[MNT]: c++11 narrowing error when building for 32 bit targets #30413
Description
Summary
this happens because get_height() and get_width() return an unsigned int, which can be losslessly narrowed into a ssize_t in 64 bit targets but not in 32 bit targets
FAILED: [code=1] src/_backend_agg.cpython-313-powerpc-linux-musl.so.p/_backend_agg_wrapper.cpp.o
clang++ -Isrc/_backend_agg.cpython-313-powerpc-linux-musl.so.p -Isrc -I../src -I../extern/agg24-svn/include -I/usr/include/freetype2 -I/usr/include/libpng16 -I/usr/include/harfbuzz -I/usr/include/glib-2.0 -I/usr/lib/glib-2.0/include -I/usr/include/sysprof-6 -I/usr/share/pkgconfig/../../lib/python3.13/site-packages/pybind11/share/pkgconfig/../../include -I/usr/include/python3.13 -fvisibility=hidden -fvisibility-inlines-hidden -flto -fdiagnostics-color=always -DNDEBUG -D_FILE_OFFSET_BITS=64 -Wall -Winvalid-pch -std=c++17 -O3 -ffile-prefix-map=/builddir/python-matplotlib-3.10.5=. -Wformat -Werror=format-security -ftrivial-auto-var-init=zero -fno-omit-frame-pointer -mtune=G4 -O2 -g1 -fPIC -DWITH_GZFILEOP -pthread -MD -MQ src/_backend_agg.cpython-313-powerpc-linux-musl.so.p/_backend_agg_wrapper.cpp.o -MF src/_backend_agg.cpython-313-powerpc-linux-musl.so.p/_backend_agg_wrapper.cpp.o.d -o src/_backend_agg.cpython-313-powerpc-linux-musl.so.p/_backend_agg_wrapper.cpp.o -c ../src/_backend_agg_wrapper.cpp
../src/_backend_agg_wrapper.cpp:253:17: error: non-constant-expression cannot be narrowed from type 'unsigned int' to 'int' in initializer list [-Wc++11-narrowing]
253 | renderer->get_height(),
| ^~~~~~~~~~~~~~~~~~~~~~
../src/_backend_agg_wrapper.cpp:253:17: note: insert an explicit cast to silence this issue
253 | renderer->get_height(),
| ^~~~~~~~~~~~~~~~~~~~~~
| static_cast<int>( )
../src/_backend_agg_wrapper.cpp:254:17: error: non-constant-expression cannot be narrowed from type 'unsigned int' to 'int' in initializer list [-Wc++11-narrowing]
254 | renderer->get_width(),
| ^~~~~~~~~~~~~~~~~~~~~
../src/_backend_agg_wrapper.cpp:254:17: note: insert an explicit cast to silence this issue
254 | renderer->get_width(),
| ^~~~~~~~~~~~~~~~~~~~~
| static_cast<int>( )
../src/_backend_agg_wrapper.cpp:258:17: error: non-constant-expression cannot be narrowed from type 'unsigned int' to 'int' in initializer list [-Wc++11-narrowing]
258 | renderer->get_width() * 4,
| ^~~~~~~~~~~~~~~~~~~~~~~~~
../src/_backend_agg_wrapper.cpp:258:17: note: insert an explicit cast to silence this issue
258 | renderer->get_width() * 4,
| ^~~~~~~~~~~~~~~~~~~~~~~~~
| static_cast<int>( )
3 errors generated.
full build log at https://build.chimera-linux.org/#/builders/7/builds/1457/steps/4/logs/pkg_user_python-matplotlib_3_10_5-r0
Proposed fix
potentially just adding the static casts as the compiler note says
diff -ruN a/src/_backend_agg_wrapper.cpp b/src/_backend_agg_wrapper.cpp
--- a/src/_backend_agg_wrapper.cpp 2025-07-31 19:00:28.000000000 +0200
+++ b/src/_backend_agg_wrapper.cpp 2025-08-10 21:50:30.146295804 +0200
@@ -250,12 +250,12 @@
.def_buffer([](RendererAgg *renderer) -> py::buffer_info {
std::vector<py::ssize_t> shape {
- renderer->get_height(),
- renderer->get_width(),
+ static_cast<py::ssize_t>(renderer->get_height()),
+ static_cast<py::ssize_t>(renderer->get_width()),
4
};
std::vector<py::ssize_t> strides {
- renderer->get_width() * 4,
+ static_cast<py::ssize_t>(renderer->get_width() * 4),
4,
1
};