Make the `markdown` filter compatible with `String`

This commit solves issue #719.

This is done by making the markdown filter borrow the string and
simplifying the filter to accept `&str` instead of `AsRef<str>`

Add test for the markdown filter using  as input

Revert markdown filter changes

Revert unnecessary changes

Improve test_markdown_owned_string test

Use cargo fmt

2 files changed, 19 insertions, 1 deletions

diff --git a/askama_derive/src/generator.rs b/askama_derive/src/generator.rs
index df15bdc..760a1f6 100644
--- a/askama_derive/src/generator.rs
+++ b/askama_derive/src/generator.rs
@@ -1200,7 +1200,7 @@ impl<'a> Generator<'a> {
         };
 
         buf.write(&format!(
-            "::askama::filters::markdown({}, ",
+            "::askama::filters::markdown({}, &",
             self.input.escaper
         ));
         self.visit_expr(buf, md)?;
diff --git a/testing/tests/markdown.rs b/testing/tests/markdown.rs
index 75163c9..04c9ec9 100644
--- a/testing/tests/markdown.rs
+++ b/testing/tests/markdown.rs
@@ -70,3 +70,21 @@ before\
 after",
     );
 }
+
+#[derive(Template)]
+#[template(source = "{{content|markdown}}", ext = "html")]
+struct MarkdownStringTemplate {
+    content: String,
+}
+
+// Tests if the markdown filter accepts String
+#[test]
+fn test_markdown_owned_string() {
+    let template = MarkdownStringTemplate {
+        content: "The markdown filter _indeed_ works with __String__".into(),
+    };
+    assert_eq!(
+        template.render().unwrap(),
+        "<p>The markdown filter <em>indeed</em> works with <strong>String</strong></p>\n"
+    )
+}