Merge pull request #9362 from gebart/pr/Wimplicit-fallthrough

make: Makefile.include: Remove -Wno-implicit-fallthrough

Makefile.include

@@ -141,10 +141,6 @@ ifeq ($(WPEDANTIC),1)
   CFLAGS += -Wpedantic
 endif
 
-# remove this once codebase is adapted
-CFLAGS += -Wno-implicit-fallthrough
-CXXFLAGS += -Wno-implicit-fallthrough
-
 ifneq (10,$(if $(RIOT_VERSION),1,0)$(if $(__RIOTBUILD_FLAG),1,0))
 
 # Provide a shallow sanity check. You cannot call `make` in a module directory.
@@ -248,6 +244,16 @@ include $(RIOTCPU)/$(CPU)/Makefile.include
 # Import all toolchain settings
 include $(RIOTMAKE)/toolchain/$(TOOLCHAIN).inc.mk
 
+# Tell ccache to pass the original file to the compiler, instead of passing the
+# preprocessed code. Without this setting, the compilation will fail with
+# -Wimplicit-fallthrough warnings even when the fall through case is properly
+# commented because the preprocessor has stripped the comments from the code.
+# This also fixes some other false warnings when compiling with LLVM/Clang.
+# The environment variable only affects builds with ccache (e.g. on CI/Murdock).
+# Non cached builds are not affected in any way.
+# For more information, see http://petereisentraut.blogspot.com/2011/09/ccache-and-clang-part-2.html
+export CCACHE_CPP2=yes
+
 # get number of interfaces straight before resolving dependencies
 GNRC_NETIF_NUMOF ?= 1
 

drivers/sht1x/sht1x_saul.c

@@ -41,6 +41,7 @@ static int read(const sht1x_dev_t *dev, int16_t *temp, int16_t *hum)
                 continue;
             case -ECANCELED:
                 puts("[sht1x] Measurement times out");
+                /* falls through */
             default:
                 /* Other failure, cannot recover so giving up */
                 return -1;