feat: add support for async constructors

2 files changed, 51 insertions, 10 deletions

diff --git a/macros/src/injectable/implementation.rs b/macros/src/injectable/implementation.rs
index e2bcd3e..a98d1ce 100644
--- a/macros/src/injectable/implementation.rs
+++ b/macros/src/injectable/implementation.rs
@@ -83,7 +83,7 @@ impl<Dep: IDependency> InjectableImpl<Dep>
         })
     }
 
-    pub fn validate(&self) -> Result<(), InjectableImplError>
+    pub fn validate(&self, is_async: bool) -> Result<(), InjectableImplError>
     {
         if matches!(self.constructor_method.sig.output, ReturnType::Default) {
             return Err(InjectableImplError::InvalidConstructorMethodReturnType {
@@ -127,10 +127,14 @@ impl<Dep: IDependency> InjectableImpl<Dep>
             });
         }
 
-        if let Some(asyncness) = self.constructor_method.sig.asyncness {
-            return Err(InjectableImplError::ConstructorMethodAsync {
-                asyncness_span: asyncness.span,
-            });
+        if !is_async {
+            if let Some(asyncness) = self.constructor_method.sig.asyncness {
+                return Err(
+                    InjectableImplError::ConstructorMethodAsyncWithMissingAsyncAttr {
+                        asyncness_span: asyncness.span,
+                    },
+                );
+            }
         }
 
         if !self.constructor_method.sig.generics.params.is_empty() {
@@ -235,6 +239,12 @@ impl<Dep: IDependency> InjectableImpl<Dep>
             .map(|index| format_ident!("dependency_{index}"))
             .collect::<Vec<_>>();
 
+        let maybe_await_constructor = if self.constructor_method.sig.asyncness.is_some() {
+            quote! { .await }
+        } else {
+            quote! {}
+        };
+
         quote! {
             #maybe_doc_hidden
             impl #generics syrette::interfaces::async_injectable::AsyncInjectable<
@@ -273,7 +283,7 @@ impl<Dep: IDependency> InjectableImpl<Dep>
 
                         Ok(syrette::ptr::TransientPtr::new(Self::#constructor(
                             #(#dependency_idents),*
-                        )))
+                        )#maybe_await_constructor))
                     })
                 }
             }
@@ -522,9 +532,15 @@ pub enum InjectableImplError
         unsafety_span: Span
     },
 
-    #[error("Constructor method is not allowed to be async"), span = asyncness_span]
-    #[note("Required by the 'injectable' attribute macro")]
-    ConstructorMethodAsync {
+    #[
+        error(concat!(
+            "Constructor method is not allowed to be async when the 'async' flag of the ",
+            "'injectable' macro is not set to true"
+        )),
+        span = asyncness_span
+    ]
+    #[help("Enable the 'async' flag here")]
+    ConstructorMethodAsyncWithMissingAsyncAttr {
         asyncness_span: Span
     },
 
diff --git a/macros/src/lib.rs b/macros/src/lib.rs
index fa84e0e..e55e23f 100644
--- a/macros/src/lib.rs
+++ b/macros/src/lib.rs
@@ -100,6 +100,30 @@ const PACKAGE_VERSION: &str = env!("CARGO_PKG_VERSION");
 ///     }
 /// }
 /// ```
+/// <br>
+///
+/// When the `async` crate feature is enabled, the constructor can be [`async`].
+/// ```
+/// # #[cfg(feature = "async")]
+/// # mod example {
+/// # use syrette::injectable;
+/// #
+/// # struct PasswordManager { value: u32}
+/// #
+/// # async fn some_async_computation() -> u32 { 1 }
+/// #
+/// #[injectable(async = true)]
+/// impl PasswordManager
+/// {
+///     pub async fn new() -> Self
+///     {
+///         let value = some_async_computation().await;
+///
+///         Self { value }
+///     }
+/// }
+/// # }
+/// ```
 ///
 /// # Attributes
 /// Attributes specific to impls with this attribute macro.
@@ -149,6 +173,7 @@ const PACKAGE_VERSION: &str = env!("CARGO_PKG_VERSION");
 /// [`Injectable`]: ../syrette/interfaces/injectable/trait.Injectable.html
 /// [`AsyncInjectable`]: ../syrette/interfaces/async_injectable/trait.AsyncInjectable.html
 /// [`di_container_bind`]: ../syrette/macro.di_container_bind.html
+/// [`async`]: https://doc.rust-lang.org/std/keyword.async.html
 #[cfg(not(tarpaulin_include))]
 #[proc_macro_error]
 #[proc_macro_attribute]
@@ -233,7 +258,7 @@ pub fn injectable(args_stream: TokenStream, input_stream: TokenStream) -> TokenS
     let injectable_impl =
         InjectableImpl::<Dependency>::new(item_impl, &constructor).unwrap_or_abort();
 
-    injectable_impl.validate().unwrap_or_abort();
+    injectable_impl.validate(is_async).unwrap_or_abort();
 
     let expanded_injectable_impl = injectable_impl.expand(no_doc_hidden, is_async);