Handle single-line comment prefixes in :reflow.

This uses the single-line comment prefixes from the language config,
so it should be able to handle different languages in a robust way. The
logic is fairly simple, and doesn't handle block comments, for example.

Fixes helix-editor#3332, helix-editor#3622

helix-core/src/wrap.rs

@@ -1,9 +1,171 @@
 use smartstring::{LazyCompact, SmartString};
+use std::fmt::Write;
 use textwrap::{Options, WordSplitter::NoHyphenation};
 
-/// Given a slice of text, return the text re-wrapped to fit it
-/// within the given width.
-pub fn reflow_hard_wrap(text: &str, text_width: usize) -> SmartString<LazyCompact> {
+fn reflow_textwrap(text: &str, text_width: usize) -> String {
     let options = Options::new(text_width).word_splitter(NoHyphenation);
     textwrap::refill(text, options).into()
 }
+
+fn tab_len(str: &str) -> usize {
+    let mut n = 0;
+    for c in str.chars() {
+        if c == '\t' {
+            n += 8 - n % 8;
+        } else {
+            n += 1;
+        }
+    }
+    n
+}
+
+fn trim_comment_prefix<'a, 'b>(
+    s: &'a str,
+    comment_prefixes: &'b [String],
+) -> Option<(&'b str, &'a str)> {
+    for pfx in comment_prefixes {
+        match s.strip_prefix(pfx) {
+            Some(s) => return Some((pfx, s.trim_start())),
+            None => continue,
+        }
+    }
+    return None;
+}
+
+/// Given a slice of text, return the text re-wrapped to fit it
+/// within the given width.
+pub fn reflow_hard_wrap(
+    text: &str,
+    text_width: usize,
+    comment_prefixes: &[String],
+) -> SmartString<LazyCompact> {
+    // Strip indent and line comment prefix from each line. We can do a
+    // better job than textwrap since we know the comment prefix.
+    let first_line = match text.lines().next() {
+        Some(x) => x,
+        // text is empty for some reason.
+        None => return "".into(),
+    };
+    let indent_end = first_line
+        .find(|c: char| !c.is_whitespace())
+        .unwrap_or(first_line.len());
+    let indent = &first_line[..indent_end];
+    let (comment_prefix, _) = match trim_comment_prefix(&first_line[indent_end..], comment_prefixes)
+    {
+        Some(x) => x,
+        // not commented
+        None => return reflow_textwrap(text, text_width).into(),
+    };
+
+    let mut stripped_text = String::new();
+    let mut sep = "";
+    // I am intentionally using .split("\n") instead of .lines() here,
+    // so that if the text has \r\n line endings we don't destroy them.
+    for line in text.split("\n") {
+        let line = line.trim_start();
+        let line = match trim_comment_prefix(line, comment_prefixes) {
+            Some((_, x)) => x,
+            None => line,
+        };
+        write!(stripped_text, "{sep}{line}").unwrap();
+        sep = "\n";
+    }
+    // Defer to textwrap for the actual wrapping, then copy back the
+    // indent and comment prefix from the first line onto all lines.
+    let wrapped_text = reflow_textwrap(
+        &stripped_text,
+        text_width
+            .saturating_sub(tab_len(indent))
+            // unfortunately this doesn't correctly count multibyte
+            // characters in the comment prefix
+            .saturating_sub(comment_prefix.len()),
+    );
+    let mut out = String::new();
+    let mut sep = "";
+    for line in wrapped_text.split("\n") {
+        out.push_str(sep);
+        if line.trim_start() != "" {
+            write!(out, "{indent}{comment_prefix} {line}").unwrap();
+        }
+        sep = "\n";
+    }
+    return out.into();
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn reflow_line() {
+        assert_eq!(
+            reflow_hard_wrap("This is a long line bla bla bla", 4, &[]),
+            "This
+is a
+long
+line
+bla
+bla
+bla"
+        );
+    }
+
+    #[test]
+    fn reflow_single_line_comment() {
+        assert_eq!(
+            reflow_hard_wrap(
+                "// As you can see, the code works really well because of the way that it is",
+                10,
+                &vec!["//".into()]
+            ),
+            "// As you
+// can see,
+// the code
+// works
+// really
+// well
+// because
+// of the
+// way that
+// it is"
+        );
+    }
+
+    #[test]
+    fn reflow_tabbed() {
+        // https://github.com/helix-editor/helix/issues/3622
+        assert_eq!(
+            reflow_hard_wrap(
+                "\t// Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod
+\t// tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim
+\t// veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea
+\t// commodo consequat. Duis aute irure dolor in reprehenderit in voluptate
+\t// velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint
+\t// occaecat cupidatat non proident, sunt in culpa qui officia deserunt
+\t// mollit anim id est laborum.
+",
+                100,
+                &vec!["//".into()]
+            ),
+            "\t// Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt
+\t// ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation
+\t// ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in
+\t// reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur
+\t// sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id
+\t// est laborum.
+"
+        );
+    }
+
+    #[test]
+    fn reflow_multiple_comment_prefixes() {
+        assert_eq!(
+            reflow_hard_wrap(
+                "// how many different\n# ways to type comments\n-- do you need?",
+                20,
+                &vec!["//".into(), "#".into(), "--".into()]
+            ),
+            "// how many different\n// ways to type\n// comments do you\n// need?",
+        );
+    }
+}

helix-term/src/commands/typed.rs

@@ -2122,7 +2122,13 @@ fn reflow(
     let selection = doc.selection(view.id);
     let transaction = Transaction::change_by_selection(rope, selection, |range| {
         let fragment = range.fragment(rope.slice(..));
-        let reflowed_text = helix_core::wrap::reflow_hard_wrap(&fragment, text_width);
+        let comment_prefixes = doc
+            .language_config()
+            .and_then(|config| config.comment_tokens.as_ref())
+            .map(|pfxs| &pfxs[..])
+            .unwrap_or(&[]);
+        let reflowed_text =
+            helix_core::wrap::reflow_hard_wrap(&fragment, text_width, comment_prefixes);
 
         (range.from(), range.to(), Some(reflowed_text))
     });