refactor(abigen): solidity types expansion (#2131)

* refactor: event input expansion

* refactor: common expand params

* refactor: method params expansion

* refactor: struct fields expansion

* refactor: types array expansion

* clippy

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

@@ -1,66 +1,8 @@
-use super::{types, util, Context};
+use super::Context;
-use ethers_core::{
+use ethers_core::macros::{ethers_contract_crate, ethers_core_crate, ethers_providers_crate};
-    abi::{Param, ParamType},
-    macros::{ethers_contract_crate, ethers_core_crate, ethers_providers_crate},
-};
 use proc_macro2::{Ident, Literal, TokenStream};
 use quote::quote;
 
-/// Expands to the `name : type` pairs for the params
-pub(crate) fn expand_params<'a, F>(
-    params: &[Param],
-    resolve_tuple: F,
-) -> eyre::Result<Vec<(TokenStream, TokenStream)>>
-where
-    F: Fn(&str) -> Option<&'a str>,
-{
-    params
-        .iter()
-        .enumerate()
-        .map(|(idx, param)| {
-            let name = util::expand_input_name(idx, &param.name);
-            let ty = expand_param_type(param, &param.kind, |s| resolve_tuple(s))?;
-            Ok((name, ty))
-        })
-        .collect()
-}
-
-/// returns the Tokenstream for the corresponding rust type
-pub(crate) fn expand_param_type<'a, F>(
-    param: &Param,
-    kind: &ParamType,
-    resolve_tuple: F,
-) -> eyre::Result<TokenStream>
-where
-    F: Fn(&str) -> Option<&'a str>,
-{
-    match kind {
-        ParamType::Array(ty) => {
-            let ty = expand_param_type(param, ty, resolve_tuple)?;
-            Ok(quote! {
-                ::std::vec::Vec<#ty>
-            })
-        }
-        ParamType::FixedArray(ty, size) => {
-            let ty = expand_param_type(param, ty, resolve_tuple)?;
-            let size = *size;
-            Ok(quote! {[#ty; #size]})
-        }
-        ParamType::Tuple(_) => {
-            let ty = if let Some(rust_struct_name) =
-                param.internal_type.as_ref().and_then(|s| resolve_tuple(s.as_str()))
-            {
-                let ident = util::ident(rust_struct_name);
-                quote! {#ident}
-            } else {
-                types::expand(kind)?
-            };
-            Ok(ty)
-        }
-        _ => types::expand(kind),
-    }
-}
-
 pub(crate) fn imports(name: &str) -> TokenStream {
     let doc_str = format!("{name} was auto-generated with ethers-rs Abigen. More information at: <https://github.com/gakonst/ethers-rs>");
 

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

@@ -1,7 +1,9 @@
 //! derive error bindings
 
-use super::{util, Context};
+use super::{
-use crate::contract::common::{expand_data_struct, expand_data_tuple, expand_params};
+    common::{expand_data_struct, expand_data_tuple},
+    types, util, Context,
+};
 use ethers_core::{
     abi::{ethabi::AbiError, ErrorExt},
     macros::{ethers_contract_crate, ethers_core_crate},
@@ -81,7 +83,9 @@ impl Context {
 
     /// Expands to the `name : type` pairs of the function's outputs
     fn expand_error_params(&self, error: &AbiError) -> Result<Vec<(TokenStream, TokenStream)>> {
-        expand_params(&error.inputs, |s| self.internal_structs.get_struct_type(s))
+        types::expand_params(&error.inputs, |p| {
+            p.internal_type.as_deref().and_then(|s| self.internal_structs.get_struct_type(s))
+        })
     }
 
     /// The name ident of the errors enum

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

@@ -1,12 +1,12 @@
 use super::{types, util, Context};
 use crate::util::can_derive_defaults;
 use ethers_core::{
-    abi::{Event, EventExt, EventParam, Param, ParamType},
+    abi::{Event, EventExt, Param},
     macros::{ethers_contract_crate, ethers_core_crate},
 };
 use eyre::Result;
 use inflector::Inflector;
-use proc_macro2::{Ident, Literal, TokenStream};
+use proc_macro2::{Ident, TokenStream};
 use quote::quote;
 use std::collections::BTreeMap;
 
@@ -136,85 +136,6 @@ impl Context {
         }
     }
 
-    /// Expands an event property type.
-    ///
-    /// Note that this is slightly different from expanding a Solidity type as
-    /// complex types like arrays and strings get emitted as hashes when they are
-    /// indexed.
-    /// If a complex types matches with a struct previously parsed by the internal structs,
-    /// we can replace it
-    fn expand_input_type(
-        &self,
-        event: &Event,
-        input: &EventParam,
-        idx: usize,
-    ) -> Result<TokenStream> {
-        let ethers_core = ethers_core_crate();
-        Ok(match (&input.kind, input.indexed) {
-            (ParamType::Array(_), true) => {
-                quote! { #ethers_core::types::H256 }
-            }
-            (ParamType::FixedArray(_, _), true) => {
-                quote! { #ethers_core::types::H256 }
-            }
-            (ParamType::Tuple(..), true) => {
-                quote! { #ethers_core::types::H256 }
-            }
-            (ParamType::Bytes, true) | (ParamType::String, true) => {
-                quote! { #ethers_core::types::H256 }
-            }
-            (ParamType::Tuple(_), false) => {
-                let ty = if let Some(rust_struct_name) =
-                    self.internal_structs.get_event_input_struct_type(&event.name, idx)
-                {
-                    let ident = util::ident(rust_struct_name);
-                    quote! {#ident}
-                } else {
-                    types::expand(&input.kind)?
-                };
-                ty
-            }
-            (ParamType::Array(_), _) => {
-                // represents an array of a struct
-                if let Some(rust_struct_name) =
-                    self.internal_structs.get_event_input_struct_type(&event.name, idx)
-                {
-                    let ty = util::ident(rust_struct_name);
-                    return Ok(quote! {::std::vec::Vec<#ty>})
-                }
-                types::expand(&input.kind)?
-            }
-            (ParamType::FixedArray(_, size), _) => {
-                // represents a fixed array of a struct
-                if let Some(rust_struct_name) =
-                    self.internal_structs.get_event_input_struct_type(&event.name, idx)
-                {
-                    let ty = util::ident(rust_struct_name);
-                    let size = Literal::usize_unsuffixed(*size);
-                    return Ok(quote! {[#ty; #size]})
-                }
-                types::expand(&input.kind)?
-            }
-            (kind, _) => types::expand(kind)?,
-        })
-    }
-
-    /// Expands the name-type pairs for the given inputs
-    fn expand_event_params(&self, event: &Event) -> Result<Vec<(TokenStream, TokenStream, bool)>> {
-        event
-            .inputs
-            .iter()
-            .enumerate()
-            .map(|(idx, input)| {
-                // NOTE: Events can contain nameless values.
-                let name = util::expand_input_name(idx, &input.name);
-                let ty = self.expand_input_type(event, input, idx)?;
-
-                Ok((name, ty, input.indexed))
-            })
-            .collect()
-    }
-
     /// Expands into a single method for contracting an event stream.
     fn expand_filter(&self, event: &Event) -> TokenStream {
         let name = &event.name;
@@ -251,7 +172,7 @@ impl Context {
 
         let event_name = event_struct_name(&event.name, sig);
 
-        let params = self.expand_event_params(event)?;
+        let params = types::expand_event_inputs(event, &self.internal_structs)?;
         // expand as a tuple if all fields are anonymous
         let all_anonymous_fields = event.inputs.iter().all(|input| input.name.is_empty());
         let data_type_definition = if all_anonymous_fields {
@@ -355,6 +276,7 @@ mod tests {
     use super::*;
     use crate::Abigen;
     use ethers_core::abi::{EventParam, Hash, ParamType};
+    use proc_macro2::Literal;
 
     /// Expands a 256-bit `Hash` into a literal representation that can be used with
     /// quasi-quoting for code generation. We do this to avoid allocating at runtime
@@ -445,7 +367,7 @@ mod tests {
         };
 
         let cx = test_context();
-        let params = cx.expand_event_params(&event).unwrap();
+        let params = types::expand_event_inputs(&event, &cx.internal_structs).unwrap();
         let name = event_struct_name(&event.name, None);
         let definition = expand_data_struct(&name, &params);
 
@@ -469,7 +391,7 @@ mod tests {
         };
 
         let cx = test_context_with_alias("Foo(bool,address)", "FooAliased");
-        let params = cx.expand_event_params(&event).unwrap();
+        let params = types::expand_event_inputs(&event, &cx.internal_structs).unwrap();
         let alias = Some(util::ident("FooAliased"));
         let name = event_struct_name(&event.name, alias);
         let definition = expand_data_struct(&name, &params);
@@ -494,7 +416,7 @@ mod tests {
         };
 
         let cx = test_context();
-        let params = cx.expand_event_params(&event).unwrap();
+        let params = types::expand_event_inputs(&event, &cx.internal_structs).unwrap();
         let name = event_struct_name(&event.name, None);
         let definition = expand_data_tuple(&name, &params);
 
@@ -515,7 +437,7 @@ mod tests {
         };
 
         let cx = test_context_with_alias("Foo(bool,address)", "FooAliased");
-        let params = cx.expand_event_params(&event).unwrap();
+        let params = types::expand_event_inputs(&event, &cx.internal_structs).unwrap();
         let alias = Some(util::ident("FooAliased"));
         let name = event_struct_name(&event.name, alias);
         let definition = expand_data_tuple(&name, &params);

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

@@ -1,10 +1,8 @@
-use std::collections::{btree_map::Entry, BTreeMap, HashMap, HashSet};
+use super::{
-
+    common::{expand_data_struct, expand_data_tuple},
-use super::{types, util, Context};
+    types, Context,
-use crate::{
-    contract::common::{expand_data_struct, expand_data_tuple, expand_param_type, expand_params},
-    util::can_derive_defaults,
 };
+use crate::util::{self, can_derive_defaults};
 use ethers_core::{
     abi::{Function, FunctionExt, Param, ParamType},
     macros::{ethers_contract_crate, ethers_core_crate},
@@ -14,6 +12,7 @@ use eyre::{Context as _, Result};
 use inflector::Inflector;
 use proc_macro2::{Literal, TokenStream};
 use quote::quote;
+use std::collections::{btree_map::Entry, BTreeMap, HashMap, HashSet};
 use syn::Ident;
 
 /// The maximum amount of overloaded functions that are attempted to auto aliased with their param
@@ -304,127 +303,45 @@ impl Context {
 
     /// Expands to the `name : type` pairs of the function's inputs
     fn expand_input_params(&self, fun: &Function) -> Result<Vec<(TokenStream, TokenStream)>> {
-        fun.inputs
+        types::expand_params(&fun.inputs, |p| {
-            .iter()
+            self.internal_structs.get_function_input_struct_type(&fun.name, &p.name)
-            .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)?;
-                Ok((name, ty))
         })
-            .collect()
     }
 
-    /// Expands to the `name : type` pairs of the function's outputs
+    /// Expands to the `name: type` pairs of the function's outputs
     fn expand_output_params(&self, fun: &Function) -> Result<Vec<(TokenStream, TokenStream)>> {
-        expand_params(&fun.outputs, |s| {
+        types::expand_params(&fun.outputs, |p| {
-            self.internal_structs.get_function_output_struct_type(&fun.name, s)
+            p.internal_type
+                .as_deref()
+                .and_then(|s| self.internal_structs.get_function_output_struct_type(&fun.name, s))
         })
     }
 
-    /// Expands to the return type of a function
-    fn expand_outputs(&self, fun: &Function) -> Result<TokenStream> {
-        let mut outputs = Vec::with_capacity(fun.outputs.len());
-        for param in fun.outputs.iter() {
-            let ty = self.expand_output_param_type(fun, param, &param.kind)?;
-            outputs.push(ty);
-        }
-
-        let return_ty = match outputs.len() {
-            0 => quote! { () },
-            1 => outputs[0].clone(),
-            _ => {
-                quote! { (#( #outputs ),*) }
-            }
-        };
-        Ok(return_ty)
-    }
-
     /// Expands the arguments for the call that eventually calls the contract
-    fn expand_contract_call_args(&self, fun: &Function) -> Result<TokenStream> {
+    fn expand_contract_call_args(&self, fun: &Function) -> TokenStream {
-        let mut call_args = Vec::with_capacity(fun.inputs.len());
+        let mut call_args = fun.inputs.iter().enumerate().map(|(idx, param)| {
-        for (idx, param) in fun.inputs.iter().enumerate() {
             let name = util::expand_input_name(idx, &param.name);
-            let call_arg = match param.kind {
+            match param.kind {
                 // this is awkward edge case where the function inputs are a single struct
-                // we need to force this argument into a tuple so it gets expanded to `((#name,))`
+                // we need to force this argument into a tuple so it gets expanded to
-                // this is currently necessary because internally `flatten_tokens` is called which
+                // `((#name,))` this is currently necessary because
-                // removes the outermost `tuple` level and since `((#name))` is not
+                // internally `flatten_tokens` is called which removes the
-                // a rust tuple it doesn't get wrapped into another tuple that will be peeled off by
+                // outermost `tuple` level and since `((#name))` is not
-                // `flatten_tokens`
+                // a rust tuple it doesn't get wrapped into another tuple that will be peeled
+                // off by `flatten_tokens`
                 ParamType::Tuple(_) if fun.inputs.len() == 1 => {
                     // make sure the tuple gets converted to `Token::Tuple`
-                    quote! {(#name,)}
+                    quote!((#name,))
                 }
                 _ => name,
-            };
-            call_args.push(call_arg);
             }
-        let call_args = match call_args.len() {
+        });
-            0 => quote! { () },
-            1 => quote! { #( #call_args )* },
-            _ => quote! { ( #(#call_args, )* ) },
-        };
 
-        Ok(call_args)
+        match fun.inputs.len() {
+            0 => quote!(()),
+            1 => call_args.next().unwrap(),
+            _ => quote!(( #( #call_args ),* )),
         }
-
-    /// returns the Tokenstream for the corresponding rust type of the param
-    fn expand_input_param_type(
-        &self,
-        fun: &Function,
-        param: &str,
-        kind: &ParamType,
-    ) -> Result<TokenStream> {
-        let ethers_core = ethers_core_crate();
-        match kind {
-            ParamType::Array(ty) => {
-                let ty = self.expand_input_param_type(fun, param, ty)?;
-                Ok(quote! {
-                    ::std::vec::Vec<#ty>
-                })
-            }
-            ParamType::FixedArray(ty, size) => {
-                let ty = match **ty {
-                    ParamType::Uint(size) => {
-                        if size / 8 == 1 {
-                            // this prevents type ambiguity with `FixedBytes`
-                            quote! { #ethers_core::types::Uint8}
-                        } else {
-                            self.expand_input_param_type(fun, param, ty)?
-                        }
-                    }
-                    _ => self.expand_input_param_type(fun, param, ty)?,
-                };
-
-                let size = *size;
-                Ok(quote! {[#ty; #size]})
-            }
-            ParamType::Tuple(_) => {
-                let ty = if let Some(rust_struct_name) =
-                    self.internal_structs.get_function_input_struct_type(&fun.name, param)
-                {
-                    let ident = util::ident(rust_struct_name);
-                    quote! {#ident}
-                } else {
-                    types::expand(kind)?
-                };
-                Ok(ty)
-            }
-            _ => types::expand(kind),
-        }
-    }
-
-    /// returns the TokenStream for the corresponding rust type of the output param
-    fn expand_output_param_type(
-        &self,
-        fun: &Function,
-        param: &Param,
-        kind: &ParamType,
-    ) -> Result<TokenStream> {
-        expand_param_type(param, kind, |s| {
-            self.internal_structs.get_function_output_struct_type(&fun.name, s)
-        })
     }
 
     /// Expands a single function with the given alias
@@ -439,12 +356,22 @@ impl Context {
 
         let selector_tokens = expand_selector(selector);
 
-        let contract_args = self.expand_contract_call_args(function)?;
+        let contract_args = self.expand_contract_call_args(function);
         let function_params =
             self.expand_input_params(function)?.into_iter().map(|(name, ty)| quote! { #name: #ty });
         let function_params = quote! { #( , #function_params )* };
 
-        let outputs = self.expand_outputs(function)?;
+        let outputs = {
+            let mut out = self.expand_output_params(function)?;
+            match out.len() {
+                0 => quote!(()),
+                1 => out.pop().unwrap().1,
+                _ => {
+                    let iter = out.into_iter().map(|(_, ty)| ty);
+                    quote!(( #( #iter ),* ))
+                }
+            }
+        };
 
         let doc_str =
             format!("Calls the contract's `{name}` (0x{}) function", hex::encode(selector));

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

@@ -93,7 +93,7 @@ impl Context {
         for field in sol_struct.fields() {
             let ty = match field.r#type() {
                 FieldType::Elementary(ty) => types::expand(ty)?,
-                FieldType::Struct(struct_ty) => expand_struct_type(struct_ty),
+                FieldType::Struct(struct_ty) => types::expand_struct_type(struct_ty),
                 FieldType::Mapping(_) => {
                     eyre::bail!("Mapping types in struct `{}` are not supported {:?}", name, field)
                 }
@@ -154,7 +154,7 @@ impl Context {
                     fields.push(quote! { pub #field_name: #ty });
                 }
                 FieldType::Struct(struct_ty) => {
-                    let ty = expand_struct_type(struct_ty);
+                    let ty = types::expand_struct_type(struct_ty);
                     fields.push(quote! { pub #field_name: #ty });
 
                     let name = struct_ty.name();
@@ -592,24 +592,6 @@ fn struct_type_projections(name: &str) -> Vec<String> {
     iter.rev().map(str::to_string).collect()
 }
 
-/// Expands to the rust struct type
-fn expand_struct_type(struct_ty: &StructFieldType) -> TokenStream {
-    match struct_ty {
-        StructFieldType::Type(ty) => {
-            let ty = util::ident(&ty.name().to_pascal_case());
-            quote! {#ty}
-        }
-        StructFieldType::Array(ty) => {
-            let ty = expand_struct_type(ty);
-            quote! {::std::vec::Vec<#ty>}
-        }
-        StructFieldType::FixedArray(ty, size) => {
-            let ty = expand_struct_type(ty);
-            quote! { [#ty; #size]}
-        }
-    }
-}
-
 #[cfg(test)]
 mod tests {
     use super::*;

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

@@ -1,9 +1,17 @@
-use ethers_core::{abi::ParamType, macros::ethers_core_crate};
+//! Types expansion
-use eyre::{bail, Result};
-use proc_macro2::{Literal, TokenStream};
-use quote::quote;
 
-pub(crate) fn expand(kind: &ParamType) -> Result<TokenStream> {
+use crate::{util, InternalStructs};
+use ethers_core::{
+    abi::{struct_def::StructFieldType, Event, EventParam, Param, ParamType},
+    macros::ethers_core_crate,
+};
+use eyre::{bail, Result};
+use inflector::Inflector;
+use proc_macro2::{Literal, TokenStream};
+use quote::{quote, ToTokens};
+
+/// Expands a ParamType Solidity type to its Rust equivalent.
+pub fn expand(kind: &ParamType) -> Result<TokenStream> {
     let ethers_core = ethers_core_crate();
 
     match kind {
@@ -16,7 +24,7 @@ pub(crate) fn expand(kind: &ParamType) -> Result<TokenStream> {
             5..=8 => Ok(quote! { i64 }),
             9..=16 => Ok(quote! { i128 }),
             17..=32 => Ok(quote! { #ethers_core::types::I256 }),
-            _ => bail!("unsupported solidity type int{}", n),
+            _ => bail!("unsupported solidity type int{n}"),
         },
         ParamType::Uint(n) => match n / 8 {
             1 => Ok(quote! { u8 }),
@@ -25,41 +33,151 @@ pub(crate) fn expand(kind: &ParamType) -> Result<TokenStream> {
             5..=8 => Ok(quote! { u64 }),
             9..=16 => Ok(quote! { u128 }),
             17..=32 => Ok(quote! { #ethers_core::types::U256 }),
-            _ => bail!("unsupported solidity type uint{}", n),
+            _ => bail!("unsupported solidity type uint{n}"),
         },
-        ParamType::Bool => Ok(quote! { bool }),
+        ParamType::Bool => Ok(quote!(bool)),
-        ParamType::String => Ok(quote! { String }),
+        ParamType::String => Ok(quote!(::std::string::String)),
-        ParamType::Array(t) => {
+        ParamType::Array(ty) => Ok(array(expand(ty)?, None)),
-            let inner = expand(t)?;
+        ParamType::FixedBytes(n) => Ok(array(quote!(u8), Some(*n))),
-            Ok(quote! { Vec<#inner> })
+        ParamType::FixedArray(ty, n) => {
-        }
+            let ty = match **ty {
-        ParamType::FixedBytes(n) => {
-            // TODO(nlordell): what is the performance impact of returning large
-            //   `FixedBytes` and `FixedArray`s with `web3`?
-            let size = Literal::usize_unsuffixed(*n);
-            Ok(quote! { [u8; #size] })
-        }
-        ParamType::FixedArray(t, n) => {
-            // TODO(nlordell): see above
-            let inner = match **t {
-                ParamType::Uint(size) => {
-                    if size / 8 == 1 {
                 // this prevents type ambiguity with `FixedBytes`
-                        quote! { #ethers_core::types::Uint8}
+                // see: https://github.com/gakonst/ethers-rs/issues/1636
-                    } else {
+                ParamType::Uint(size) if size / 8 == 1 => quote!(#ethers_core::types::Uint8),
-                        expand(t)?
+                _ => expand(ty)?,
-                    }
-                }
-                _ => expand(t)?,
             };
-            let size = Literal::usize_unsuffixed(*n);
+            Ok(array(ty, Some(*n)))
-            Ok(quote! { [#inner; #size] })
         }
         ParamType::Tuple(members) => {
             eyre::ensure!(!members.is_empty(), "Tuple must have at least 1 member");
 
             let members = members.iter().map(expand).collect::<Result<Vec<_>, _>>()?;
-            Ok(quote! { (#(#members,)*) })
+            Ok(quote!(( #( #members ),* )))
         }
     }
 }
+
+/// Expands the event's inputs.
+pub fn expand_event_inputs(
+    event: &Event,
+    internal_structs: &InternalStructs,
+) -> Result<Vec<(TokenStream, TokenStream, bool)>> {
+    event
+        .inputs
+        .iter()
+        .enumerate()
+        .map(|(index, input)| {
+            // NOTE: Events can contain nameless values.
+            expand_event_input(input, &event.name, index, internal_structs)
+                .map(|ty| (util::expand_input_name(index, &input.name), ty, input.indexed))
+        })
+        .collect()
+}
+
+/// Expands an event property type.
+///
+/// Note that this is slightly different from expanding a Solidity type as complex types like arrays
+/// and strings get emitted as hashes when they are indexed.
+///
+/// If a complex types matches with a struct previously parsed by the internal structs, we can
+/// replace it.
+fn expand_event_input(
+    input: &EventParam,
+    name: &str,
+    index: usize,
+    internal_structs: &InternalStructs,
+) -> Result<TokenStream> {
+    let kind = &input.kind;
+    match (kind, input.indexed) {
+        (ParamType::Array(_), true) |
+        (ParamType::FixedArray(_, _), true) |
+        (ParamType::Tuple(_), true) |
+        (ParamType::Bytes, true) |
+        (ParamType::String, true) => {
+            let ethers_core = ethers_core_crate();
+            Ok(quote!(#ethers_core::types::H256))
+        }
+
+        (ParamType::Array(_), false) |
+        (ParamType::FixedArray(_, _), false) |
+        (ParamType::Tuple(_), false) => {
+            match internal_structs.get_event_input_struct_type(name, index) {
+                Some(ty) => {
+                    let ty = util::ident(ty);
+                    match kind {
+                        ParamType::Array(_) => Ok(array(ty, None)),
+                        ParamType::FixedArray(_, size) => Ok(array(ty, Some(*size))),
+                        ParamType::Tuple(_) => Ok(quote!(#ty)),
+                        _ => unreachable!(),
+                    }
+                }
+                None => expand(kind),
+            }
+        }
+
+        _ => expand(kind),
+    }
+}
+
+/// Expands `params` to `(name, type)` tokens pairs, while resolving tuples' types using the given
+/// function.
+pub fn expand_params<'a, 'b, F: Fn(&'a Param) -> Option<&'b str>>(
+    params: &'a [Param],
+    resolve_tuple: F,
+) -> Result<Vec<(TokenStream, TokenStream)>> {
+    params
+        .iter()
+        .enumerate()
+        .map(|(idx, param)| {
+            // NOTE: Params can be unnamed.
+            expand_resolved(&param.kind, param, &resolve_tuple)
+                .map(|ty| (util::expand_input_name(idx, &param.name), ty))
+        })
+        .collect()
+}
+
+/// Expands a ParamType Solidity type to its Rust equivalent, while resolving tuples' types using
+/// the given function.
+fn expand_resolved<'a, 'b, F: Fn(&'a Param) -> Option<&'b str>>(
+    kind: &'a ParamType,
+    param: &'a Param,
+    resolve_tuple: &F,
+) -> Result<TokenStream> {
+    match kind {
+        ParamType::Array(ty) => Ok(array(expand_resolved(ty, param, resolve_tuple)?, None)),
+        ParamType::FixedArray(ty, size) => {
+            Ok(array(expand_resolved(ty, param, resolve_tuple)?, Some(*size)))
+        }
+        ParamType::Tuple(_) => match resolve_tuple(param) {
+            Some(ty) => {
+                let ty = util::ident(ty);
+                Ok(quote!(#ty))
+            }
+            None => expand(kind),
+        },
+        _ => expand(kind),
+    }
+}
+
+/// Expands to the Rust struct type.
+pub fn expand_struct_type(struct_ty: &StructFieldType) -> TokenStream {
+    match struct_ty {
+        StructFieldType::Type(ty) => {
+            let ty = util::ident(&ty.name().to_pascal_case());
+            quote!(#ty)
+        }
+        StructFieldType::Array(ty) => array(expand_struct_type(ty), None),
+        StructFieldType::FixedArray(ty, size) => array(expand_struct_type(ty), Some(*size)),
+    }
+}
+
+/// Expands `ty` into a Rust array or vector.
+fn array<T: ToTokens>(ty: T, size: Option<usize>) -> TokenStream {
+    match size {
+        Some(size) => {
+            let size = Literal::usize_unsuffixed(size);
+            quote!([#ty; #size])
+        }
+        None => quote!(::std::vec::Vec<#ty>),
+    }
+}