feat(forge doc): include @Custom natspec (foundry-rs#9075)

* feat(`forge doc`): include @Custom natspec

* chore: make clippy happy

* test: implement test for `is_custom`

* chore: make rustfmt happy

* doc: nit

* chore: format custom tags

crates/doc/src/parser/comment.rs

@@ -96,6 +96,11 @@ impl Comment {
             },
         )
     }
+
+    /// Check if this comment is a custom tag.
+    pub fn is_custom(&self) -> bool {
+        matches!(self.tag, CommentTag::Custom(_))
+    }
 }
 
 /// The collection of natspec [Comment] items.
@@ -157,18 +162,18 @@ impl From<Vec<DocCommentTag>> for Comments {
 pub struct CommentsRef<'a>(Vec<&'a Comment>);
 
 impl<'a> CommentsRef<'a> {
-    /// Filter a collection of comments and return only those that match a provided tag
+    /// Filter a collection of comments and return only those that match a provided tag.
     pub fn include_tag(&self, tag: CommentTag) -> Self {
         self.include_tags(&[tag])
     }
 
-    /// Filter a collection of comments and return only those that match provided tags
+    /// Filter a collection of comments and return only those that match provided tags.
     pub fn include_tags(&self, tags: &[CommentTag]) -> Self {
         // Cloning only references here
         CommentsRef(self.iter().cloned().filter(|c| tags.contains(&c.tag)).collect())
     }
 
-    /// Filter a collection of comments and return  only those that do not match provided tags
+    /// Filter a collection of comments and return only those that do not match provided tags.
     pub fn exclude_tags(&self, tags: &[CommentTag]) -> Self {
         // Cloning only references here
         CommentsRef(self.iter().cloned().filter(|c| !tags.contains(&c.tag)).collect())
@@ -192,6 +197,11 @@ impl<'a> CommentsRef<'a> {
             .find(|c| matches!(c.tag, CommentTag::Inheritdoc))
             .and_then(|c| c.value.split_whitespace().next())
     }
+
+    /// Filter a collection of comments and only return the custom tags.
+    pub fn get_custom_tags(&self) -> Self {
+        CommentsRef(self.iter().cloned().filter(|c| c.is_custom()).collect())
+    }
 }
 
 impl<'a> From<&'a Comments> for CommentsRef<'a> {
@@ -228,4 +238,32 @@ mod tests {
         assert_eq!(CommentTag::from_str("custom"), None);
         assert_eq!(CommentTag::from_str("sometag"), None);
     }
+
+    #[test]
+    fn test_is_custom() {
+        // Test custom tag.
+        let custom_comment = Comment::new(
+            CommentTag::from_str("custom:test").unwrap(),
+            "dummy custom tag".to_owned(),
+        );
+        assert!(custom_comment.is_custom(), "Custom tag should return true for is_custom");
+
+        // Test non-custom tags.
+        let non_custom_tags = [
+            CommentTag::Title,
+            CommentTag::Author,
+            CommentTag::Notice,
+            CommentTag::Dev,
+            CommentTag::Param,
+            CommentTag::Return,
+            CommentTag::Inheritdoc,
+        ];
+        for tag in non_custom_tags {
+            let comment = Comment::new(tag.clone(), "Non-custom comment".to_string());
+            assert!(
+                !comment.is_custom(),
+                "Non-custom tag {tag:?} should return false for is_custom"
+            );
+        }
+    }
 }

crates/doc/src/writer/as_doc.rs

@@ -46,18 +46,32 @@ impl AsDoc for CommentsRef<'_> {
 
         // Write notice tags
         let notices = self.include_tag(CommentTag::Notice);
-        for notice in notices.iter() {
-            writer.writeln_raw(&notice.value)?;
+        for n in notices.iter() {
+            writer.writeln_raw(&n.value)?;
             writer.writeln()?;
         }
 
         // Write dev tags
         let devs = self.include_tag(CommentTag::Dev);
-        for dev in devs.iter() {
-            writer.write_italic(&dev.value)?;
+        for d in devs.iter() {
+            writer.write_italic(&d.value)?;
             writer.writeln()?;
         }
 
+        // Write custom tags
+        let customs = self.get_custom_tags();
+        if !customs.is_empty() {
+            writer.write_bold(&format!("Note{}:", if customs.len() == 1 { "" } else { "s" }))?;
+            for c in customs.iter() {
+                writer.writeln_raw(format!(
+                    "{}{}",
+                    if customs.len() == 1 { "" } else { "- " },
+                    &c.value
+                ))?;
+                writer.writeln()?;
+            }
+        }
+
         Ok(writer.finish())
     }
 }
@@ -234,7 +248,7 @@ impl AsDoc for Document {
                             func.params.iter().filter_map(|p| p.1.as_ref()).collect::<Vec<_>>();
                         writer.try_write_param_table(CommentTag::Param, &params, &item.comments)?;
 
-                        // Write function parameter comments in a table
+                        // Write function return parameter comments in a table
                         let returns =
                             func.returns.iter().filter_map(|p| p.1.as_ref()).collect::<Vec<_>>();
                         writer.try_write_param_table(
@@ -303,7 +317,7 @@ impl Document {
         let params = func.params.iter().filter_map(|p| p.1.as_ref()).collect::<Vec<_>>();
         writer.try_write_param_table(CommentTag::Param, &params, &comments)?;
 
-        // Write function parameter comments in a table
+        // Write function return parameter comments in a table
         let returns = func.returns.iter().filter_map(|p| p.1.as_ref()).collect::<Vec<_>>();
         writer.try_write_param_table(CommentTag::Return, &returns, &comments)?;