Multiple overrides for the same package

[TyberiusPrime]

For I have the equivalent of

 (final: prev: {
    "pysam" = prev."pysam".overridePythonAttrs (
      old: {
        buildInputs = (builtins.trace "two" (old.builtInputs or [])) ++ [pkgs.bzip2];
        nativeBuildInputs = builtins.trace "two-b" (old.nativeBuildInputs or []);
      }
    );
  })
  (final: prev: {
    "pysam" = prev."pysam".overridePythonAttrs (
      old: {
        buildInputs = (builtins.trace "one" (old.builtInputs or [])) ++ [pkgs.zlib];
      }
    );
  })

in my overrides, and find that it's not toking the first one.
The traces read
'one'
'two-b'

and I'd like to know if I'm holding it wrong or if this is how it's supposed to work?

[heimalne]

The trace seems weird indeed regarding the evaluation order. In order to evaluate the final pysam value we use the latest/last entry (prints "one"), but this dependes on the previous/old on, which when evaluated should print "two".

[TyberiusPrime]

Thanks @heimalne that's how I understood 'a list of overlays' should work, the 'old' in the 2nd one should be what the first one produced.