mainline_modules_sdks.py: Optimize snapshot build order

Previously, the snapshots would be built in the order in which the
build releases were defined. This change groups the snapshots with the
same build environment and builds them in sequence in order to minimize
the regeneration of the ninja files.

The test revealed that the produce_bundled_dist_for_build_release
method would call build_snapshots even if there were no bundled
snapshots needed which was a waste so that was also optimized as part
of this change.

Test: atest --host mainline_modules_sdks_test
      packages/modules/common/build/mainline_modules_sdks.sh
      pyformat -s 4 --force_quote_type double -i build/mainline_modules_sdks*.py
      /usr/bin/pylint --rcfile $ANDROID_BUILD_TOP/tools/repohooks/tools/pylintrc build/mainline_modules_sdks*.py
Change-Id: I5bb8d864a50318b4b5390a8e5a3601aa33c18fef

build/mainline_modules_sdks.py

@@ -28,6 +28,7 @@ import subprocess
 import sys
 import tempfile
 import typing
+from collections import defaultdict
 from typing import Callable, List
 import zipfile
 
@@ -848,7 +849,14 @@ class SdkDistProducer:
         # Prepare the dist directory for the sdks.
         self.prepare()
 
+        # Group build releases so that those with the same Soong environment are
+        # run consecutively to avoid having to regenerate ninja files.
+        grouped_by_env = defaultdict(list)
         for build_release in build_releases:
+            grouped_by_env[str(build_release.soong_env)].append(build_release)
+        ordered = [br for _, group in grouped_by_env.items() for br in group]
+
+        for build_release in ordered:
             # Only build modules that are required for this build release.
             filtered_modules = [
                 m for m in modules if m.is_required_for(build_release)
@@ -883,11 +891,11 @@ class SdkDistProducer:
 
     def produce_bundled_dist_for_build_release(self, build_release, modules):
         modules = [m for m in modules if m.is_bundled()]
-        sdk_versions = build_release.sdk_versions
+        if modules:
-        snapshots_dir = self.snapshot_builder.build_snapshots(
+            sdk_versions = build_release.sdk_versions
-            build_release, sdk_versions, modules)
+            snapshots_dir = self.snapshot_builder.build_snapshots(
-        self.populate_bundled_dist(build_release, modules, snapshots_dir)
+                build_release, sdk_versions, modules)
-        return snapshots_dir
+            self.populate_bundled_dist(build_release, modules, snapshots_dir)
 
     def populate_unbundled_dist(self, build_release, sdk_versions, modules,
                                 snapshots_dir):

build/mainline_modules_sdks_test.py

@@ -300,17 +300,6 @@ class TestProduceDist(unittest.TestCase):
                 ["current"],
                 ["com.android.ipsec", "com.google.android.wifi"],
             ),
-            (
-                "S",
-                {
-                    "SOONG_SDK_SNAPSHOT_TARGET_BUILD_RELEASE": "S"
-                },
-                ["current"],
-                [
-                    "com.android.art", "com.android.ipsec",
-                    "com.google.android.wifi"
-                ],
-            ),
             (
                 "latest",
                 {},
@@ -320,7 +309,6 @@ class TestProduceDist(unittest.TestCase):
                     "com.google.android.wifi"
                 ],
             ),
-            ('latest', {}, ['current'], []),
             (
                 "legacy",
                 {},
@@ -330,6 +318,17 @@ class TestProduceDist(unittest.TestCase):
                     "com.google.android.wifi"
                 ],
             ),
+            (
+                "S",
+                {
+                    "SOONG_SDK_SNAPSHOT_TARGET_BUILD_RELEASE": "S"
+                },
+                ["current"],
+                [
+                    "com.android.art", "com.android.ipsec",
+                    "com.google.android.wifi"
+                ],
+            ),
         ], snapshot_builder.snapshots)