Plan viewer: the Wait Stats header's tooltip matches PerformanceStudio

Darling/Darling.Tests/Viewer4571Tests.cs

@@ -0,0 +1,23 @@
+using PerformanceMonitor.PlanAnalysis;
+using Xunit;
+
+namespace Darling.Tests;
+
+/// <summary>
+/// Pins the Wait Stats card header's tooltip (#4571), matching erikdarlingdata/PerformanceStudio's
+/// desktop viewer: null when there are no waits, otherwise the total wait time and wait-type count.
+/// </summary>
+public class Viewer4571Tests
+{
+    [Fact]
+    public void WaitStatsHeaderTooltip_NoWaits_IsNull()
+    {
+        Assert.Null(PlanDisplayText.WaitStatsHeaderTooltip(0, 0));
+    }
+
+    [Fact]
+    public void WaitStatsHeaderTooltip_WithWaits_DescribesCountAndTotal()
+    {
+        Assert.Equal("1,234 ms of waits across 3 wait types", PlanDisplayText.WaitStatsHeaderTooltip(3, 1234));
+    }
+}

PerformanceMonitor.PlanAnalysis/PlanDisplayText.cs

@@ -17,6 +17,13 @@ public static class PlanDisplayText
     public static string? ParseErrorMessage(ParsedPlan plan) =>
         plan.ParseError == null ? null : $"This plan couldn't be parsed: {plan.ParseError}";
 
+    /// <summary>
+    /// The Wait Stats card's header tooltip, matching erikdarlingdata/PerformanceStudio's desktop viewer:
+    /// shown only when there are waits to describe.
+    /// </summary>
+    public static string? WaitStatsHeaderTooltip(int waitCount, long totalWaitMs) =>
+        waitCount > 0 ? $"{totalWaitMs:N0} ms of waits across {waitCount} wait types" : null;
+
     /// <summary>
     /// The CPU:Elapsed ratio shown in the runtime summary, matching
     /// erikdarlingdata/PerformanceStudio@28d4c74's row: CPU time with external-wait time

PerformanceMonitor.Ui/PlanViewerControl.Properties.cs

@@ -1067,6 +1067,7 @@ private void ShowWaitStats(List<WaitStatInfo> waits, bool isActualPlan)
         if (waits.Count == 0)
         {
             WaitStatsHeader.Text = "Wait Stats";
+            WaitStatsHeader.ToolTip = PlanDisplayText.WaitStatsHeaderTooltip(0, 0);
             WaitStatsEmpty.Text = isActualPlan
                 ? "No wait stats recorded"
                 : "No wait stats (estimated plan)";
@@ -1081,6 +1082,7 @@ private void ShowWaitStats(List<WaitStatInfo> waits, bool isActualPlan)
         var totalWait = sorted.Sum(w => w.WaitTimeMs);
 
         WaitStatsHeader.Text = $"  Wait Stats \u2014 {totalWait:N0}ms total";
+        WaitStatsHeader.ToolTip = PlanDisplayText.WaitStatsHeaderTooltip(sorted.Count, totalWait);
 
         var longestName = sorted.Max(w => w.WaitType.Length);
         var nameColWidth = longestName * 6.5 + 10;