From ea49e02d20947e8c9beae2e6393ec0fe4ee7df22 Mon Sep 17 00:00:00 2001
From: Callum Oakley <hello@callumoakley.net>
Date: Sun, 6 Aug 2023 10:42:31 +0100
Subject: [PATCH] workaround for textwrap's broken tab handling while reflowing

---
 helix-core/src/wrap.rs           | 47 ++++++++++++++++++++++++++++++--
 helix-term/src/commands/typed.rs |  7 ++++-
 2 files changed, 51 insertions(+), 3 deletions(-)

diff --git a/helix-core/src/wrap.rs b/helix-core/src/wrap.rs
index 2ba8d173ee1d..19030f1a9458 100644
--- a/helix-core/src/wrap.rs
+++ b/helix-core/src/wrap.rs
@@ -1,7 +1,50 @@
+use once_cell::sync::Lazy;
+use regex::{Captures, Regex};
 use smartstring::{LazyCompact, SmartString};
 
+use crate::indent::IndentStyle;
+
+static LEADING_TABS: Lazy<Regex> = Lazy::new(|| Regex::new(r"(?m)^\t+").unwrap());
+static LEADING_SPACES: Lazy<Regex> = Lazy::new(|| Regex::new(r"(?m)^ +").unwrap());
+
 /// 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> {
-    textwrap::refill(text, text_width).into()
+pub fn reflow_hard_wrap(
+    text: &str,
+    text_width: usize,
+    indent_style: IndentStyle,
+    tab_width: usize,
+) -> SmartString<LazyCompact> {
+    if indent_style == IndentStyle::Tabs {
+        // textwrap doesn't handle tabs correctly (see
+        // <https://github.com/helix-editor/helix/issues/3622>). So as a
+        // workaround, expand leading tabs before wrapping and change them back
+        // afterwards.
+        //
+        // If/when <https://github.com/mgeisler/textwrap/pull/490> is merged
+        // upstream we can remove this workaround.
+        let text = LEADING_TABS.replace_all(text, |captures: &Captures| {
+            " ".repeat(captures[0].len() * tab_width)
+        });
+        let text = textwrap::refill(&text, text_width);
+        LEADING_SPACES
+            .replace_all(&text, |captures: &Captures| {
+                "\t".repeat(captures[0].len() / tab_width)
+            })
+            .into()
+    } else {
+        textwrap::refill(text, text_width).into()
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_reflow_hard_wrap_tabs() {
+        let text = "\t\t// The quick brown fox jumps over\n\t\t// the lazy dog.\n";
+        let expected = "\t\t// The quick brown fox jumps\n\t\t// over the lazy dog.\n";
+        assert_eq!(reflow_hard_wrap(text, 40, IndentStyle::Tabs, 4), expected);
+    }
 }
diff --git a/helix-term/src/commands/typed.rs b/helix-term/src/commands/typed.rs
index 67640f79764f..74a0a965d245 100644
--- a/helix-term/src/commands/typed.rs
+++ b/helix-term/src/commands/typed.rs
@@ -1993,7 +1993,12 @@ 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 reflowed_text = helix_core::wrap::reflow_hard_wrap(
+            &fragment,
+            text_width,
+            doc.indent_style,
+            doc.tab_width(),
+        );
 
         (range.from(), range.to(), Some(reflowed_text))
     });