T17 review fixes: hidden numbers draw, empty edits and read-only commands change nothing, hints stay in a ghost-cut row, the newest cursor leads, a composition undoes in one step, call keys carry their place, references count matches, trailing-space hits and **/ globs, name-only switcher marks, pin and remove stay on their button, settings show their places; decimals moves to typography::format

src/typography/format.rs

@@ -136,6 +136,21 @@ pub fn duration(seconds: u64, style: DurationStyle) -> String {
     }
 }
 
+/// Digits kept past a step's first; float noise sits near the sixteenth.
+const DIGITS: usize = 6;
+
+/// Places after the point that show every multiple of `step` exactly: none for whole steps, four for 0.0025.
+pub(crate) fn decimals(step: f64) -> usize {
+    assert!(
+        step.is_finite() && step > 0.0,
+        "a step is positive, not {step}"
+    );
+    let leading = (-step.log10().floor()).max(0.0) as usize;
+    let text = format!("{step:.*}", leading + DIGITS);
+    let fraction = text.split_once('.').map_or("", |(_, fraction)| fraction);
+    fraction.trim_end_matches('0').len()
+}
+
 /// "1 file", "12,345 files".
 pub fn plural(count: u64, one: &str, other: &str) -> String {
     let word = if count == 1 { one } else { other };
@@ -189,6 +204,26 @@ pub fn datetime(at: Timestamp, zone: &TimeZone, pattern: &str) -> Result<String,
 mod tests {
     use super::*;
 
+    #[test]
+    fn steps_read_to_the_places_they_need() {
+        assert_eq!(
+            (
+                decimals(10.0),
+                decimals(0.5),
+                decimals(0.05),
+                decimals(0.001)
+            ),
+            (0, 1, 2, 3)
+        );
+        assert_eq!(decimals(0.0025), 4, "a quarter of a cent needs four places");
+        assert_eq!(
+            decimals(110.2 - 110.0),
+            1,
+            "float noise from a difference drops away"
+        );
+        assert_eq!(decimals(1e-11), 11, "a tiny step keeps its places");
+    }
+
     #[test]
     fn number_groups_and_rounds() {
         assert_eq!(number(1234567.891, 2, Separators::EN), "1,234,567.89");