Merge "Add a doc about `dex_preopt_check`."

per-file dex_preopt*.* = ngeoffray@google.com,skvadrik@google.com

per-file *dex_preopt*.* = ngeoffray@google.com,skvadrik@google.com

per-file verify_uses_libraries.sh = ngeoffray@google.com,skvadrik@google.com

# For version updates

# `dex_preopt_check`

`dex_preopt_check` is a build-time check to make sure that all system server

jars are dexpreopted. When the check fails, you will see the following error

message:

```

FAILED:

build/make/core/tasks/dex_preopt_check.mk:13: warning:  Missing compilation artifacts. Dexpreopting is not working for some system server jars

Offending entries:

```

Possible causes are:

1.  There is an APEX/SDK mismatch. (E.g., the APEX is built from source while

    the SDK is built from prebuilt.)

1.  The `systemserverclasspath_fragment` is not added as

    `systemserverclasspath_fragments` of the corresponding `apex` module, or not

    added as `exported_systemserverclasspath_fragments` of the corresponding

    `prebuilt_apex`/`apex_set` module when building from prebuilt.

1.  The expected version of the system server java library is not preferred.

    (E.g., the `java_import` module has `prefer: false` when building from

    prebuilt.)

1.  Dexpreopting is disabled for the system server java library. This can be due

    to various reasons including but not limited to:

    - The java library has `dex_preopt: { enabled: false }` in the Android.bp

      file.

    - The java library is listed in `DEXPREOPT_DISABLED_MODULES` in a Makefile.

    - The java library is missing `installable: true` in the Android.bp

      file when building from source.

    - Sanitizer is enabled.

1.  `PRODUCT_SYSTEM_SERVER_JARS`, `PRODUCT_APEX_SYSTEM_SERVER_JARS`,

    `PRODUCT_STANDALONE_SYSTEM_SERVER_JARS`, or

    `PRODUCT_APEX_STANDALONE_SYSTEM_SERVER_JARS` has an extra entry that is not

    needed by the product.

  ifneq (,$(filter services,$(PRODUCT_PACKAGES)))

    $(call maybe-print-list-and-error,\

      $(filter-out $(ALL_DEFAULT_INSTALLED_MODULES),$(DEXPREOPT_SYSTEMSERVER_ARTIFACTS)),\

      Missing compilation artifacts. Dexpreopting is not working for some system server jars \

      Missing compilation artifacts. Dexpreopting is not working for some system server jars. See \

      https://cs.android.com/android/platform/superproject/+/master:build/make/core/tasks/README.dex_preopt_check.md \

    )

  endif

endif