sphinx: Patch source file for normalization

One of the test files has a different encoding depending on the
filesystem's normalization. By picking a character that does not have
multiple possible encodings we make the source indifferent to
normalization. This allows the FOD hash to match across platforms with
differently normalizing filesystems.

pkgs/development/python-modules/sphinx/0001-test-images-Use-normalization-equivalent-character.patch

···
+From 181617387841b695ee77b162babf9fb177002fcb Mon Sep 17 00:00:00 2001
+From: toonn <[e-mail]>
+Date: Mon, 20 Sep 2021 11:39:46 +0200
+Subject: [PATCH] test-images: Use normalization equivalent character
+MIME-Version: 1.0
+Content-Type: text/plain; charset=UTF-8
+Content-Transfer-Encoding: 8bit
+
+One of the test images used a combining character `ä` that can be
+encoded multiple ways. This means the file's name can end up encoded
+differently depending on whether/which normal form the filesystem uses.
+
+For Nix this causes a different hash for a FOD depending on the
+filesystem where it is evaluated. This is problematic because hashes
+fail to match up when evaluating the FOD across multiple platforms.
+---
+ tests/roots/test-images/index.rst | 2 +-
+ 1 file changed, 1 insertion(+), 1 deletion(-)
+
+diff --git a/tests/roots/test-images/index.rst b/tests/roots/test-images/index.rst
+index 14a2987..219842e 100644
+--- a/tests/roots/test-images/index.rst
++++ b/tests/roots/test-images/index.rst
+@@ -13,7 +13,7 @@ test-image
+ 
+    The caption of img
+ 
+-.. image:: testimäge.png
++.. image:: testimæge.png
+ 
+ .. image:: rimg.png
+    :target: https://www.sphinx-doc.org/
+-- 
+2.17.2 (Apple Git-113)
+

pkgs/development/python-modules/sphinx/default.nix

···
     owner = "sphinx-doc";
     repo = pname;
     rev = "v${version}";
-    sha256 = "1i38n5bxqiycjwmiv9dl72r3f5ks4zmif30znqg8zilclbx6g16x";
+    sha256 = "1bl0k326h32dag41axbsjq1d9w59rm11naj6bfirg116nqw56mk6";
+    extraPostFetch = ''
+      cd $out
+      mv tests/roots/test-images/testimäge.png \
+        tests/roots/test-images/testimæge.png
+      patch -p1 < ${./0001-test-images-Use-normalization-equivalent-character.patch}
+    '';
   };
 
   propagatedBuildInputs = [