Add "warm" starting to mobile-install.

This introduces a new way to stop applications when deploying incremental
changes that saves the current app state for the next run. This allows things
like the back stack, and View/Fragment/Activity saved state to be restored when
the app next launches, making it easier to quickly iterate on code changes.

It adds a "--start" flag to mobile-install that replaces "--start_app".
--start accepts an argument describing the mode: no, cold, or warm. "no" is
now the equivalent of "--nostart_app", "cold" is the equivalent of
"--start_app", and "warm" is the new start mode.

Note that this is only useful with incremental installs, as Android clears out
any previously saved state when an APK is replaced.

--
MOS_MIGRATED_REVID=99508790

2 files changed, 45 insertions, 5 deletions

diff --git a/src/main/java/com/google/devtools/build/lib/rules/android/WriteAdbArgsAction.java b/src/main/java/com/google/devtools/build/lib/rules/android/WriteAdbArgsAction.java
index 41b2111ed4..8f5c677029 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/android/WriteAdbArgsAction.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/android/WriteAdbArgsAction.java
@@ -21,6 +21,7 @@ import com.google.devtools.build.lib.actions.Executor;
 import com.google.devtools.build.lib.analysis.actions.AbstractFileWriteAction;
 import com.google.devtools.build.lib.events.EventHandler;
 import com.google.devtools.build.lib.util.Fingerprint;
+import com.google.devtools.common.options.EnumConverter;
 import com.google.devtools.common.options.Option;
 import com.google.devtools.common.options.OptionsBase;
 
@@ -67,11 +68,20 @@ public class WriteAdbArgsAction extends AbstractFileWriteAction {
         help = "The verbosity for incremental install. Set to 1 for debug logging.")
     public String incrementalInstallVerbosity;
 
+    @Option(name = "start",
+        category = "mobile-install",
+        converter = StartTypeConverter.class,
+        defaultValue = "NO",
+        help = "How the app should be started after installing it. Set to WARM to preserve "
+            + "and restore application state on incremental installs.")
+    public StartType start;
+
     @Option(name = "start_app",
         category = "mobile-install",
-        defaultValue = "false",
-        help = "Whether to start the app after installing it.")
-    public boolean startApp;
+        defaultValue = "null",
+        help = "Whether to start the app after installing it.",
+        expansion = {"--start=COLD"})
+    public Void startApp;
   }
 
   public WriteAdbArgsAction(ActionOwner owner, Artifact outputFile) {
@@ -86,7 +96,7 @@ public class WriteAdbArgsAction extends AbstractFileWriteAction {
     final String adb = options.adb;
     final int adbJobs = options.adbJobs;
     final String incrementalInstallVerbosity = options.incrementalInstallVerbosity;
-    final boolean startApp = options.startApp;
+    final StartType start = options.start;
     final String userHomeDirectory = executor.getContext(
         WriteAdbArgsActionContext.class).getUserHomeDirectory();
 
@@ -109,7 +119,8 @@ public class WriteAdbArgsAction extends AbstractFileWriteAction {
           ps.printf("--verbosity=%s\n", incrementalInstallVerbosity);
         }
 
-        ps.printf("--start_app=%s\n", startApp);
+        ps.printf("--start=%s\n", start.name().toLowerCase());
+
 
         if (userHomeDirectory != null) {
           ps.printf("--user_home_dir=%s\n", userHomeDirectory);
@@ -140,4 +151,24 @@ public class WriteAdbArgsAction extends AbstractFileWriteAction {
         .addString(GUID)
         .hexDigestAndReset();
   }
+
+  /** Specifies how the app should be started/stopped. */
+  public enum StartType {
+    /** The app will not be restarted after install. */
+    NO,
+    /** The app will be restarted from a clean state after install. */
+    COLD,
+    /**
+     * The app will save its state before installing, and be restored from that state after
+     * installing.
+     */
+    WARM
+  }
+
+  /** Converter for the --start option. */
+  public static class StartTypeConverter extends EnumConverter<StartType> {
+    public StartTypeConverter() {
+      super(StartType.class, "start type");
+    }
+  }
 }
diff --git a/src/main/java/com/google/devtools/build/lib/runtime/commands/MobileInstallCommand.java b/src/main/java/com/google/devtools/build/lib/runtime/commands/MobileInstallCommand.java
index b68adb859e..13e2837dff 100644
--- a/src/main/java/com/google/devtools/build/lib/runtime/commands/MobileInstallCommand.java
+++ b/src/main/java/com/google/devtools/build/lib/runtime/commands/MobileInstallCommand.java
@@ -16,7 +16,9 @@ package com.google.devtools.build.lib.runtime.commands;
 import com.google.common.collect.ImmutableList;
 import com.google.devtools.build.lib.analysis.OutputGroupProvider;
 import com.google.devtools.build.lib.buildtool.BuildRequest;
+import com.google.devtools.build.lib.events.Event;
 import com.google.devtools.build.lib.rules.android.WriteAdbArgsAction;
+import com.google.devtools.build.lib.rules.android.WriteAdbArgsAction.StartType;
 import com.google.devtools.build.lib.runtime.BlazeCommand;
 import com.google.devtools.build.lib.runtime.BlazeRuntime;
 import com.google.devtools.build.lib.runtime.Command;
@@ -64,6 +66,13 @@ public class MobileInstallCommand implements BlazeCommand {
 
   @Override
   public ExitCode exec(BlazeRuntime runtime, OptionsProvider options) {
+    Options mobileInstallOptions = options.getOptions(Options.class);
+    WriteAdbArgsAction.Options adbOptions = options.getOptions(WriteAdbArgsAction.Options.class);
+    if (adbOptions.start == StartType.WARM && !mobileInstallOptions.incremental) {
+      runtime.getReporter().handle(Event.warn(
+         "Warm start is enabled, but will have no effect on a non-incremental build"));
+    }
+
     List<String> targets = ProjectFileSupport.getTargets(runtime, options);
     BuildRequest request = BuildRequest.create(
         this.getClass().getAnnotation(Command.class).name(), options,