Fix unique filter implementation

Author: GuillaumeGomez

askama/src/filters/std.rs

@@ -1,3 +1,4 @@
+use core::convert::Infallible;
 use std::collections::HashMap;
 use std::collections::hash_map::Entry;
 use std::hash::Hash;
@@ -9,8 +10,7 @@ use std::rc::Rc;
 /// the data is wrapped inside `Rc`.
 ///
 /// ```
-/// # #[cfg(feature = "code-in-doc")] {
-/// # use askama::{Template, filters};
+/// # use askama::Template;
 /// #[derive(Template)]
 /// #[template(ext = "html", source = "{% for elem in example|unique %}{{ elem }},{% endfor %}")]
 /// struct Example<'a> {
@@ -19,22 +19,23 @@ use std::rc::Rc;
 ///
 /// assert_eq!(
 ///     Example { example: vec!["a", "b", "a", "c"] }.to_string(),
-///     "a,b,c"
+///     "a,b,c,"
 /// );
-/// # }
 /// ```
-pub fn unique<T: Hash + Eq>(it: impl IntoIterator<Item = T>) -> impl Iterator<Item = Rc<T>> {
+pub fn unique<T: Hash + Eq>(
+    it: impl IntoIterator<Item = T>,
+) -> Result<impl Iterator<Item = Rc<T>>, Infallible> {
     let mut set = HashMap::new();
 
-    it.into_iter().filter_map(move |elem| {
+    Ok(it.into_iter().filter_map(move |elem| {
         // To prevent cloning the data, we need to use `Rc`, like that we can clone `elem` as
         // key of the `HashSet` and return it.
         if let Entry::Vacant(entry) = set.entry(Rc::new(elem)) {
             Some(Rc::clone(entry.insert_entry(()).key()))
         } else {
             None
         }
-    })
+    }))
 }
 
 #[cfg(test)]
@@ -47,15 +48,15 @@ mod test {
     #[test]
     fn test_unique() {
         assert_eq!(
-            unique(["a", "b", "a", "c"]).collect::<Vec<_>>(),
+            unique(["a", "b", "a", "c"]).unwrap().collect::<Vec<_>>(),
             vec![Rc::new("a"), Rc::new("b"), Rc::new("c")]
         );
         assert_eq!(
-            unique([1, 1, 1, 2, 1]).collect::<Vec<_>>(),
+            unique([1, 1, 1, 2, 1]).unwrap().collect::<Vec<_>>(),
             vec![Rc::new(1), Rc::new(2)]
         );
         assert_eq!(
-            unique("hello".chars()).collect::<Vec<_>>(),
+            unique("hello".chars()).unwrap().collect::<Vec<_>>(),
             vec![Rc::new('h'), Rc::new('e'), Rc::new('l'), Rc::new('o')]
         );
     }