commit 4aaa1a1fd8e7eb23ac5557cd326d1a48efdb54cd
author Ying Wang <wangying@google.com> Tue Mar 22 18:23:13 2016 -0700
committer Ying Wang <wangying@google.com> Tue Mar 22 18:23:13 2016 -0700
tree 98f3b28bf3d2da420a174bdcca9f5003ad4f1422
parent 6d41f7e1233da88714edaf3f21f88ff8023558f4

Create empty .a on Darwin when there is no obj file.

On Darwin ar would fail if there is no object file to add.
We work around by adding a dummy.o to the .a and then deleting it.

Bug: 27800477
Change-Id: I68bbebea2726058c25863d7026a645a520d05167

core/binary.mk

diff --git a/core/binary.mk b/core/binary.mk
index dc43463..38e9f06 100644
--- a/core/binary.mk
+++ b/core/binary.mk
@@ -1375,7 +1375,7 @@
 $(LOCAL_INTERMEDIATE_TARGETS): PRIVATE_ALL_SHARED_LIBRARIES := $(built_shared_libraries)
 $(LOCAL_INTERMEDIATE_TARGETS): PRIVATE_ALL_STATIC_LIBRARIES := $(built_static_libraries)
 $(LOCAL_INTERMEDIATE_TARGETS): PRIVATE_ALL_WHOLE_STATIC_LIBRARIES := $(built_whole_libraries)
-$(LOCAL_INTERMEDIATE_TARGETS): PRIVATE_ALL_OBJECTS := $(all_objects)
+$(LOCAL_INTERMEDIATE_TARGETS): PRIVATE_ALL_OBJECTS := $(strip $(all_objects))
 
 ###########################################################
 # Define library dependencies.

core/definitions.mk

diff --git a/core/definitions.mk b/core/definitions.mk
index 8eed422..c36d352 100644
--- a/core/definitions.mk
+++ b/core/definitions.mk
@@ -1518,6 +1518,23 @@
     $(call _extract-and-include-single-host-whole-static-lib, $(lib)))
 endef
 
+ifeq ($(HOST_OS),darwin)
+# On Darwin the host ar fails if there is nothing to add to .a at all.
+# We work around by adding a dummy.o and then deleting it.
+define create-dummy.o-if-no-objs
+$(if $(PRIVATE_ALL_OBJECTS),,$(hide) touch $(dir $@)dummy.o)
+endef
+
+define get-dummy.o-if-no-objs
+$(if $(PRIVATE_ALL_OBJECTS),,$(dir $@)dummy.o)
+endef
+
+define delete-dummy.o-if-no-objs
+$(if $(PRIVATE_ALL_OBJECTS),,$(hide) $($(PRIVATE_2ND_ARCH_VAR_PREFIX)$(PRIVATE_PREFIX)AR) d $@ $(dir $@)dummy.o \
+  && rm -f $(dir $@)dummy.o)
+endef
+endif  # HOST_OS is darwin
+
 # Explicitly delete the archive first so that ar doesn't
 # try to add to an existing archive.
 define transform-host-o-to-static-lib
@@ -1525,9 +1542,11 @@
 @mkdir -p $(dir $@)
 @rm -f $@
 $(extract-and-include-host-whole-static-libs)
+$(create-dummy.o-if-no-objs)
 $(call split-long-arguments,$($(PRIVATE_2ND_ARCH_VAR_PREFIX)$(PRIVATE_PREFIX)AR) \
     $($(PRIVATE_2ND_ARCH_VAR_PREFIX)$(PRIVATE_PREFIX)GLOBAL_ARFLAGS) \
-    $(PRIVATE_ARFLAGS) $@,$(PRIVATE_ALL_OBJECTS))
+    $(PRIVATE_ARFLAGS) $@,$(PRIVATE_ALL_OBJECTS) $(get-dummy.o-if-no-objs))
+$(delete-dummy.o-if-no-objs)
 endef