platform_build/Changes.md

Build System Changes for Android.mk Writers

Deprecating / obsoleting envsetup.sh variables in Makefiles

It is not required to source envsetup.sh before running a build. Many scripts, including a majority of our automated build systems, do not do so. Make will transparently make every environment variable available as a make variable. This means that relying on environment variables only set up in envsetup.sh will produce different output for local users and scripted users.

Many of these variables also include absolute path names, which we'd like to keep out of the generated files, so that you don't need to do a full rebuild if you move the source tree.

To fix this, we're marking the variables that are set in envsetup.sh as deprecated in the makefiles. This will trigger a warning every time one is read (or written) inside Kati. Once all the warnings have been removed for a particular variable, we'll switch it to obsolete, and any references will become errors.

envsetup.sh variables with make equivalents

instead of	use
OUT {#OUT}	OUT_DIR
ANDROID_HOST_OUT {#ANDROID_HOST_OUT}	HOST_OUT
ANDROID_PRODUCT_OUT {#ANDROID_PRODUCT_OUT}	PRODUCT_OUT
ANDROID_HOST_OUT_TESTCASES {#ANDROID_HOST_OUT_TESTCASES}	HOST_OUT_TESTCASES
ANDROID_TARGET_OUT_TESTCASES {#ANDROID_TARGET_OUT_TESTCASES}	TARGET_OUT_TESTCASES

All of the make variables may be relative paths from the current directory, or absolute paths if the output directory was specified as an absolute path. If you need an absolute variable, convert it to absolute during a rule, so that it's not expanded into the generated ninja file:

$(PRODUCT_OUT)/gen.img: my/src/path/gen.sh
	export PRODUCT_OUT=$$(cd $(PRODUCT_OUT); pwd); cd my/src/path; ./gen.sh -o $${PRODUCT_OUT}/gen.img

ANDROID_BUILD_TOP

In Android.mk files, you can always assume that the current directory is the root of the source tree, so this can just be replaced with '.' (which is what $TOP is hardcoded to), or removed entirely. If you need an absolute path, see the instructions above.

Stop using PATH directly

This isn't only set by envsetup.sh, but it is modified by it. Due to that it's rather easy for this to change between different shells, and it's not ideal to reread the makefiles every time this changes.

In most cases, you shouldn't need to touch PATH at all. When you need to have a rule reference a particular binary that's part of the source tree or outputs, it's preferrable to just use the path to the file itself (since you should already be adding that as a dependency).

Depending on the rule, passing the file path itself may not be feasible due to layers of unchangable scripts/binaries. In that case, be sure to add the dependency, but modify the PATH within the rule itself:

$(TARGET): myscript my/path/binary
	PATH=my/path:$$PATH myscript -o $@

Stop using PYTHONPATH directly

Like PATH, this isn't only set by envsetup.sh, but it is modified by it. Due to that it's rather easy for this to change between different shells, and it's not ideal to reread the makefiles every time.

The best solution here is to start switching to Soong's python building support, which packages the python interpreter, libraries, and script all into one file that no longer needs PYTHONPATH. See fontchain_lint for examples of this:

• external/fonttools/Lib/fontTools/Android.bp for python_library_host
• frameworks/base/Android.bp for python_binary_host
• frameworks/base/data/fonts/Android.mk to execute the python binary

If you still need to use PYTHONPATH, do so within the rule itself, just like path:

$(TARGET): myscript.py $(sort $(shell find my/python/lib -name '*.py'))
	PYTHONPATH=my/python/lib:$$PYTHONPATH myscript.py -o $@

Other envsetup.sh variables

• ANDROID_TOOLCHAIN
• ANDROID_TOOLCHAIN_2ND_ARCH
• ANDROID_DEV_SCRIPTS
• ANDROID_EMULATOR_PREBUILTS
• ANDROID_PRE_BUILD_PATHS

These are all exported from envsetup.sh, but don't have clear equivalents within the makefile system. If you need one of them, you'll have to set up your own version.