make the UI a lot snappier

Before, we were recalculating after each char, even though the char's
knowledge was Unknown (so we didn't actually have anything new to
report)! Change that, so that we only recalculate when we need to. This
makes the UI go from very sluggish to snappy.

src/guess/guesses.rs

@@ -2,7 +2,7 @@ use std::slice::Iter;
 
 use crate::guess::known_word_constraints::CharKnowledge;
 
-#[derive(Default)]
+#[derive(Default, Clone, PartialEq, Eq)]
 pub struct GuessChar {
     knowledge: CharKnowledge,
     ch: Option<char>,
@@ -37,6 +37,7 @@ impl GuessChar {
             return false;
         }
         self.ch = Some(ch.to_ascii_uppercase());
+        self.knowledge = CharKnowledge::Unknown;
         true
     }
 

src/guess/known_word_constraints.rs

@@ -3,7 +3,7 @@ use std::cmp::{max, min};
 use std::collections::{HashMap, HashSet};
 use strum::{EnumCount, FromRepr};
 
-#[derive(Copy, Clone, PartialEq, EnumCount, FromRepr)]
+#[derive(Copy, Clone, PartialEq, Eq, EnumCount, FromRepr)]
 pub enum CharKnowledge {
     Unknown,
     WrongPosition,

src/ui/guesses_ui.rs

@@ -73,10 +73,9 @@ impl<'a, const N: usize, const R: usize> Widget for GuessesUI<N, R> {
             Input::Character('\n') => self.handle_newline(),
             Input::Character('\x7F') => self.unset_active_ch(), // delete
             Input::Character(input_ch) if input_ch.is_ascii_alphabetic() => {
-                if self.set_active_ch(input_ch) {
-                    self.has_new_knowledge.set(true);
-                } else {
+                if !(self.set_active_ch(input_ch)) {
                     return Some(input);
+                } else {
                 }
             }
             _ => {
@@ -186,8 +185,14 @@ impl<const N: usize, const R: usize> GuessesUI<N, R> {
 
     fn set_active_ch(&mut self, ch: char) -> bool {
         let guess_str = &mut self.grid.guess_mut(self.active_row);
+        let had_knowledge_before =
+            guess_str.guesses()[self.active_col].knowledge() != CharKnowledge::Unknown;
         if guess_str.guess_mut(self.active_col).set_ch(ch) {
             self.move_active_ch(true);
+            if had_knowledge_before {
+                // We don't have knowledge after set_ch, so if we used to, that's a change.
+                self.has_new_knowledge.set(true);
+            }
             true
         } else {
             false