Parse project language and use in infra/helper.py (#3834)

* Parse project language and use in infra/helper.py

* Fix exception message.

infra/helper.py

@@ -56,6 +56,8 @@
     'gs://{project_name}-backup.clusterfuzz-external.appspot.com/corpus/'
     'libFuzzer/{fuzz_target}/')
 
+PROJECT_LANGUAGE_REGEX = re.compile(r'\s*language\s*:\s*([^\s]+)')
+
 
 def main():  # pylint: disable=too-many-branches,too-many-return-statements,too-many-statements
   """Get subcommand from program arguments and do it."""
@@ -284,6 +286,20 @@ def _get_work_dir(project_name=''):
   return os.path.join(BUILD_DIR, 'work', project_name)
 
 
+def _get_project_language(project_name):
+  """Returns project language."""
+  project_yaml_path = os.path.join(OSS_FUZZ_DIR, 'projects', project_name,
+                                   'project.yaml')
+  with open(project_yaml_path) as file_handle:
+    content = file_handle.read()
+    for line in content.splitlines():
+      match = PROJECT_LANGUAGE_REGEX.match(line)
+      if match:
+        return match.group(1)
+
+  raise Exception('language attribute not found in project.yaml.')
+
+
 def _add_architecture_args(parser, choices=('x86_64', 'i386')):
   """Add common architecture args."""
   parser.add_argument('--architecture', default='x86_64', choices=choices)
@@ -449,7 +465,7 @@ def build_image(args):
   return 1
 
 
-def build_fuzzers_impl(  # pylint: disable=too-many-arguments
+def build_fuzzers_impl(  # pylint: disable=too-many-arguments,too-many-locals
     project_name,
     clean,
     engine,
@@ -465,6 +481,7 @@ def build_fuzzers_impl(  # pylint: disable=too-many-arguments
 
   project_out_dir = _get_output_dir(project_name)
   project_work_dir = _get_work_dir(project_name)
+  project_language = _get_project_language(project_name)
 
   if clean:
     print('Cleaning existing build artifacts.')
@@ -486,7 +503,7 @@ def build_fuzzers_impl(  # pylint: disable=too-many-arguments
     print('Keeping existing build artifacts as-is (if any).')
   env = [
       'FUZZING_ENGINE=' + engine,
-      'FUZZING_LANGUAGE=c++',  # TODO: Replace with actual language.
+      'FUZZING_LANGUAGE=' + project_language,
       'SANITIZER=' + sanitizer,
       'ARCHITECTURE=' + architecture,
   ]