Update check.py to check formatting, etc

Author: ongardie

README.md

@@ -16,6 +16,10 @@ you want to run it locally, you'll need the
 pip3 install jsonschema
 ```
 
+You can use a Python virtual environment if you are unable to or don't want to
+install jsonschema globally. See <https://docs.python.org/3/tutorial/venv.html>
+for instructions.
+
 The website is hosted as a GitHub static page at <https://raft.github.io>. To
 run it locally, make sure you've checked out all the submodules:
 ```

check.py

@@ -1,22 +1,47 @@
 #!/usr/bin/env python3
 
+import difflib
 import json
 import jsonschema
+import sys
 
 schema = json.load(open('implementation.schema.json'))
 
+errors = []
 raw_data = open('implementations.json').read()
-if not raw_data.endswith(']\n'):
-    raise ValueError('implementations.json should end in one \\n')
 data = json.loads(raw_data)
 
 for impl in data:
-    jsonschema.validate(impl, schema)
+    try:
+        jsonschema.validate(impl, schema)
+    except jsonschema.exceptions.ValidationError as e:
+        errors.append(e)
 
 sorted_data = sorted(data, key=lambda impl: impl['repoURL'])
 for expected, actual in zip(sorted_data, data):
     if expected['repoURL'] != actual['repoURL']:
-        print('Expected:', expected['repoURL'])
-        print('Found:   ', actual['repoURL'])
-        raise ValueError('Implementations should be sorted by repoURL')
+        errors.append(ValueError(
+            'Implementations should be sorted by repoURL.\n' +
+            f"Expected: {expected['repoURL']}\n" +
+            f"Found:    {actual['repoURL']}"))
+        break
+
+diff = ''.join(difflib.unified_diff(
+    raw_data.splitlines(keepends=True),
+    (json.dumps(data, indent=4) + '\n').splitlines(keepends=True),
+    fromfile='implementations.json (current)',
+    tofile='implementations.json (expected formatting)'))
+if diff != '':
+    errors.append(ValueError('Formatting error:\n' + diff))
+
+# Saving the file without a trailing newline is a common error. It's already
+# caught by difflib above, but this error message is clearer.
+if not raw_data.endswith(']\n'):
+    errors.append(ValueError('implementations.json should end in one \\n'))
 
+if errors:
+    print(f'Encountered {len(errors)} errors:')
+    for error in errors:
+        print()
+        print(error)
+    sys.exit(1)

implementations.json

@@ -133,7 +133,7 @@
             "logCompaction": false
         }
     },
-        {
+    {
         "repoURL": "https://github.com/RedisLabs/redisraft",
         "name": "RedisRaft",
         "authors": [
@@ -1850,7 +1850,7 @@
             "persistence": true
         }
     },
-	{
+    {
         "repoURL": "https://github.com/scaars10/pecan-raft",
         "name": "PecanRaft",
         "authors": [