Bug 1623862 - Properly handle errors when the ESLint process fails. r=ahal

In the failure case, errors has value, but output doesn't. So previously we were printing the errors but returning success to the lint handler.

Differential Revision: https://phabricator.services.mozilla.com/D67670

--HG--
extra : moz-landing-system : lando

tools/lint/eslint/__init__.py

@@ -102,7 +102,10 @@ def lint(paths, config, binary=None, fix=None, setup=None, **lintargs):
 
     if errors:
         errors = errors.decode(encoding, "replace")
-        print(errors)
+        print(ESLINT_ERROR_MESSAGE.format(errors))
+
+    if proc.returncode >= 2:
+        return 1
 
     if not output:
         return []  # no output means success

tools/lint/test/files/eslint/import/bad_import.js

@@ -0,0 +1 @@
+/* import-globals-from notpresent/notpresent.js */

tools/lint/test/test_eslint.py

@@ -6,7 +6,7 @@ LINTER = 'eslint'
 
 
 def test_lint_with_global_exclude(lint, config, paths):
-    config['exclude'] = ['subdir']
+    config['exclude'] = ['subdir', 'import']
     results = lint(paths(), config=config, root=build.topsrcdir)
     assert len(results) == 0
 
@@ -21,5 +21,10 @@ def test_no_files_to_lint(lint, config, paths):
     assert len(results) == 1
 
 
+def test_bad_import(lint, config, paths):
+    results = lint(paths('import'), config=config, root=build.topsrcdir)
+    assert results == 1
+
+
 if __name__ == '__main__':
     mozunit.main()