Add deref builtin filter

askama_derive/src/generator.rs

@@ -1230,6 +1230,7 @@ impl<'a> Generator<'a> {
     ) -> Result<DisplayWrap, CompileError> {
         match name {
             "as_ref" => return self._visit_as_ref_filter(buf, args),
+            "deref" => return self._visit_deref_filter(buf, args),
             "escape" | "e" => return self._visit_escape_filter(buf, args),
             "fmt" => return self._visit_fmt_filter(buf, args),
             "format" => return self._visit_format_filter(buf, args),
@@ -1263,6 +1264,20 @@ impl<'a> Generator<'a> {
         Ok(DisplayWrap::Unwrapped)
     }
 
+    fn _visit_deref_filter(
+        &mut self,
+        buf: &mut Buffer,
+        args: &[Expr<'_>],
+    ) -> Result<DisplayWrap, CompileError> {
+        let arg = match args {
+            [arg] => arg,
+            _ => return Err("unexpected argument(s) in `deref` filter".into()),
+        };
+        buf.write("*");
+        self.visit_expr(buf, arg)?;
+        Ok(DisplayWrap::Unwrapped)
+    }
+
     fn _visit_json_filter(
         &mut self,
         buf: &mut Buffer,

book/src/filters.md

@@ -24,6 +24,7 @@ Enable it with Cargo features (see below for more information).
   [`as_ref`][#as_ref],
   [`capitalize`][#capitalize],
   [`center`][#center],
+  [`deref`][#deref],
   [`escape|e`][#escape],
   [`filesizeformat`][#filesizeformat],
   [`fmt`][#fmt],
@@ -108,6 +109,24 @@ Output:
 -  a  -
 ```
 
+### deref
+[#deref]: #deref
+
+Dereferences the given argument.
+
+```
+{% let s = String::from("a")|as_ref %}
+{% if s|deref == String::from("b") %}
+{% endif %}
+```
+
+will become:
+
+```
+let s = &String::from("a");
+if *s == String::from("b") {}
+```
+
 ### escape | e
 [#escape]: #escape--e
 

testing/tests/filters.rs

@@ -311,7 +311,12 @@ fn test_json_script() {
 }
 
 #[derive(askama::Template)]
-#[template(source = "{% let word = s|as_ref %}{{ word }}", ext = "html")]
+#[template(
+    source = r#"{% let word = s|as_ref %}{{ word }}
+{%- let hello = String::from("hello") %}
+{%- if word|deref == hello %}1{% else %}2{% endif %}"#,
+    ext = "html"
+)]
 struct LetBorrow {
     s: String,
 }
@@ -321,5 +326,5 @@ fn test_let_borrow() {
     let template = LetBorrow {
         s: "hello".to_owned(),
     };
-    assert_eq!(template.render().unwrap(), "hello")
+    assert_eq!(template.render().unwrap(), "hello1")
 }