Continue comments when opening a new line

helix-core/src/comment.rs

@@ -1,5 +1,7 @@
-//! This module contains the functionality toggle comments on lines over the selection
-//! using the comment character defined in the user's `languages.toml`
+//! This module contains the some comment-related features
+//! using the comment character defined in the user's `languages.toml`:
+//! * toggle comments on lines over the selection.
+//! * continue comment when opening a new line.
 
 use crate::{
     find_first_non_whitespace_char, Change, Rope, RopeSlice, Selection, Tendril, Transaction,
@@ -94,6 +96,22 @@ pub fn toggle_line_comments(doc: &Rope, selection: &Selection, token: Option<&st
     Transaction::change(doc, changes.into_iter())
 }
 
+pub fn continue_comment<'a>(doc: &Rope, line: usize, token: Option<&'a str>) -> Option<&'a str> {
+    let token = token?;
+
+    let line_slice = doc.line(line);
+    let commented = find_first_non_whitespace_char(line_slice)
+        .map(|pos| {
+            let len = line_slice.len_chars();
+            // line can be shorter than pos + token len
+            let fragment = Cow::from(line_slice.slice(pos..std::cmp::min(pos + token.len(), len)));
+            fragment == token
+        })
+        .unwrap_or_default();
+
+    commented.then(|| token)
+}
+
 #[cfg(test)]
 mod test {
     use super::*;

helix-term/src/commands.rs

@@ -2293,6 +2293,16 @@ fn open(cx: &mut Context, open: Open) {
         let mut text = String::with_capacity(1 + indent_len);
         text.push_str(doc.line_ending.as_str());
         text.push_str(&indent);
+
+        let token = doc
+            .language_config()
+            .and_then(|lc| lc.comment_token.as_ref())
+            .map(|tc| tc.as_ref());
+        if let Some(token) = comment::continue_comment(doc.text(), cursor_line, token) {
+            text.push_str(token);
+            text.push(' ');
+        }
+
         let text = text.repeat(count);
 
         // calculate new selection ranges
@@ -2312,6 +2322,9 @@ fn open(cx: &mut Context, open: Open) {
     transaction = transaction.with_selection(Selection::new(ranges, selection.primary_index()));
 
     doc.apply(&transaction, view.id);
+
+    // Since we might have added a comment token, move to the end of the line.
+    goto_line_end_newline(cx);
 }
 
 // o inserts a new line after each line with a selection
@@ -2774,6 +2787,16 @@ pub mod insert {
                 text.reserve_exact(1 + indent.len());
                 text.push_str(doc.line_ending.as_str());
                 text.push_str(&indent);
+
+                let token = doc
+                    .language_config()
+                    .and_then(|lc| lc.comment_token.as_ref())
+                    .map(|tc| tc.as_ref());
+                if let Some(token) = comment::continue_comment(doc.text(), current_line, token) {
+                    text.push_str(token);
+                    text.push(' ');
+                }
+
                 pos + offs + text.chars().count()
             };