‘defaultValue’ may be used uninitialized in this function

[danzel]

Platform: Debian Stretch (QT)

Steps to trigger behavior

Trying to build BUILDTYPE=Release make qt-app fails with the following error

[199/374] Building CXX object CMakeFiles/mbgl-core.dir/src/mbgl/style/conversion/function.cpp.o
FAILED: CMakeFiles/mbgl-core.dir/src/mbgl/style/conversion/function.cpp.o
/usr/bin/c++   -DMBGL_USE_GLES2 -DQT_CORE_LIB -DQT_GUI_LIB -DQT_NO_DEBUG -DQT_OPENGL_LIB -DQT_WIDGETS_LIB -DRAPIDJSON_HAS_STDSTRING=1 -D_GLIBCXX_USE_CXX11_ABI=1 -D__QT__ -I../../../include -I../../../src -I../../../mason_packages/headers/geometry/0.9.3/include -I../../../mason_packages/headers/variant/1.1.4/include -I../../../mason_packages/headers/unique_resource/cba309e/include -I../../../mason_packages/headers/rapidjson/1.1.0/include -I../../../mason_packages/headers/boost/1.65.1/include -I../../../mason_packages/headers/geojson/0.4.2/include -I../../../mason_packages/headers/geojsonvt/6.6.0/include -I../../../mason_packages/headers/supercluster/0.2.2/include -I../../../mason_packages/headers/kdbush/0.1.1-1/include -I../../../mason_packages/headers/earcut/0.12.4/include -I../../../mason_packages/headers/protozero/1.5.2/include -I../../../mason_packages/headers/polylabel/1.0.3/include -I../../../mason_packages/headers/wagyu/0.4.3/include -I../../../mason_packages/headers/shelf-pack/2.1.1/include -I../../../mason_packages/headers/vector-tile/1.0.2/include -I../../../platform/default -I../../../platform/qt -I../../../platform/qt/include -I../../../mason_packages/linux-x86_64/libjpeg-turbo/1.5.0/include -I../../../mason_packages/linux-x86_64/libpng/1.6.25/include/libpng16 -I../../../mason_packages/linux-x86_64/webp/0.5.1/include -isystem /usr/include/x86_64-linux-gnu/qt5 -isystem /usr/include/x86_64-linux-gnu/qt5/QtCore -isystem /usr/lib/x86_64-linux-gnu/qt5/mkspecs/linux-g++-64 -isystem /usr/include/x86_64-linux-gnu/qt5/QtGui -isystem /usr/include/x86_64-linux-gnu/qt5/QtOpenGL -isystem /usr/include/x86_64-linux-gnu/qt5/QtWidgets -I../../../vendor/nunicode/include -I../../../vendor/icu/include -ftemplate-depth=1024 -Wall -Wextra -Wshadow -Wnon-virtual-dtor -Wno-variadic-macros -Wno-unknown-pragmas -Werror -fext-numeric-literals -O3 -DNDEBUG -Os -DNDEBUG -fPIC -fvisibility=hidden -fvisibility-inlines-hidden   -fPIC -std=c++14 -MD -MT CMakeFiles/mbgl-core.dir/src/mbgl/style/conversion/function.cpp.o -MF CMakeFiles/mbgl-core.dir/src/mbgl/style/conversion/function.cpp.o.d -o CMakeFiles/mbgl-core.dir/src/mbgl/style/conversion/function.cpp.o -c /usr/src/app/mapbox-gl-native/src/mbgl/style/conversion/function.cpp
In function ‘mbgl::optional<mbgl::style::PropertyExpression<T> > mbgl::style::conversion::convertFunctionToExpression(const mbgl::style::conversion::Convertible&, mbgl::style::conversion::Error&, bool) [with T = mbgl::style::AlignmentType]’:
cc1plus: error: ‘defaultValue’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
/usr/src/app/mapbox-gl-native/src/mbgl/style/conversion/function.cpp:82:17: note: ‘defaultValue’ was declared here
     optional<T> defaultValue;
                 ^~~~~~~~~~~~

Bigger snippet of the build logs https://gist.github.com/danzel/e1e7fea51ab6ba6b30e7c6df5eb6ee8d

Attempting to build with latest git (e947fa0) fails.
Building with 9df9f5f succeeds. (Chosen as it is the parent of the commit that I believe broke this)

The code the error is coming from was moved around in #12665 by @kkaefer, it does sorta look like it may be using the variable without assigning it.
https://github.com/mapbox/mapbox-gl-native/blob/master/src/mbgl/style/conversion/function.cpp#L75-L94

Otherwise maybe could be g++ version, circleci seems to build with 5.4.0, which is older than 6.3.0 that I am using.

g++ --version
g++ (Debian 6.3.0-18+deb9u1) 6.3.0 20170516

[brunoabinader]

Hi @danzel - apologies for the delay - is this still an issue?

[pozdnyakov]

Fixed with bf785f5

[danzel]

Cool thanks!