wezterm: display tab indices in tab bar by default

More details in the included changelog update

refs: https://github.com/wez/wezterm/issues/157#issuecomment-699520149

docs/changelog.markdown

@@ -17,6 +17,11 @@ brief notes about them may accumulate here.
   you would write `{key="T", mods="CTRL|SHIFT"}`, after updating to
   this release you need to write `{key="T", mods="CTRL"}` in order
   for your key bindings to take effect.
+* Added `show_tab_index_in_tab_bar` option which defaults to true.
+  Causes the tab's ordinal index to be prefixed to tab titles.
+  The displayed number is 1-based.  You can set
+  `tab_and_split_indices_are_zero_based=true` if you prefer the
+  number to be zero based.
 * Experimental support for splits/panes.  Not currently
   supported for multiplexer connections.
   See [#157](https://github.com/wez/wezterm/issues/157) for

src/config/mod.rs

@@ -464,6 +464,15 @@ pub struct Config {
     #[serde(default = "default_true")]
     pub enable_tab_bar: bool,
 
+    /// If true, tab bar titles are prefixed with the tab index
+    #[serde(default = "default_true")]
+    pub show_tab_index_in_tab_bar: bool,
+
+    /// If true, show_tab_index_in_tab_bar uses a zero-based index.
+    /// The default is false and the tab shows a one-based index.
+    #[serde(default)]
+    pub tab_and_split_indices_are_zero_based: bool,
+
     /// Specifies the maximum width that a tab can have in the
     /// tab bar.  Defaults to 16 glyphs in width.
     #[serde(default = "default_tab_max_width")]

src/frontend/gui/tabbar.rs

@@ -1,4 +1,4 @@
-use crate::config::TabBarColors;
+use crate::config::{ConfigHandle, TabBarColors};
 use crate::mux::window::Window as MuxWindow;
 use std::cell::Ref;
 use termwiz::cell::unicode_column_width;
@@ -48,7 +48,7 @@ impl TabBarState {
         mouse_x: Option<usize>,
         window: &Ref<MuxWindow>,
         colors: Option<&TabBarColors>,
-        tab_width_max: usize,
+        config: &ConfigHandle,
     ) -> Self {
         // We ultimately want to produce a line looking like this:
         // ` | tab1-title x | tab2-title x |  +      . - X `
@@ -60,9 +60,21 @@ impl TabBarState {
 
         let tab_titles: Vec<String> = window
             .iter()
-            .map(|tab| {
+            .enumerate()
+            .map(|(idx, tab)| {
                 if let Some(pane) = tab.get_active_pane() {
                     let mut title = pane.get_title();
+                    if config.show_tab_index_in_tab_bar {
+                        title = format!(
+                            "{}: {}",
+                            idx + if config.tab_and_split_indices_are_zero_based {
+                                0
+                            } else {
+                                1
+                            },
+                            title
+                        );
+                    }
                     // We have a preferred soft minimum on tab width to make it
                     // easier to click on tab titles, but we'll still go below
                     // this if there are too many tabs to fit the window at
@@ -88,7 +100,7 @@ impl TabBarState {
             // We need to clamp the length to balance them out
             available_cells / number_of_tabs
         }
-        .min(tab_width_max);
+        .min(config.tab_max_width);
 
         let colors = colors.cloned().unwrap_or_else(TabBarColors::default);
 

src/frontend/gui/termwindow.rs

@@ -1287,7 +1287,7 @@ impl TermWindow {
             },
             &window,
             config.colors.as_ref().and_then(|c| c.tab_bar.as_ref()),
-            config.tab_max_width,
+            &config,
         );
         if new_tab_bar != self.tab_bar {
             self.tab_bar = new_tab_bar;