Commit 571a07d7 authored by sternenseemann's avatar sternenseemann
Browse files

doc/haskell: don't use lib.recursiveUpdate in overlays 

`lib.recursiveUpdate` indiscriminately recurses into all attribute sets,
also into derivations. This means that it is possible that evaluating a
derivation in the final haskell package set can cause something in
`prev.haskell` to be forced by `recursiveUpdate`, potentially causing an
evaluation error that should not happen.

It can be fixed using a well-crafted predicate for
`lib.recursiveUpdateUntil`, but most robust is just explicitly writing
out the desired merging manually.
parent 82ee0694

doc/languages-frameworks/haskell.section.md

+33 −29
Original line number Diff line number Diff line
@@ -1229,12 +1229,14 @@ in 
  in



  {

    haskell = lib.recursiveUpdate prev.haskell {

      compiler.${ghcName} = prev.haskell.compiler.${ghcName}.override {

    haskell = prev.haskell // {

      compiler = prev.haskell.compiler // {

        ${ghcName} = prev.haskell.compiler.${ghcName}.override {

          # Unfortunately, the GHC setting is named differently for historical reasons

          enableProfiledLibs = enableProfiling;

        };

      };

    };

  })



  (final: prev:
@@ -1244,8 +1246,9 @@ in 
  in



  {

    haskell = lib.recursiveUpdate prev.haskell {

      packages.${ghcName} = prev.haskell.packages.${ghcName}.override {

    haskell = prev.haskell // {

      packages = prev.haskell.packages // {

        ${ghcName} = prev.haskell.packages.${ghcName}.override {

          overrides = hfinal: hprev: {

            mkDerivation = args: hprev.mkDerivation (args // {

              # Since we are forcing our ideas upon mkDerivation, this change will
@@ -1272,6 +1275,7 @@ in 
          };

        };

      };

    };

  })

]

```