[Hot Reload] Do not refresh browser until changes are applied (#51210)

Author: tmat

src/BuiltInTools/HotReloadClient/Web/AbstractBrowserRefreshServer.cs

@@ -299,14 +299,7 @@ public ValueTask RefreshBrowserAsync(CancellationToken cancellationToken)
     public ValueTask ReportCompilationErrorsInBrowserAsync(ImmutableArray<string> compilationErrors, CancellationToken cancellationToken)
     {
         logger.Log(LogEvents.UpdatingDiagnostics);
-        if (compilationErrors.IsEmpty)
-        {
-            return SendJsonMessageAsync(new AspNetCoreHotReloadApplied(), cancellationToken);
-        }
-        else
-        {
-            return SendJsonMessageAsync(new HotReloadDiagnostics { Diagnostics = compilationErrors }, cancellationToken);
-        }
+        return SendJsonMessageAsync(new HotReloadDiagnostics { Diagnostics = compilationErrors }, cancellationToken);
     }
 
     public async ValueTask UpdateStaticAssetsAsync(IEnumerable<string> relativeUrls, CancellationToken cancellationToken)

test/dotnet-watch.Tests/Browser/BrowserTests.cs

@@ -79,8 +79,13 @@ await App.WaitUntilOutputContains("""
             🧪 Received: Reload
             """);
 
+        // no other browser message sent:
+        Assert.Equal(2, App.Process.Output.Count(line => line.Contains("🧪")));
+
         await App.WaitForOutputLineContaining(MessageDescriptor.WaitingForChanges);
 
+        App.Process.ClearOutput();
+
         // another rude edit:
         UpdateSourceFile(homePagePath, src => src.Replace("public virtual int F() => 1;", "/* member placeholder */"));
 
@@ -98,13 +103,25 @@ await App.WaitUntilOutputContains("""
             🧪 Received: Reload
             """);
 
+        // no other browser message sent:
+        Assert.Equal(2, App.Process.Output.Count(line => line.Contains("🧪")));
+
+        App.Process.ClearOutput();
+
         // valid edit:
         UpdateSourceFile(homePagePath, src => src.Replace("/* member placeholder */", "public int F() => 1;"));
 
         await App.WaitForOutputLineContaining(MessageDescriptor.HotReloadSucceeded);
 
+        await App.WaitUntilOutputContains($$"""
+            🧪 Received: {"type":"HotReloadDiagnosticsv1","diagnostics":[]}
+            """);
+
         await App.WaitUntilOutputContains($$"""
             🧪 Received: {"type":"AspNetCoreHotReloadApplied"}
             """);
+
+        // no other browser message sent:
+        Assert.Equal(2, App.Process.Output.Count(line => line.Contains("🧪")));
     }
 }