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use proc_macro::TokenStream;
use proc_macro2::TokenStream as TokenStream2;
use quote::{format_ident, quote};
use syn::{FnArg, Item, ItemTrait, ReturnType, TraitItem, TypeParamBound};
fn process_item_trait(mut input: ItemTrait) -> TokenStream2 {
let trait_name = input.ident.clone();
let mock_name = format_ident!("Mock{}", trait_name);
let builder_name = format_ident!("Mock{}Builder", trait_name);
// Fix default supertrait
{
let mut has_default = false;
input.supertraits.iter().for_each(|item| {
//
if let TypeParamBound::Trait(val) = item {
let name = val.path.segments.last().unwrap().ident.to_string();
if &name == "Default" {
has_default = true;
}
}
});
if !has_default {
let value: syn::TraitBound = syn::parse_quote! {Default};
input.supertraits.insert(0, TypeParamBound::Trait(value));
}
}
// Collect method names and generate mock method
let fields = input
.items
.iter()
.filter_map(|item| {
if let TraitItem::Method(method) = item {
Some(format_ident!("__mock_{}__", method.sig.ident))
} else {
None
}
})
.collect::<Vec<_>>();
let mock_method: syn::TraitItemMethod = syn::parse_quote! {
fn mock() -> #builder_name<Self> {
#builder_name {
inner: #mock_name {
__mock_fallback__: Default::default(),
#(#fields: None,)*
}
}
}
};
let mut builder_methods: Vec<TokenStream2> = vec![];
// Generate mock struct
let mock = {
let fields = input
.items
.iter()
.filter_map(|item| {
if let TraitItem::Method(method) = item {
let inputs = method
.sig
.inputs
.iter()
.filter_map(|input| {
if let FnArg::Typed(typed) = input {
Some(typed.ty.clone())
} else {
None
}
})
.collect::<Vec<_>>();
let field = format_ident!("__mock_{}__", method.sig.ident);
match method.sig.output {
ReturnType::Default => {
let builder_method = {
let method_name = &method.sig.ident;
quote! {
fn #method_name<F>(mut self, when: F) -> Self
where
F: Fn(#(#inputs),*) + 'static,
{
self.inner.#field = Some(Box::new(when));
self
}
}
};
builder_methods.push(builder_method);
Some(quote! {#field: Option<Box<dyn Fn(#(#inputs),*)>>})
}
ReturnType::Type(_, ref ty) => {
let output = ty.clone();
let builder_method = {
let method_name = &method.sig.ident;
quote! {
fn #method_name<F>(mut self, when: F) -> Self
where
F: Fn(#(#inputs),*) -> #output + 'static,
{
self.inner.#field = Some(Box::new(when));
self
}
}
};
builder_methods.push(builder_method);
Some(quote! {#field: Option<Box<dyn Fn(#(#inputs),*) -> #output>>})
}
}
} else {
None
}
})
.collect::<Vec<_>>();
quote! {
#[derive(Default)]
struct #mock_name<T>
where
T: #trait_name,
{
__mock_fallback__: T,
#(#fields),*
}
}
};
let mock_impl = {
let methods = input
.items
.iter()
.filter_map(|item| {
if let TraitItem::Method(method) = item {
let sig = method.sig.clone();
let args = sig
.inputs
.iter()
.filter_map(|input| {
if let FnArg::Typed(syn::PatType { pat, .. }) = input {
if let syn::Pat::Ident(ident) = pat.as_ref() {
Some(&ident.ident)
} else {
panic!("Unhandled function argument");
}
} else {
None
}
})
.collect::<Vec<_>>();
let ident = &sig.ident;
let field = format_ident!("__mock_{}__", sig.ident);
Some(quote! {
#sig {
match self.#field {
Some(ref func) => func(#(#args),*),
None => self.__mock_fallback__.#ident(#(#args),*),
}
}
})
} else {
None
}
})
.collect::<Vec<_>>();
quote! {
impl<T> #trait_name for #mock_name<T>
where
T: #trait_name,
{
#(#methods)*
}
}
};
let builder = quote! {
struct #builder_name<T>
where
T: #trait_name,
{
inner: #mock_name<T>,
}
};
let builder_impl = quote! {
impl<T> #builder_name<T>
where
T: #trait_name,
{
#(#builder_methods)*
fn build(self) -> #mock_name<T> {
self.inner
}
}
};
// output
input.items.push(TraitItem::Method(mock_method));
quote! {
#input
#mock
#mock_impl
#builder
#builder_impl
}
}
pub(crate) fn mock(_attr: TokenStream, input: TokenStream) -> TokenStream {
let item: Item = syn::parse2(input.into()).unwrap();
match item {
Item::Trait(item) => process_item_trait(item).into(),
_ => panic!("Traits only supported for mocking"),
}
}