export QT_NO_<foo> equivalents to the build system

this makes it possible to properly exclude entire subprojects based on the
availability of features, rather than stuffing every single source file
with #ifdefs.

the defines are aggregated from the -qconfig <profile>,
-no-feature-<foo> and some other configure flags.

usage:

load(qfeatures)
!contains(QT_DISABLED_FEATURES, textarea): SUBDIRS += textstuff

Task-number: QTBUG-28102
Change-Id: I83400632d64312fa4b907e1318dddfe27c432387
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@digia.com>
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>
Reviewed-by: Peter Hartmann <phartmann@blackberry.com>
Reviewed-by: Tasuku Suzuki <stasuku@gmail.com>

configure

@@ -6682,6 +6682,16 @@ echo "QT_BUILD_PARTS += $CFG_BUILD_PARTS" >> "$QTMODULE.tmp"
 if [ -n "$CFG_SKIP_MODULES" ]; then
     echo "QT_SKIP_MODULES += $CFG_SKIP_MODULES" >> "$QTMODULE.tmp"
 fi
+DISABLED_FEATURES=
+for cfg in $QCONFIG_FLAGS; do
+    ncfg=${cfg#QT_NO_}
+    if [ x$ncfg != x$cfg ]; then
+        DISABLED_FEATURES="$DISABLED_FEATURES $ncfg"
+    fi
+done
+if [ -n "$DISABLED_FEATURES" ]; then
+    echo "QT_NO_DEFINES = $DISABLED_FEATURES" >> "$QTMODULE.tmp"
+fi
 echo "QT_QCONFIG_PATH = ${CFG_QCONFIG_PATH#$relpath/src/corelib/global/}" >> "$QTMODULE.tmp"
 
 cat >>"$QTMODULE.tmp" <<EOF

mkspecs/features/qfeatures.prf

@@ -0,0 +1,4 @@
+# This file needs to be loaded explicitly, as the evaluation is relatively
+# expensive, and not many projects will actually need it.
+QMAKE_QT_FEATURES = $$[QT_HOST_DATA/get]/mkspecs/qfeatures.pri
+include($$QMAKE_QT_FEATURES) | error("Failed to load $$QMAKE_QT_FEATURES")

qtbase.pro

@@ -131,12 +131,16 @@ FEATURES_H = \
     " *" \
     " * This list is generated by qmake from <qtbase>/src/corelib/global/qfeatures.txt" \
     " */"
+FEATURES_PRI =
 for (ft, features) {
     !isEmpty(features.$${ft}.depends) {
         FEATURES_H += \
             "$${LITERAL_HASH}if !defined(QT_NO_$$ft) && ($$join($$list($$split(features.$${ft}.depends)), ") || defined(QT_NO_", "defined(QT_NO_", ")"))" \
             "$${LITERAL_HASH}  define QT_NO_$$ft" \
             "$${LITERAL_HASH}endif"
+        FEATURES_PRI += \
+            "contains(QT_DISABLED_FEATURES, "^($$lower($$join($$list($$replace(features.$${ft}.depends, _, -)), "|")))$"): \\" \
+            "    QT_DISABLED_FEATURES += $$lower($$replace(ft, _, -))"
     }
 }
 write_file($$OUT_PWD/src/corelib/global/qfeatures.h, FEATURES_H)|error("Aborting.")
@@ -145,6 +149,7 @@ FWD_FEATURES_H = \
     '$${LITERAL_HASH}include "../../src/corelib/global/qfeatures.h"'
 write_file($$OUT_PWD/include/QtCore/qfeatures.h, FWD_FEATURES_H)|error("Aborting.")
 
+no_features =
 lines = $$cat($$absolute_path($$QT_QCONFIG_PATH, $$PWD/src/corelib/global), lines)
 for (line, lines) {
     # We ignore all defines that don't follow the #ifndef + indent pattern.
@@ -153,8 +158,22 @@ for (line, lines) {
     !isEqual(t, $$line) {
         isEmpty(features.$${t}.name): \
             error("$$QT_QCONFIG_PATH disables unknown feature $$t")
+        no_features += $$t
     }
 }
+for (def, QT_NO_DEFINES) {
+    !isEmpty(features.$${def}.name): \
+        no_features += $$def
+}
+no_features = $$unique(no_features)
+
+# Can't simply add these to QT_CONFIG, as e.g., contains(QT_CONFIG, accessibility) matches no-accessibililty.
+FEATURES_PRI = \
+    "$${LITERAL_HASH} Features disabled by configure:" \
+    "QT_DISABLED_FEATURES =$$lower($$join($$list($$replace(no_features, _, -)), " ", " "))" \
+    "$$escape_expand(\\n)$${LITERAL_HASH} Dependencies derived from <qtbase>/src/corelib/global/qfeatures.txt:" \
+    $$FEATURES_PRI
+write_file($$OUT_PWD/mkspecs/qfeatures.pri, FEATURES_PRI)|error("Aborting.")
 
 #mkspecs
 mkspecs.path = $$[QT_HOST_DATA]/mkspecs