Merge pull request #211783 from R-VdP/fix_disallowed_references

stdenv: don't include drvs in disallowedRefs as build-time deps.

pkgs/stdenv/generic/make-derivation.nix

···
   separateDebugInfo' = separateDebugInfo && stdenv.hostPlatform.isLinux && !(stdenv.hostPlatform.useLLVM or false);
   outputs' = outputs ++ lib.optional separateDebugInfo' "debug";
 
+  # Turn a derivation into its outPath without a string context attached.
+  # See the comment at the usage site.
+  unsafeDerivationToUntrackedOutpath = drv:
+    if lib.isDerivation drv
+    then builtins.unsafeDiscardStringContext drv.outPath
+    else drv;
+
   noNonNativeDeps = builtins.length (depsBuildTarget ++ depsBuildTargetPropagated
                                   ++ depsHostHost ++ depsHostHostPropagated
                                   ++ buildInputs ++ propagatedBuildInputs
···
         "/bin/sh"
       ];
       __propagatedImpureHostDeps = computedPropagatedImpureHostDeps ++ __propagatedImpureHostDeps;
+    } //
+    # If we use derivations directly here, they end up as build-time dependencies.
+    # This is especially problematic in the case of disallowed*, since the disallowed
+    # derivations will be built by nix as build-time dependencies, while those
+    # derivations might take a very long time to build, or might not even build
+    # successfully on the platform used.
+    # We can improve on this situation by instead passing only the outPath,
+    # without an attached string context, to nix. The out path will be a placeholder
+    # which will be replaced by the actual out path if the derivation in question
+    # is part of the final closure (and thus needs to be built). If it is not
+    # part of the final closure, then the placeholder will be passed along,
+    # but in that case we know for a fact that the derivation is not part of the closure.
+    # This means that passing the out path to nix does the right thing in either
+    # case, both for disallowed and allowed references/requisites, and we won't
+    # build the derivation if it wouldn't be part of the closure, saving time and resources.
+    # While the problem is less severe for allowed*, since we want the derivation
+    # to be built eventually, we would still like to get the error early and without
+    # having to wait while nix builds a derivation that might not be used.
+    # See also https://github.com/NixOS/nix/issues/4629
+    lib.optionalAttrs (attrs ? disallowedReferences) {
+      disallowedReferences =
+        map unsafeDerivationToUntrackedOutpath attrs.disallowedReferences;
+    } //
+    lib.optionalAttrs (attrs ? disallowedRequisites) {
+      disallowedRequisites =
+        map unsafeDerivationToUntrackedOutpath attrs.disallowedRequisites;
+    } //
+    lib.optionalAttrs (attrs ? allowedReferences) {
+      allowedReferences =
+        lib.mapNullable unsafeDerivationToUntrackedOutpath attrs.allowedReferences;
+    } //
+    lib.optionalAttrs (attrs ? allowedRequisites) {
+      allowedRequisites =
+        lib.mapNullable unsafeDerivationToUntrackedOutpath attrs.allowedRequisites;
     };
 
   validity = checkMeta { inherit meta attrs; };