CMake: Fix reconfiguration when -no-opengl is specified

In a previous change, we ensured that all INPUT_foo cache variables are
unset at the end of configuration, so they don't influence feature
re-evaluation in case if a command line flag like -no-gui is not
specified upon second reconfiguration and a FEATURE_foo is manually
toggled in the CMakeCache.txt, effectively getting rid of
stale INPUT_foo values.

Unfortunately that causes an issue when configuring with -no-opengl
and then trying to reconfigure with 'cmake .'

Specifically various feature options like ENABLE / DISABLE use
INPUT_foo variables in their expressions.
qt_configure_add_report_entry CONDITIONs also use them.

These expect the INPUT_foo variables to be persisted, and if they are
removed, the expressions might be re-evaluated to a different value,
and cause re-configuration to fail or unexpectedly toggle features.

To support both cases described above, instead of removing all INPUT
variables when configuration ends, only unset those INPUT variables
whose corresponding FEATURE_foo variable has been manually toggled in
CMakeCache.txt or via an IDE.

Toggling a FEATURE_foo manually is intentional, which means the
INPUT_foo value should be discarded. Whereas pre-existing INPUT_bar
variables will persist, thus not breaking cases like the -no-opengl
report CONDITION.

Amends 2799391703e44a34b6557e234462e425a61785f2

Pick-to: 6.6
Fixes: QTBUG-116973
Task-number: QTBUG-112957
Change-Id: I5851255bfa41a9a1d116630a5d9f7b9a74aa93ed
Reviewed-by: Alexey Edelev <[email protected]>

2 files changed, 17 insertions, 15 deletions

diff --git a/cmake/QtBuildInternals/QtBuildInternalsConfig.cmake b/cmake/QtBuildInternals/QtBuildInternalsConfig.cmake
index dda9f8f0939..c34b4e83991 100644
--- a/cmake/QtBuildInternals/QtBuildInternalsConfig.cmake
+++ b/cmake/QtBuildInternals/QtBuildInternalsConfig.cmake
@@ -106,6 +106,8 @@ endif()
 include(QtPlatformSupport)
 
 # Set FEATURE_${feature} if INPUT_${feature} is set in certain circumstances.
+# Set FEATURE_${feature}_computed_from_input to TRUE or FALSE depending on whether the
+# INPUT_${feature} value has overridden the FEATURE_${feature} variable.
 #
 # Needs to be in QtBuildInternalsConfig.cmake instead of QtFeature.cmake because it's used in
 # qt_build_internals_disable_pkg_config_if_needed.
@@ -126,6 +128,9 @@ function(qt_internal_compute_feature_value_from_possible_input feature)
         endif()
 
         set(FEATURE_${feature} "${FEATURE_${feature}}" PARENT_SCOPE)
+        set(FEATURE_${feature}_computed_from_input TRUE PARENT_SCOPE)
+    else()
+        set(FEATURE_${feature}_computed_from_input FALSE PARENT_SCOPE)
     endif()
 endfunction()
 
@@ -635,9 +640,6 @@ function(qt_internal_qt_configure_end)
     # reconfigurations that are done by calling cmake directly don't trigger configure specific
     # logic.
     unset(QT_INTERNAL_CALLED_FROM_CONFIGURE CACHE)
-
-    # Clean up stale feature input values.
-    qt_internal_clean_feature_inputs()
 endfunction()
 
 macro(qt_build_repo)
diff --git a/cmake/QtFeature.cmake b/cmake/QtFeature.cmake
index 207abd58c97..9620c1df581 100644
--- a/cmake/QtFeature.cmake
+++ b/cmake/QtFeature.cmake
@@ -883,6 +883,18 @@ function(qt_internal_detect_dirty_features)
                     "to ${FEATURE_${feature}}")
                 set(dirty_build TRUE)
                 set_property(GLOBAL APPEND PROPERTY _qt_dirty_features "${feature}")
+
+                # If the user changed the value of the feature directly (e.g by editing
+                # CMakeCache.txt), and not via its associated INPUT variable, unset the INPUT cache
+                # variable before it is used in feature evaluation, to ensure a stale value doesn't
+                # influence other feature values, especially when QT_INTERNAL_CALLED_FROM_CONFIGURE
+                # is TRUE and the INPUT_foo variable is not passed.
+                # e.g. first configure -no-gui, then manually toggle FEATURE_gui to ON in
+                # CMakeCache.txt, then reconfigure (with the configure script) without -no-gui.
+                # Without this unset(), we'd have switched FEATURE_gui to OFF again.
+                if(NOT FEATURE_${feature}_computed_from_input)
+                    unset("INPUT_${feature}" CACHE)
+                endif()
             endif()
             unset("QT_FEATURE_${feature}" CACHE)
         endforeach()
@@ -899,18 +911,6 @@ function(qt_internal_detect_dirty_features)
     endif()
 endfunction()
 
-function(qt_internal_clean_feature_inputs)
-    foreach(feature IN LISTS QT_KNOWN_FEATURES)
-        # Unset the INPUT_foo cache variables after they were used in feature evaluation, to
-        # ensure stale values don't influence features upon reconfiguration when
-        # QT_INTERNAL_CALLED_FROM_CONFIGURE is TRUE and the INPUT_foo variable is not passed.
-        # e.g. first configure -no-gui, then manually toggle FEATURE_gui to ON in
-        # CMakeCache.txt, then reconfigure (with the configure script) without -no-gui.
-        # Without this unset(), we'd have switched FEATURE_gui to OFF again.
-        unset(INPUT_${feature} CACHE)
-    endforeach()
-endfunction()
-
 function(qt_config_compile_test name)
     if(DEFINED "TEST_${name}")
         return()