Improve generics with lifetimes

dummy/src/main.rs

@@ -1,9 +1,9 @@
 use nutype::nutype;
+use std::borrow::Cow;
 
 #[nutype(
-    sanitize(with = |v| v),
-    validate(predicate = |v| !v.is_empty() )
+    validate(predicate = |s| s.len() >= 3),
 )]
-struct NonEmptyVec<T>(Vec<T>);
+struct Clarabelle<'a>(Cow<'a, str>);
 
 fn main() {}

examples/any_generics/src/main.rs

@@ -7,10 +7,7 @@ use std::borrow::Cow;
 )]
 struct NotEmpty<T>(Vec<T>);
 
-#[nutype(
-    derive(Debug),
-    validate(predicate = |s| s.len() >= 3),
-)]
+#[nutype(derive(Debug))]
 struct Clarabelle<'b>(Cow<'b, str>);
 
 fn main() {
@@ -24,7 +21,7 @@ fn main() {
     }
 
     {
-        let c1 = Clarabelle::new(Cow::Borrowed("Muu")).unwrap();
+        let c1 = Clarabelle::new(Cow::Borrowed("Muu"));
         assert_eq!(c1.into_inner(), Cow::Borrowed("Muu"));
     }
 }

nutype_macros/src/any/gen/mod.rs

@@ -72,7 +72,7 @@ impl GenerateNewtype for AnyNewtype {
             .map(|validator| match validator {
                 AnyValidator::Predicate(predicate) => {
                     let inner_type_ref: syn::Type = parse_quote!(
-                        &'a #inner_type
+                        &'nutype_a #inner_type
                     );
                     let typed_predicate: TypedCustomFunction = predicate
                         .clone()
@@ -88,7 +88,20 @@ impl GenerateNewtype for AnyNewtype {
             .collect();
 
         quote!(
-            fn __validate__<'a>(val: &'a #inner_type) -> ::core::result::Result<(), #error_name> {
+            // NOTE 1: we're using a unique lifetime name `nutype_a` in a hope that it will not clash
+            // with any other lifetimes in the user's code.
+            //
+            // NOTE 2:
+            // When inner type is Cow<'a, str>, the generated code will look like this (with 2
+            // lifetimes):
+            //
+            //     fn __validate__<'nutype_a>(val: &'nutype_a Cow<'a, str>)
+            //
+            // Clippy does not like passing a reference to a Cow. So we need to ignore the `clippy::ptr_arg` warning.
+            // Since this code is generic which is used for different inner types (not only Cow), we cannot easily fix it to make
+            // clippy happy.
+            #[allow(clippy::ptr_arg)]
+            fn __validate__<'nutype_a>(val: &'nutype_a #inner_type) -> ::core::result::Result<(), #error_name> {
                 #validations
                 Ok(())
             }

test_suite/tests/any.rs

@@ -1,4 +1,5 @@
 use nutype::nutype;
+use std::borrow::Cow;
 use test_suite::test_helpers::traits::*;
 
 // Inner custom type, which is unknown to nutype
@@ -482,4 +483,23 @@ mod with_generics {
     //     assert_eq!(err, NonEmptyVecError::PredicateViolated);
     // }
     // }
+
+    #[test]
+    fn test_generic_with_lifetime_cow() {
+        #[nutype(
+            validate(predicate = |s| s.len() >= 3),
+            derive(Debug)
+        )]
+        struct Clarabelle<'a>(Cow<'a, str>);
+
+        {
+            let clarabelle = Clarabelle::new(Cow::Borrowed("Clarabelle")).unwrap();
+            assert_eq!(clarabelle.into_inner(), Cow::Borrowed("Clarabelle"));
+        }
+
+        {
+            let err = Clarabelle::new(Cow::Borrowed("Mu")).unwrap_err();
+            assert_eq!(err, ClarabelleError::PredicateViolated);
+        }
+    }
 }