Makefile.features: declare FEATURES_USED and make use of it

Put the definition of `FEATURES_USED` in common and use the variable
instead of duplicating code.

This required defining 'FEATURES_OPTIONAL_ONLY|USED' to not overwrite
the value of 'FEATURES_OPTIONAL' as was done before.

Also add 'FEATURES_OPTIONAL_MISSING' to list optional features that were
not included as not provided.

This removes the need to print FEATURES_MISSING with the optional
features too.

Makefile.dep

@@ -865,10 +865,9 @@ FEATURES_OPTIONAL += periph_pm
 # include package dependencies
 -include $(USEPKG:%=$(RIOTPKG)/%/Makefile.dep)
 
-# add all optional but provided features to the list of used features
-FEATURES_USED := $(sort $(FEATURES_REQUIRED) $(filter $(FEATURES_OPTIONAL),$(FEATURES_PROVIDED)))
 
 # all periph features correspond to a periph submodule
+# FEATURES_USED is defined in Makefile.features
 USEMODULE += $(filter periph_%,$(FEATURES_USED))
 
 # select cpu_check_address pseudomodule if the corresponding feature is used

Makefile.features

@@ -9,3 +9,13 @@ include $(RIOTBOARD)/$(BOARD)/Makefile.features
 # Features that are required by the application but not provided by the BSP
 # Having features missing may case the build to fail.
 FEATURES_MISSING = $(sort $(filter-out $(FEATURES_PROVIDED),$(FEATURES_REQUIRED)))
+
+# Features that are only optional and not required at the same time.
+# The policy is to by default use by features if they are provided by the BSP.
+FEATURES_OPTIONAL_ONLY = $(sort $(filter-out $(FEATURES_REQUIRED),$(FEATURES_OPTIONAL)))
+FEATURES_OPTIONAL_USED = $(sort $(filter $(FEATURES_PROVIDED),$(FEATURES_OPTIONAL_ONLY)))
+# Optional features that will not be used because they are not provided
+FEATURES_OPTIONAL_MISSING = $(sort $(filter-out $(FEATURES_PROVIDED),$(FEATURES_OPTIONAL_ONLY)))
+
+# Features that are used for an application
+FEATURES_USED = $(sort $(FEATURES_REQUIRED) $(FEATURES_OPTIONAL_USED))

makefiles/info.inc.mk

@@ -1,6 +1,7 @@
 .PHONY: info-objsize info-buildsizes info-build info-boards-supported \
         info-features-missing info-modules info-cpu \
         info-features-provided info-features-required \
+        info-features-used \
         info-debug-variable-% info-toolchains-supported \
         check-toolchain-supported
 
@@ -46,16 +47,16 @@ info-build:
 	@echo 'HEXFILE: $(HEXFILE)'
 	@echo 'FLASHFILE: $(FLASHFILE)'
 	@echo ''
+	@echo 'FEATURES_USED:'
+	@echo '         $(or $(FEATURES_USED), -none-)'
 	@echo 'FEATURES_REQUIRED:'
 	@echo '         $(or $(sort $(FEATURES_REQUIRED)), -none-)'
-	@echo 'FEATURES_OPTIONAL (optional that are not required, strictly "nice to have"):'
-	@echo '         $(or $(sort $(filter-out $(FEATURES_REQUIRED),$(FEATURES_OPTIONAL))),-none)'
-	@echo 'FEATURES_OPTIONAL (unused optional features):'
-	@echo '         $(or $(sort $(filter-out $(FEATURES_PROVIDED),$(FEATURES_OPTIONAL))), -none-)'
+	@echo 'FEATURES_OPTIONAL_ONLY (optional that are not required, strictly "nice to have"):'
+	@echo '         $(or $(FEATURES_OPTIONAL_ONLY), -none-)'
+	@echo 'FEATURES_OPTIONAL_MISSING (missing optional features):'
+	@echo '         $(or $(FEATURES_OPTIONAL_MISSING), -none-)'
 	@echo 'FEATURES_PROVIDED (by the board or USEMODULE'"'"'d drivers):'
 	@echo '         $(or $(sort $(FEATURES_PROVIDED)), -none-)'
-	@echo 'FEATURES_MISSING (incl. optional features):'
-	@echo '         $(or $(sort $(filter-out $(FEATURES_PROVIDED), $(FEATURES_REQUIRED) $(FEATURES_OPTIONAL))), -none-)'
 	@echo 'FEATURES_MISSING (only non optional features):'
 	@echo '         $(or $(FEATURES_MISSING), -none-)'
 	@echo ''
@@ -132,6 +133,9 @@ info-features-required:
 info-features-missing:
 	@for i in $(FEATURES_MISSING); do echo $$i; done
 
+info-features-used:
+	@for i in $(FEATURES_USED); do echo $$i; done
+
 info-debug-variable-%:
 	@echo $($*)