pango: devdoc target is not reproducible

[raboof]

Describe the bug

Building the devdoc output of pango does not produce the exact same output each time it is build.

Having bit-by-bit reproducible derivations makes auditing build processes easier. This package is especially interesting since it is part of the milestone tracked by https://r13y.com

To Reproduce
Steps to reproduce the behavior:

nix-build "<nixpkgs>" -A pango.devdoc --check

Expected behavior

Success!

Additional context

There is an upstream patch to gi-docgen at https://gitlab.gnome.org/GNOME/gi-docgen/-/merge_requests/53/diffs.patch that might help, but doesn't seem to completely fix the issue yet. Starting point:

diff --git a/pkgs/development/tools/documentation/gi-docgen/default.nix b/pkgs/development/tools/documentation/gi-docgen/default.nix
index 72b5364eb45..57dbe62a667 100644
--- a/pkgs/development/tools/documentation/gi-docgen/default.nix
+++ b/pkgs/development/tools/documentation/gi-docgen/default.nix
@@ -61,6 +61,11 @@ python3.pkgs.buildPythonApplication rec {
       url = "https://gitlab.gnome.org/jtojnar/gi-docgen/commit/08dcc31f62be1a5af9bd9f8f702f321f4b5cffde.patch";
       sha256 = "vAT8s7zQ9zCoZWK+6PsxcD5/48ZAfIOl4RSNljRCGWQ=";
     })
+    # make DevHelp sections & index.json have stable ordering
+    (fetchpatch {
+      url = "https://gitlab.gnome.org/GNOME/gi-docgen/-/merge_requests/53/diffs.patch";
+      sha256 = "sha256-nG0Dt///w7agXAvWNtGdBQSaKMXNHraGO1svmn9FynI=";
+    })
   ];
 
   nativeBuildInputs = [

[zopieux]

The latest commit should address all issues, but I need help reproducing the (lack of) reproducibility. Can anyone check compiling pango before/after patching, to confirm the devhelp and index.json diffs are now gone? Thanks.

[zopieux]

OK managed to reproduce pango not being reproducible at HEAD. With the patch, I cannot get it to fail after multiple attempts, even under stress(1) load.

[zopieux]

Now waiting for upstream to merge.

It's merged!

[raboof]

Can confirm this fixes it here as well!

PR'ed as #118978 to get the patch in for 21.05

[oxalica]

Maybe this can be closed now?