Detect empty links on markdown rendering and issue an error (#884)

* Detect empty links on markdown rendering and issue an error

* Add a test for empty links stopping rendering with an error

* Assert error message is the expected one

When testing for empty links detection compare the error message
to make sure it's the correct error that stopped the process
and not some unrelated issue.

components/rendering/src/markdown.rs

@@ -243,6 +243,10 @@ pub fn markdown_to_html(content: &str, context: &RenderContext) -> Result<Render
 
                         Event::Start(Tag::Image(link_type, src, title))
                     }
+                    Event::Start(Tag::Link(link_type, link, title)) if link.is_empty() => {
+                        error = Some(Error::msg("There is a link that is missing a URL"));
+                        Event::Start(Tag::Link(link_type, "#".into(), title))
+                    }
                     Event::Start(Tag::Link(link_type, link, title)) => {
                         let fixed_link = match fix_link(
                             link_type,

components/rendering/tests/markdown.rs

@@ -857,3 +857,27 @@ fn leaves_custom_url_scheme_untouched() {
 
     assert_eq!(res.body, expected);
 }
+
+#[test]
+fn stops_with_an_error_on_an_empty_link() {
+    let content = r#"[some link]()"#;
+
+    let tera_ctx = Tera::default();
+    let config = Config::default();
+    let permalinks_ctx = HashMap::new();
+
+    let context = RenderContext::new(
+        &tera_ctx,
+        &config,
+        "https://vincent.is/",
+        &permalinks_ctx,
+        InsertAnchor::None,
+    );
+
+    let res = render_content(content, &context);
+
+    let expected = "There is a link that is missing a URL";
+
+    assert!(res.is_err());
+    assert_eq!(res.unwrap_err().to_string(), expected);
+}