Direction lattice

site/src/comparison.rs

@@ -166,12 +166,10 @@ async fn populate_report(
 ) {
     let (primary, secondary) = comparison.clone().summarize_by_category(&benchmark_map);
     // Get the combined direction of the primary and secondary summaries
-    let direction = match (primary.direction(), secondary.direction()) {
-        (Some(d1), Some(d2)) if d1 != d2 => Direction::Mixed,
-        (Some(d), Some(_) | None) => d,
-        (None, Some(d)) => d,
-        (None, None) => return,
-    };
+    let direction = Direction::join(primary.direction(), secondary.direction());
+    if direction == Direction::None {
+        return;
+    }
 
     let include_in_triage = deserves_attention_icount(&primary, &secondary);
 
@@ -338,9 +336,9 @@ impl ArtifactComparisonSummary {
     }
 
     /// The direction of the changes
-    pub fn direction(&self) -> Option<Direction> {
+    pub fn direction(&self) -> Direction {
         if self.relevant_comparisons.len() == 0 {
-            return None;
+            return Direction::None;
         }
 
         let (regressions, improvements): (Vec<&TestResultComparison>, _) = self
@@ -349,11 +347,11 @@ impl ArtifactComparisonSummary {
             .partition(|c| c.is_regression());
 
         if regressions.len() == 0 {
-            return Some(Direction::Improvement);
+            return Direction::Improvement;
         }
 
         if improvements.len() == 0 {
-            return Some(Direction::Regression);
+            return Direction::Regression;
         }
 
         let total_num = self.relevant_comparisons.len();
@@ -369,28 +367,28 @@ impl ArtifactComparisonSummary {
             has_medium_and_above_improvements,
             has_medium_and_above_regressions,
         ) {
-            (true, true) => return Some(Direction::Mixed),
+            (true, true) => return Direction::Mixed,
             (true, false) => {
                 if regressions_ratio >= 0.15 {
-                    Some(Direction::Mixed)
+                    Direction::Mixed
                 } else {
-                    Some(Direction::Improvement)
+                    Direction::Improvement
                 }
             }
             (false, true) => {
                 if regressions_ratio < 0.85 {
-                    Some(Direction::Mixed)
+                    Direction::Mixed
                 } else {
-                    Some(Direction::Regression)
+                    Direction::Regression
                 }
             }
             (false, false) => {
                 if regressions_ratio >= 0.1 && regressions_ratio <= 0.9 {
-                    Some(Direction::Mixed)
+                    Direction::Mixed
                 } else if regressions_ratio <= 0.1 {
-                    Some(Direction::Improvement)
+                    Direction::Improvement
                 } else {
-                    Some(Direction::Regression)
+                    Direction::Regression
                 }
             }
         }
@@ -1222,19 +1220,30 @@ impl std::hash::Hash for TestResultComparison {
 // The direction of a performance change
 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug)]
 pub enum Direction {
+    None,
     Improvement,
     Regression,
     Mixed,
 }
 
-impl std::fmt::Display for Direction {
-    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        let description = match self {
-            Direction::Improvement => "improvement",
-            Direction::Regression => "regression",
-            Direction::Mixed => "mixed",
-        };
-        write!(f, "{}", description)
+// The direction of a performance change. Forms a lattice:
+//
+//          Mixed
+//          /    \
+// Improvement  Regression
+//          \    /
+//           None
+//
+impl Direction {
+    // Also known as the "least upper bound".
+    pub fn join(a: Self, b: Self) -> Self {
+        match (a, b) {
+            (Self::None, b) => b,
+            (a, Self::None) => a,
+            (Self::Improvement, Self::Improvement) => Self::Improvement,
+            (Self::Regression, Self::Regression) => Self::Regression,
+            _ => Self::Mixed,
+        }
     }
 }
 

site/src/github/comparison_summary.rs

@@ -166,7 +166,7 @@ async fn summarize_run(
         ));
 
         let (primary, secondary) = comparison.summarize_by_category(&benchmark_map);
-        table_written |= write_metric_summary(primary, secondary, hidden, &mut message).await;
+        table_written |= write_metric_summary(primary, secondary, hidden, &mut message);
     }
 
     if table_written {
@@ -177,7 +177,7 @@ async fn summarize_run(
     please file an issue in [rust-lang/rustc-perf](https://github.com/rust-lang/rustc-perf/issues/new).";
     let footer = format!("{DISAGREEMENT}{errors}");
 
-    let direction = inst_primary.direction().or(inst_secondary.direction());
+    let direction = Direction::join(inst_primary.direction(), inst_secondary.direction());
     let next_steps = next_steps(inst_primary, inst_secondary, direction, is_master_commit);
 
     write!(&mut message, "\n{footer}\n{next_steps}").unwrap();
@@ -186,7 +186,7 @@ async fn summarize_run(
 }
 
 /// Returns true if a summary table was written to `message`.
-async fn write_metric_summary(
+fn write_metric_summary(
     primary: ArtifactComparisonSummary,
     secondary: ArtifactComparisonSummary,
     hidden: bool,
@@ -227,12 +227,12 @@ async fn write_metric_summary(
 fn next_steps(
     primary: ArtifactComparisonSummary,
     secondary: ArtifactComparisonSummary,
-    direction: Option<Direction>,
+    direction: Direction,
     is_master_commit: bool,
 ) -> String {
     let deserves_attention = deserves_attention_icount(&primary, &secondary);
     let (is_regression, label) = match (deserves_attention, direction) {
-        (true, Some(Direction::Regression | Direction::Mixed)) => (true, "+perf-regression"),
+        (true, Direction::Regression | Direction::Mixed) => (true, "+perf-regression"),
         _ => (false, "-perf-regression"),
     };
 
@@ -303,15 +303,15 @@ fn generate_short_summary(summary: &ArtifactComparisonSummary) -> String {
     let num_regressions = summary.number_of_regressions();
 
     match summary.direction() {
-        Some(Direction::Improvement) => format!(
+        Direction::Improvement => format!(
             "✅ relevant {} found",
             ending("improvement", num_improvements)
         ),
-        Some(Direction::Regression) => format!(
+        Direction::Regression => format!(
             "❌ relevant {} found",
             ending("regression", num_regressions)
         ),
-        Some(Direction::Mixed) => "mixed results".to_string(),
-        None => "no relevant changes found".to_string(),
+        Direction::Mixed => "mixed results".to_string(),
+        Direction::None => "no relevant changes found".to_string(),
     }
 }