From 0dd9f16e95baf6fdbbb784bc09dcfaea4f5ba114 Mon Sep 17 00:00:00 2001
From: Dimitri Merejkowsky <dimitri@dmerej.info>
Date: Wed, 12 May 2021 14:31:28 +0200
Subject: [PATCH 1/2] blurb: extract `write_news()` function

---
 blurb/blurb.py | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/blurb/blurb.py b/blurb/blurb.py
index 2b9475b..7c87c56 100755
--- a/blurb/blurb.py
+++ b/blurb/blurb.py
@@ -1064,8 +1064,10 @@ def merge(output=None, *, forced=False):
         builtins.print("You already have a", repr(output), "file.")
         require_ok("Type ok to overwrite")
 
-    news = open(output, "wt", encoding="utf-8")
+    write_news(output, versions=versions)
 
+
+def write_news(output, *, versions):
     def print(*a, sep=" "):
         s = sep.join(str(x) for x in a)
         return builtins.print(s, file=news)

From cf225d674a4efa3508bd2188ba1474dfcf27b1bc Mon Sep 17 00:00:00 2001
From: Dimitri Merejkowsky <dimitri@dmerej.info>
Date: Wed, 12 May 2021 14:31:52 +0200
Subject: [PATCH 2/2] blurb: don't overwrite output when not necessary

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.
---
 blurb/blurb.py | 21 +++++++++++++++++++--
 1 file changed, 19 insertions(+), 2 deletions(-)

diff --git a/blurb/blurb.py b/blurb/blurb.py
index 7c87c56..0cb87cc 100755
--- a/blurb/blurb.py
+++ b/blurb/blurb.py
@@ -49,10 +49,12 @@
 from collections import OrderedDict
 import glob
 import hashlib
+import io
 import inspect
 import itertools
 import math
 import os
+from pathlib import Path
 import re
 import shlex
 import shutil
@@ -1068,9 +1070,11 @@ 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 ("""
 +++++++++++
@@ -1131,7 +1135,20 @@ def print(*a, sep=" "):
             print(text)
     print()
     print("**(For information about older versions, consult the HISTORY file.)**")
-    news.close()
+
+
+    new_contents = buff.getvalue()
+
+    # Only write in `output` if the contents are different
+    # This speeds up subsequent Sphinx builds
+    try:
+        previous_contents = Path(output).read_text(encoding="UTF-8")
+    except (FileNotFoundError, UnicodeError):
+        previous_contents = None
+    if new_contents != previous_contents:
+        Path(output).write_text(new_contents, encoding="UTF-8")
+    else:
+        builtins.print(output, "is already up to date")
 
 
 git_add_files = []