Add new variable TARGET_SHELL := ash (default; or mksh)

Besides that, add enough magic to build everything tagged
as "shell_$(TARGET_SHELL)" and permit ash/mksh as not unusual

Change-Id: I36c0590ba49f45251d24dc179cb27c8368c3662a

core/base_rules.mk

@@ -65,7 +65,7 @@ endif
 # Only the tags mentioned in this test are expected to be set by module
 # makefiles. Anything else is either a typo or a source of unexpected
 # behaviors.
-ifneq ($(filter-out user debug eng tests optional samples,$(LOCAL_MODULE_TAGS)),)
+ifneq ($(filter-out user debug eng tests optional samples shell_ash shell_mksh,$(LOCAL_MODULE_TAGS)),)
 $(warning unusual tags $(LOCAL_MODULE_TAGS) on $(LOCAL_MODULE) at $(LOCAL_PATH))
 endif
 

core/build-system.html

@@ -247,6 +247,7 @@ <h3>Build flavors/types</h3>
         for <code>eng</code>.
         <ul>
         <li>Installs modules tagged with: <code>eng</code>, <code>debug</code>,
+            <code>shell_</code>$(TARGET_SHELL),
             <code>user</code>, and/or <code>development</code>.
         <li>Installs non-APK modules that have no tags specified.
         <li>Installs APKs according to the product definition files, in
@@ -266,7 +267,7 @@ <h3>Build flavors/types</h3>
         <p>
         This is the flavor intended to be the final release bits.
         <ul>
-        <li>Installs modules tagged with <code>user</code>.
+        <li>Installs modules tagged with <code>shell_</code>$(TARGET_SHELL) and <code>user</code>.
         <li>Installs non-APK modules that have no tags specified.
         <li>Installs APKs according to the product definition files; tags
             are ignored for APK modules.
@@ -681,7 +682,8 @@ <h4>LOCAL_C_INCLUDES</h4>
 <h4>LOCAL_MODULE_TAGS</h4>
 <p>Set <code>LOCAL_MODULE_TAGS</code> to any number of whitespace-separated
 tags.  If the tag list is empty or contains <code>droid</code>, the module
-will get installed as part of a <code>make droid</code>.  Otherwise, it will
+will get installed as part of a <code>make droid</code>.  Modules with the tag
+<code>shell_</code>$(TARGET_SHELL) will also be installed. Otherwise, it will
 only get installed by running <code>make &lt;your-module&gt;</code>
 or with the <code>make all</code> pseudotarget.</p>
 

core/config.mk

@@ -105,6 +105,9 @@ TARGET_COMPRESS_MODULE_SYMBOLS := false
 # Default is to prelink modules.
 TARGET_PRELINK_MODULE := true
 
+# Default shell is ash. Other possible value is mksh.
+TARGET_SHELL := ash
+
 # ###############################################################
 # Include sub-configuration files
 # ###############################################################

core/main.mk

@@ -561,7 +561,7 @@ else
 endif
 # Use tags to get the non-APPS user modules.  Use the product
 # definition files to get the APPS user modules.
-user_MODULES := $(sort $(call get-tagged-modules,user))
+user_MODULES := $(sort $(call get-tagged-modules,user shell_$(TARGET_SHELL)))
 user_MODULES := $(user_MODULES) $(user_PACKAGES)
 
 eng_MODULES := $(sort $(call get-tagged-modules,eng))