Implement neutral delta times (#768)

If the delta time is exactly 0, then it shouldn't have a sign at all and
be considered neither semantically ahead or behind, like a skipped
delta, and thus it gets assigned a neutral color (i.e. the text color).

src/analysis/state_helper.rs

@@ -319,7 +319,7 @@ pub fn split_color(
 ) -> SemanticColor {
     if show_best_segments && check_best_segment(timer, segment_index, method) {
         SemanticColor::BestSegment
-    } else if let Some(time_difference) = time_difference {
+    } else if let Some(time_difference) = time_difference.filter(|t| t != &TimeSpan::zero()) {
         let last_delta = segment_index
             .checked_sub(1)
             .and_then(|n| last_delta(timer.run(), n, comparison, method));

src/analysis/tests/mod.rs

@@ -1 +1,2 @@
 mod empty_run;
+mod semantic_colors;

src/analysis/tests/semantic_colors.rs

@@ -0,0 +1,46 @@
+use crate::{
+    analysis::split_color,
+    comparison,
+    settings::SemanticColor,
+    util::tests_helper::{
+        create_timer, make_progress_run_with_splits_opt, run_with_splits, span, start_run,
+    },
+    Timer, TimingMethod,
+};
+
+#[test]
+fn segment_colors_are_correct() {
+    let mut timer = create_timer(&["A", "B"]);
+
+    run_with_splits(&mut timer, &[10.0, 20.0]);
+
+    start_run(&mut timer);
+    make_progress_run_with_splits_opt(&mut timer, &[Some(7.0)]);
+
+    assert_eq!(color(&timer, -2.5), SemanticColor::AheadLosingTime);
+    assert_eq!(color(&timer, -5.0), SemanticColor::AheadGainingTime);
+
+    assert_eq!(color(&timer, 0.0), SemanticColor::Default);
+
+    timer.reset(false);
+
+    start_run(&mut timer);
+    make_progress_run_with_splits_opt(&mut timer, &[Some(15.0)]);
+
+    assert_eq!(color(&timer, 2.5), SemanticColor::BehindGainingTime);
+    assert_eq!(color(&timer, 8.0), SemanticColor::BehindLosingTime);
+
+    assert_eq!(color(&timer, 0.0), SemanticColor::Default);
+}
+
+fn color(timer: &Timer, delta: f64) -> SemanticColor {
+    split_color(
+        timer,
+        Some(span(delta)),
+        1,
+        true,
+        false,
+        comparison::personal_best::NAME,
+        TimingMethod::GameTime,
+    )
+}

src/timing/formatter/delta.rs

@@ -26,6 +26,7 @@ pub struct Inner {
 /// * Hours without Decimal Dropping `+12:34:56.1`
 /// * Hours with Decimal Dropping `+12:34:56`
 /// * Negative Times `−23.1`
+/// * Exactly zero `0.0`
 pub struct Delta(bool, Accuracy);
 
 impl Delta {
@@ -74,11 +75,14 @@ impl Display for Inner {
     fn fmt(&self, f: &mut Formatter<'_>) -> Result {
         if let Some(time) = self.time {
             let (total_seconds, nanoseconds) = time.to_seconds_and_subsec_nanoseconds();
-            let (total_seconds, nanoseconds) = if (total_seconds | nanoseconds as i64) < 0 {
+            let bit_or = total_seconds | nanoseconds as i64;
+            let (total_seconds, nanoseconds) = if bit_or < 0 {
                 f.write_str(MINUS)?;
                 ((-total_seconds) as u64, (-nanoseconds) as u32)
             } else {
-                f.write_str(PLUS)?;
+                if bit_or > 0 {
+                    f.write_str(PLUS)?;
+                }
                 (total_seconds as u64, nanoseconds as u32)
             };
             // These are intentionally not data dependent, such that the CPU can
@@ -115,3 +119,36 @@ impl Display for Inner {
         }
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn sign_works() {
+        assert_eq!(
+            Delta::new()
+                .format(TimeSpan::from_seconds(-1.5))
+                .to_string(),
+            "−1.5"
+        );
+        assert_eq!(
+            Delta::new()
+                .format(TimeSpan::from_seconds(-0.5))
+                .to_string(),
+            "−0.5"
+        );
+
+        // We drop the sign entirely when it's exactly 0.
+        assert_eq!(Delta::new().format(TimeSpan::zero()).to_string(), "0.0");
+
+        assert_eq!(
+            Delta::new().format(TimeSpan::from_seconds(0.5)).to_string(),
+            "+0.5"
+        );
+        assert_eq!(
+            Delta::new().format(TimeSpan::from_seconds(1.5)).to_string(),
+            "+1.5"
+        );
+    }
+}