Recover the complicated situation after my bad merge

I made a mistake merge.  Reverting it in c778945806 undid the state
on master, but now I realize it crippled the git merge mechanism.
As the merge contained a mix of commits from `master..staging-next`
and other commits from `staging-next..staging`, it got the
`staging-next` branch into a state that was difficult to recover.

I reconstructed the "desired" state of staging-next tree by:
 - checking out the last commit of the problematic range: 4effe769e2
 - `git rebase -i --preserve-merges a8a018ddc0` - dropping the mistaken
   merge commit and its revert from that range (while keeping
   reapplication from 4effe769e2)
 - merging the last unaffected staging-next commit (803ca85c20)
 - fortunately no other commits have been pushed to staging-next yet
 - applying a diff on staging-next to get it into that state

pkgs/development/libraries/expat/default.nix

@@ -1,16 +1,18 @@
-{ stdenv, fetchurl }:
+{ stdenv, fetchurl, lib }:
 
 # Note: this package is used for bootstrapping fetchurl, and thus
 # cannot use fetchpatch! All mutable patches (generated by GitHub or
 # cgit) that are needed here should be included directly in Nixpkgs as
 # files.
 
-stdenv.mkDerivation rec {
-  name = "expat-2.2.8";
+let
+  version = "2.2.10";
+in stdenv.mkDerivation rec {
+  name = "expat-${version}";
 
   src = fetchurl {
-    url = "https://github.com/libexpat/libexpat/releases/download/R_2_2_8/${name}.tar.xz";
-    sha256 = "16vpj5mk3lps3x7fr8cs03rffx3ir4jilyqw0frayn6q94daijk1";
+    url = "https://github.com/libexpat/libexpat/releases/download/R_${lib.replaceStrings ["."] ["_"] version}/${name}.tar.xz";
+    sha256 = "sha256-Xf5Tj4tbY/A+mO2sUg19mmpNIuSC5cltTQb8xUhcJfI=";
   };
 
   outputs = [ "out" "dev" ]; # TODO: fix referrers