref [_, address_space._value.value]arg: type
    ) -> UnsafePointer[
        type,
        address_space,
        is_mutable = _is_mutable_origin[__origin_of(arg)].result,
        origin = __origin_of(arg),
    ] as result:
        """Gets the address of the argument.

        Args:
            arg: The value to get the address of.

        Returns:
            An UnsafePointer which contains the address of the argument.
        """
        return __type_of(result)(
            __mlir_op.`lit.ref.to_pointer`(__get_mvalue_as_litref(arg))
        )

Though if there is a cleaner way to extract an attribute from __origin_of() I'm all ears

[soraros]

Can we turn these into conditional conformance?

[martinvuyk]

Theoretically the compiler won't even let you mutate the origin. I added them for convenience so that users get a clear error message. Conditional Conformance doesn't give you that, only a cryptic error that some parameters can't be inferred.