add wezterm.truncate_to_width

refs: https://github.com/wez/wezterm/issues/647

Cargo.lock

@@ -700,6 +700,7 @@ dependencies = [
  "termwiz",
  "toml",
  "umask",
+ "unicode-segmentation",
  "wezterm-input-types",
  "wezterm-term",
  "winapi 0.3.9",

config/Cargo.toml

@@ -36,6 +36,7 @@ terminfo = "0.7"
 termwiz = { path = "../termwiz" }
 toml = "0.5"
 umask = { path = "../umask" }
+unicode-segmentation = "1.7"
 wezterm-input-types = { path = "../wezterm-input-types" }
 wezterm-term = { path = "../term", features=["use_serde"] }
 

config/src/lua.rs

@@ -7,10 +7,11 @@ use mlua::{Lua, Table, Value};
 use serde::*;
 use smol::prelude::*;
 use std::path::Path;
-use termwiz::cell::{unicode_column_width, AttributeChange, CellAttributes};
+use termwiz::cell::{grapheme_column_width, unicode_column_width, AttributeChange, CellAttributes};
 use termwiz::color::{AnsiColor, ColorAttribute, ColorSpec, RgbColor};
 use termwiz::input::Modifiers;
 use termwiz::surface::change::Change;
+use unicode_segmentation::UnicodeSegmentation;
 
 /// Set up a lua context for executing some code.
 /// The path to the directory containing the configuration is
@@ -120,6 +121,36 @@ pub fn make_lua_context(config_file: &Path) -> anyhow::Result<Lua> {
             lua.create_function(|_, s: String| Ok(unicode_column_width(&s)))?,
         )?;
 
+        wezterm_mod.set(
+            "truncate_to_width",
+            lua.create_function(
+                |_, (s, max_width, min_width): (String, usize, Option<usize>)| {
+                    let mut result = String::new();
+                    let mut len = 0;
+                    for g in s.graphemes(true) {
+                        let g_len = grapheme_column_width(g);
+                        if g_len + len > max_width {
+                            break;
+                        }
+                        result.push_str(g);
+                        len += g_len;
+                    }
+
+                    if let Some(min_width) = min_width {
+                        while len < min_width {
+                            if len >= max_width {
+                                break;
+                            }
+                            result.push(' ');
+                            len += 1;
+                        }
+                    }
+
+                    Ok(result)
+                },
+            )?,
+        )?;
+
         wezterm_mod.set("font", lua.create_function(font)?)?;
         wezterm_mod.set(
             "font_with_fallback",

docs/changelog.md

@@ -46,6 +46,7 @@ As features stabilize some brief notes about them will accumulate here.
 * Fixed: tabs would remain hovered after moving the mouse down into the main terminal area [#591](https://github.com/wez/wezterm/issues/591)
 * New: [tab_bar_at_bottom](config/lua/config/tab_bar_at_bottom.md) setting to put the tab bar at the bottom of the window [#278](https://github.com/wez/wezterm/issues/278)
 * New: [wezterm.column_width](config/lua/wezterm/column_width.md) function for measuring the displayed width of a string
+* New: [wezterm.truncate_to_width](config/lua/wezterm/truncate_to_width.md) function for truncating/padding a string based on its displayed width
 
 ### 20210405-110924-a5bb5be8
 

docs/config/lua/wezterm/truncate_to_width.md

@@ -0,0 +1,11 @@
+# wezterm.truncate_to_width(string, max_width, min_width)
+
+*Since: nightly builds only*
+
+Returns a copy of `string` that is no longer than `max_width` columns
+(as measured by [wezterm.column_width](column_width.md)), and, optionally,
+no shorter than `min_width` columns, padding out with spaces.
+
+For example, `wezterm.truncate_to_width("hello", 3)` returns `"hel"`,
+and `wezterm.truncate_to_width("a", 10, 5)` returns "a    "`.
+

docs/config/lua/window-events/format-tab-title.md

@@ -87,13 +87,17 @@ wezterm.on("format-tab-title", function(tab, tabs, panes, config, hover, max_wid
 
   local edge_foreground = background
 
+  -- ensure that the titles fit in the available space,
+  -- and that we have room for the edges
+  local title = wezterm.truncate_to_width(tab.active_pane.title, max_width-2)
+
   return {
     {Background={Color=edge_background}},
     {Foreground={Color=edge_foreground}},
     {Text=SOLID_LEFT_ARROW},
     {Background={Color=background}},
     {Foreground={Color=foreground}},
-    {Text=tab.active_pane.title},
+    {Text=title},
     {Background={Color=edge_background}},
     {Foreground={Color=edge_foreground}},
     {Text=SOLID_RIGHT_ARROW},