makefiles/cflags.inc.mk: Add -Wno-missing-field-initializers to CXXFLAGS

This allows including C headers from C++. It sadly reduced the
diagnostics on C++ code as well, were there warning may make sense as
unintended side effect. We may be able to drop that later on, when more
C APIs are properly wrapped in native C++ APIs, so that C headers do no
longer need to be compatible with C++ compilers.

makefiles/cflags.inc.mk

@@ -87,6 +87,13 @@ ifeq (,$(filter -DDEVELHELP,$(CFLAGS)))
     CFLAGS += -DNDEBUG
   endif
 endif
-
 # Add the optional flags that are not architecture/toolchain blacklisted
 CFLAGS += $(filter-out $(OPTIONAL_CFLAGS_BLACKLIST),$(OPTIONAL_CFLAGS))
+
+# Improve C++ compatibility with our C headers: In C it is both valid and good
+# practise to implicitly initialize struct members with zero by omitting them
+# in a initializer list. The C++ compiler greatly frowns upon this, even within
+# `extern "C" { ... }`. The best would be to configure the C++ compiler to
+# accept good C practises within `extern "C" { ... }` while enforcing good C++
+# practises elsewhere. But in absence of this, we disable the warning for now.
+CXXEXFLAGS += -Wno-missing-field-initializers

pkg/cryptoauthlib/Makefile

@@ -14,7 +14,6 @@ CFLAGS += $(INCLUDES)
 CFLAGS += -DATCA_HAL_I2C
 CFLAGS += -Wno-cast-align
 CFLAGS += -Wno-char-subscripts
-CFLAGS += -Wno-missing-field-initializers
 CFLAGS += -Wno-overflow
 CFLAGS += -Wno-pointer-to-int-cast
 CFLAGS += -Wno-sign-compare

pkg/semtech-loramac/Makefile.loramac_region

@@ -1,6 +1,7 @@
 MODULE = semtech_loramac_mac_region
 
-CFLAGS += -Wno-missing-field-initializers -Wno-unused-parameter -Wno-sign-compare
+CFLAGS += -Wno-sign-compare
+CFLAGS += -Wno-unused-parameter
 
 INCLUDES += -I$(PKGDIRBASE)/semtech-loramac/src/boards \
             -I$(PKGDIRBASE)/semtech-loramac/src/radio

pkg/tensorflow-lite/Makefile.tensorflow-lite-kernels

@@ -1,6 +1,5 @@
 MODULE = tensorflow-lite-kernels
 
-CXXEXFLAGS += -Wno-missing-field-initializers
 CXXEXFLAGS += -Wno-unused-function
 CXXEXFLAGS += -Wno-unused-parameter
 

pkg/tensorflow-lite/Makefile.tensorflow-lite-kernels-internal

@@ -1,6 +1,5 @@
 MODULE = tensorflow-lite-kernels-internal
 
-CXXEXFLAGS += -Wno-missing-field-initializers
 CXXEXFLAGS += -Wno-unused-function
 CXXEXFLAGS += -Wno-unused-parameter
 

pkg/tensorflow-lite/Makefile.tensorflow-lite-micro-kernels

@@ -1,6 +1,5 @@
 MODULE = tensorflow-lite-micro-kernels
 
-CXXEXFLAGS += -Wno-missing-field-initializers
 CXXEXFLAGS += -Wno-strict-overflow
 CXXEXFLAGS += -Wno-type-limits
 CXXEXFLAGS += -Wno-unused-parameter

pkg/uwb-core/Makefile

@@ -12,7 +12,6 @@ CFLAGS += -Wno-strict-prototypes
 CFLAGS += -Wno-maybe-uninitialized
 CFLAGS += -Wno-missing-braces
 CFLAGS += -Wno-missing-declarations
-CFLAGS += -Wno-missing-field-initializers
 CFLAGS += -Wno-old-style-definition
 CFLAGS += -Wno-return-type
 CFLAGS += -Wno-sign-compare

sys/ztimer/Makefile

@@ -10,7 +10,4 @@ SRC := core.c util.c periodic.c
 # enable submodules
 SUBMODULES := 1
 
-# disable obsolete warning
-CFLAGS += -Wno-missing-field-initializers
-
 include $(RIOTBASE)/Makefile.base

tests/can_trx/Makefile

@@ -25,7 +25,4 @@ ifneq (,$(filter ncv7356,$(TRX_TO_BUILD)))
 	CFLAGS += -DNCV7356_MODE1_PIN=$(NCV7356_MODE1_PIN)
 endif
 
-# Some boards throw a missing-field-initializers error
-CFLAGS += -Wno-missing-field-initializers
-
 include $(RIOTBASE)/Makefile.include

tests/conn_can/Makefile

@@ -37,9 +37,6 @@ endif
 CFLAGS += -DCAN_PKT_BUF_SIZE=64
 CFLAGS += -DCAN_ROUTER_MAX_FILTER=32
 
-# Some boards throw a missing-field-initializers error
-CFLAGS += -Wno-missing-field-initializers
-
 include $(RIOTBASE)/Makefile.include
 
 ifndef CONFIG_GNRC_PKTBUF_SIZE