Handle import statements in args.gn files

Did you know that args.gn files can have import statements and
conditionals? I did not, but apparently some developers make use of both
of these.

Supporting import statements is not too hard, so this change adds this
support. Supporting conditionals is possible, but risks turning
autoninja into a turing complete language which is more than I think we
want to do.

This doesn't use the similar code in tools/mb/mb.py because that
code is complex, and relies on the script location to find the src
directory.

This change also updates two of the existing test conditionals that
were not quite sufficient - ninja/autoninja default to num-cores
plus 2 so > cpu_count() is actually not sufficient to prove
anything.

Bug: 1482404
Change-Id: I0539d8068af59d11927cbdad260278a24ab912e6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/4864898
Reviewed-by: Takuto Ikuta <tikuta@chromium.org>
Commit-Queue: Bruce Dawson <brucedawson@chromium.org>

autoninja.py

@@ -8,6 +8,10 @@ whether a build is accelerated using a service like goma. If so, it runs with a
 large -j value, and otherwise it chooses a small one. This auto-adjustment
 makes using remote build acceleration simpler and safer, and avoids errors that
 can cause slow goma builds or swap-storms on unaccelerated builds.
+
+autoninja tries to detect relevant build settings such as use_remoteexec, and it
+does handle import statements, but it can't handle conditional setting of build
+settings.
 """
 
 import multiprocessing
@@ -23,6 +27,25 @@ if sys.platform in ['darwin', 'linux']:
 SCRIPT_DIR = os.path.dirname(os.path.realpath(__file__))
 
 
+def _gn_lines(output_dir, path):
+    """
+    Generator function that returns args.gn lines one at a time, following
+    import directives as needed.
+    """
+    import_re = re.compile(r'\s*import\("(.*)"\)')
+    with open(path, encoding='utf-8') as f:
+        for line in f:
+            match = import_re.match(line)
+            if match:
+                import_path = os.path.normpath(
+                    os.path.join(output_dir, '..', '..',
+                                 match.groups()[0][2:]))
+                for import_line in _gn_lines(output_dir, import_path):
+                    yield import_line
+            else:
+                yield line
+
+
 def main(args):
     # The -t tools are incompatible with -j
     t_specified = False
@@ -71,8 +94,7 @@ def main(args):
     # builds, where we look for args.gn in the build tree, and cmake-based
     # builds where we look for rules.ninja.
     if os.path.exists(os.path.join(output_dir, 'args.gn')):
-        with open(os.path.join(output_dir, 'args.gn')) as file_handle:
-            for line in file_handle:
+        for line in _gn_lines(output_dir, os.path.join(output_dir, 'args.gn')):
             # use_goma, use_remoteexec, or use_rbe will activate build
             # acceleration.
             #
@@ -130,7 +152,7 @@ def main(args):
         ]:
             path = os.path.join(output_dir, relative_path, 'rules.ninja')
             if os.path.exists(path):
-                with open(path) as file_handle:
+                with open(path, encoding='utf-8') as file_handle:
                     for line in file_handle:
                         if re.match(r'^\s*command\s*=\s*\S+gomacc', line):
                             use_goma = True

tests/autoninja_test.py

@@ -57,7 +57,7 @@ class AutoninjaTest(trial_dir.TestCase):
 
         self.assertIn('-j', args)
         parallel_j = int(args[args.index('-j') + 1])
-        self.assertGreater(parallel_j, multiprocessing.cpu_count())
+        self.assertGreater(parallel_j, multiprocessing.cpu_count() * 2)
         self.assertIn(os.path.join(autoninja.SCRIPT_DIR, 'ninja.py'), args)
 
     def test_autoninja_reclient(self):
@@ -73,7 +73,30 @@ class AutoninjaTest(trial_dir.TestCase):
 
         self.assertIn('-j', args)
         parallel_j = int(args[args.index('-j') + 1])
-        self.assertGreater(parallel_j, multiprocessing.cpu_count())
+        self.assertGreater(parallel_j, multiprocessing.cpu_count() * 2)
+        self.assertIn(os.path.join(autoninja.SCRIPT_DIR, 'ninja_reclient.py'),
+                      args)
+
+    def test_autoninja_import(self):
+        out_dir = os.path.join('out', 'dir')
+        # Make sure nested import directives work. This is based on the
+        # reclient test.
+        write(os.path.join(out_dir, 'args.gn'), 'import("//out/common.gni")')
+        write(os.path.join('out', 'common.gni'), 'import("//out/common_2.gni")')
+        # The test will only pass if both imports work and
+        # 'use_remoteexec=true' is seen.
+        write(os.path.join('out', 'common_2.gni'), 'use_remoteexec=true')
+        write('.gclient', '')
+        write('.gclient_entries', 'entries = {"buildtools": "..."}')
+        write(os.path.join('buildtools', 'reclient_cfgs', 'reproxy.cfg'),
+              'RBE_v=2')
+        write(os.path.join('buildtools', 'reclient', 'version.txt'), '0.0')
+
+        args = autoninja.main(['autoninja.py', '-C', out_dir]).split()
+
+        self.assertIn('-j', args)
+        parallel_j = int(args[args.index('-j') + 1])
+        self.assertGreater(parallel_j, multiprocessing.cpu_count() * 2)
         self.assertIn(os.path.join(autoninja.SCRIPT_DIR, 'ninja_reclient.py'),
                       args)