feat[lang]: export interfaces (#3919)

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.

---------

Co-authored-by: cyberthirst <cyberthirst.eth@gmail.com>

tests/functional/codegen/modules/test_exports.py

@@ -1,3 +1,9 @@
+import pytest
+
+from vyper.compiler import compile_code
+from vyper.utils import method_id
+
+
 def test_simple_export(make_input_bundle, get_contract):
     lib1 = """
 @external
@@ -147,3 +153,290 @@ def foo() -> uint256:
     c = get_contract(main, input_bundle=input_bundle)
 
     assert c.foo() == 5
+
+
+@pytest.fixture
+def simple_library(make_input_bundle):
+    ifoo = """
+@external
+def foo() -> uint256:
+    ...
+
+@external
+def bar() -> uint256:
+    ...
+    """
+    ibar = """
+@external
+def bar() -> uint256:
+    ...
+
+@external
+def qux() -> uint256:
+    ...
+    """
+    lib1 = """
+import ifoo
+import ibar
+
+implements: ifoo
+implements: ibar
+
+@external
+def foo() -> uint256:
+    return 1
+
+@external
+def bar() -> uint256:
+    return 2
+
+@external
+def qux() -> uint256:
+    return 3
+    """
+    return make_input_bundle({"lib1.vy": lib1, "ifoo.vyi": ifoo, "ibar.vyi": ibar})
+
+
+@pytest.fixture
+def send_failing_tx_to_signature(w3, tx_failed):
+    def _send_transaction(c, method_sig):
+        data = method_id(method_sig)
+        with tx_failed():
+            w3.eth.send_transaction({"to": c.address, "data": data})
+
+    return _send_transaction
+
+
+def test_exports_interface_simple(get_contract, simple_library):
+    main = """
+import lib1
+
+exports: lib1.__interface__
+    """
+    c = get_contract(main, input_bundle=simple_library)
+    assert c.foo() == 1
+    assert c.bar() == 2
+    assert c.qux() == 3
+
+
+def test_exports_interface2(get_contract, send_failing_tx_to_signature, simple_library):
+    main = """
+import lib1
+
+exports: lib1.ifoo
+    """
+    out = compile_code(
+        main, output_formats=["abi"], contract_path="main.vy", input_bundle=simple_library
+    )
+    fnames = [item["name"] for item in out["abi"]]
+    assert fnames == ["foo", "bar"]
+
+    c = get_contract(main, input_bundle=simple_library)
+    assert c.foo() == 1
+    assert c.bar() == 2
+    assert not hasattr(c, "qux")
+    send_failing_tx_to_signature(c, "qux()")
+
+
+def test_exported_fun_part_of_interface(get_contract, make_input_bundle):
+    main = """
+import lib2
+
+exports: lib2.__interface__
+    """
+    lib1 = """
+@external
+def bar() -> uint256:
+    return 1
+    """
+    lib2 = """
+import lib1
+
+@external
+def foo() -> uint256:
+    return 2
+
+exports: lib1.bar
+    """
+    input_bundle = make_input_bundle({"lib1.vy": lib1, "lib2.vy": lib2})
+    c = get_contract(main, input_bundle=input_bundle)
+    assert c.bar() == 1
+    assert c.foo() == 2
+
+
+def test_imported_module_not_part_of_interface(
+    send_failing_tx_to_signature, get_contract, make_input_bundle
+):
+    main = """
+import lib2
+
+exports: lib2.__interface__
+    """
+    lib1 = """
+@external
+def bar() -> uint256:
+    return 1
+    """
+    lib2 = """
+import lib1
+
+@external
+def foo() -> uint256:
+    return 2
+    """
+    input_bundle = make_input_bundle({"lib1.vy": lib1, "lib2.vy": lib2})
+    c = get_contract(main, input_bundle=input_bundle)
+    assert c.foo() == 2
+    send_failing_tx_to_signature(c, "bar()")
+
+
+def test_export_unimplemented_function(
+    send_failing_tx_to_signature, get_contract, make_input_bundle
+):
+    ifoo = """
+@external
+def foo() -> uint256:
+    ...
+    """
+    lib1 = """
+import ifoo
+implements: ifoo
+
+@external
+def foo() -> uint256:
+    return 1
+
+@external
+def bar() -> uint256:
+    return 2
+    """
+    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)
+    assert c.foo() == 1
+    send_failing_tx_to_signature(c, "bar()")
+
+
+# sanity check that when multiple modules implement an interface, the
+# correct one (specified by the user) gets selected for export.
+def test_export_interface_multiple_choices(get_contract, make_input_bundle):
+    ifoo = """
+@external
+def foo() -> uint256:
+    ...
+    """
+    lib1 = """
+import ifoo
+implements: ifoo
+
+@external
+def foo() -> uint256:
+    return 1
+    """
+    lib2 = """
+import ifoo
+implements: ifoo
+
+@external
+def foo() -> uint256:
+    return 2
+    """
+    main = """
+import lib1
+import lib2
+
+exports: lib1.ifoo
+    """
+    main2 = """
+import lib1
+import lib2
+
+exports: lib2.ifoo
+    """
+    input_bundle = make_input_bundle({"lib1.vy": lib1, "lib2.vy": lib2, "ifoo.vyi": ifoo})
+
+    c = get_contract(main, input_bundle=input_bundle)
+    assert c.foo() == 1
+
+    c = get_contract(main2, input_bundle=input_bundle)
+    assert c.foo() == 2
+
+
+def test_export_module_with_init(get_contract, make_input_bundle):
+    lib1 = """
+@deploy
+def __init__():
+    pass
+
+@external
+def foo() -> uint256:
+    return 1
+    """
+    main = """
+import lib1
+
+exports: lib1.__interface__
+    """
+    input_bundle = make_input_bundle({"lib1.vy": lib1})
+    c = get_contract(main, input_bundle=input_bundle)
+    assert c.foo() == 1
+
+
+def test_export_module_with_getter(get_contract, make_input_bundle):
+    lib1 = """
+counter: public(uint256)
+
+@external
+def foo():
+    self.counter += 1
+    """
+    main = """
+import lib1
+
+initializes: lib1
+exports: lib1.__interface__
+
+@deploy
+def __init__():
+    lib1.counter = 100
+    """
+    input_bundle = make_input_bundle({"lib1.vy": lib1})
+    c = get_contract(main, input_bundle=input_bundle)
+    assert c.counter() == 100
+    c.foo(transact={})
+    assert c.counter() == 101
+
+
+def test_export_module_with_default(w3, get_contract, make_input_bundle):
+    lib1 = """
+counter: public(uint256)
+
+@external
+def foo() -> uint256:
+    return 1
+
+@external
+def __default__():
+    self.counter += 1
+    """
+    main = """
+import lib1
+initializes: lib1
+
+@deploy
+def __init__():
+    lib1.counter = 5
+
+exports: lib1.__interface__
+    """
+    input_bundle = make_input_bundle({"lib1.vy": lib1})
+    c = get_contract(main, input_bundle=input_bundle)
+    assert c.foo() == 1
+    assert c.counter() == 5
+    # call `c.__default__()`
+    w3.eth.send_transaction({"to": c.address})
+    assert c.counter() == 6