deser macros: prepare for second lifetime parameter

As DeserializeValue and DeserializeRow are going to be parametrized by
two lifetimes instead of one, the common code for generating unique
lifetimes in derive macros is adjusted to generate two lifetimes.

For now, only the first generated lifetime is used (the second is
ignored), because DeserializeValue and DeserializeRow still have only
one lifetime.

Author: wprzytula

scylla-macros/src/deserialize/mod.rs

@@ -40,7 +40,7 @@ struct StructDescForDeserialize<Attrs, Field> {
     attrs: Attrs,
     fields: Vec<Field>,
     constraint_trait: syn::Path,
-    constraint_lifetime: syn::Lifetime,
+    constraint_lifetimes: (syn::Lifetime, syn::Lifetime),
 
     generics: syn::Generics,
 }
@@ -70,14 +70,14 @@ where
             .map(Field::from_field)
             .collect::<Result<_, _>>()?;
 
-        let constraint_lifetime = generate_unique_lifetime_for_impl(&input.generics);
+        let constraint_lifetimes = generate_pair_of_unique_lifetimes_for_impl(&input.generics);
 
         Ok(Self {
             name: input.ident.clone(),
             attrs,
             fields,
             constraint_trait,
-            constraint_lifetime,
+            constraint_lifetimes,
             generics: input.generics.clone(),
         })
     }
@@ -86,8 +86,8 @@ where
         &self.attrs
     }
 
-    fn constraint_lifetime(&self) -> &syn::Lifetime {
-        &self.constraint_lifetime
+    fn constraint_lifetimes(&self) -> &(syn::Lifetime, syn::Lifetime) {
+        &self.constraint_lifetimes
     }
 
     fn fields(&self) -> &[Field] {
@@ -99,7 +99,7 @@ where
         trait_: syn::Path,
         items: impl IntoIterator<Item = syn::ImplItem>,
     ) -> syn::ItemImpl {
-        let constraint_lifetime = &self.constraint_lifetime;
+        let (constraint_lifetime, _) = self.constraint_lifetimes();
         let (_, ty_generics, _) = self.generics.split_for_impl();
         let impl_generics = &self.generics.params;
 
@@ -108,7 +108,7 @@ where
         let predicates = generate_lifetime_constraints_for_impl(
             &self.generics,
             self.constraint_trait.clone(),
-            &self.constraint_lifetime,
+            constraint_lifetime,
         )
         .chain(generate_default_constraints(&self.fields));
         let trait_: syn::Path = parse_quote!(#macro_internal::#trait_);
@@ -168,16 +168,31 @@ fn generate_lifetime_constraints_for_impl<'a>(
     lifetime_constraints.chain(type_constraints)
 }
 
-/// Generates a new lifetime parameter, with a different name to any of the
+/// Generates a pair of new lifetime parameters, with a different name to any of the
 /// existing generic lifetimes.
-fn generate_unique_lifetime_for_impl(generics: &syn::Generics) -> syn::Lifetime {
+fn generate_pair_of_unique_lifetimes_for_impl(
+    generics: &syn::Generics,
+) -> (syn::Lifetime, syn::Lifetime) {
     let mut constraint_lifetime_name = "'lifetime".to_string();
-    while generics
-        .lifetimes()
-        .any(|l| l.lifetime.to_string() == constraint_lifetime_name)
-    {
+    fn lifetime_occupied(generics: &syn::Generics, lifetime_name: &str) -> bool {
+        generics
+            .lifetimes()
+            .any(|l| l.lifetime.to_string() == lifetime_name)
+    }
+
+    while lifetime_occupied(generics, &constraint_lifetime_name) {
+        // Extend the lifetime name with another underscore.
+        constraint_lifetime_name += "_";
+    }
+
+    let lifetime1 = syn::Lifetime::new(&constraint_lifetime_name, Span::call_site());
+    constraint_lifetime_name += "_";
+
+    while lifetime_occupied(generics, &constraint_lifetime_name) {
         // Extend the lifetime name with another underscore.
         constraint_lifetime_name += "_";
     }
-    syn::Lifetime::new(&constraint_lifetime_name, Span::call_site())
+    let lifetime2 = syn::Lifetime::new(&constraint_lifetime_name, Span::call_site());
+
+    (lifetime1, lifetime2)
 }

scylla-macros/src/deserialize/row.rs

@@ -206,7 +206,7 @@ impl<'sd> TypeCheckAssumeOrderGenerator<'sd> {
         // of the columns correspond fields' names/types.
 
         let macro_internal = self.0.struct_attrs().macro_internal_path();
-        let constraint_lifetime = self.0.constraint_lifetime();
+        let (constraint_lifetime, _) = self.0.constraint_lifetimes();
 
         let required_fields_iter = || {
             self.0
@@ -281,7 +281,7 @@ impl<'sd> DeserializeAssumeOrderGenerator<'sd> {
         let macro_internal = self.0.struct_attrs().macro_internal_path();
         let cql_name_literal = field.cql_name_literal();
         let deserializer = field.deserialize_target();
-        let constraint_lifetime = self.0.constraint_lifetime();
+        let (constraint_lifetime, _) = self.0.constraint_lifetimes();
 
         let name_check: Option<syn::Stmt> = (!self.0.struct_attrs().skip_name_checks).then(|| parse_quote! {
             if col.spec.name() != #cql_name_literal {
@@ -315,7 +315,7 @@ impl<'sd> DeserializeAssumeOrderGenerator<'sd> {
 
     fn generate(&self) -> syn::ImplItemFn {
         let macro_internal = self.0.struct_attrs().macro_internal_path();
-        let constraint_lifetime = self.0.constraint_lifetime();
+        let (constraint_lifetime, _) = self.0.constraint_lifetimes();
 
         let fields = self.0.fields();
         let field_idents = fields.iter().map(|f| f.ident.as_ref().unwrap());
@@ -362,7 +362,7 @@ impl<'sd> TypeCheckUnorderedGenerator<'sd> {
     fn generate_type_check(&self, field: &Field) -> Option<syn::Block> {
         (!field.skip).then(|| {
             let macro_internal = self.0.struct_attrs().macro_internal_path();
-            let constraint_lifetime = self.0.constraint_lifetime();
+            let (constraint_lifetime, _) = self.0.constraint_lifetimes();
             let visited_flag = Self::visited_flag_variable(field);
             let typ = field.deserialize_target();
             let cql_name_literal = field.cql_name_literal();
@@ -516,7 +516,7 @@ impl<'sd> DeserializeUnorderedGenerator<'sd> {
     fn generate_deserialization(&self, column_index: usize, field: &Field) -> syn::Expr {
         assert!(!field.skip);
         let macro_internal = self.0.struct_attrs().macro_internal_path();
-        let constraint_lifetime = self.0.constraint_lifetime();
+        let (constraint_lifetime, _) = self.0.constraint_lifetimes();
         let deserialize_field = Self::deserialize_field_variable(field);
         let deserializer = field.deserialize_target();
 
@@ -557,7 +557,7 @@ impl<'sd> DeserializeUnorderedGenerator<'sd> {
 
     fn generate(&self) -> syn::ImplItemFn {
         let macro_internal = self.0.struct_attrs().macro_internal_path();
-        let constraint_lifetime = self.0.constraint_lifetime();
+        let (constraint_lifetime, _) = self.0.constraint_lifetimes();
         let fields = self.0.fields();
 
         let deserialize_field_decls = fields

scylla-macros/src/deserialize/value.rs

@@ -229,7 +229,7 @@ impl<'sd> TypeCheckAssumeOrderGenerator<'sd> {
     // Generates name and type validation for given Rust struct's field.
     fn generate_field_validation(&self, rust_field_idx: usize, field: &Field) -> syn::Expr {
         let macro_internal = self.0.struct_attrs().macro_internal_path();
-        let constraint_lifetime = self.0.constraint_lifetime();
+        let (constraint_lifetime, _) = self.0.constraint_lifetimes();
         let rust_field_name = field.cql_name_literal();
         let rust_field_typ = field.deserialize_target();
         let default_when_missing = field.default_when_missing;
@@ -413,7 +413,7 @@ impl<'sd> DeserializeAssumeOrderGenerator<'sd> {
         let macro_internal = self.0.struct_attrs().macro_internal_path();
         let cql_name_literal = field.cql_name_literal();
         let deserializer = field.deserialize_target();
-        let constraint_lifetime = self.0.constraint_lifetime();
+        let (constraint_lifetime, _) = self.0.constraint_lifetimes();
         let default_when_missing = field.default_when_missing;
         let default_when_null = field.default_when_null;
         let skip_name_checks = self.0.attrs.skip_name_checks;
@@ -532,7 +532,7 @@ impl<'sd> DeserializeAssumeOrderGenerator<'sd> {
         // We can assume that type_check was called.
 
         let macro_internal = self.0.struct_attrs().macro_internal_path();
-        let constraint_lifetime = self.0.constraint_lifetime();
+        let (constraint_lifetime, _) = self.0.constraint_lifetimes();
         let fields = self.0.fields();
 
         let field_idents = fields.iter().map(|f| f.ident.as_ref().unwrap());
@@ -592,7 +592,7 @@ impl<'sd> TypeCheckUnorderedGenerator<'sd> {
     fn generate_type_check(&self, field: &Field) -> Option<syn::Block> {
         (!field.skip).then(|| {
             let macro_internal = self.0.struct_attrs().macro_internal_path();
-            let constraint_lifetime = self.0.constraint_lifetime();
+            let (constraint_lifetime, _) = self.0.constraint_lifetimes();
             let visited_flag = Self::visited_flag_variable(field);
             let typ = field.deserialize_target();
             let cql_name_literal = field.cql_name_literal();
@@ -770,7 +770,7 @@ impl<'sd> DeserializeUnorderedGenerator<'sd> {
     fn generate_deserialization(&self, field: &Field) -> Option<syn::Expr> {
         (!field.skip).then(|| {
             let macro_internal = self.0.struct_attrs().macro_internal_path();
-            let constraint_lifetime = self.0.constraint_lifetime();
+            let (constraint_lifetime, _) = self.0.constraint_lifetimes();
             let deserialize_field = Self::deserialize_field_variable(field);
             let cql_name_literal = field.cql_name_literal();
             let deserializer = field.deserialize_target();
@@ -833,7 +833,7 @@ impl<'sd> DeserializeUnorderedGenerator<'sd> {
 
     fn generate(&self) -> syn::ImplItemFn {
         let macro_internal = self.0.struct_attrs().macro_internal_path();
-        let constraint_lifetime = self.0.constraint_lifetime();
+        let (constraint_lifetime, _) = self.0.constraint_lifetimes();
         let fields = self.0.fields();
 
         let deserialize_field_decls = fields.iter().map(Self::generate_deserialize_field_decl);