From 47ed450cf1c0233f845102502b4ecd1a98954c97 Mon Sep 17 00:00:00 2001
From: Marc Wouts <marc.wouts@gmail.com>
Date: Thu, 31 Oct 2019 00:21:05 +0100
Subject: [PATCH] Determine the auto extension from jupytext.mainlanguage

when available
---
 jupytext/formats.py |  6 +++---
 tests/test_cli.py   | 14 --------------
 2 files changed, 3 insertions(+), 17 deletions(-)

diff --git a/jupytext/formats.py b/jupytext/formats.py
index f28494ce4..7e0c09b2c 100644
--- a/jupytext/formats.py
+++ b/jupytext/formats.py
@@ -567,10 +567,10 @@ def auto_ext_from_metadata(metadata):
     auto_ext = metadata.get('language_info', {}).get('file_extension')
 
     if auto_ext is None:
-        kernel_language = metadata.get('kernelspec', {}).get('language')
-        if kernel_language:
+        language = metadata.get('kernelspec', {}).get('language') or metadata.get('jupytext', {}).get('main_language')
+        if language:
             for ext in _SCRIPT_EXTENSIONS:
-                if same_language(kernel_language, _SCRIPT_EXTENSIONS[ext]['language']):
+                if same_language(language, _SCRIPT_EXTENSIONS[ext]['language']):
                     auto_ext = ext
                     break
 
diff --git a/tests/test_cli.py b/tests/test_cli.py
index c2052b47b..c2440aa73 100644
--- a/tests/test_cli.py
+++ b/tests/test_cli.py
@@ -990,17 +990,3 @@ def test_339_require_to(tmpdir):
 
     with pytest.raises(ValueError, match='--to'):
         jupytext([tmp_py, '--test-strict'])
-
-
-@requires_black
-def test_detailed_message_missing_language_info(tmpdir):
-    text = """```python
-1 + 1
-```
-"""
-    tmp_md = str(tmpdir.join('test.md'))
-    with open(tmp_md, 'w') as fp:
-        fp.write(text)
-
-    with pytest.raises(ValueError, match='--pipe-fmt'):
-        jupytext([tmp_md, '--pipe', 'black'])