fix[tool]: include structs in -f interface output (#4294)

the `-f interface` output was missing struct definitions; this commit
fixes the issue.

this commit also does some small code touchups in the
`build_interface_output()` function, and makes the number of newlines
between functions, events and structs consistent - to be 2 `\n`
characters.

---------

Co-authored-by: Charles Cooper <cooper.charles.m@gmail.com>

tests/functional/codegen/test_interfaces.py

@@ -13,6 +13,7 @@
 )
 
 
+# TODO CMC 2024-10-13: this should probably be in tests/unit/compiler/
 def test_basic_extract_interface():
     code = """
 # Events
@@ -22,6 +23,7 @@ def test_basic_extract_interface():
     _to: address
     _value: uint256
 
+
 # Functions
 
 @view
@@ -37,6 +39,7 @@ def allowance(_owner: address, _spender: address) -> (uint256, uint256):
     assert code_pass.strip() == out.strip()
 
 
+# TODO CMC 2024-10-13: this should probably be in tests/unit/compiler/
 def test_basic_extract_external_interface():
     code = """
 @view
@@ -68,6 +71,7 @@ def test(_owner: address): nonpayable
     assert interface.strip() == out.strip()
 
 
+# TODO CMC 2024-10-13: should probably be in syntax tests
 def test_basic_interface_implements(assert_compile_failed):
     code = """
 from ethereum.ercs import IERC20
@@ -82,6 +86,7 @@ def test() -> bool:
     assert_compile_failed(lambda: compile_code(code), InterfaceViolation)
 
 
+# TODO CMC 2024-10-13: should probably be in syntax tests
 def test_external_interface_parsing(make_input_bundle, assert_compile_failed):
     interface_code = """
 @external
@@ -126,6 +131,7 @@ def foo() -> uint256:
         compile_code(not_implemented_code, input_bundle=input_bundle)
 
 
+# TODO CMC 2024-10-13: should probably be in syntax tests
 def test_log_interface_event(make_input_bundle, assert_compile_failed):
     interface_code = """
 event Foo:
@@ -160,6 +166,7 @@ def bar() -> uint256:
 ]
 
 
+# TODO CMC 2024-10-13: should probably be in syntax tests
 @pytest.mark.parametrize("code,filename", VALID_IMPORT_CODE)
 def test_extract_file_interface_imports(code, filename, make_input_bundle):
     input_bundle = make_input_bundle({filename: ""})
@@ -177,6 +184,7 @@ def test_extract_file_interface_imports(code, filename, make_input_bundle):
 ]
 
 
+# TODO CMC 2024-10-13: should probably be in syntax tests
 @pytest.mark.parametrize("code,exception_type", BAD_IMPORT_CODE)
 def test_extract_file_interface_imports_raises(
     code, exception_type, assert_compile_failed, make_input_bundle
@@ -726,3 +734,43 @@ def bar() -> uint256:
     c = get_contract(code, input_bundle=input_bundle)
 
     assert c.foo() == c.bar() == 1
+
+
+def test_interface_with_structures():
+    code = """
+struct MyStruct:
+    a: address
+    b: uint256
+
+event Transfer:
+    sender: indexed(address)
+    receiver: indexed(address)
+    value: uint256
+
+struct Voter:
+    weight: int128
+    voted: bool
+    delegate: address
+    vote: int128
+
+@external
+def bar():
+    pass
+
+event Buy:
+    buyer: indexed(address)
+    buy_order: uint256
+
+@external
+@view
+def foo(s: MyStruct) -> MyStruct:
+    return s
+    """
+
+    out = compile_code(code, contract_path="code.vy", output_formats=["interface"])["interface"]
+
+    assert "# Structs" in out
+    assert "struct MyStruct:" in out
+    assert "b: uint256" in out
+    assert "struct Voter:" in out
+    assert "voted: bool" in out

vyper/compiler/output.py

@@ -128,22 +128,33 @@ def build_interface_output(compiler_data: CompilerData) -> str:
     interface = compiler_data.annotated_vyper_module._metadata["type"].interface
     out = ""
 
-    if interface.events:
-        out = "# Events\n\n"
+    if len(interface.structs) > 0:
+        out += "# Structs\n\n"
+        for struct in interface.structs.values():
+            out += f"struct {struct.name}:\n"
+            for member_name, member_type in struct.members.items():
+                out += f"    {member_name}: {member_type}\n"
+            out += "\n\n"
+
+    if len(interface.events) > 0:
+        out += "# Events\n\n"
         for event in interface.events.values():
             encoded_args = "\n    ".join(f"{name}: {typ}" for name, typ in event.arguments.items())
-            out = f"{out}event {event.name}:\n    {encoded_args if event.arguments else 'pass'}\n"
+            out += f"event {event.name}:\n    {encoded_args if event.arguments else 'pass'}\n\n\n"
 
-    if interface.functions:
-        out = f"{out}\n# Functions\n\n"
+    if len(interface.functions) > 0:
+        out += "# Functions\n\n"
         for func in interface.functions.values():
             if func.visibility == FunctionVisibility.INTERNAL or func.name == "__init__":
                 continue
             if func.mutability != StateMutability.NONPAYABLE:
-                out = f"{out}@{func.mutability.value}\n"
+                out += f"@{func.mutability.value}\n"
             args = ", ".join([f"{arg.name}: {arg.typ}" for arg in func.arguments])
             return_value = f" -> {func.return_type}" if func.return_type is not None else ""
-            out = f"{out}@external\ndef {func.name}({args}){return_value}:\n    ...\n\n"
+            out += f"@external\ndef {func.name}({args}){return_value}:\n    ...\n\n\n"
+
+    out = out.rstrip("\n")
+    out += "\n"
 
     return out