Support build targets with no installable apps/packages

Specifically, do not error out if no installable apps are found.

- When creating an archive of all the apps, and if no apps exist
for the target, generate an empty archive file.
- If building for a target with no installable jar(s) or apk(s),
generate an empty package stats file.

The former is just an output artifact. The latter is used
by the upload_pkg_stats.py script which correctly handles
an empty input file.

BUG: 23421592

Change-Id: I48db9f9e1f61914d8fd938130e09b41849685450

core/Makefile

@@ -314,7 +314,12 @@ $(PACKAGE_STATS_FILE): $(PACKAGES_TO_STAT)
 	@echo Package stats: $@
 	@mkdir -p $(dir $@)
 	$(hide) rm -f $@
+ifeq ($(PACKAGES_TO_STAT),)
+# Create empty package stats file if target builds no jar(s) or apk(s).
+	$(hide) touch $@
+else
 	$(hide) build/tools/dump-package-stats $^ > $@
+endif
 
 .PHONY: package-stats
 package-stats: $(PACKAGE_STATS_FILE)
@@ -1736,8 +1741,13 @@ $(APPS_ZIP): $(INSTALLED_SYSTEMIMAGE)
 	@echo "Package apps: $@"
 	$(hide) rm -rf $@
 	$(hide) mkdir -p $(dir $@)
-	$(hide) zip -qj $@ $(TARGET_OUT_APPS)/*/*.apk $(TARGET_OUT_APPS_PRIVILEGED)/*/*.apk
-
+	$(hide) apps_to_zip=`find $(TARGET_OUT_APPS) $(TARGET_OUT_APPS_PRIVILEGED) -mindepth 2 -maxdepth 3 -name "*.apk"`; \
+	if [ -z "$$apps_to_zip" ]; then \
+		echo "No apps to zip up. Generating empty apps archive." ; \
+		a=$$(mktemp /tmp/XXXXXXX) && touch $$a && zip $@ $$a && zip -d $@ $$a; \
+	else \
+		zip -qj $@ $$apps_to_zip; \
+	fi
 
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