lesson-check.py: read config.yml only once

1. Read `config.yml` file only once and store the contents in a global
   variable `CONFIG`. We're currently reading this file twice.
2. Detect lesson life cycle in `main` instead of making `check_config`
   return it.
3. Replace `using_remote_theme` function with a single test that checks
   that `remote_theme` keyword is present in `_config.yml`
4. CheckEpisode class: `check` method: move "remote theme test" inside the `check_reference_inclusion`.
5. main: mvoe "remote theme test" inside the `read_references`

bin/lesson_check.py

@@ -9,7 +9,7 @@
 import sys
 from argparse import ArgumentParser
 
-# This uses the `__all__` list in `util.py` to determine what objects to import 
+# This uses the `__all__` list in `util.py` to determine what objects to import
 # see https://docs.python.org/3/tutorial/modules.html#importing-from-a-package
 from util import *
 from reporter import Reporter
@@ -119,21 +119,29 @@
 # Please keep this in sync with .editorconfig!
 MAX_LINE_LEN = 100
 
+# Contents of _config.yml
+CONFIG = {}
 
 def main():
     """Main driver."""
 
     args = parse_args()
     args.reporter = Reporter()
-    life_cycle = check_config(args.reporter, args.source_dir)
+
+    global CONFIG
+    config_file = os.path.join(args.source_dir, '_config.yml')
+    CONFIG = load_yaml(config_file)
+    CONFIG["config_file"] = config_file
+
+    life_cycle = CONFIG.get('life_cycle', None)
     # pre-alpha lessons should report without error
     if life_cycle == "pre-alpha":
         args.permissive = True
+
+    check_config(args.reporter)
     check_source_rmd(args.reporter, args.source_dir, args.parser)
 
-    args.references = {}
-    if not using_remote_theme(args.source_dir):
-        args.references = read_references(args.reporter, args.reference_path)
+    args.references = read_references(args.reporter, args.reference_path)
 
     docs = read_all_markdown(args.source_dir, args.parser)
     check_fileset(args.source_dir, args.reporter, list(docs.keys()))
@@ -196,22 +204,15 @@ def parse_args():
 
     return args
 
-def using_remote_theme(source_dir):
-    config_file = os.path.join(source_dir, '_config.yml')
-    config = load_yaml(config_file)
-    return 'remote_theme' in config
-
-def check_config(reporter, source_dir):
+def check_config(reporter):
     """Check configuration file."""
 
-    config_file = os.path.join(source_dir, '_config.yml')
-    config = load_yaml(config_file)
-    reporter.check_field(config_file, 'configuration',
-                         config, 'kind', 'lesson')
-    reporter.check_field(config_file, 'configuration',
-                         config, 'carpentry', ('swc', 'dc', 'lc', 'cp', 'incubator'))
-    reporter.check_field(config_file, 'configuration', config, 'title')
-    reporter.check_field(config_file, 'configuration', config, 'email')
+    reporter.check_field(CONFIG["config_file"], 'configuration',
+                         CONFIG, 'kind', 'lesson')
+    reporter.check_field(CONFIG["config_file"], 'configuration',
+                         CONFIG, 'carpentry', ('swc', 'dc', 'lc', 'cp', 'incubator'))
+    reporter.check_field(CONFIG["config_file"], 'configuration', CONFIG, 'title')
+    reporter.check_field(CONFIG["config_file"], 'configuration', CONFIG, 'email')
 
     for defaults in [
             {'values': {'root': '.', 'layout': 'page'}},
@@ -223,13 +224,9 @@ def check_config(reporter, source_dir):
         layout = defaults["values"]["layout"]
         error_message = error_text.format(root, layout)
 
-        defaults_test = defaults in config.get('defaults', [])
+        defaults_test = defaults in CONFIG.get('defaults', [])
         reporter.check(defaults_test, 'configuration', error_message)
 
-    if 'life_cycle' not in config:
-        config['life_cycle'] = None
-    return config['life_cycle']
-
 def check_source_rmd(reporter, source_dir, parser):
     """Check that Rmd episode files include `source: Rmd`"""
 
@@ -249,6 +246,9 @@ def read_references(reporter, ref_path):
     {symbolic_name : URL}
     """
 
+    if 'remote_theme' in CONFIG:
+        return {}
+
     if not ref_path:
         raise Warning("No filename has been provided.")
 
@@ -548,8 +548,7 @@ def check(self):
         """Run extra tests."""
 
         super().check()
-        if not using_remote_theme(self.args.source_dir):
-            self.check_reference_inclusion()
+        self.check_reference_inclusion()
 
     def check_metadata(self):
         super().check_metadata()
@@ -579,6 +578,9 @@ def check_metadata_fields(self, expected):
     def check_reference_inclusion(self):
         """Check that links file has been included."""
 
+        if 'remote_theme' in CONFIG:
+            return
+
         if not self.args.reference_path:
             return