dotnet watch run shouldn't disable the browser refresh logic inject…

src/BuiltInTools/dotnet-watch/LaunchBrowserFilter.cs

@@ -25,9 +25,8 @@ public sealed class LaunchBrowserFilter : IWatchFilter, IAsyncDisposable
         private readonly bool _suppressBrowserRefresh;
         private readonly string _browserPath;
 
-        private bool _canLaunchBrowser;
+        private bool _attemptedBrowserLaunch;
         private Process _browserProcess;
-        private bool _browserLaunched;
         private BrowserRefreshServer _refreshServer;
         private IReporter _reporter;
         private string _launchPath;
@@ -59,7 +58,6 @@ public async ValueTask ProcessAsync(DotNetWatchContext context, CancellationToke
                 if (CanLaunchBrowser(context, out var launchPath))
                 {
                     context.Reporter.Verbose("dotnet-watch is configured to launch a browser on ASP.NET Core application startup.");
-                    _canLaunchBrowser = true;
                     _launchPath = launchPath;
                     _cancellationToken = cancellationToken;
 
@@ -81,14 +79,10 @@ public async ValueTask ProcessAsync(DotNetWatchContext context, CancellationToke
                     }
                 }
             }
-
-            if (_canLaunchBrowser)
+            else if (!_suppressBrowserRefresh)
             {
-                if (context.Iteration > 0)
-                {
-                    // We've detected a change. Notify the browser.
-                    await SendMessage(WaitMessage, cancellationToken);
-                }
+                // We've detected a change. Notify the browser.
+                await SendMessage(WaitMessage, cancellationToken);
             }
         }
 
@@ -117,18 +111,30 @@ private void OnOutput(object sender, DataReceivedEventArgs eventArgs)
                 var process = (Process)sender;
                 process.OutputDataReceived -= OnOutput;
 
-                if (!_browserLaunched)
+                if (!_attemptedBrowserLaunch)
                 {
+                    _attemptedBrowserLaunch = true;
+
                     _reporter.Verbose("Launching browser.");
+
                     try
                     {
                         LaunchBrowser(launchUrl);
-                        _browserLaunched = true;
                     }
                     catch (Exception ex)
                     {
-                        _reporter.Output($"Unable to launch browser: {ex}");
-                        _canLaunchBrowser = false;
+                        _reporter.Verbose($"An exception occurred when attempting to launch a browser: {ex}");
+                        _browserProcess = null;
+                    }
+
+                    if (_browserProcess is null || _browserProcess.HasExited)
+                    {
+                        // dotnet-watch, by default, relies on URL file association to launch browsers. On Windows and MacOS, this works fairly well
+                        // where URLs are associated with the default browser. On Linux, this is a bit murky.
+                        // From emperical observation, it's noted that failing to launch a browser results in either Process.Start returning a null-value
+                        // or for the process to have immediately exited.
+                        // We can use this to provide a helpful message.
+                        _reporter.Output($"Unable to launch the browser. Navigate to {launchUrl}");
                     }
                 }
                 else
@@ -175,13 +181,6 @@ private static bool CanLaunchBrowser(DotNetWatchContext context, out string laun
                 return false;
             }
 
-            if (!RuntimeInformation.IsOSPlatform(OSPlatform.Windows) && !RuntimeInformation.IsOSPlatform(OSPlatform.OSX))
-            {
-                // Launching a browser requires file associations that are not available in all operating systems.
-                reporter.Verbose("Browser refresh is only supported in Windows and MacOS.");
-                return false;
-            }
-
             var dotnetCommand = context.ProcessSpec.Arguments.FirstOrDefault();
             if (!string.Equals(dotnetCommand, "run", StringComparison.Ordinal))
             {
@@ -236,4 +235,4 @@ public async ValueTask DisposeAsync()
             }
         }
     }
-}
+}

src/Tests/dotnet-watch.Tests/BrowserLaunchTests.cs

@@ -5,6 +5,7 @@
 using System.IO;
 using System.Threading.Tasks;
 using Microsoft.NET.TestFramework;
+using Xunit;
 using Xunit.Abstractions;
 
 namespace Microsoft.DotNet.Watcher.Tools
@@ -22,7 +23,7 @@ public BrowserLaunchTests(ITestOutputHelper logger)
             _logger = logger;
         }
 
-        [PlatformSpecificFact(Xunit.TestPlatforms.Windows | Xunit.TestPlatforms.OSX)]
+        [Fact]
         public async Task LaunchesBrowserOnStart()
         {
             var expected = "watch : Launching browser: https://localhost:5001/";
@@ -40,7 +41,7 @@ public async Task LaunchesBrowserOnStart()
             await app.Process.GetOutputLineStartsWithAsync(expected, TimeSpan.FromMinutes(2));
         }
 
-        [PlatformSpecificFact(Xunit.TestPlatforms.Windows | Xunit.TestPlatforms.OSX)]
+        [Fact]
         public async Task RefreshesBrowserOnChange()
         {
             var launchBrowserMessage = "watch : Launching browser: https://localhost:5001/";
@@ -64,7 +65,7 @@ public async Task RefreshesBrowserOnChange()
             await app.Process.GetOutputLineStartsWithAsync(refreshBrowserMessage, TimeSpan.FromMinutes(2));
         }
 
-        [PlatformSpecificFact(Xunit.TestPlatforms.Windows | Xunit.TestPlatforms.OSX)]
+        [Fact]
         public async Task UsesBrowserSpecifiedInEnvironment()
         {
             var launchBrowserMessage = "watch : Launching browser: mycustombrowser.bat https://localhost:5001/";