"cabal-plan" is missing when using latest hackage.nix

[m4dc4p]

Somewhere between February & June, hackage.nix changed and for some reason I can't build my shell anymore. It fails with:

       error: attribute 'cabal-plan' missing
       at /nix/store/imvcsn32zp098brrgxkzh9hn580a0b4p-source/overlays/haskell.nix:761:34:
          760|                             then components.library
          761|                             else components.${haskellLib.prefixComponent.${builtins.elemAt m 0}}.${builtins.elemAt m 1};
             |                                  ^
          762|

I'm using the latest haskell.nix (125a3d1); with hackage.nix at revision 0a903b36 (from about Feb 23rd), I can build. When I try to update to a newer hackage.nix (7b8331e1), my build fails. The failure is coming from somewhere in the haskell.nix code.

Any hints on debugging? I haven't had time to bisect the commit where this started.

Here is the full trace (the /nix/store derivation imvcsn32zp098brrgxkzh9hn580a0b4p-source is the haskell.nix sources at 125a3d1):

error:
       … while calling the 'derivationStrict' builtin
         at «nix-internal»/derivation-internal.nix:37:12:
           36|
           37|   strict = derivationStrict drvAttrs;
             |            ^
           38|

       … while evaluating derivation 'ghc-shell-for-packages'
         whose name attribute is located at /nix/store/42k3knjp8qlqaa2mxaqhsh6mv421v32n-source/pkgs/stdenv/generic/make-derivation.nix:336:7

       … while evaluating attribute '__impureHostDeps' of derivation 'ghc-shell-for-packages'
         at /nix/store/42k3knjp8qlqaa2mxaqhsh6mv421v32n-source/pkgs/stdenv/generic/make-derivation.nix:451:7:
          450|       __propagatedSandboxProfile = unique (computedPropagatedSandboxProfile ++ [ propagatedSandboxProfile ]);
          451|       __impureHostDeps = computedImpureHostDeps ++ computedPropagatedImpureHostDeps ++ __propagatedImpureHostDeps ++ __impureHostDeps ++ stdenv.__extraImpureHostDeps ++ [
             |       ^
          452|         "/dev/zero"

       … while calling the 'foldl'' builtin
         at /nix/store/42k3knjp8qlqaa2mxaqhsh6mv421v32n-source/pkgs/stdenv/generic/make-derivation.nix:435:11:
          434|         computedImpureHostDeps =
          435|           unique (concatMap (input: input.__propagatedImpureHostDeps or [])
             |           ^
          436|             (stdenv.extraNativeBuildInputs

       … while calling the 'concatMap' builtin
         at /nix/store/42k3knjp8qlqaa2mxaqhsh6mv421v32n-source/pkgs/stdenv/generic/make-derivation.nix:435:19:
          434|         computedImpureHostDeps =
          435|           unique (concatMap (input: input.__propagatedImpureHostDeps or [])
             |                   ^
          436|             (stdenv.extraNativeBuildInputs

       … while calling anonymous lambda
         at /nix/store/42k3knjp8qlqaa2mxaqhsh6mv421v32n-source/pkgs/stdenv/generic/make-derivation.nix:435:30:
          434|         computedImpureHostDeps =
          435|           unique (concatMap (input: input.__propagatedImpureHostDeps or [])
             |                              ^
          436|             (stdenv.extraNativeBuildInputs

       … from call site
         at /nix/store/42k3knjp8qlqaa2mxaqhsh6mv421v32n-source/pkgs/stdenv/generic/make-derivation.nix:435:37:
          434|         computedImpureHostDeps =
          435|           unique (concatMap (input: input.__propagatedImpureHostDeps or [])
             |                                     ^
          436|             (stdenv.extraNativeBuildInputs

       … while calling anonymous lambda
         at /nix/store/42k3knjp8qlqaa2mxaqhsh6mv421v32n-source/pkgs/stdenv/generic/make-derivation.nix:307:13:
          306|       (map (drv: getDev drv.__spliced.buildBuild or drv) (checkDependencyList "depsBuildBuild" depsBuildBuild))
          307|       (map (drv: getDev drv.__spliced.buildHost or drv) (checkDependencyList "nativeBuildInputs" nativeBuildInputs'))
             |             ^
          308|       (map (drv: getDev drv.__spliced.buildTarget or drv) (checkDependencyList "depsBuildTarget" depsBuildTarget))

       … from call site
         at /nix/store/42k3knjp8qlqaa2mxaqhsh6mv421v32n-source/pkgs/stdenv/generic/make-derivation.nix:307:18:
          306|       (map (drv: getDev drv.__spliced.buildBuild or drv) (checkDependencyList "depsBuildBuild" depsBuildBuild))
          307|       (map (drv: getDev drv.__spliced.buildHost or drv) (checkDependencyList "nativeBuildInputs" nativeBuildInputs'))
             |                  ^
          308|       (map (drv: getDev drv.__spliced.buildTarget or drv) (checkDependencyList "depsBuildTarget" depsBuildTarget))

       … while calling 'getOutput'
         at /nix/store/42k3knjp8qlqaa2mxaqhsh6mv421v32n-source/lib/attrsets.nix:1796:23:
         1795|   */
         1796|   getOutput = output: pkg:
             |                       ^
         1797|     if ! pkg ? outputSpecified || ! pkg.outputSpecified

       … while evaluating a branch condition
         at /nix/store/42k3knjp8qlqaa2mxaqhsh6mv421v32n-source/lib/attrsets.nix:1797:5:
         1796|   getOutput = output: pkg:
         1797|     if ! pkg ? outputSpecified || ! pkg.outputSpecified
             |     ^
         1798|       then pkg.${output} or pkg.out or pkg

       … in the left operand of the OR (||) operator
         at /nix/store/42k3knjp8qlqaa2mxaqhsh6mv421v32n-source/lib/attrsets.nix:1797:32:
         1796|   getOutput = output: pkg:
         1797|     if ! pkg ? outputSpecified || ! pkg.outputSpecified
             |                                ^
         1798|       then pkg.${output} or pkg.out or pkg

       … in the argument of the not operator
         at /nix/store/42k3knjp8qlqaa2mxaqhsh6mv421v32n-source/lib/attrsets.nix:1797:10:
         1796|   getOutput = output: pkg:
         1797|     if ! pkg ? outputSpecified || ! pkg.outputSpecified
             |          ^
         1798|       then pkg.${output} or pkg.out or pkg

       … from call site
         at /nix/store/42k3knjp8qlqaa2mxaqhsh6mv421v32n-source/pkgs/stdenv/generic/make-derivation.nix:307:25:
          306|       (map (drv: getDev drv.__spliced.buildBuild or drv) (checkDependencyList "depsBuildBuild" depsBuildBuild))
          307|       (map (drv: getDev drv.__spliced.buildHost or drv) (checkDependencyList "nativeBuildInputs" nativeBuildInputs'))
             |                         ^
          308|       (map (drv: getDev drv.__spliced.buildTarget or drv) (checkDependencyList "depsBuildTarget" depsBuildTarget))

       … while calling anonymous lambda
         at /nix/store/42k3knjp8qlqaa2mxaqhsh6mv421v32n-source/lib/lists.nix:335:29:
          334|   */
          335|   imap1 = f: list: genList (n: f (n + 1) (elemAt list n)) (length list);
             |                             ^
          336|

       … from call site
         at /nix/store/42k3knjp8qlqaa2mxaqhsh6mv421v32n-source/lib/lists.nix:335:32:
          334|   */
          335|   imap1 = f: list: genList (n: f (n + 1) (elemAt list n)) (length list);
             |                                ^
          336|

       … while calling anonymous lambda
         at /nix/store/42k3knjp8qlqaa2mxaqhsh6mv421v32n-source/pkgs/stdenv/generic/make-derivation.nix:281:15:
          280|     imap1
          281|       (index: dep:
             |               ^
          282|         if isDerivation dep || dep == null || builtins.isString dep || builtins.isPath dep then dep

       … while evaluating a branch condition
         at /nix/store/42k3knjp8qlqaa2mxaqhsh6mv421v32n-source/pkgs/stdenv/generic/make-derivation.nix:282:9:
          281|       (index: dep:
          282|         if isDerivation dep || dep == null || builtins.isString dep || builtins.isPath dep then dep
             |         ^
          283|         else if isList dep then checkDependencyList' ([index] ++ positions) name dep

       … in the left operand of the OR (||) operator
         at /nix/store/42k3knjp8qlqaa2mxaqhsh6mv421v32n-source/pkgs/stdenv/generic/make-derivation.nix:282:69:
          281|       (index: dep:
          282|         if isDerivation dep || dep == null || builtins.isString dep || builtins.isPath dep then dep
             |                                                                     ^
          283|         else if isList dep then checkDependencyList' ([index] ++ positions) name dep

       … in the left operand of the OR (||) operator
         at /nix/store/42k3knjp8qlqaa2mxaqhsh6mv421v32n-source/pkgs/stdenv/generic/make-derivation.nix:282:44:
          281|       (index: dep:
          282|         if isDerivation dep || dep == null || builtins.isString dep || builtins.isPath dep then dep
             |                                            ^
          283|         else if isList dep then checkDependencyList' ([index] ++ positions) name dep

       … in the left operand of the OR (||) operator
         at /nix/store/42k3knjp8qlqaa2mxaqhsh6mv421v32n-source/pkgs/stdenv/generic/make-derivation.nix:282:29:
          281|       (index: dep:
          282|         if isDerivation dep || dep == null || builtins.isString dep || builtins.isPath dep then dep
             |                             ^
          283|         else if isList dep then checkDependencyList' ([index] ++ positions) name dep

       … from call site
         at /nix/store/42k3knjp8qlqaa2mxaqhsh6mv421v32n-source/pkgs/stdenv/generic/make-derivation.nix:282:12:
          281|       (index: dep:
          282|         if isDerivation dep || dep == null || builtins.isString dep || builtins.isPath dep then dep
             |            ^
          283|         else if isList dep then checkDependencyList' ([index] ++ positions) name dep

       … while calling 'isDerivation'
         at /nix/store/42k3knjp8qlqaa2mxaqhsh6mv421v32n-source/lib/attrsets.nix:1282:5:
         1281|   isDerivation =
         1282|     value: value.type or null == "derivation";
             |     ^
         1283|

       … while calling the 'elemAt' builtin
         at /nix/store/42k3knjp8qlqaa2mxaqhsh6mv421v32n-source/lib/lists.nix:335:43:
          334|   */
          335|   imap1 = f: list: genList (n: f (n + 1) (elemAt list n)) (length list);
             |                                           ^
          336|

       … while calling 'tool''
         at /nix/store/imvcsn32zp098brrgxkzh9hn580a0b4p-source/overlays/tools.nix:95:50:
           94|   # tool with a default evalPackages to use.
           95|   tool' = evalPackages: compiler-nix-name: name: versionOrMod:
             |                                                  ^
           96|       final.haskell-nix.hackage-tool (

       … from call site
         at /nix/store/imvcsn32zp098brrgxkzh9hn580a0b4p-source/overlays/tools.nix:96:7:
           95|   tool' = evalPackages: compiler-nix-name: name: versionOrMod:
           96|       final.haskell-nix.hackage-tool (
             |       ^
           97|            final.haskell-nix.haskellLib.versionOrModToMods versionOrMod

       … while calling 'hackage-tool'
         at /nix/store/imvcsn32zp098brrgxkzh9hn580a0b4p-source/overlays/tools.nix:66:18:
           65|
           66|   hackage-tool = projectModules:
             |                  ^
           67|     let

       … from call site
         at /nix/store/imvcsn32zp098brrgxkzh9hn580a0b4p-source/overlays/tools.nix:86:8:
           85|       exeName = final.haskell-nix.packageToolName.${name} or name;
           86|     in package.getComponent "exe:${exeName}";
             |        ^
           87|

       … while calling 'getComponent'
         at /nix/store/imvcsn32zp098brrgxkzh9hn580a0b4p-source/overlays/haskell.nix:754:38:
          753|                       # Look up a component in the package based on ctype:name
          754|                       getComponent = componentName:
             |                                      ^
          755|                         let m = builtins.match "(lib|flib|exe|test|bench):([^:]*)" componentName;

       error: attribute 'cabal-plan' missing
       at /nix/store/imvcsn32zp098brrgxkzh9hn580a0b4p-source/overlays/haskell.nix:761:34:
          760|                             then components.library
          761|                             else components.${haskellLib.prefixComponent.${builtins.elemAt m 0}}.${builtins.elemAt m 1};
             |                                  ^
          762|

[m4dc4p]

Well, I had cabal-plan in the tools entry for my project; not sure why or what it was being used for, but removing it fixed this problem. Its still on hackage so I'm not sure why this error popped up, but does seem to be a local problem.

[hamishmack]

This is the cabal solver disabling cabal-plan's automatic exe flag, not a haskell.nix regression as such.

cabal-plan defines its executable behind an automatic flag whose stated purpose is exactly this:

flag exe
  -- this automatic flag allows the cabal solver to disable the exe:cabal-plan component (& its build-deps)
  description: Enable exe:cabal-plan component

When you bumped hackage.nix, the solver started preferring to resolve cabal-plan library-only (the exe flag off), so the exe:cabal-plan component no longer existed — and haskell.nix's getComponent "exe:cabal-plan" then blew up with the unhelpful attribute 'cabal-plan' missing.

To fix it, force the flag back on in the tool's module:

tools.cabal-plan = {
  version = "0.7.6.0";
  cabalProjectLocal = ''
    package cabal-plan
      flags: +exe
  '';
};

Two possible outcomes:

• It resolves and you get the exe back (confirmed here on ghc984 — the flag had only been dispreferred, not truly unsolvable).
• The solver now fails — which is actually the good case: the failure message spells out the real dependency conflict that made cabal turn the flag off, so you can see which dependency to constrain or which cabal-plan version to pin. That's far more useful than the silent flag-disable you were getting.

I've opened #2530 to improve the error itself, so instead of attribute 'cabal-plan' missing you'll get a message that names the package, lists the components that do exist, explains the automatic-flag cause, and suggests this cabalProjectLocal recipe.