Conflicting plan-sha256 reported

[nomeata]

I am using haskell.nix to provide (among other things) Windows builds of a project of mine, and this usually works great.

Since the latest upgrade, though, I have trouble with the windows build: It keeps telling me to switch the plan-sha256 between two values.

To reproduce check out entropia/tip-toi-reveng#290 at revision a64a59b587980896fa3e87de9163ed61bb86412f and run

nix-build -A windows-exe --extra-substituters https://tttool.cachix.org/\ https://cache.iog.io --extra-trusted-public-keys tttool.cachix.org-1:e/5HpIa6ZqwatH07kmO7di1p9K+AMrgkNHl/OGUUMzU=\ hydra.iohk.io:f/Ea+s+dFdN+3Y/G+FDgSq+a5NEWhJGzdjvKNGv0/EQ= --arg checkMaterialization true

The hash is stored at

https://github.com/entropia/tip-toi-reveng/blob/a64a59b587980896fa3e87de9163ed61bb86412f/default.nix#L103

One of the plan hashes is the same as the linux one, so maybe a currentSystem snuck in somewhere where it shouldn’t?

If I set the hash to null, the build succeeds.

Not sure if it is relevant, but maybe it’s somehow related to how I help haskell.nix not get stuck on system depenedencies hier:

https://github.com/entropia/tip-toi-reveng/blob/a64a59b587980896fa3e87de9163ed61bb86412f/default.nix#L15-L19

A hint would be appreciated!

[nomeata]

Adding --show-trace shows that somehow c2hs is involved:

       … while evaluating the attribute 'buildPackages.c2hs.components.exes.c2hs'

So here is a theory: It tries to build c2hs as a build tool in the non-cross way, and in order to do so it checks the build plan of that tool?

[nomeata]

I found this work-around; not sure how idiomatic that is:

diff --git a/default.nix b/default.nix
index 6f06728..487dfc3 100644
--- a/default.nix
+++ b/default.nix
@@ -53,6 +53,9 @@ let
       modules = [{
         # smaller files
         packages.tttool.dontStrip = false;
+        packages.proteaaudio.components.library.build-tools = pkgs.lib.mkForce [
+          pkgs.buildPackages.haskellPackages.c2hs
+        ];
       }] ++
       pkgs.lib.optional pkgs.hostPlatform.isMusl {
         packages.tttool.configureFlags = [ "--ghc-option=-static" ];
~

[andreabedini]

@nomeata Thanks for the updates. I haven't had the chance of looking into this but I just want to say it didn't go unnoticed.

[andreabedini]

Ok, I spent some times on this and I haven't got the bottom of it unfortunately. There must be something wrong with which pkgs is being used for the evaluating plan.

If I reproduced this correctly:

❯ nix-build -A windows-exe --arg checkMaterialization true
...
       > Calculated hash for haskell-project-plan-to-nix-pkgs was not 0674c017qxng0xil4yi4wsf2kr7yb9dyzpzxq7jd50dflzvm3qzz. New hash is :
       >     plan-sha256 = "0jmcpd8l6smj0zqkx4cx6ma2v3cvxmwws0s92ssrc6ginpis3gkb";
       For full logs, run 'nix log /nix/store/swa7qajzskxhad4pvbng24aamkls5v9b-haskell-project-plan-to-nix-pkgs.drv'.

❯ nix log /nix/store/swa7qajzskxhad4pvbng24aamkls5v9b-haskell-project-plan-to-nix-pkgs.drv
Changes to haskell-project-plan-to-nix-pkgs not reflected in plan-sha256
diff -ru /nix/store/giba13w486j458p7l3jwg0rqc2zvw4fd-haskell-project-plan-to-nix-pkgs/default.nix /nix/store/6c8mdm4a5a151nxn8yjm04mc1a2hq7zz-haskell-project-plan-to-nix-pkgs/default.nix
...
Calculated hash for haskell-project-plan-to-nix-pkgs was not 0674c017qxng0xil4yi4wsf2kr7yb9dyzpzxq7jd50dflzvm3qzz. New hash is :
    plan-sha256 = "0jmcpd8l6smj0zqkx4cx6ma2v3cvxmwws0s92ssrc6ginpis3gkb";

The script calculateMaterializedSha computes the hash of calculateNoHash, but if I call it

❯ nix-build -A windows-exe.project.plan-nix.passthru.calculateMaterializedSha
/nix/store/9wazjkh39l2bi8pwgrx6d9sq5j24v9fk-calculateSha

❯ /nix/store/9wazjkh39l2bi8pwgrx6d9sq5j24v9fk-calculateSha
0674c017qxng0xil4yi4wsf2kr7yb9dyzpzxq7jd50dflzvm3qzz

which is the hash we have passed! Let's see how the check is done:

❯ nix derivation show /nix/store/swa7qajzskxhad4pvbng24aamkls5v9b-haskell-project-plan-to-nix-pkgs.drv^* | jq -r '.[].env.buildCommand'
ERR=$(mktemp -d)/errors.txt
NEW_HASH=$(/nix/store/g3bd66c23mzspxdqik6hr4ppgal3k08x-calculateSha)
if [[ 0674c017qxng0xil4yi4wsf2kr7yb9dyzpzxq7jd50dflzvm3qzz != $NEW_HASH ]]; then
  echo Changes to haskell-project-plan-to-nix-pkgs not reflected in plan-sha256
  diff -ru /nix/store/giba13w486j458p7l3jwg0rqc2zvw4fd-haskell-project-plan-to-nix-pkgs /nix/store/6c8mdm4a5a151nxn8yjm04mc1a2hq7zz-haskell-project-plan-to-nix-pkgs || true
  echo "Calculated hash for haskell-project-plan-to-nix-pkgs was not 0674c017qxng0xil4yi4wsf2kr7yb9dyzpzxq7jd50dflzvm3qzz. New hash is :" >> $ERR
  echo "    plan-sha256 = \"$NEW_HASH\";"                      >> $ERR
else
  echo plan-sha256 used for haskell-project-plan-to-nix-pkgs is correct
fi
if [[ -e $ERR ]]; then
  cat $ERR
  false
else
  cp -Lr /nix/store/giba13w486j458p7l3jwg0rqc2zvw4fd-haskell-project-plan-to-nix-pkgs $out
  # Make sure output files can be removed from the sandbox
  chmod -R +w $out
fi

where NEW_HASH is

❯ /nix/store/g3bd66c23mzspxdqik6hr4ppgal3k08x-calculateSha
0jmcpd8l6smj0zqkx4cx6ma2v3cvxmwws0s92ssrc6ginpis3gkb

which is the other hash.

Surely we should not say Calculated hash for haskell-project-plan-to-nix-pkgs was not 0674c017qxng0xil4yi4wsf2kr7yb9dyzpzxq7jd50dflzvm3qzz if project.plan-nix.passthru.calculateMaterializedSha returns that exact hash.

One thing I don't understand is that looking at

diff -ru /nix/store/giba13w486j458p7l3jwg0rqc2zvw4fd-haskell-project-plan-to-nix-pkgs /nix/store/6c8mdm4a5a151nxn8yjm04mc1a2hq7zz-haskell-project-plan-to-nix-pkgs

one can identify

haskell.nix/lib/materialize.nix

Line 78 in 1ad94ae

diff -ru ${calculateUseHash} ${calculateNoHash} || true

• calculateUseHash -> /nix/store/giba13w486j458p7l3jwg0rqc2zvw4fd-haskell-project-plan-to-nix-pkgs
• calculateNoHash -> /nix/store/6c8mdm4a5a151nxn8yjm04mc1a2hq7zz-haskell-project-plan-to-nix-pkgs

Whose definition is

haskell.nix/lib/materialize.nix

Lines 131 to 139 in 1ad94ae

	calculateNoHash = derivation;
	calculateUseHash =
	# Use `cp -Lr` here to get rid of symlinks so we know the result
	# can be safely materialized (no symlinks to the store).
	runCommand name hashArgs ''
	cp -Lr ${derivation} $out
	# Make sure output files can be removed from the sandbox
	chmod -R +w $out
	'';

One would expect calculateUseHash to be a wrapper around calculateNoHash but

❯ nix derivation show /nix/store/giba13w486j458p7l3jwg0rqc2zvw4fd-haskell-project-plan-to-nix-pkgs | jq -r '.[].env.buildCommand'
cp -Lr /nix/store/20s0023rxwcik9qj5yww8avz156i821h-haskell-project-plan-to-nix-pkgs $out
# Make sure output files can be removed from the sandbox
chmod -R +w $out

which is "the other" plan.

Maybe @hamishmack has better insight.

[stale]

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