blurb: don't overwrite output when not necessary

dmerejkowsky · dmerejkowsky · commit e085df3d23b0 · 2021-05-13T10:50:34.000+02:00
This speeds up doc generation.

With this change, blurb won't update the NEWS file unnecessarily, which
means Sphinx will then use a cache instead of parsing it again.
diff --git a/blurb/blurb.py b/blurb/blurb.py
@@ -49,6 +49,7 @@
 from collections import OrderedDict
 import glob
 import hashlib
+import io
 import inspect
 import itertools
 import math
@@ -1068,9 +1069,11 @@ def merge(output=None, *, forced=False):
 
 
 def write_news(output, *, versions):
+    buff = io.StringIO()
+
     def print(*a, sep=" "):
         s = sep.join(str(x) for x in a)
-        return builtins.print(s, file=news)
+        return builtins.print(s, file=buff)
 
     print ("""
 +++++++++++
@@ -1131,8 +1134,17 @@ def print(*a, sep=" "):
             print(text)
     print()
     print("**(For information about older versions, consult the HISTORY file.)**")
-    news.close()
 
+    with open(output, "r", encoding="utf-8") as file:
+        previous_contents = file.read()
+
+    new_contents = buff.getvalue()
+
+    if new_contents != previous_contents:
+        with open(output, "wt", encoding="utf-8") as file:
+            file.write(buff.getvalue())
+    else:
+        builtins.print(output, "is already up to date")
 
 git_add_files = []
 def flush_git_add_files():
