util: add ValidateField trait

src/util/validate.rs

@@ -10,11 +10,17 @@ pub struct Sane<T>(T);
 #[repr(transparent)]
 pub struct Insane<T>(T);
 
-/// Anything that can be validated (used for transforming [Insane] to [Sane])
+/// Anything that can be validated (used for transforming [`Insane`] to [`Sane`])
 pub trait Validate: Sized {
     fn validate(&self, builder: ResultBuilder) -> ResultBuilder;
 }
 
+/// A field in a struct that can be validated and that is reused in multiple places.
+/// Primarily useful for newtype structs.
+pub trait ValidateField<'a>: Sized {
+    fn validate_field(builder: FieldResultBuilder<'a, Self>) -> FieldResultBuilder<'a, Self>;
+}
+
 /// Validation error
 #[derive(Debug)]
 pub struct Error {
@@ -82,34 +88,42 @@ impl ResultBuilder {
     }
 
     /// Begin sanitization on a single field
-    pub fn field<T, N, F>(mut self, val: &T, name: N, check: F) -> Self
+    pub fn field<'a, T, N, F>(mut self, val: &'a T, name: N, check: F) -> Self
     where
-        N: Into<String>,
+        N: Into<&'a str>,
         F: FnOnce(FieldResultBuilder<T>) -> FieldResultBuilder<T>,
     {
         let builder = check(FieldResultBuilder {
             val,
             errors: Vec::with_capacity(0),
         });
-        let name = name.into();
+        builder.append_errors(name.into(), &mut self.errors);
-        self.errors.extend(
+        self
-            builder
+    }
-                .errors
+
-                .into_iter()
+    /// Validate a field that implements [`ValidateField`]
-                .map(|msg| (name.clone(), msg.clone())),
+    pub fn field_auto<'a, T, N>(mut self, val: &'a T, name: N) -> Self
-        );
+    where
+        T: ValidateField<'a>,
+        N: Into<&'a str>,
+    {
+        let builder = T::validate_field(FieldResultBuilder {
+            val,
+            errors: Vec::with_capacity(0),
+        });
+        builder.append_errors(name.into(), &mut self.errors);
         self
     }
 
     /// Obtain the final result of the validation
     fn result<T>(self, success_val: T) -> Result<T> {
-        if self.errors.len() > 0 {
+        if self.errors.is_empty() {
+            Ok(success_val)
+        } else {
             Err(Error {
                 errors: self.errors,
             }
             .into())
-        } else {
-            Ok(success_val)
         }
     }
 }
@@ -126,6 +140,14 @@ impl<'a, T> FieldResultBuilder<'a, T> {
         }
         self
     }
+
+    fn append_errors(self, field_name: &str, errors: &mut Vec<(String, String)>) {
+        errors.extend(
+            self.errors
+                .into_iter()
+                .map(|msg| (String::from(field_name), msg)),
+        );
+    }
 }
 
 impl fmt::Display for Error {