feat[lang]: export interfaces

[charles-cooper]

What I did

How I did it

How to verify it

examples:

# example1.vy

from snekmate.tokens import ERC20 as base_token
initializes: base_token

exports: base_token.__interface__

@deploy
def __init__():
    base_token.__init__("My Token", "TOK", 100_000_000, "My DApp", "v0.0.1")

# example2.vy

from snekmate.tokens import ERC20 as base_token

from ethereum.ercs import IERC20

implements: base_token.IERC20
initializes: base_token

exports: base_token.IERC20

@deploy
def __init__():
    base_token.__init__("My Token", "TOK", 100_000_000, "My DApp", "v0.0.1")

Commit message

this commit allows exporting of `module.<interface>`, and also adds
`module.__interface__` which gives the interface type of the module.
in particular, this makes it easier for users to export all functions
from a module, since they do not need to list out every single function
manually.

note that since `module.__interface__` is actually an interface type, it
can theoretically be used in type expressions, e.g.,
```vyper
    x: module.__interface__ = module.__interface__(msg.sender)
```

however, it doesn't work yet as some additional work is required to
properly thread the type into the type analysis system
(see related: GH #3943).

this commit includes the restriction that only `implement`ed interfaces
can be exported, this makes the most sense from a UX / user intuition
perspective.

Description for the changelog

Cute Animal Picture

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 77.50000% with 9 lines in your changes are missing coverage. Please review.

Project coverage is 89.10%. Comparing base (cb94068) to head (8f50fcb).

Files	Patch %	Lines
vyper/semantics/analysis/module.py	73.52%	5 Missing and 4 partials ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3919      +/-   ##
==========================================
- Coverage   90.85%   89.10%   -1.75%     
==========================================
  Files          95       95              
  Lines       14416    14436      +20     
  Branches     3192     3201       +9     
==========================================
- Hits        13097    12863     -234     
- Misses        913     1118     +205     
- Partials      406      455      +49     

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[fubuloubu]

Add at least a few tests

[cyberthirst]

this test crashes the compiler (btw it tries to test selector clashes when exporting via interfaces, though the issue seems unrelated)

    ifoo = """
@external
def gsf():
    ...
    """
    lib1 = """
import ifoo

@external
@view
def tgeo() -> uint256:
    return 1
    """
    main = """
import lib1

exports: lib1.ifoo
    """
    input_bundle = make_input_bundle({"lib1.vy": lib1, "ifoo.vyi": ifoo})
    c = get_contract(main, input_bundle=input_bundle)

.0 = <dict_valueiterator object at 0x120977510>

    funcs = [
>       module_exposed_fns[f.name] for f in info.typ.functions.values() if f.is_external
    ]
E   vyper.exceptions.CompilerPanic: unhandled exception 'gsf'
E   
E     line 4:0 
E          3
E     ---> 4 exports: lib1.ifoo
E     -------^
E          5
E   

[charles-cooper]

this test crashes the compiler (btw it tries to test selector clashes when exporting via interfaces, though the issue seems unrelated)

fixed in 6650768

Addressed

[pcaversaccio]

There is currently an issue wrt the __init__ handling:

During handling of the above exception, another exception occurred:

vyper.exceptions.CompilerPanic: unhandled exception '__init__'

To replicate: use my TimelockControllerMock.vy and replace the exports with:

exports: tc.__interface__

[pcaversaccio]

Tested on snekmate contracts and tests pass. I recommend adding an additional test for __default__ function. Otherwise, lgtm.

[pcaversaccio]

There is currently an issue wrt the __init__ handling:

During handling of the above exception, another exception occurred:

vyper.exceptions.CompilerPanic: unhandled exception '__init__'

To replicate: use my TimelockControllerMock.vy and replace the exports with:

exports: tc.__interface__

Fixed via 0450173.