pretty_file: Added detection whether reformatting is necessary

cfbs/pretty.py

@@ -201,10 +201,13 @@ def pretty_check_string(s, sorting_rules=None):
 
 def pretty_file(filename, sorting_rules=None):
     with open(filename) as f:
-        data = pretty_string(f.read(), sorting_rules)
-    with open(filename, "w") as f:
-        f.write(data)
-        f.write("\n")
+        old_data = f.read()
+    new_data = pretty_string(old_data, sorting_rules) + "\n"
+    if old_data != new_data:
+        with open(filename, "w") as f:
+            f.write(new_data)
+        return True
+    return False
 
 
 def pretty_string(s, sorting_rules=None):

tests/test_pretty.py

@@ -1,6 +1,6 @@
 from collections import OrderedDict
-from cfbs.pretty import pretty, pretty_check_string, pretty_string
-from cfbs.utils import item_index
+from cfbs.pretty import pretty, pretty_check_string, pretty_string, pretty_file
+from cfbs.utils import item_index, mkdir, read_file
 
 
 def test_pretty():
@@ -205,6 +205,15 @@ def test_pretty_string():
     assert pretty_string(test) == expected
 
 
+def test_pretty_file():
+    mkdir("tests/tmp/", exist_ok=True)
+    with open("tests/tmp/test_pretty_file.json", "w") as f:
+        f.write(" {} \n")
+    assert pretty_file("tests/tmp/test_pretty_file.json") == True
+    assert read_file("tests/tmp/test_pretty_file.json") == "{}\n"
+    assert pretty_file("tests/tmp/test_pretty_file.json") == False
+
+
 def test_pretty_check_string():
     assert pretty_check_string(' "Hello" ') == False
     assert pretty_check_string('"Hello"') == True