2 files changed, 106 insertions, 0 deletions
diff --git a/helix-core/src/comment.rs b/helix-core/src/comment.rs
new file mode 100644
index 00000000..87becfa3
--- /dev/null
+++ b/helix-core/src/comment.rs
@@ -0,0 +1,105 @@
+use crate::{find_first_non_whitespace_char2, Change, RopeSlice, State, Transaction};
+use core::ops::Range;
+use std::borrow::Cow;
+
+fn find_line_comment(
+    token: &str,
+    text: RopeSlice,
+    lines: Range<usize>,
+) -> (bool, Vec<usize>, usize) {
+    // selection ranges map char_to_line from() .. to()
+    let mut commented = true;
+    let mut skipped = Vec::new();
+    let mut min = usize::MAX; // minimum col for find_first_non_whitespace_char
+    for line in lines {
+        let line_slice = text.line(line);
+        if let Some(pos) = find_first_non_whitespace_char2(line_slice) {
+            let len = line_slice.len_chars();
+
+            if pos < min {
+                min = pos;
+            }
+
+            // line can be shorter than pos + token len
+            let fragment = Cow::from(line_slice.slice(pos..std::cmp::min(pos + token.len(), len)));
+
+            if fragment != token {
+                // as soon as one of the non-blank lines doesn't have a comment, the whole block is
+                // considered uncommented.
+                commented = false;
+            }
+        } else {
+            // blank line
+            skipped.push(line);
+        }
+    }
+    (commented, skipped, min)
+}
+
+fn toggle_line_comments(state: &State) -> Transaction {
+    let text = state.doc.slice(..);
+    let mut changes: Vec<Change> = Vec::new();
+
+    let token = "//";
+
+    for selection in state.selection.ranges() {
+        let start = text.char_to_line(selection.from());
+        let end = text.char_to_line(selection.to());
+        let lines = start..end + 1;
+        let (commented, skipped, min) = find_line_comment(token, text, lines.clone());
+
+        changes.reserve(end - start - skipped.len());
+
+        for line in lines {
+            if skipped.contains(&line) {
+                continue;
+            }
+
+            let pos = text.line_to_char(line) + min;
+
+            if !commented {
+                // comment line
+                changes.push((pos, pos, Some(format!("{} ", token).into())))
+            } else {
+                // uncomment line
+                let margin = 1; // TODO: margin is hardcoded 1 but could easily be 0
+                changes.push((pos, pos + token.len() + margin, None))
+            }
+        }
+    }
+    Transaction::change(state, changes.into_iter())
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn test_find_line_comment() {
+        use crate::{Rope, Selection};
+
+        // four lines, two space indented, except for line 1 which is blank.
+        let doc = Rope::from("  1\n\n  2\n  3");
+
+        let mut state = State::new(doc);
+        // select whole document
+        state.selection = Selection::single(0, state.doc.len_chars() - 1);
+
+        let text = state.doc.slice(..);
+
+        let res = find_line_comment("//", text, 0..3);
+        // (commented = true, skipped = [line 1], min = col 2)
+        assert_eq!(res, (false, vec![1], 2));
+
+        // comment
+        let transaction = toggle_line_comments(&state);
+        transaction.apply(&mut state);
+
+        assert_eq!(state.doc, "  // 1\n\n  // 2\n  // 3");
+
+        // uncomment
+        let transaction = toggle_line_comments(&state);
+        transaction.apply(&mut state);
+        assert_eq!(state.doc, "  1\n\n  2\n  3");
+    }
+}
diff --git a/helix-core/src/lib.rs b/helix-core/src/lib.rs
index f9fe4bd4..977129ef 100644
--- a/helix-core/src/lib.rs
+++ b/helix-core/src/lib.rs
@@ -1,4 +1,5 @@
 #![allow(unused)]
+pub mod comment;
 mod diagnostic;
 pub mod graphemes;
 mod history;