graphics/py-matplotlib with MODPY_PYBUILD=mesonpy via

  /usr/local/lib/python3.14/site-packages/mesonbuild/envconfig.py:        return ExternalProgram('sccache', silent=True)                      

detects /usr/local/bin/sccache and uses that over default "c++",
leading to build failure with PORTS_PRIVSEP=yes:

  sccache: error: failed to create directory `/py-matplotlib-3.10.8_writes_to_HOME/.cache/sccache/preprocessor`: Permission denied (os error 13)

Environmental CXX takes priority, but is not set compared to CC,
which is how I tracked this down not knowing anything about how
Python builds C++ code.

Setting CXX where CC comes from fixes it and seems safe.

tb@ mentioned COMPILER_LANGS, but I don't fully understand the
implications of having CXX in the environment for Python ports
doing COMPILER_LANGS=C (if they exist), so I just gated it.

This fixes matplotlib for me when sccache is installed.

Feedback? OK?


Index: python.port.mk
===================================================================
RCS file: /cvs/ports/lang/python/3/python.port.mk,v
diff -u -p -r1.28 python.port.mk
--- python.port.mk	19 Jun 2026 13:49:04 -0000	1.28
+++ python.port.mk	4 Sep 2026 16:56:30 -0000
@@ -224,6 +224,9 @@ MODPY_DISTUTILS_INSTALL ?=	install --pre
 				--root=${DESTDIR}
 
 MAKE_ENV +=		CC=${CC}
+.if ${COMPILER_LANGS:Mc++}
+MAKE_ENV +=		CXX=${CXX}
+.endif
 CONFIGURE_ENV +=	PYTHON="${MODPY_BIN}"
 .if ${CONFIGURE_STYLE:Mgnu}
 CONFIGURE_ENV +=	ac_cv_prog_PYTHON="${MODPY_BIN}" \