Fix broken links to images in summary

Restores the change of relative to absolute links for colocated files
that was removed in commit 4086b07 / PR getzola#1582.

components/rendering/src/markdown.rs

@@ -1,5 +1,6 @@
 use lazy_static::lazy_static;
 use pulldown_cmark as cmark;
+use regex::Regex;
 
 use crate::context::RenderContext;
 use crate::table_of_contents::{make_table_of_contents, Heading};
@@ -64,6 +65,26 @@ fn is_external_link(link: &str) -> bool {
     link.starts_with("http:") || link.starts_with("https:")
 }
 
+/// Returns whether the given string starts with a schema.
+///
+/// Although there exists [a list of registered URI schemes][uri-schemes], a link may use arbitrary,
+/// private schemes. This function checks if the given string starts with something that just looks
+/// like a scheme, i.e., a case-insensitive identifier followed by a colon.
+///
+/// [uri-schemes]: https://www.iana.org/assignments/uri-schemes/uri-schemes.xhtml
+fn starts_with_schema(s: &str) -> bool {
+    lazy_static! {
+        static ref PATTERN: Regex = Regex::new(r"^[0-9A-Za-z\-]+:").unwrap();
+    }
+    PATTERN.is_match(s)
+}
+
+/// Colocated asset links refers to the files in the same directory,
+/// there it shouldn't start with / or a schema
+fn is_colocated_asset_link(link: &str) -> bool {
+    !link.starts_with("/") && !starts_with_schema(link)
+}
+
 fn fix_link(
     link_type: LinkType,
     link: &str,
@@ -89,6 +110,8 @@ fn fix_link(
                 return Err(format!("Relative link {} not found.", link).into());
             }
         }
+    } else if is_colocated_asset_link(link) {
+    	format!("{}{}", context.current_page_permalink, link)
     } else {
         if is_external_link(link) {
             external_links.push(link.to_owned());
@@ -298,6 +321,14 @@ pub fn markdown_to_html(
                     code_block = None;
                     events.push(Event::Html("</code></pre>\n".into()));
                 }
+                Event::Start(Tag::Image(link_type, src, title)) => {
+                    if is_colocated_asset_link(&src) {
+                        let link = format!("{}{}", context.current_page_permalink, &*src);
+                        events.push(Event::Start(Tag::Image(link_type, link.into(), title)));
+                    } else {
+                    	events.push(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"));
                     events.push(Event::Start(Tag::Link(link_type, "#".into(), title)));

components/rendering/tests/markdown.rs

@@ -1017,7 +1017,7 @@ fn can_make_permalinks_with_colocated_assets_for_link() {
         InsertAnchor::None,
     );
     let res = render_content("[an image](image.jpg)", &context).unwrap();
-    assert_eq!(res.body, "<p><a href=\"image.jpg\">an image</a></p>\n");
+    assert_eq!(res.body, "<p><a href=\"https://vincent.is/about/image.jpg\">an image</a></p>\n");
 }
 
 #[test]
@@ -1033,7 +1033,7 @@ fn can_make_permalinks_with_colocated_assets_for_image() {
         InsertAnchor::None,
     );
     let res = render_content("![alt text](image.jpg)", &context).unwrap();
-    assert_eq!(res.body, "<p><img src=\"image.jpg\" alt=\"alt text\" /></p>\n");
+    assert_eq!(res.body, "<p><img src=\"https://vincent.is/about/image.jpg\" alt=\"alt text\" /></p>\n");
 }
 
 #[test]