Support setting a default severity level for QLoggingCategory

Allow to alter the default configuration for categories by passing a
message type: All message types with lower severity are disabled in this
category.

This is useful for libraries, which shouldn't mess with the category
registry itself: Setting rules, a category filter ... might cause
conflicts and ordering problems, so this API should be reserved to the
specific application.

For the Qt categories, we have code in the default category filter that
disables the 'debug' category. However, this is hardcoded, and there's no
way so far for other libraries to get the same behavior. With this patch
one can get the same behavior:

Q_LOGGING_CATEGORY(DRIVER_USB_EVENTS, "driver.usb.events", QtWarningMsg);

[ChangeLog][QtCore][Logging] Added QtMsgType argument to QLoggingCategory
constructor and Q_LOGGING_CATEGORY macro that controls the default
category configuration.

Change-Id: Ib2902f755f9f7285d79888ec30e8f3cef95ae628
Reviewed-by: Alex Blasche <alexander.blasche@digia.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/src/corelib/doc/snippets/qloggingcategory/main.cpp b/src/corelib/doc/snippets/qloggingcategory/main.cpp
index efbf9c55d3..3c6424921e 100644
--- a/src/corelib/doc/snippets/qloggingcategory/main.cpp
+++ b/src/corelib/doc/snippets/qloggingcategory/main.cpp
@@ -49,6 +49,9 @@ Q_DECLARE_LOGGING_CATEGORY(driverUsb)
 Q_LOGGING_CATEGORY(driverUsb, "driver.usb")
 //![1]
 
+//![5]
+Q_LOGGING_CATEGORY(driverUsbEvents, "driver.usb.events", QtWarningMsg)
+//![5]
 
 // Completely made up example, inspired by en.wikipedia.org/wiki/USB :)
 struct UsbEntry {