fix[lang]: disallow absolute relative imports

[sandbubbles]

What I did

• fix import system allows absolute relative imports #4184

How I did it

• Removed implicit relative imports in submodules, eliminating ambiguity in import paths.
• Removed the lines that added the current directory to the top of the search paths. As a result, the poke_search_path function may no longer be necessary.

How to verify it

• added tests

Commit message

this commit changes the behavior of search paths within
submodules. previously the current module's parent was appended to
the search path in the import recursion. this means that given the
following directory structure, this code is legal:

```
# directory structure:
# subdir/foo.vy
# subdir/bar.vy
```

```
# subdir/foo.vy
import bar
```

which has the same semantics as

```
# subdir/foo.vy
from . import bar
```

this represented a divergence wrt python's import system. in python,
only the second example is allowed.

this commit changes the semantics to match python, so that relative
imports use the current directory as search path, but absolute imports
can only use the top-level search path. (the directory containing the
top-level compilation target is still included in the search path, but
this only happens at the top of the recursion, same as in python -
https://docs.python.org/3/library/sys_path_init.html).

misc/refactor:
- remove dead `add_search_path()` method
- remove now-dead `poke_search_path()`

Description for the changelog

Cute Animal Picture

[charles-cooper]

yes, i think poke_search_paths is probably dead now. can you check? if so, let's remove it!

[charles-cooper]

i guess we can fuse load_import_helper right?

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.46%. Comparing base (ebe26a6) to head (be01034).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4268      +/-   ##
==========================================
- Coverage   91.12%   88.46%   -2.67%     
==========================================
  Files         115      115              
  Lines       16235    16236       +1     
  Branches     2732     2733       +1     
==========================================
- Hits        14794    14363     -431     
- Misses       1004     1352     +348     
- Partials      437      521      +84     

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[cyberthirst]

@charles-cooper, have you considered the concept of packages? because we don't have it, we allow relative imports that can point even outside the project's directory

[cyberthirst]

yeah i know, those will raise a compiler panic if you try to create an input bundle.

i have main.vy in ./tests/custom and run vyper from the same dir as in which tests are

from .... import lib1

exports: lib1.__interface__

so the import targets a file which is in the parent of the project's dir (from which vyper's run) .. and it compiles fine

i tried to create an output bundle (vyper -f archive) with this setup and it led to compiler panic

Error compiling: tests/custom/test4.vy
vyper.exceptions.CompilerPanic: Invalid path: /Users/blabla/lib1.vy

This is an unhandled internal compiler error. Please create an issue on Github to notify the developers!
https://github.com/vyperlang/vyper/issues/new?template=bug.md

[charles-cooper]

@sandbubbles please resolve merge conflicts

[charles-cooper]

Suggested change

	self.input_bundle.search_paths += [current_search_path]
	self.input_bundle.search_paths.append(current_search_path)

[charles-cooper]

this is kind of weird actually because on line 221, we already set search_paths to [current_search_path]

[sandbubbles]

I think the issue is we need to set it temporarily to only one path, but then we need to add it to search paths in case there is an absolute import that uses it

[charles-cooper]

isn't that handled in the recursion by line 221?
https://github.com/vyperlang/vyper/pull/4268/files/c91f13e870bce8001eeec83dd96b8320c53d4343#diff-dc7dbf75948a3fce0db2cfa0fa819c964a534604d06f72ae88d18e3e3eef78b6R221

[charles-cooper]

i pushed a clean up in a140226

[sandbubbles]

I must have though that example such as the following should work (but its what we were fixing in the first place).

#a.vy
from .subdir import b

and

#b.vy
from subdir.subsubdir import c

[sandbubbles]

This should be ready for rereview

[charles-cooper]

lgtm, thank you