fix: mutability check for interface implements

examples/tokens/ERC1155ownable.vy

@@ -393,7 +393,7 @@ def setContractURI(contractUri: String[MAX_URI_LENGTH]):
     self.contractURI = contractUri
     log URI(contractUri, 0)
 
-@pure
+@view
 @external
 def supportsInterface(interfaceId: bytes4) -> bool:
     """

examples/tokens/ERC721.vy

@@ -93,7 +93,7 @@ def __init__():
     self.baseURL = "https://api.babby.xyz/metadata/"
 
 
-@pure
+@view
 @external
 def supportsInterface(interface_id: bytes4) -> bool:
     """

tests/functional/syntax/test_interfaces.py

@@ -210,6 +210,50 @@ def approve(_spender : address, _value : uint256) -> bool:
     """,
         InterfaceViolation,
     ),
+    (
+        # `payable` decorator not implemented
+        """
+interface testI:
+    def foo() -> uint256: payable
+
+implements: testI
+
+@external
+def foo() -> uint256:
+    return 0
+    """,
+        InterfaceViolation,
+    ),
+    (
+        # decorators must be strictly identical
+        """
+interface Self:
+    def protected_view_fn() -> String[100]: nonpayable
+
+implements: Self
+
+@external
+@pure
+def protected_view_fn() -> String[100]:
+    return empty(String[100])
+    """,
+        InterfaceViolation,
+    ),
+    (
+        # decorators must be strictly identical
+        """
+interface Self:
+    def protected_view_fn() -> String[100]: view
+
+implements: Self
+
+@external
+@pure
+def protected_view_fn() -> String[100]:
+    return empty(String[100])
+    """,
+        InterfaceViolation,
+    ),
 ]
 
 

vyper/semantics/types/function.py

@@ -480,10 +480,7 @@ def implements(self, other: "ContractFunctionT") -> bool:
         if return_type and not return_type.compare_type(other_return_type):  # type: ignore
             return False
 
-        if self.mutability > other.mutability:
-            return False
-
-        return True
+        return self.mutability == other.mutability
 
     @cached_property
     def default_values(self) -> dict[str, vy_ast.VyperNode]: