Generate structs for the return data of abigen-erated contracts (#1440)

* convert some helper functions

* use said helpers

* more

* don't derive EthCall on return structs

* move return structs to separate function

* remove unused

* remove duplicate code

* reduce code duplication

also use an iterator instead of a presized vector

* comments

* stuck

* fix wrong field

* rename

* don't generate structs for no-output functions

* cosmetic changes

* test: decode and verify result

* more testing

unnamed output (tuple struct)
no output (doesn't exist) -> can't verify this in code though

* Update ethers-contract/ethers-contract-abigen/src/contract/methods.rs

Co-authored-by: Matthias Seitz <matthias.seitz@outlook.de>

* remove dbg print

oops :(

Co-authored-by: Matthias Seitz <matthias.seitz@outlook.de>

ethers-contract/ethers-contract-abigen/src/contract/methods.rs

@@ -37,9 +37,15 @@ impl Context {
             .collect::<Result<Vec<_>>>()?;
 
         let function_impls = quote! { #( #functions )* };
-        let call_structs = self.expand_call_structs(aliases)?;
+        let call_structs = self.expand_call_structs(aliases.clone())?;
+        let return_structs = self.expand_return_structs(aliases)?;
 
-        Ok((function_impls, call_structs))
+        let all_structs = quote! {
+            #call_structs
+            #return_structs
+        };
+
+        Ok((function_impls, all_structs))
     }
 
     /// Returns all deploy (constructor) implementations
@@ -135,7 +141,47 @@ impl Context {
         })
     }
 
-    /// Expands all structs
+    /// Expands to the corresponding struct type based on the inputs of the given function
+    fn expand_return_struct(
+        &self,
+        function: &Function,
+        alias: Option<&MethodAlias>,
+    ) -> Result<TokenStream> {
+        let struct_name = expand_return_struct_name(function, alias);
+        let fields = self.expand_output_params(function)?;
+        // no point in having structs when there is no data returned
+        if function.outputs.is_empty() {
+            return Ok(TokenStream::new())
+        }
+        // expand as a tuple if all fields are anonymous
+        let all_anonymous_fields = function.outputs.iter().all(|output| output.name.is_empty());
+        let return_type_definition = if all_anonymous_fields {
+            // expand to a tuple struct
+            expand_data_tuple(&struct_name, &fields)
+        } else {
+            // expand to a struct
+            expand_data_struct(&struct_name, &fields)
+        };
+        let abi_signature = function.abi_signature();
+        let doc = format!(
+            "Container type for all return fields from the `{}` function with signature `{}` and selector `{:?}`",
+            function.name,
+            abi_signature,
+            function.selector()
+        );
+        let abi_signature_doc = util::expand_doc(&doc);
+        let ethers_contract = ethers_contract_crate();
+        // use the same derives as for events
+        let derives = util::expand_derives(&self.event_derives);
+
+        Ok(quote! {
+            #abi_signature_doc
+            #[derive(Clone, Debug, Default, Eq, PartialEq, #ethers_contract::EthAbiType, #ethers_contract::EthAbiCodec, #derives)]
+            pub #return_type_definition
+        })
+    }
+
+    /// Expands all call structs
     fn expand_call_structs(&self, aliases: BTreeMap<String, MethodAlias>) -> Result<TokenStream> {
         let mut struct_defs = Vec::new();
         let mut struct_names = Vec::new();
@@ -214,20 +260,52 @@ impl Context {
         })
     }
 
+    /// Expands all return structs
+    fn expand_return_structs(&self, aliases: BTreeMap<String, MethodAlias>) -> Result<TokenStream> {
+        let mut struct_defs = Vec::new();
+        for function in self.abi.functions.values().flatten() {
+            let signature = function.abi_signature();
+            let alias = aliases.get(&signature);
+            struct_defs.push(self.expand_return_struct(function, alias)?);
+        }
+
+        let struct_def_tokens = quote! {
+            #(#struct_defs)*
+        };
+
+        Ok(struct_def_tokens)
+    }
+
     /// The name ident of the calls enum
     fn expand_calls_enum_name(&self) -> Ident {
         util::ident(&format!("{}Calls", self.contract_ident))
     }
 
-    /// Expands to the `name : type` pairs of the function's inputs
-    fn expand_input_params(&self, fun: &Function) -> Result<Vec<(TokenStream, TokenStream)>> {
-        let mut args = Vec::with_capacity(fun.inputs.len());
-        for (idx, param) in fun.inputs.iter().enumerate() {
+    /// Expands to the `name : type` pairs of the function's parameters
+    fn expand_params(
+        &self,
+        fun: &Function,
+        params: &[Param],
+    ) -> Result<Vec<(TokenStream, TokenStream)>> {
+        params
+            .iter()
+            .enumerate()
+            .map(|(idx, param)| {
                 let name = util::expand_input_name(idx, &param.name);
                 let ty = self.expand_input_param_type(fun, &param.name, &param.kind)?;
-            args.push((name, ty));
+                Ok((name, ty))
+            })
+            .collect()
     }
-        Ok(args)
+
+    /// Expands to the `name : type` pairs of the function's inputs
+    fn expand_input_params(&self, fun: &Function) -> Result<Vec<(TokenStream, TokenStream)>> {
+        self.expand_params(fun, &fun.inputs)
+    }
+
+    /// Expands to the `name : type` pairs of the function's outputs
+    fn expand_output_params(&self, fun: &Function) -> Result<Vec<(TokenStream, TokenStream)>> {
+        self.expand_params(fun, &fun.outputs)
     }
 
     /// Expands to the return type of a function
@@ -607,16 +685,30 @@ fn expand_function_name(function: &Function, alias: Option<&MethodAlias>) -> Ide
     }
 }
 
-/// Expands to the name of the call struct
-fn expand_call_struct_name(function: &Function, alias: Option<&MethodAlias>) -> Ident {
+/// Expands the name of a struct by a postfix
+fn expand_struct_name_postfix(
+    function: &Function,
+    alias: Option<&MethodAlias>,
+    postfix: &str,
+) -> Ident {
     let name = if let Some(alias) = alias {
-        format!("{}Call", alias.struct_name)
+        format!("{}{}", alias.struct_name, postfix)
     } else {
-        format!("{}Call", util::safe_pascal_case(&function.name))
+        format!("{}{}", util::safe_pascal_case(&function.name), postfix)
     };
     util::ident(&name)
 }
 
+/// Expands to the name of the call struct
+fn expand_call_struct_name(function: &Function, alias: Option<&MethodAlias>) -> Ident {
+    expand_struct_name_postfix(function, alias, "Call")
+}
+
+/// Expands to the name of the return struct
+fn expand_return_struct_name(function: &Function, alias: Option<&MethodAlias>) -> Ident {
+    expand_struct_name_postfix(function, alias, "Return")
+}
+
 /// Expands to the name of the call struct
 fn expand_call_struct_variant_name(function: &Function, alias: Option<&MethodAlias>) -> Ident {
     if let Some(alias) = alias {

ethers-contract/tests/abigen.rs

@@ -1,7 +1,7 @@
 #![cfg(feature = "abigen")]
 #![allow(unused)]
 //! Test cases to validate the `abigen!` macro
-use ethers_contract::{abigen, EthCall, EthEvent};
+use ethers_contract::{abigen, Abigen, EthCall, EthEvent};
 use ethers_core::{
     abi::{AbiDecode, AbiEncode, Address, Tokenizable},
     types::{transaction::eip2718::TypedTransaction, Eip1559TransactionRequest, U256},
@@ -167,6 +167,34 @@ fn can_generate_internal_structs_multiple() {
     let _ = contract.verify(vec![], proof, vk);
 }
 
+#[test]
+fn can_gen_return_struct() {
+    abigen!(MultiInputOutput, "ethers-contract/tests/solidity-contracts/MultiInputOutput.json");
+
+    fn verify<T: AbiEncode + AbiDecode + Clone + std::fmt::Debug + std::cmp::PartialEq>(
+        binding: T,
+    ) {
+        let encoded = binding.clone().encode();
+        let decoded = T::decode(&encoded).unwrap();
+        assert_eq!(binding, decoded);
+    }
+
+    // just make sure they are accessible and work
+
+    let dupe = DupeIntReturn { out_one: 5.into(), out_two: 1234.into() };
+    verify(dupe);
+
+    let array =
+        ArrayRelayerReturn { outputs: vec![4.into(), 9.into(), 2.into()], some_number: 42.into() };
+    verify(array);
+
+    let single = SingleUnnamedReturn { 0: 4321.into() };
+    verify(single);
+
+    // doesnt exist:
+    // let nonexistant = CallWithoutReturnDataReturn;
+}
+
 #[test]
 fn can_gen_human_readable_with_structs() {
     abigen!(

ethers-contract/tests/solidity-contracts/MultiInputOutput.json

@@ -0,0 +1 @@
+{"abi":[{"inputs":[{"internalType":"uint256[]","name":"inputs","type":"uint256[]"}],"name":"arrayRelayer","outputs":[{"internalType":"uint256[]","name":"outputs","type":"uint256[]"},{"internalType":"uint256","name":"someNumber","type":"uint256"}],"stateMutability":"pure","type":"function"},{"inputs":[{"internalType":"uint256","name":"input","type":"uint256"}],"name":"callWithoutReturnData","outputs":[],"stateMutability":"pure","type":"function"},{"inputs":[{"internalType":"uint256","name":"input","type":"uint256"}],"name":"dupeInt","outputs":[{"internalType":"uint256","name":"outOne","type":"uint256"},{"internalType":"uint256","name":"outTwo","type":"uint256"}],"stateMutability":"pure","type":"function"},{"inputs":[],"name":"singleUnnamed","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"stateMutability":"pure","type":"function"}]}

ethers-contract/tests/solidity-contracts/MultiInputOutput.sol

@@ -0,0 +1,24 @@
+pragma solidity >=0.6.0;
+pragma experimental ABIEncoderV2;
+
+contract MultiInputOutput {
+	function dupeInt(uint256 input) public pure returns (uint256 outOne, uint256 outTwo) {
+		return (input, input);
+	}
+	function arrayRelayer(uint256[] memory inputs) public pure returns (uint256[] memory outputs, uint someNumber) {
+		outputs = new uint[](inputs.length);
+		for(uint256 i = 0; i < inputs.length; i++) {
+			outputs[i] = inputs[i];
+		}
+		someNumber = 42;
+	}
+	function singleUnnamed() public pure returns (uint) {
+		return 0x45;
+	}
+	function callWithoutReturnData(uint256 input) public pure {
+		// silence unused errors
+		uint nothing = input;
+		input = nothing;
+		return;
+	}
+}