Bug 1485793 - [eslint] Don't print an error message if there aren't any files to lint, r=Standard8

This case is expected in the mozlint world (e.g, when running all linters).
This will still print a warning, just a far less scary one and will still
return 0. There is a case to be made that we should silently ignore this as no
other linters print this warning, but it's useful enough to warrant keeping.

Differential Revision: https://phabricator.services.mozilla.com/D37414

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

tools/lint/eslint/__init__.py

@@ -6,6 +6,7 @@
 
 import json
 import os
+import re
 import signal
 import sys
 sys.path.append(os.path.join(os.path.dirname(__file__), "eslint"))
@@ -97,7 +98,12 @@ def lint(paths, config, binary=None, fix=None, setup=None, **lintargs):
     try:
         jsonresult = json.loads(proc.output[0])
     except ValueError:
-        print(ESLINT_ERROR_MESSAGE.format("\n".join(proc.output)))
+        output = "\n".join(proc.output)
+        if re.search(r'No files matching the pattern "(.*)" were found.', output):
+            print("warning: no files to lint (eslint)")
+            return []
+
+        print(ESLINT_ERROR_MESSAGE.format(output))
         return 1
 
     results = []

tools/lint/test/test_eslint.py

@@ -11,5 +11,10 @@ def test_lint_with_global_exclude(lint, config, paths):
     assert len(results) == 0
 
 
+def test_no_files_to_lint(lint, config, paths):
+    ret = lint(paths('nolint'), root=build.topsrcdir)
+    assert ret == []
+
+
 if __name__ == '__main__':
     mozunit.main()