Add support for safe feature checking at compile time

Added a qtConfig(feature) function to qmake, and a QT_CONFIG(feature)
macro. These can safely check whether a certain compile time feature of
Qt is enabled or not.

For this to work the feature has to have a publicFeature or
privateFeature output in the configure.json file.

In pro files, please use the qtConfig(feature) test function
instead of checking contains(QT_CONFIG, feature), as the latter
will be unreliable with the upcoming modularization (it requires a
load(qt_module_config) before doing any such checks). Note that
feature names are now lowercase, and identical (except for hyphens
versus underscores currently) in the pro and c++ files.

This makes the logic easier to follow, as we avoid all double negations,
and most importantly, QT_CONFIG and qtConfig are implemented in a
way that you'll get a build error for a mistyped or non-existent
feature. This will also prevent accidental use of a widget feature
in gui in the future.

This gives us complete symmetry between the handling in pro and
c++ files.

Change-Id: I60404f97953724e639ffb6386cce2e8b1e4b735a
Reviewed-by: Lars Knoll <lars.knoll@qt.io>
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@theqtcompany.com>

1 files changed, 9 insertions, 0 deletions

diff --git a/mkspecs/features/qt_functions.prf b/mkspecs/features/qt_functions.prf
index f03472d940..7e6433814b 100644
--- a/mkspecs/features/qt_functions.prf
+++ b/mkspecs/features/qt_functions.prf
@@ -302,3 +302,12 @@ defineTest(prepareRecursiveTarget) {
     export($${target}.CONFIG)
     export($${target}.recurse_target)
 }
+
+defineTest(qtConfig) {
+    contains(QT.global.enabled_features, $$1): \
+        return(true)
+    contains(QT.global.disabled_features, $$1): \
+        return(false)
+
+    error("Could not find feature $${1}.")
+}