[infra][docs] Be more explicit about code coverage being supported for C/C++ only (#4284). (#4303)

* [infra][docs] Be more explicit about code coverage being supported for C/C++ only (#4284).

* fix typos and pass env variable

2 files changed, 18 insertions, 4 deletions

diff --git a/docs/advanced-topics/code_coverage.md b/docs/advanced-topics/code_coverage.md
index 6e56c402..3b0acc26 100644
--- a/docs/advanced-topics/code_coverage.md
+++ b/docs/advanced-topics/code_coverage.md
@@ -9,9 +9,11 @@ permalink: /advanced-topics/code-coverage/
 # Code Coverage
 {: .no_toc}
 
-You can generate code coverage reports for your project using Clang source-based
-code coverage. This page walks you through the basic steps. For more details,
-see [Clang's documentation].
+For projects written in C/C++, you can generate code coverage reports using
+Clang source-based code coverage. This page walks you through the basic steps.
+For more details, see [Clang's documentation].
+
+Code coverage reports generation for other languages is not supported yet.
 
 - TOC
 {:toc}
@@ -124,4 +126,4 @@ coverage_extra_args: -ignore-filename-regex=.*crc.* -ignore-filename-regex=.*adl
 
 [Clang's documentation]: https://clang.llvm.org/docs/SourceBasedCodeCoverage.html
 [gsutil tool]: https://cloud.google.com/storage/docs/gsutil_install
-[llvm-cov tool]: https://llvm.org/docs/CommandGuide/llvm-cov.html
\ No newline at end of file
+[llvm-cov tool]: https://llvm.org/docs/CommandGuide/llvm-cov.html
diff --git a/infra/helper.py b/infra/helper.py
index b1266c28..99d87112 100755
--- a/infra/helper.py
+++ b/infra/helper.py
@@ -58,6 +58,9 @@ CORPUS_BACKUP_URL_FORMAT = (
 
 PROJECT_LANGUAGE_REGEX = re.compile(r'\s*language\s*:\s*([^\s]+)')
 
+# Languages from project.yaml that have code coverage support.
+LANGUAGES_WITH_COVERAGE_SUPPORT = ['c', 'c++']
+
 
 def main():  # pylint: disable=too-many-branches,too-many-return-statements,too-many-statements
   """Get subcommand from program arguments and do it."""
@@ -727,12 +730,21 @@ def coverage(args):
   if not check_project_exists(args.project_name):
     return 1
 
+  project_language = _get_project_language(args.project_name)
+  if project_language not in LANGUAGES_WITH_COVERAGE_SUPPORT:
+    print(
+        'ERROR: Project is written in %s, coverage for it is not supported yet.'
+        % project_language,
+        file=sys.stderr)
+    return 1
+
   if not args.no_corpus_download and not args.corpus_dir:
     if not download_corpora(args):
       return 1
 
   env = [
       'FUZZING_ENGINE=libfuzzer',
+      'FUZZING_LANGUAGE=%s' % project_language,
       'PROJECT=%s' % args.project_name,
       'SANITIZER=coverage',
       'HTTP_PORT=%s' % args.port,