diff --git a/core/build_id.mk b/core/build_id.mk
index 0e8e2cf..5a012b9 100644
--- a/core/build_id.mk
+++ b/core/build_id.mk
@@ -18,4 +18,4 @@
 # (like "CRB01").  It must be a single word, and is
 # capitalized by convention.
 
-export BUILD_ID=MASTER
+export BUILD_ID=NYC
diff --git a/core/definitions.mk b/core/definitions.mk
index 4cf81dd..f8b4a77 100644
--- a/core/definitions.mk
+++ b/core/definitions.mk
@@ -2069,6 +2069,38 @@
 $(if $(PRIVATE_JAR_MANIFEST), $(hide) echo unsupported options JAR_MANIFEST in $@; exit 53)
 endef
 
+# Invoke Jack to compile java source just to check it compiles correctly.
+#
+# Some historical notes:
+# - below we write the list of java files to java-source-list to avoid argument
+#   list length problems with Cygwin
+# - we filter out duplicate java file names because Jack doesn't like them.
+define jack-check-java
+$(hide) rm -f $@
+$(hide) rm -f $@.java-source-list
+$(hide) rm -f $@.java-source-list-uniq
+$(hide) mkdir -p $(dir $@)
+$(if $(PRIVATE_JACK_INCREMENTAL_DIR),$(hide) mkdir -p $(PRIVATE_JACK_INCREMENTAL_DIR))
+$(call dump-words-to-file,$(PRIVATE_JAVA_SOURCES),$@.java-source-list)
+$(hide) if [ -d "$(PRIVATE_SOURCE_INTERMEDIATES_DIR)" ]; then \
+          find $(PRIVATE_SOURCE_INTERMEDIATES_DIR) -name '*.java' >> $@.java-source-list; \
+fi
+$(hide) tr ' ' '\n' < $@.java-source-list \
+    | sort -u > $@.java-source-list-uniq
+$(hide) if [ -s $@.java-source-list-uniq ] ; then \
+	$(call call-jack,$(PRIVATE_JACK_EXTRA_ARGS)) \
+	    $(strip $(PRIVATE_JACK_FLAGS)) \
+	    $(strip $(PRIVATE_JACK_DEBUG_FLAGS)) \
+	    $(addprefix --classpath ,$(strip \
+	        $(call normalize-path-list,$(call reverse-list,$(PRIVATE_STATIC_JACK_LIBRARIES)) $(PRIVATE_BOOTCLASSPATH_JAVA_LIBRARIES) $(PRIVATE_ALL_JACK_LIBRARIES)))) \
+	    -D jack.import.resource.policy=keep-first \
+	    -D jack.import.type.policy=keep-first \
+	    $(if $(PRIVATE_JACK_INCREMENTAL_DIR),--incremental-folder $(PRIVATE_JACK_INCREMENTAL_DIR)) \
+	    @$@.java-source-list-uniq; \
+fi
+touch $@
+endef
+
 define transform-jar-to-jack
 	$(hide) mkdir -p $(dir $@)
 	$(hide) mkdir -p $@.tmpjill.res
diff --git a/core/host_dalvik_java_library.mk b/core/host_dalvik_java_library.mk
index 8617449..0d32559 100644
--- a/core/host_dalvik_java_library.mk
+++ b/core/host_dalvik_java_library.mk
@@ -35,6 +35,7 @@
 full_classes_jarjar_jar := $(intermediates.COMMON)/classes-jarjar.jar
 full_classes_jar := $(intermediates.COMMON)/classes.jar
 full_classes_jack := $(intermediates.COMMON)/classes.jack
+jack_check_timestamp := $(intermediates.COMMON)/jack.check.timestamp
 built_dex := $(intermediates.COMMON)/classes.dex
 
 LOCAL_INTERMEDIATE_TARGETS += \
@@ -42,12 +43,17 @@
     $(full_classes_jarjar_jar) \
     $(full_classes_jack) \
     $(full_classes_jar) \
+    $(jack_check_timestamp) \
     $(built_dex)
 
 # See comment in java.mk
 ifndef LOCAL_CHECKED_MODULE
+ifdef LOCAL_JACK_ENABLED
+LOCAL_CHECKED_MODULE := $(jack_check_timestamp)
+else
 LOCAL_CHECKED_MODULE := $(full_classes_compiled_jar)
 endif
+endif
 
 #######################################
 include $(BUILD_SYSTEM)/base_rules.mk
@@ -120,16 +126,21 @@
 $(LOCAL_INTERMEDIATE_TARGETS): \
 	PRIVATE_JACK_INCREMENTAL_DIR :=
 endif
+$(LOCAL_INTERMEDIATE_TARGETS): PRIVATE_JACK_FLAGS := $(GLOBAL_JAVAC_DEBUG_FLAGS) $(LOCAL_JACK_FLAGS)
+$(LOCAL_INTERMEDIATE_TARGETS): PRIVATE_JACK_VERSION := $(LOCAL_JACK_VERSION)
 
-$(built_dex): PRIVATE_CLASSES_JACK := $(full_classes_jack)
-$(built_dex): PRIVATE_JACK_FLAGS := $(GLOBAL_JAVAC_DEBUG_FLAGS) $(LOCAL_JACK_FLAGS)
-$(built_dex): PRIVATE_JACK_VERSION := $(LOCAL_JACK_VERSION)
-$(built_dex): $(java_sources) $(java_resource_sources) $(full_jack_deps) \
+jack_all_deps := $(java_sources) $(java_resource_sources) $(full_jack_deps) \
         $(jar_manifest_file) $(proto_java_sources_file_stamp) $(LOCAL_MODULE_MAKEFILE_DEP) \
-        $(LOCAL_ADDITIONAL_DEPENDENCIES) $(JACK) | setup-jack-server
+        $(LOCAL_ADDITIONAL_DEPENDENCIES) $(JACK)
+$(built_dex): PRIVATE_CLASSES_JACK := $(full_classes_jack)
+$(built_dex): $(jack_all_deps) | setup-jack-server
 	@echo Building with Jack: $@
 	$(jack-java-to-dex)
 
+$(jack_check_timestamp): $(jack_all_deps) | setup-jack-server
+	@echo Checking build with Jack: $@
+	$(jack-check-java)
+
 # $(full_classes_jack) is just by-product of $(built_dex).
 # The dummy command was added because, without it, make misses the fact the $(built_dex) also
 # change $(full_classes_jack).
diff --git a/core/host_dalvik_static_java_library.mk b/core/host_dalvik_static_java_library.mk
index 17b2922..d86c6ca 100644
--- a/core/host_dalvik_static_java_library.mk
+++ b/core/host_dalvik_static_java_library.mk
@@ -34,8 +34,9 @@
 include $(BUILD_SYSTEM)/host_java_library.mk
 # proguard is not supported
 # *.proto files are not supported
-$(full_classes_jack): PRIVATE_JACK_FLAGS := $(GLOBAL_JAVAC_DEBUG_FLAGS) $(LOCAL_JACK_FLAGS)
-$(full_classes_jack): PRIVATE_JACK_VERSION := $(LOCAL_JACK_VERSION)
+$(LOCAL_INTERMEDIATE_TARGETS): PRIVATE_JACK_FLAGS := $(GLOBAL_JAVAC_DEBUG_FLAGS) $(LOCAL_JACK_FLAGS)
+$(LOCAL_INTERMEDIATE_TARGETS): PRIVATE_JACK_VERSION := $(LOCAL_JACK_VERSION)
+
 $(full_classes_jack): PRIVATE_JARJAR_RULES := $(LOCAL_JARJAR_RULES)
 $(full_classes_jack): \
 	PRIVATE_JACK_INTERMEDIATES_DIR := $(intermediates.COMMON)/jack-rsc
diff --git a/core/host_java_library.mk b/core/host_java_library.mk
index 052c571..97079fd 100644
--- a/core/host_java_library.mk
+++ b/core/host_java_library.mk
@@ -30,13 +30,15 @@
 endif
 
 full_classes_compiled_jar := $(intermediates.COMMON)/classes-full-debug.jar
+full_classes_jarjar_jar := $(intermediates.COMMON)/classes-jarjar.jar
 emma_intermediates_dir := $(intermediates.COMMON)/emma_out
 # emma is hardcoded to use the leaf name of its input for the output file --
 # only the output directory can be changed
-full_classes_emma_jar := $(emma_intermediates_dir)/lib/$(notdir $(full_classes_compiled_jar))
+full_classes_emma_jar := $(emma_intermediates_dir)/lib/$(notdir $(full_classes_jarjar_jar))
 
 LOCAL_INTERMEDIATE_TARGETS += \
     $(full_classes_compiled_jar) \
+    $(full_classes_jarjar_jar) \
     $(full_classes_emma_jar)
 
 #######################################
@@ -49,30 +51,6 @@
 
 include $(BUILD_SYSTEM)/java_common.mk
 
-ifeq (true,$(LOCAL_EMMA_INSTRUMENT))
-$(full_classes_emma_jar): PRIVATE_EMMA_COVERAGE_FILE := $(intermediates.COMMON)/coverage.em
-$(full_classes_emma_jar): PRIVATE_EMMA_INTERMEDIATES_DIR := $(emma_intermediates_dir)
-ifdef LOCAL_EMMA_COVERAGE_FILTER
-$(full_classes_emma_jar): PRIVATE_EMMA_COVERAGE_FILTER := $(LOCAL_EMMA_COVERAGE_FILTER)
-else
-# by default, avoid applying emma instrumentation onto emma classes itself,
-# otherwise there will be exceptions thrown
-$(full_classes_emma_jar): PRIVATE_EMMA_COVERAGE_FILTER := *,-emma,-emmarun,-com.vladium.*
-endif
-# this rule will generate both $(PRIVATE_EMMA_COVERAGE_FILE) and
-# $(full_classes_emma_jar)
-$(full_classes_emma_jar) : $(full_classes_compiled_jar) | $(EMMA_JAR)
-	$(transform-classes.jar-to-emma)
-
-$(built_javalib_jar) : $(full_classes_emma_jar)
-	@echo Copying: $@
-	$(hide) $(ACP) -fp $< $@
-
-else # LOCAL_EMMA_INSTRUMENT
-# Directly build into $(built_javalib_jar).
-full_classes_compiled_jar := $(built_javalib_jar)
-endif # LOCAL_EMMA_INSTRUMENT
-
 # The layers file allows you to enforce a layering between java packages.
 # Run build/tools/java-layers.py for more details.
 layers_file := $(addprefix $(LOCAL_PATH)/, $(LOCAL_JAVA_LAYERS_FILE))
@@ -91,3 +69,41 @@
         $(LOCAL_MODULE_MAKEFILE_DEP) \
         $(LOCAL_ADDITIONAL_DEPENDENCIES)
 	$(transform-host-java-to-package)
+
+# Run jarjar if necessary, otherwise just copy the file.
+ifneq ($(strip $(LOCAL_JARJAR_RULES)),)
+$(full_classes_jarjar_jar): PRIVATE_JARJAR_RULES := $(LOCAL_JARJAR_RULES)
+$(full_classes_jarjar_jar): $(full_classes_compiled_jar) $(LOCAL_JARJAR_RULES) | $(JARJAR)
+	@echo JarJar: $@
+	$(hide) java -jar $(JARJAR) process $(PRIVATE_JARJAR_RULES) $< $@
+else
+$(full_classes_jarjar_jar): $(full_classes_compiled_jar) | $(ACP)
+	@echo Copying: $@
+	$(hide) $(ACP) -fp $< $@
+endif
+
+ifeq (true,$(LOCAL_EMMA_INSTRUMENT))
+$(full_classes_emma_jar): PRIVATE_EMMA_COVERAGE_FILE := $(intermediates.COMMON)/coverage.em
+$(full_classes_emma_jar): PRIVATE_EMMA_INTERMEDIATES_DIR := $(emma_intermediates_dir)
+ifdef LOCAL_EMMA_COVERAGE_FILTER
+$(full_classes_emma_jar): PRIVATE_EMMA_COVERAGE_FILTER := $(LOCAL_EMMA_COVERAGE_FILTER)
+else
+# by default, avoid applying emma instrumentation onto emma classes itself,
+# otherwise there will be exceptions thrown
+$(full_classes_emma_jar): PRIVATE_EMMA_COVERAGE_FILTER := *,-emma,-emmarun,-com.vladium.*
+endif
+# this rule will generate both $(PRIVATE_EMMA_COVERAGE_FILE) and
+# $(full_classes_emma_jar)
+$(full_classes_emma_jar) : $(full_classes_jarjar_jar) | $(EMMA_JAR)
+	$(transform-classes.jar-to-emma)
+
+$(built_javalib_jar) : $(full_classes_emma_jar)
+	@echo Copying: $@
+	$(hide) $(ACP) -fp $< $@
+
+else # LOCAL_EMMA_INSTRUMENT
+$(built_javalib_jar): $(full_classes_jarjar_jar) | $(ACP)
+	@echo Copying: $@
+	$(hide) $(ACP) -fp $< $@
+endif # LOCAL_EMMA_INSTRUMENT
+
diff --git a/core/java.mk b/core/java.mk
index 5848fca..173db79 100644
--- a/core/java.mk
+++ b/core/java.mk
@@ -123,6 +123,7 @@
 full_classes_jack := $(intermediates.COMMON)/classes.jack
 # intermediate Jack library without shrink and obfuscation
 noshrob_classes_jack := $(intermediates.COMMON)/classes.noshrob.jack
+jack_check_timestamp := $(intermediates.COMMON)/jack.check.timestamp
 
 LOCAL_INTERMEDIATE_TARGETS += \
     $(full_classes_compiled_jar) \
@@ -133,6 +134,7 @@
     $(built_dex_intermediate) \
     $(full_classes_jack) \
     $(noshrob_classes_jack) \
+    $(jack_check_timestamp) \
     $(built_dex) \
     $(full_classes_stubs_jar)
 
@@ -330,9 +332,13 @@
 # command line.
 ifndef LOCAL_CHECKED_MODULE
 ifdef full_classes_jar
+ifdef LOCAL_JACK_ENABLED
+LOCAL_CHECKED_MODULE := $(jack_check_timestamp)
+else
 LOCAL_CHECKED_MODULE := $(full_classes_compiled_jar)
 endif
 endif
+endif
 
 #######################################
 include $(BUILD_SYSTEM)/base_rules.mk
@@ -638,9 +644,13 @@
 ifeq ($(LOCAL_JACK_ENABLED),incremental)
 $(LOCAL_INTERMEDIATE_TARGETS): \
 	PRIVATE_JACK_INCREMENTAL_DIR := $(intermediates.COMMON)/jack-incremental
+$(noshrob_classes_jack): PRIVATE_JACK_INCREMENTAL_DIR := $(intermediates.COMMON)/jack-noshrob-incremental
+$(jack_check_timestamp): PRIVATE_JACK_INCREMENTAL_DIR := $(intermediates.COMMON)/jack-check-incremental
 else
 $(LOCAL_INTERMEDIATE_TARGETS): \
 	PRIVATE_JACK_INCREMENTAL_DIR :=
+$(noshrob_classes_jack): PRIVATE_JACK_INCREMENTAL_DIR :=
+$(jack_check_timestamp): PRIVATE_JACK_INCREMENTAL_DIR :=
 endif
 
 ifdef full_classes_jar
@@ -673,6 +683,10 @@
         $(proto_java_sources_file_stamp) $(LOCAL_ADDITIONAL_DEPENDENCIES) $(LOCAL_JARJAR_RULES) \
         $(LOCAL_MODULE_MAKEFILE_DEP) $(JACK)
 
+$(jack_check_timestamp): $(jack_all_deps)
+	@echo Checking build with Jack: $@
+	$(jack-check-java)
+
 ifeq ($(LOCAL_IS_STATIC_JAVA_LIBRARY),true)
 $(full_classes_jack): $(jack_all_deps) | setup-jack-server
 	@echo Building with Jack: $@
@@ -710,11 +724,6 @@
 endif #LOCAL_IS_STATIC_JAVA_LIBRARY
 
 $(noshrob_classes_jack): PRIVATE_JACK_INTERMEDIATES_DIR := $(intermediates.COMMON)/jack-noshrob-rsc
-ifeq ($(LOCAL_JACK_ENABLED),incremental)
-$(noshrob_classes_jack): PRIVATE_JACK_INCREMENTAL_DIR := $(intermediates.COMMON)/jack-noshrob-incremental
-else
-$(noshrob_classes_jack): PRIVATE_JACK_INCREMENTAL_DIR :=
-endif
 $(noshrob_classes_jack): PRIVATE_JACK_PROGUARD_FLAGS :=
 $(noshrob_classes_jack): $(jack_all_deps) | setup-jack-server
 	@echo Building with Jack: $@
diff --git a/core/package_internal.mk b/core/package_internal.mk
index 2ffbcd4..cbe0afe 100644
--- a/core/package_internal.mk
+++ b/core/package_internal.mk
@@ -150,7 +150,7 @@
 my_res_package := $(intermediates)/package-res.apk
 LOCAL_INTERMEDIATE_TARGETS += $(my_res_package)
 
-# Always run aapt2
+# Always run aapt2, because we need to at least compile the AndroidManifest.xml.
 need_compile_res := true
 
 else  # LOCAL_USE_AAPT2
@@ -388,6 +388,7 @@
 endif
 ifneq ($(full_classes_jack),)
 $(full_classes_jack): $(R_file_stamp)
+$(jack_check_timestamp): $(R_file_stamp)
 endif
 endif # LOCAL_JACK_ENABLED
 
diff --git a/core/static_java_library.mk b/core/static_java_library.mk
index 0b521d5..442b99d 100644
--- a/core/static_java_library.mk
+++ b/core/static_java_library.mk
@@ -38,7 +38,14 @@
 # A static Java library needs to explicily set LOCAL_RESOURCE_DIR.
 ifdef LOCAL_RESOURCE_DIR
 need_compile_res := true
+endif
+ifdef LOCAL_USE_AAPT2
+ifneq ($(LOCAL_STATIC_ANDROID_LIBRARIES),)
+need_compile_res := true
+endif
+endif
 
+ifeq ($(need_compile_res),true)
 all_resources := $(strip \
     $(foreach dir, $(LOCAL_RESOURCE_DIR), \
       $(addprefix $(dir)/, \
@@ -162,6 +169,7 @@
 ifdef LOCAL_JACK_ENABLED
 $(noshrob_classes_jack): $(R_file_stamp)
 $(full_classes_jack): $(R_file_stamp)
+$(jack_check_timestamp): $(R_file_stamp)
 endif # LOCAL_JACK_ENABLED
 $(full_classes_compiled_jar): $(R_file_stamp)