Merge "Add a doc about dex_preopt_check."

core/OWNERS

@@ -1,4 +1,4 @@
-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

core/tasks/README.dex_preopt_check.md

@@ -0,0 +1,43 @@
+# `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.

core/tasks/dex_preopt_check.mk

@@ -12,7 +12,8 @@ ifneq (true,$(DISABLE_DEXPREOPT_CHECK))
   ifneq (,$(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