Make width measuring optional and disabled by default

src/widthdb.rs

@@ -11,6 +11,7 @@ use unicode_width::UnicodeWidthStr;
 /// Measures and stores the with (in terminal coordinates) of graphemes.
 #[derive(Debug, Default)]
 pub struct WidthDB {
+    pub active: bool,
     known: HashMap<String, u8>,
     requested: HashSet<String>,
 }
@@ -22,6 +23,9 @@ impl WidthDB {
     /// Unicode Standard Annex #11.
     pub fn grapheme_width(&mut self, grapheme: &str) -> u8 {
         assert_eq!(Some(grapheme), grapheme.graphemes(true).next());
+        if !self.active {
+            return grapheme.width() as u8;
+        }
         if let Some(width) = self.known.get(grapheme) {
             *width
         } else {
@@ -35,6 +39,9 @@ impl WidthDB {
     /// If the width of a grapheme has not been measured yet, it is estimated
     /// using the Unicode Standard Annex #11.
     pub fn width(&mut self, s: &str) -> usize {
+        if !self.active {
+            return s.width();
+        }
         let mut total: usize = 0;
         for grapheme in s.graphemes(true) {
             total += if let Some(width) = self.known.get(grapheme) {
@@ -50,7 +57,7 @@ impl WidthDB {
     /// Whether any new graphemes have been seen since the last time
     /// [`Self::measure_widths`] was called.
     pub fn measuring_required(&self) -> bool {
-        !self.requested.is_empty()
+        self.active && !self.requested.is_empty()
     }
 
     /// Measure the width of all new graphemes that have been seen since the
@@ -60,6 +67,9 @@ impl WidthDB {
     /// the terminal. After it finishes, the terminal's contents should be
     /// assumed to be garbage and a full redraw should be performed.
     pub fn measure_widths(&mut self, out: &mut impl Write) -> io::Result<()> {
+        if !self.active {
+            return Ok(());
+        }
         for grapheme in self.requested.drain() {
             out.queue(Clear(ClearType::All))?
                 .queue(MoveTo(0, 0))?