add support for ref into with lifetime

Author: vnghia

README.md

@@ -147,7 +147,11 @@ And here's the code that `o2o` generates (from here on, generated code is produc
   - [Tuple structs](#tuple-structs)
   - [Tuples](#tuples)
   - [Type hints](#type-hints)
+  - [From ref with lifetime](#from-ref-with-lifetime)
+  - [Ref into with lifetime](#ref-into-with-lifetime)
+  - [Lifetime both ways](#lifetime-both-ways)
   - [Generics](#generics)
+  - [Generics both ways](#generics-both-ways)
   - [Where clauses](#where-clauses)
   - [Mapping to multiple structs](#mapping-to-multiple-structs)
   - [Avoiding proc macro attribute name collisions (alternative instruction syntax)](#avoiding-proc-macro-attribute-name-collisions-alternative-instruction-syntax)
@@ -169,6 +173,7 @@ And here's the code that `o2o` generates (from here on, generated code is produc
 - [Contributions](#contributions)
 - [License](#license)
 
+
 ## Traits and `o2o` *trait instructions*
 
 To let o2o know what traits you want implemented, you have to use type-level `o2o` *trait instructions* (i.e. proc macro attributes):
@@ -1443,7 +1448,7 @@ struct EntityDto{
   ```
 </details>
 
-### Reference with lifetime
+### From ref with lifetime
 
 ```rust
 use o2o::o2o;
@@ -1480,6 +1485,43 @@ pub struct EntityDto<'a, 'b> {
   ```
 </details>
 
+### Ref into with lifetime
+
+```rust
+use o2o::o2o;
+
+#[derive(o2o)]
+#[ref_into(EntityDto<'a, 'b>)]
+pub struct Entity {
+    #[into(~.as_str())]
+    pub some_a: String,
+    #[into(~.as_str())]
+    pub some_b: String,
+}
+
+pub struct EntityDto<'a, 'b> {
+    pub some_a: &'a str,
+    pub some_b: &'b str,
+}
+```
+<details>
+  <summary>View generated code</summary>
+
+  ``` rust ignore
+  impl<'a, 'b, 'o2o> ::core::convert::Into<EntityDto<'a, 'b>> for &'o2o Entity
+  where
+      'o2o: 'a + 'b,
+  {
+      fn into(self) -> EntityDto<'a, 'b> {
+          EntityDto {
+              some_a: self.some_a.as_str(),
+              some_b: self.some_b.as_str(),
+          }
+      }
+  }
+  ```
+</details>
+
 ### Lifetime both ways
 
 ```rust

o2o-impl/src/expand.rs

@@ -11,8 +11,8 @@ use crate::{
 use proc_macro2::{Span, TokenStream};
 use quote::{format_ident, quote, ToTokens};
 use syn::{
-    parse2, parse_quote, punctuated::Punctuated, Data, DeriveInput, Error, Index, Member, Result,
-    Token, Type,
+    parse2, parse_quote, punctuated::Punctuated, Data, DeriveInput, Error, GenericArgument,
+    GenericParam, Index, Lifetime, Member, PathArguments, Result, Token, TypePath,
 };
 
 pub fn derive(node: &DeriveInput) -> Result<TokenStream> {
@@ -417,11 +417,11 @@ fn struct_main_code_block(input: &Struct, ctx: &ImplContext) -> TokenStream {
         Kind::OwnedInto | Kind::RefInto => {
             let dst = if ctx.struct_attr.ty.nameless_tuple || ctx.has_post_init {
                 TokenStream::new()
-            } else if let Ok(Type::Path(mut path)) = parse2::<Type>(ctx.dst_ty.clone()) {
+            } else if let Ok(mut path) = parse2::<TypePath>(ctx.dst_ty.clone()) {
                 // In this case we want to transform something like `mod1::mod2::Entity<T>` to `mod1::mod2::Entity`.
                 // So set all segments arguments to None.
                 path.path.segments.iter_mut().for_each(|segment| {
-                    segment.arguments = syn::PathArguments::None;
+                    segment.arguments = PathArguments::None;
                 });
                 path.to_token_stream()
             } else {
@@ -1442,29 +1442,70 @@ struct QuoteTraitParams<'a> {
 }
 
 fn get_quote_trait_params<'a>(input: &DataType, ctx: &'a ImplContext) -> QuoteTraitParams<'a> {
-    // If there is at least one lifetime in generics,we add a new lifetime `'o2o` and add a bound `'o2o: 'a + 'b`.
     let generics = input.get_generics();
-    let (gens_impl, where_clause, r) = if ctx.kind.is_ref() && generics.lifetimes().next().is_some()
-    {
-        let lifetimes: Vec<_> = generics
-            .lifetimes()
-            .map(|params| params.lifetime.clone())
-            .collect();
+    let mut generics_impl = generics.clone();
+    let mut lifetimes: Vec<Lifetime> = vec![];
+
+    if let Ok(dst_ty) = parse2::<syn::TypePath>(ctx.dst_ty.clone()) {
+        // The idea is to check if all lifetimes of the dst are included in the input generics or not.
+        // If not, we will add the missing ones to the input generics.
+
+        let dst_generics = match &dst_ty.path.segments.last().unwrap().arguments {
+            PathArguments::None => syn::punctuated::Punctuated::new(),
+            PathArguments::AngleBracketed(args) => args.args.clone(),
+            PathArguments::Parenthesized(_) => {
+                unimplemented!("Only Struct<T> syntax is supported")
+            }
+        };
+
+        for dst_generic in dst_generics {
+            if let GenericArgument::Lifetime(arg) = &dst_generic {
+                lifetimes.push(parse_quote!(#dst_generic));
+                if generics.params.iter().all(|param| {
+                    if let GenericParam::Lifetime(param) = param {
+                        &param.lifetime != arg
+                    } else {
+                        // Skip any other generic param
+                        false
+                    }
+                }) {
+                    generics_impl.params.push(parse_quote!(#dst_generic));
+                }
+            }
+        }
+    }
 
-        let mut generics = generics.clone();
-        generics.params.push(parse_quote!('o2o));
+    // If there is at least one lifetime in generics, we add a new lifetime `'o2o` and add a bound `'o2o: 'a + 'b`.
+    let (gens_impl, where_clause, r) = if ctx.kind.is_ref() {
+        // If lifetime is empty, we assume that lifetime generics come from the other structure (src <-> dst).
+        let lifetimes: Vec<_> = if lifetimes.is_empty() {
+            generics
+                .lifetimes()
+                .map(|params| params.lifetime.clone())
+                .collect()
+        } else {
+            lifetimes
+        };
 
         let mut where_clause = input
             .get_attrs()
             .where_attr(&ctx.struct_attr.ty)
-            .map(|x| x.where_clause.clone())
-            .unwrap_or_default();
-        where_clause.push(parse_quote!('o2o: #( #lifetimes )+*));
+            .map(|x| x.where_clause.clone());
+
+        let r = if !lifetimes.is_empty() {
+            generics_impl.params.push(parse_quote!('o2o));
+            let mut where_clause_punctuated = where_clause.unwrap_or_default();
+            where_clause_punctuated.push(parse_quote!('o2o: #( #lifetimes )+*));
+            where_clause = Some(where_clause_punctuated);
+            Some(quote!(&'o2o))
+        } else {
+            Some(quote!(&))
+        };
 
         (
-            generics.to_token_stream(),
-            Some(quote!(where #where_clause)),
-            Some(quote!(&'o2o)),
+            generics_impl.to_token_stream(),
+            where_clause.map(|where_clause| quote!(where #where_clause)),
+            r,
         )
     } else {
         (