Fuchsia: Generate depfiles for incremental building of package contents.

Generating a depfile from the manifest building step gives Ninja
the information it needs to trigger incremental rebuilds when static
assets or shared libraries have been modified.

Bug: 839496
Change-Id: I15aee25e8684f9d1fd6a8ad63318cc74639237f0
Reviewed-on: https://chromium-review.googlesource.com/1043047
Commit-Queue: Kevin Marshall <kmarshall@chromium.org>
Reviewed-by: Scott Graham <scottmg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#555887}

build/config/fuchsia/build_manifest.py

@@ -90,10 +90,13 @@ def _IsBinary(path):
 
 
 def BuildManifest(root_dir, out_dir, app_name, app_filename,
-                  sandbox_policy_path, runtime_deps_file, output_path):
-  with open(output_path, 'w') as output:
+                  sandbox_policy_path, runtime_deps_file, depfile_path,
+                  output_path):
+  with open(output_path, 'w') as manifest, open(depfile_path, 'w') as depfile:
     # Process the runtime deps file for file paths, recursively walking
-    # directories as needed.
+    # directories as needed. File paths are stored in absolute form,
+    # so that MakePackagePath() may relativize to either the source root or
+    # output directory.
     # runtime_deps may contain duplicate paths, so use a set for
     # de-duplication.
     expanded_files = set()
@@ -124,14 +127,15 @@ def BuildManifest(root_dir, out_dir, app_name, app_filename,
       # The source path is relativized so that it can be used on multiple
       # environments with differing parent directory structures,
       # e.g. builder bots and swarming clients.
-      output.write('%s=%s\n' % (in_package_path,
-                                os.path.relpath(current_file, out_dir)))
+      manifest.write('%s=%s\n' % (in_package_path,
+                                  os.path.relpath(current_file, out_dir)))
 
       # Use libc.so's dynamic linker by aliasing libc.so to ld.so.1.
       # Fuchsia always looks for the linker implementation in ld.so.1.
       if os.path.basename(in_package_path) == 'libc.so':
-        output.write('%s=%s\n' % (os.path.dirname(in_package_path) + '/ld.so.1',
-                                  os.path.relpath(current_file, out_dir)))
+        manifest.write(
+            '%s=%s\n' % (os.path.dirname(in_package_path) + '/ld.so.1',
+                         os.path.relpath(current_file, out_dir)))
 
     if not app_found:
       raise Exception('Could not locate executable inside runtime_deps.')
@@ -139,12 +143,16 @@ def BuildManifest(root_dir, out_dir, app_name, app_filename,
     with open(os.path.join(os.path.dirname(output_path), 'package'), 'w') \
         as package_json:
       json.dump({'version': '0', 'name': app_name}, package_json)
-      output.write('meta/package=%s\n' %
+      manifest.write('meta/package=%s\n' %
                    os.path.relpath(package_json.name, out_dir))
 
-    output.write('meta/sandbox=%s\n' %
+    manifest.write('meta/sandbox=%s\n' %
                  os.path.relpath(os.path.join(root_dir, sandbox_policy_path),
                                  out_dir))
+    depfile.write(
+        "%s: %s" % (os.path.relpath(output_path, out_dir),
+                    " ".join([os.path.relpath(f, out_dir)
+                              for f in expanded_files])))
 
   return 0
 

build/config/fuchsia/package.gni

@@ -38,6 +38,8 @@ template("package") {
   # Generates a manifest file based on the GN runtime deps
   # suitable for "pm" tool consumption.
   action(_write_manifest_target) {
+    _depfile = "${target_gen_dir}/${target_name}_stamp.d"
+
     forward_variables_from(invoker,
                            [
                              "deps",
@@ -58,6 +60,10 @@ template("package") {
 
     data_deps = pkg.deps
 
+    # Use a depfile to trigger package rebuilds if any of the files (static
+    # assets, shared libraries, etc.) included by the package have changed.
+    depfile = _depfile
+
     # Include the SDK's core dynamic libraries in the package.
     data = [
       dist_libroot,
@@ -71,6 +77,7 @@ template("package") {
       pkg.binary,
       rebase_path(pkg.sandbox_policy),
       rebase_path(_runtime_deps_file),
+      rebase_path(_depfile),
       rebase_path(_manifest_file),
     ]