Imprecise Duplicate Import Check

[cyberthirst]

Version Information

• vyper Version (output of vyper --version): commit 4b4e188

Issue description

In ModuleAnalyzer._load_import_helper(), the following check ensures
that a given file is not imported multiple times:

if path in self._imported_modules:
    previous_import_stmt = self._imported_modules[path]
    raise DuplicateImport(f"{alias} imported more than once!", previous_import_stmt, node)

However, the check is not performed using a normalized path as it is
being done in the input bundle. This means that for a lib1 in the
directory project, it can be bypassed as follows:

import lib1
from ..project import lib1 as lib2

Note however that since paths are normalized in the input bundle, if the
two modules are initialized, for example, the compiler will raise an
exception.

credits: @trocher