Fix --watch hangs. (#8585)

* Fix --watch hangs.

* Don't prebuild in watch mode.

* Fix up merge.

Author: mitchdenny

src/Aspire.Cli/Commands/RunCommand.cs

@@ -74,29 +74,32 @@ protected override async Task<int> ExecuteAsync(ParseResult parseResult, Cancell
                 return ExitCodeConstants.FailedToTrustCertificates;
             }
 
-            appHostCompatabilityCheck = await AppHostHelper.CheckAppHostCompatabilityAsync(_runner, effectiveAppHostProjectFile, cancellationToken);
+            var watch = parseResult.GetValue<bool>("--watch");
 
-            if (!appHostCompatabilityCheck?.IsCompatableAppHost ?? throw new InvalidOperationException("IsCompatableAppHost is null"))
+            if (!watch)
             {
-                return ExitCodeConstants.FailedToDotnetRunAppHost;
-            }
-
-            var watch = parseResult.GetValue<bool>("--watch");
+                var buildExitCode = await AppHostHelper.BuildAppHostAsync(_runner, effectiveAppHostProjectFile, cancellationToken);
 
-            var buildExitCode = await AppHostHelper.BuildAppHostAsync(_runner, effectiveAppHostProjectFile, cancellationToken);
+                if (buildExitCode != 0)
+                {
+                    AnsiConsole.MarkupLine($"[red bold]:thumbs_down: The project could not be built. For more information run with --debug switch.[/]");
+                    return ExitCodeConstants.FailedToBuildArtifacts;
+                }
+            }
+            
+            appHostCompatabilityCheck = await AppHostHelper.CheckAppHostCompatabilityAsync(_runner, effectiveAppHostProjectFile, cancellationToken);
 
-            if (buildExitCode != 0)
+            if (!appHostCompatabilityCheck?.IsCompatableAppHost ?? throw new InvalidOperationException("IsCompatableAppHost is null"))
             {
-                AnsiConsole.MarkupLine($"[red bold]:thumbs_down: The project could not be built. For more information run with --debug switch.[/]");
-                return ExitCodeConstants.FailedToBuildArtifacts;
+                return ExitCodeConstants.FailedToDotnetRunAppHost;
             }
 
             var backchannelCompletitionSource = new TaskCompletionSource<AppHostBackchannel>();
 
             var pendingRun = _runner.RunAsync(
                 effectiveAppHostProjectFile,
                 watch,
-                true,
+                !watch,
                 Array.Empty<string>(),
                 env,
                 backchannelCompletitionSource,

src/Aspire.Cli/DotNetCliRunner.cs

@@ -126,7 +126,9 @@ public async Task<int> RunAsync(FileInfo projectFile, bool watch, bool noBuild,
 
         if (watch && noBuild)
         {
-            throw new InvalidOperationException("Cannot use --watch and --no-build at the same time.");
+            var ex = new InvalidOperationException("Cannot use --watch and --no-build at the same time.");
+            backchannelCompletionSource?.SetException(ex);
+            throw ex;
         }
 
         var watchOrRunCommand = watch ? "watch" : "run";