1 files changed, 52 insertions, 0 deletions
diff --git a/include/make/options.mk b/include/make/options.mk
new file mode 100644
index 0000000..022981c
--- /dev/null
+++ b/include/make/options.mk
@@ -0,0 +1,52 @@
+# this contains various functions and macros used to manipulate USE_* options
+# and their flags
+
+# Depending on the target platform, some options are set, as well as some
+# CFLAGS and LDFLAGS. All variables pre-set here will not appear in the build
+# options string. They may be set to any value, but are historically set to
+# "implicit" which eases debugging. You should not have to change anything
+# there unless you're adding support for a new platform.
+default_opts = $(foreach name,$(1),$(eval $(name)=implicit))
+
+# Return USE_xxx=$(USE_xxx) if the variable was set from the environment or the
+# command line.
+ignore_implicit = $(if $(subst environment,,$(origin $(1))),         \
+                       $(if $(subst command line,,$(origin $(1))),,  \
+                            $(1)=$($(1))),                           \
+                       $(1)=$($(1)))                                 \
+
+# This macro collects all USE_* values except those set to "implicit". This
+# is used to report a list of all flags which were used to build this version.
+# Do not assign anything to it.
+build_options   = $(foreach opt,$(use_opts),$(call ignore_implicit,$(opt)))
+
+# Make a list of all known features with +/- prepended depending on their
+# activation status. Must be a macro so that dynamically enabled ones are
+# evaluated with their current status.
+build_features  = $(foreach opt,$(patsubst USE_%,%,$(sort $(use_opts))),$(if $(USE_$(opt)),+$(opt),-$(opt)))
+
+# This returns a list of -DUSE_* for all known USE_* that are set
+opts_as_defines = $(foreach opt,$(use_opts),$(if $($(opt)),-D$(opt),))
+
+# Lists all enabled or disabled options without the "USE_" prefix
+enabled_opts    = $(foreach opt,$(patsubst USE_%,%,$(use_opts)),$(if $(USE_$(opt)),$(opt),))
+disabled_opts   = $(foreach opt,$(patsubst USE_%,%,$(use_opts)),$(if $(USE_$(opt)),,$(opt)))
+
+# preset all XXX_{INC,LIB,CFLAGS,LDFLAGS,SRC} variables to empty for $1=XXX
+reset_opt_vars = $(foreach name,INC LIB CFLAGS LDFLAGS SRC,$(eval $(1)_$(name)=))
+
+# preset all variables for all supported build options among use_opts
+reset_opts_vars = $(foreach opt,$(patsubst USE_%,%,$(use_opts)),$(call reset_opt_vars,$(opt)))
+
+# append $(1)_{C,LD}FLAGS into OPTIONS_{C,LD}FLAGS if not empty
+define collect_opt_flags
+  ifneq ($$($(1)_CFLAGS),)
+    OPTIONS_CFLAGS += $$($(1)_CFLAGS)
+  endif
+  ifneq ($$($(1)_LDFLAGS),)
+    OPTIONS_LDFLAGS += $$($(1)_LDFLAGS)
+  endif
+endef
+
+# collect all enabled USE_foo's foo_{C,LD}FLAGS into OPTIONS_{C,LD}FLAGS
+collect_opts_flags = $(foreach opt,$(enabled_opts),$(eval $(call collect_opt_flags,$(opt))))