ProgramHost: Print exception when no UnhandledException handlers are set.

Author: alexrp

src/hosting/ProgramContext.cs

@@ -39,12 +39,12 @@ internal ProgramContext(ReadOnlyMemory<string> arguments)
     // The following methods must never throw.
 
     [SuppressMessage("", "CA1031")]
-    internal void RaiseUnhandledException(Exception exception)
+    internal bool RaiseUnhandledException(Exception exception)
     {
         var ev = UnhandledException;
 
         if (ev == null)
-            return;
+            return false;
 
         foreach (var dg in ev.GetInvocationList())
         {
@@ -56,6 +56,8 @@ internal void RaiseUnhandledException(Exception exception)
             {
             }
         }
+
+        return true;
     }
 
     [SuppressMessage("", "CA1031")]

src/hosting/ProgramHost.cs

@@ -30,7 +30,12 @@ public static async Task RunAsync<TProgram>(ReadOnlyMemory<string> arguments)
 
         domain.UnhandledException += (_, e) =>
         {
-            context.RaiseUnhandledException((Exception)e.ExceptionObject);
+            var ex = (Exception)e.ExceptionObject;
+
+            // The terminal might be in raw mode when this happens and checking IsRawMode is racey. To ensure sensible
+            // output, just always use CRLF here.
+            if (!context.RaiseUnhandledException(ex))
+                Terminal.Error($"Unhandled exception. {ex.ToString().ReplaceLineEndings("\r\n")}\r\n");
 
             // Most users expect ProcessExit to run on both normal and abnormal termination. This call makes that happen
             // and also ensures that the terminal cleanup we do in ProcessExit runs. One unfortunate downside of this