Fix tabs across linewrap

This resolves an issue with tabs not breaking across line boundaries,
instead the characters would just all get written to the last column and
thus be lost.

It also tweaks the behavior of what happens when the terminal resizes
with the default tabspaces changed, using something like the `tabs`
program. Previously all tabstops would be reset to the default on
resize, which is what URxvt does. Now the tabspaces are kept and the new
columns are filled with the default tabstops, which emulates Termite.

2 files changed, 27 insertions, 9 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 53506f44..f3e6ded1 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -57,6 +57,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Config reload creating alternate screen history instead of updating scrollback
 - Crash on Wayland compositors supporting `wl_seat` version 7+
 - Message bar not hiding after fixing wrong color value in config
+- Tabstops cleared on resize
+- Tabstops not breaking across lines
 
 ### Removed
 
diff --git a/alacritty_terminal/src/term/mod.rs b/alacritty_terminal/src/term/mod.rs
index a91f41ef..f198c59b 100644
--- a/alacritty_terminal/src/term/mod.rs
+++ b/alacritty_terminal/src/term/mod.rs
@@ -44,7 +44,7 @@ pub mod color;
 /// Used to match equal brackets, when performing a bracket-pair selection.
 const BRACKET_PAIRS: [(char, char); 4] = [('(', ')'), ('[', ']'), ('{', '}'), ('<', '>')];
 
-/// Max size of the window title stack
+/// Max size of the window title stack.
 const TITLE_STACK_MAX_DEPTH: usize = 4096;
 
 /// A type that can expand a given point to a region
@@ -812,9 +812,6 @@ pub struct Term<T> {
     /// Whether to permit updating the terminal title
     dynamic_title: bool,
 
-    /// Number of spaces in one tab
-    tabspaces: usize,
-
     /// Clipboard access coupled to the active window
     clipboard: Clipboard,
 
@@ -947,7 +944,6 @@ impl<T> Term<T> {
             cursor_style: None,
             default_cursor_style: config.cursor.style,
             dynamic_title: config.dynamic_title(),
-            tabspaces,
             clipboard,
             event_proxy,
             is_focused: true,
@@ -1188,7 +1184,7 @@ impl<T> Term<T> {
         self.cursor_save_alt.point.line = min(self.cursor_save_alt.point.line, num_lines - 1);
 
         // Recreate tabs list
-        self.tabs = TabStops::new(self.grid.num_cols(), self.tabspaces);
+        self.tabs.resize(self.grid.num_cols());
     }
 
     #[inline]
@@ -1542,9 +1538,14 @@ impl<T: EventListener> Handler for Term<T> {
         self.goto(move_to, Column(0))
     }
 
+    /// Insert tab at cursor position.
     #[inline]
     fn put_tab(&mut self, mut count: i64) {
-        trace!("Putting tab: {}", count);
+        // A tab after the last column is the same as a linebreak
+        if self.input_needs_wrap {
+            self.wrapline();
+            return;
+        }
 
         while self.cursor.point.col < self.grid.num_cols() && count != 0 {
             count -= 1;
@@ -1566,8 +1567,6 @@ impl<T: EventListener> Handler for Term<T> {
                 }
             }
         }
-
-        self.input_needs_wrap = false;
     }
 
     /// Backspace `count` characters
@@ -2155,22 +2154,39 @@ impl<T: EventListener> Handler for Term<T> {
 
 struct TabStops {
     tabs: Vec<bool>,
+    tabspaces: usize,
 }
 
 impl TabStops {
+    #[inline]
     fn new(num_cols: Column, tabspaces: usize) -> TabStops {
         TabStops {
+            tabspaces,
             tabs: IndexRange::from(Column(0)..num_cols)
                 .map(|i| (*i as usize) % tabspaces == 0)
                 .collect::<Vec<bool>>(),
         }
     }
 
+    /// Remove all tabstops.
+    #[inline]
     fn clear_all(&mut self) {
         unsafe {
             ptr::write_bytes(self.tabs.as_mut_ptr(), 0, self.tabs.len());
         }
     }
+
+    /// Increase tabstop capacity.
+    #[inline]
+    fn resize(&mut self, num_cols: Column) {
+        let tabspaces = self.tabspaces;
+        let mut index = self.tabs.len();
+        self.tabs.resize_with(num_cols.0, || {
+            let is_tabstop = index % tabspaces == 0;
+            index += 1;
+            is_tabstop
+        });
+    }
 }
 
 impl Index<Column> for TabStops {