Ensure uncaught throwables in task fibers are visible to the user.

Prefers logFatal over stderr.writeln so that the error also ends up in log files that may be configured. Also displays a message box for subsystem "windows" executables that don't have a console attached.

source/vibe/core/task.d

@@ -412,12 +412,35 @@ final package class TaskFiber : Fiber {
 		} catch (Throwable th) {
 			import std.stdio : stderr, writeln;
 			import core.stdc.stdlib : abort;
+			import core.memory : GC;
 			try {
-				stderr.writeln("TaskFiber getting terminated due to an uncaught ", th.classinfo.name);
-				stderr.writeln(th);
+				version (Windows) {
+					import core.sys.windows.windows : MessageBoxA, MB_ICONERROR, GetConsoleWindow;
+					import std.format : formattedWrite;
+					import vibe.container.internal.appender : BufferOverflowMode, FixedAppender;
+
+					if (!GetConsoleWindow()) {
+						FixedAppender!(char[], 2048, BufferOverflowMode.ignore) msg = void;
+						msg.formattedWrite("%s: %s\r\n\r\n", th.classinfo.name, th.msg);
+						foreach (ln; th.info)
+							msg.formattedWrite("%s\r\n", ln);
+						msg.put('\0');
+						msg.data[msg.data.length-1] = '\0';
+						MessageBoxA(null, msg.data.ptr, "FATAL: Uncaught exception in task fiber", MB_ICONERROR);
+					}
+				}
+				if (GC.inFinalizer) {
+					stderr.writeln("TaskFiber getting terminated due to an uncaught ", th.classinfo.name, ": ", th.msg);
+					foreach (ln; th.info) stderr.writeln(ln);
+				} else {
+					logFatal("TaskFiber getting terminated due to an uncaught %s: %s", th.classinfo.name, th.msg);
+					foreach (ln; th.info) logFatal("%s", ln);
+				}
 			} catch (Exception e) {
-				try stderr.writeln(th.msg);
-				catch (Exception e) {}
+				if (GC.inFinalizer) {
+					try stderr.writeln(th.msg);
+					catch (Exception e) {}
+				} else logFatal("%s", th.msg);
 			}
 			abort();
 		}