Description: install a message handler for Qt
 If the QT_MESSAGE_PATTERN envvar is set (i.e. the user has defined
 their own log pattern), just skip loglevel debug messages unless
 running in debug mode. Otherwise (default), format messages in the
 Debian-præfixed style and with file/function/line number.
Author: mirabilos <tg@debian.org>
Forwarded: no

--- a/mscore/musescore.cpp
+++ b/mscore/musescore.cpp
@@ -2843,6 +2843,104 @@ static void mscoreMessageHandler(QtMsgTy
          abort();
          }
      }
+#else
+// helper
+static void
+mudeb_debmsgout(const void *s_)
+{
+	const unsigned char *s;
+	unsigned char c;
+
+	s = (const unsigned char *)s_;
+	if (!s || !*s) {
+		fputs("(nil)\n", stderr);
+		return;
+	}
+	do {
+		c = *s++;
+		putc(c, stderr);
+		if (c == '\n' && *s) {
+			putc('N', stderr);
+			putc(':', stderr);
+			putc(' ', stderr);
+		}
+	} while (*s);
+	if (c != '\n')
+		putc('\n', stderr);
+}
+
+// by default; Debian loglevel præficēs, file/func/line, silence debug unless enabled
+static void
+mudeb_debmsghandler(QtMsgType type, const QMessageLogContext &ctx, const QString &msg)
+{
+	QString s;
+	bool needsp;
+
+	switch (type) {
+	case QtDebugMsg:
+		if (!MScore::debugMode)
+			return;
+		putc('D', stderr);
+		break;
+	case QtWarningMsg:
+		putc('W', stderr);
+		break;
+	case QtCriticalMsg:
+	case QtFatalMsg:
+		putc('E', stderr);
+		break;
+	default:
+		putc('I', stderr);
+	}
+	putc(':', stderr);
+	if (ctx.category && strcmp(ctx.category, "default") != 0) {
+		putc(' ', stderr);
+		putc('<', stderr);
+		fputs(ctx.category, stderr);
+		putc('>', stderr);
+	}
+	needsp = true;
+	if (ctx.file) {
+		if (needsp) {
+			putc(' ', stderr);
+			needsp = false;
+		}
+		fputs(ctx.file, stderr);
+	}
+	if (ctx.function) {
+		if (needsp) {
+			putc(' ', stderr);
+			needsp = false;
+		}
+		putc('{', stderr);
+		fputs(ctx.function, stderr);
+		putc('}', stderr);
+	}
+	if (ctx.line && (ctx.file || ctx.function))
+		fprintf(stderr, ":%d", ctx.line);
+	if (!needsp)
+		putc(':', stderr);
+	putc(' ', stderr);
+	mudeb_debmsgout(qPrintable(msg));
+	fflush(stderr);
+}
+
+#if QT_VERSION >= QT_VERSION_CHECK(5, 4, 0)
+// if QT_MESSAGE_PATTERN is set: silence debug unless enabled
+static void
+mudeb_qtmsghandler(QtMsgType type, const QMessageLogContext &ctx, const QString &msg)
+{
+	if (type == QtDebugMsg && !MScore::debugMode)
+		return;
+
+	QString s = qFormatLogMessage(type, ctx, msg);
+	if (s.isNull())
+		return;
+	fputs(qPrintable(s), stderr);
+	putc('\n', stderr);
+	fflush(stderr);
+}
+#endif
 #endif
 
 //---------------------------------------------------------
@@ -5769,8 +5867,14 @@ int main(int argc, char* av[])
       QApplication::setDesktopSettingsAware(true);
 #if defined(QT_DEBUG) && defined(Q_OS_WIN)
       MScore::msgHandler = mscoreMessageHandler;
-      qInstallMessageHandler(mscoreMessageHandler);
+#else
+      MScore::msgHandler = mudeb_debmsghandler;
+#if QT_VERSION >= QT_VERSION_CHECK(5, 4, 0)
+      if (getenv("QT_MESSAGE_PATTERN") != NULL)
+            MScore::msgHandler = mudeb_qtmsghandler;
+#endif
 #endif
+      qInstallMessageHandler(MScore::msgHandler);
 
       QFile f(":/revision.h");
       f.open(QIODevice::ReadOnly);