diff --git a/scripts/construct_context.py b/scripts/construct_context.py
index 3f601c3..fc3a89e 100755
--- a/scripts/construct_context.py
+++ b/scripts/construct_context.py
@@ -19,6 +19,7 @@
 from __future__ import print_function
 
 import argparse
+import json
 import sys
 
 from manifest import compare_version_gt
@@ -33,20 +34,14 @@
         dest='sdk',
         help='specify target SDK version (as it appears in the manifest)')
     parser.add_argument(
-        '--host-context-for-sdk',
-        dest='host_contexts',
-        action='append',
-        nargs=2,
-        metavar=('sdk', 'context'),
-        help='specify context on host for a given SDK version or "any" version')
+        '--context-json',
+        default='',
+        dest='context_json',
+    )
     parser.add_argument(
-        '--target-context-for-sdk',
-        dest='target_contexts',
-        action='append',
-        nargs=2,
-        metavar=('sdk', 'context'),
-        help='specify context on target for a given SDK version or "any" '
-        'version'
+        '--product-packages',
+        default='',
+        dest='product_packages_file',
     )
     return parser.parse_args(args)
 
@@ -55,28 +50,69 @@
 # context regardless of the target SDK version.
 any_sdk = 'any'
 
-
-# We assume that the order of context arguments passed to this script is
-# correct (matches the order computed by package manager). It is possible to
-# sort them here, but Soong needs to use deterministic order anyway, so it can
-# as well use the correct order.
-def construct_context(versioned_contexts, target_sdk):
-    context = []
-    for [sdk, ctx] in versioned_contexts:
-        if sdk == any_sdk or compare_version_gt(sdk, target_sdk):
-            context.append(ctx)
-    return context
+context_sep = '#'
 
 
-def construct_contexts(args):
-    host_context = construct_context(args.host_contexts, args.sdk)
-    target_context = construct_context(args.target_contexts, args.sdk)
-    context_sep = '#'
+def encode_class_loader(context, product_packages):
+    host_sub_contexts, target_sub_contexts = encode_class_loaders(
+            context['Subcontexts'], product_packages)
+
+    return ('PCL[%s]%s' % (context['Host'], host_sub_contexts),
+            'PCL[%s]%s' % (context['Device'], target_sub_contexts))
+
+
+def encode_class_loaders(contexts, product_packages):
+    host_contexts = []
+    target_contexts = []
+
+    for context in contexts:
+        if not context['Optional'] or context['Name'] in product_packages:
+            host_context, target_context = encode_class_loader(
+                    context, product_packages)
+            host_contexts.append(host_context)
+            target_contexts.append(target_context)
+
+    if host_contexts:
+        return ('{%s}' % context_sep.join(host_contexts),
+                '{%s}' % context_sep.join(target_contexts))
+    else:
+        return '', ''
+
+
+def construct_context_args(target_sdk, context_json, product_packages):
+    all_contexts = []
+
+    # CLC for different SDK versions should come in specific order that agrees
+    # with PackageManager. Since PackageManager processes SDK versions in
+    # ascending order and prepends compatibility libraries at the front, the
+    # required order is descending, except for any_sdk that has numerically
+    # the largest order, but must be the last one. Example of correct order:
+    # [30, 29, 28, any_sdk]. There are Python tests to ensure that someone
+    # doesn't change this by accident, but there is no way to guard against
+    # changes in the PackageManager, except for grepping logcat on the first
+    # boot for absence of the following messages:
+    #
+    #   `logcat | grep -E 'ClassLoaderContext [a-z ]+ mismatch`
+
+    for sdk, contexts in sorted(
+            ((sdk, contexts)
+             for sdk, contexts in context_json.items()
+             if sdk != any_sdk and compare_version_gt(sdk, target_sdk)),
+            key=lambda item: int(item[0]), reverse=True):
+        all_contexts += contexts
+
+    if any_sdk in context_json:
+        all_contexts += context_json[any_sdk]
+
+    host_contexts, target_contexts = encode_class_loaders(
+            all_contexts, product_packages)
+
     return (
-        'class_loader_context_arg=--class-loader-context=PCL[]{%s} ; ' %
-        context_sep.join(host_context) +
-        'stored_class_loader_context_arg=--stored-class-loader-context=PCL[]{%s}' #pylint: disable=line-too-long
-        % context_sep.join(target_context))
+        'class_loader_context_arg=--class-loader-context=PCL[]%s ; ' %
+        host_contexts +
+        'stored_class_loader_context_arg='
+        '--stored-class-loader-context=PCL[]%s'
+        % target_contexts)
 
 
 def main():
@@ -85,12 +121,12 @@
         args = parse_args(sys.argv[1:])
         if not args.sdk:
             raise SystemExit('target sdk version is not set')
-        if not args.host_contexts:
-            args.host_contexts = []
-        if not args.target_contexts:
-            args.target_contexts = []
 
-        print(construct_contexts(args))
+        context_json = json.loads(args.context_json)
+        with open(args.product_packages_file, 'r') as f:
+            product_packages = set(line.strip() for line in f if line.strip())
+
+        print(construct_context_args(args.sdk, context_json, product_packages))
 
     # pylint: disable=broad-except
     except Exception as err:
diff --git a/scripts/construct_context_test.py b/scripts/construct_context_test.py
index 2ff5ac5..34a0e16 100755
--- a/scripts/construct_context_test.py
+++ b/scripts/construct_context_test.py
@@ -24,62 +24,249 @@
 sys.dont_write_bytecode = True
 
 
-def construct_contexts(arglist):
-    args = cc.parse_args(arglist)
-    return cc.construct_contexts(args)
+CONTEXT_JSON = {
+    '28': [
+        {
+            'Name': 'z',
+            'Optional': False,
+            'Host': 'out/zdir/z.jar',
+            'Device': '/system/z.jar',
+            'Subcontexts': [],
+        },
+    ],
+    '29': [
+        {
+            'Name': 'x',
+            'Optional': False,
+            'Host': 'out/xdir/x.jar',
+            'Device': '/system/x.jar',
+            'Subcontexts': [],
+        },
+        {
+            'Name': 'y',
+            'Optional': False,
+            'Host': 'out/ydir/y.jar',
+            'Device': '/product/y.jar',
+            'Subcontexts': [],
+        },
+    ],
+    'any': [
+        {
+            'Name': 'a',
+            'Optional': False,
+            'Host': 'out/adir/a.jar',
+            'Device': '/system/a.jar',
+            'Subcontexts': [
+                {  # Not installed optional, being the only child.
+                    'Name': 'a1',
+                    'Optional': True,
+                    'Host': 'out/a1dir/a1.jar',
+                    'Device': '/product/a1.jar',
+                    'Subcontexts': [],
+                },
+            ],
+        },
+        {
+            'Name': 'b',
+            'Optional': True,
+            'Host': 'out/bdir/b.jar',
+            'Device': '/product/b.jar',
+            'Subcontexts': [
+                {  # Not installed but required.
+                    'Name': 'b1',
+                    'Optional': False,
+                    'Host': 'out/b1dir/b1.jar',
+                    'Device': '/product/b1.jar',
+                    'Subcontexts': [],
+                },
+                {  # Installed optional.
+                    'Name': 'b2',
+                    'Optional': True,
+                    'Host': 'out/b2dir/b2.jar',
+                    'Device': '/product/b2.jar',
+                    'Subcontexts': [],
+                },
+                {  # Not installed optional.
+                    'Name': 'b3',
+                    'Optional': True,
+                    'Host': 'out/b3dir/b3.jar',
+                    'Device': '/product/b3.jar',
+                    'Subcontexts': [],
+                },
+                {  # Installed optional with one more level of nested deps.
+                    'Name': 'b4',
+                    'Optional': True,
+                    'Host': 'out/b4dir/b4.jar',
+                    'Device': '/product/b4.jar',
+                    'Subcontexts': [
+                        {
+                            'Name': 'b41',
+                            'Optional': True,
+                            'Host': 'out/b41dir/b41.jar',
+                            'Device': '/product/b41.jar',
+                            'Subcontexts': [],
+                        },
+                        {
+                            'Name': 'b42',
+                            'Optional': True,
+                            'Host': 'out/b42dir/b42.jar',
+                            'Device': '/product/b42.jar',
+                            'Subcontexts': [],
+                        },
+                    ],
+                },
+            ],
+        },
+        {  # Not installed optional, at the top-level.
+            'Name': 'c',
+            'Optional': True,
+            'Host': 'out/cdir/c.jar',
+            'Device': '/product/c.jar',
+            'Subcontexts': [],
+        },
+    ],
+}
 
 
-contexts = [
-    '--host-context-for-sdk',
-    '28',
-    'PCL[out/zdir/z.jar]',
-    '--target-context-for-sdk',
-    '28',
-    'PCL[/system/z.jar]',
-    '--host-context-for-sdk',
-    '29',
-    'PCL[out/xdir/x.jar]#PCL[out/ydir/y.jar]',
-    '--target-context-for-sdk',
-    '29',
-    'PCL[/system/x.jar]#PCL[/product/y.jar]',
-    '--host-context-for-sdk',
-    'any',
-    'PCL[out/adir/a.jar]#PCL[out/bdir/b.jar]',
-    '--target-context-for-sdk',
-    'any',
-    'PCL[/system/a.jar]#PCL[/product/b.jar]',
-]
+PRODUCT_PACKAGES = ['a', 'b', 'b2', 'b4', 'b41', 'b42', 'x', 'y', 'z']
 
-#pylint: disable=line-too-long
+
+def construct_context_args(target_sdk):
+    return cc.construct_context_args(target_sdk, CONTEXT_JSON, PRODUCT_PACKAGES)
+
+
 class ConstructContextTest(unittest.TestCase):
+    def test_construct_context_27(self):
+        actual = construct_context_args('27')
+        # The order matters.
+        expected = (
+            'class_loader_context_arg='
+            '--class-loader-context=PCL[]{'
+            'PCL[out/xdir/x.jar]#'
+            'PCL[out/ydir/y.jar]#'
+            'PCL[out/zdir/z.jar]#'
+            'PCL[out/adir/a.jar]#'
+            'PCL[out/bdir/b.jar]{'
+            'PCL[out/b1dir/b1.jar]#'
+            'PCL[out/b2dir/b2.jar]#'
+            'PCL[out/b4dir/b4.jar]{'
+            'PCL[out/b41dir/b41.jar]#'
+            'PCL[out/b42dir/b42.jar]'
+            '}'
+            '}'
+            '}'
+            ' ; '
+            'stored_class_loader_context_arg='
+            '--stored-class-loader-context=PCL[]{'
+            'PCL[/system/x.jar]#'
+            'PCL[/product/y.jar]#'
+            'PCL[/system/z.jar]#'
+            'PCL[/system/a.jar]#'
+            'PCL[/product/b.jar]{'
+            'PCL[/product/b1.jar]#'
+            'PCL[/product/b2.jar]#'
+            'PCL[/product/b4.jar]{'
+            'PCL[/product/b41.jar]#'
+            'PCL[/product/b42.jar]'
+            '}'
+            '}'
+            '}')
+        self.assertEqual(actual, expected)
 
     def test_construct_context_28(self):
-        args = ['--target-sdk-version', '28'] + contexts
-        result = construct_contexts(args)
-        expect = (
-            'class_loader_context_arg=--class-loader-context=PCL[]{PCL[out/xdir/x.jar]#PCL[out/ydir/y.jar]#PCL[out/adir/a.jar]#PCL[out/bdir/b.jar]}'
+        actual = construct_context_args('28')
+        expected = (
+            'class_loader_context_arg='
+            '--class-loader-context=PCL[]{'
+            'PCL[out/xdir/x.jar]#'
+            'PCL[out/ydir/y.jar]#'
+            'PCL[out/adir/a.jar]#'
+            'PCL[out/bdir/b.jar]{'
+            'PCL[out/b1dir/b1.jar]#'
+            'PCL[out/b2dir/b2.jar]#'
+            'PCL[out/b4dir/b4.jar]{'
+            'PCL[out/b41dir/b41.jar]#'
+            'PCL[out/b42dir/b42.jar]'
+            '}'
+            '}'
+            '}'
             ' ; '
-            'stored_class_loader_context_arg=--stored-class-loader-context=PCL[]{PCL[/system/x.jar]#PCL[/product/y.jar]#PCL[/system/a.jar]#PCL[/product/b.jar]}')
-        self.assertEqual(result, expect)
+            'stored_class_loader_context_arg='
+            '--stored-class-loader-context=PCL[]{'
+            'PCL[/system/x.jar]#'
+            'PCL[/product/y.jar]#'
+            'PCL[/system/a.jar]#'
+            'PCL[/product/b.jar]{'
+            'PCL[/product/b1.jar]#'
+            'PCL[/product/b2.jar]#'
+            'PCL[/product/b4.jar]{'
+            'PCL[/product/b41.jar]#'
+            'PCL[/product/b42.jar]'
+            '}'
+            '}'
+            '}')
+        self.assertEqual(actual, expected)
 
     def test_construct_context_29(self):
-        args = ['--target-sdk-version', '29'] + contexts
-        result = construct_contexts(args)
-        expect = (
-            'class_loader_context_arg=--class-loader-context=PCL[]{PCL[out/adir/a.jar]#PCL[out/bdir/b.jar]}'
+        actual = construct_context_args('29')
+        expected = (
+            'class_loader_context_arg='
+            '--class-loader-context=PCL[]{'
+            'PCL[out/adir/a.jar]#'
+            'PCL[out/bdir/b.jar]{'
+            'PCL[out/b1dir/b1.jar]#'
+            'PCL[out/b2dir/b2.jar]#'
+            'PCL[out/b4dir/b4.jar]{'
+            'PCL[out/b41dir/b41.jar]#'
+            'PCL[out/b42dir/b42.jar]'
+            '}'
+            '}'
+            '}'
             ' ; '
-            'stored_class_loader_context_arg=--stored-class-loader-context=PCL[]{PCL[/system/a.jar]#PCL[/product/b.jar]}')
-        self.assertEqual(result, expect)
+            'stored_class_loader_context_arg='
+            '--stored-class-loader-context=PCL[]{'
+            'PCL[/system/a.jar]#'
+            'PCL[/product/b.jar]{'
+            'PCL[/product/b1.jar]#'
+            'PCL[/product/b2.jar]#'
+            'PCL[/product/b4.jar]{'
+            'PCL[/product/b41.jar]#'
+            'PCL[/product/b42.jar]'
+            '}'
+            '}'
+            '}')
+        self.assertEqual(actual, expected)
 
     def test_construct_context_S(self):
-        args = ['--target-sdk-version', 'S'] + contexts
-        result = construct_contexts(args)
-        expect = (
-            'class_loader_context_arg=--class-loader-context=PCL[]{PCL[out/adir/a.jar]#PCL[out/bdir/b.jar]}'
+        actual = construct_context_args('S')
+        expected = (
+            'class_loader_context_arg='
+            '--class-loader-context=PCL[]{'
+            'PCL[out/adir/a.jar]#'
+            'PCL[out/bdir/b.jar]{'
+            'PCL[out/b1dir/b1.jar]#'
+            'PCL[out/b2dir/b2.jar]#'
+            'PCL[out/b4dir/b4.jar]{'
+            'PCL[out/b41dir/b41.jar]#'
+            'PCL[out/b42dir/b42.jar]'
+            '}'
+            '}'
+            '}'
             ' ; '
-            'stored_class_loader_context_arg=--stored-class-loader-context=PCL[]{PCL[/system/a.jar]#PCL[/product/b.jar]}')
-        self.assertEqual(result, expect)
-#pylint: enable=line-too-long
+            'stored_class_loader_context_arg='
+            '--stored-class-loader-context=PCL[]{'
+            'PCL[/system/a.jar]#'
+            'PCL[/product/b.jar]{'
+            'PCL[/product/b1.jar]#'
+            'PCL[/product/b2.jar]#'
+            'PCL[/product/b4.jar]{'
+            'PCL[/product/b41.jar]#'
+            'PCL[/product/b42.jar]'
+            '}'
+            '}'
+            '}')
+        self.assertEqual(actual, expected)
+
 
 if __name__ == '__main__':
     unittest.main(verbosity=2)