callCabal2nix works

default.nix

@@ -46,7 +46,7 @@ let
 
   # Static derivation for the PostgREST executable.
   drvStatic =
-    import nix/static.nix {
+    import nix/static {
       inherit pkgs name src;
       # Currently only works with GHC 8.6.5.
       compiler = "ghc865";

nix/nixpkgs-version.nix

@@ -1,6 +1,6 @@
 # Pinned version of Nixpkgs, generated with nixpkgs-upgrade.
 {
-  date = "2020-04-19";
+  date = "2020-04-23";
   rev = "10100a97c8964e82b30f180fda41ade8e6f69e41";
   tarballHash = "011f36kr3c1ria7rag7px26bh73d1b0xpqadd149bysf4hg17rln";
 }

nix/static/Cabal.nix

@@ -0,0 +1,27 @@
+{ mkDerivation, array, base, base-compat, base-orphans, binary
+, bytestring, containers, deepseq, Diff, directory, filepath
+, integer-logarithms, mtl, optparse-applicative, parsec, pretty
+, process, QuickCheck, stdenv, stm, tagged, tar, tasty
+, tasty-golden, tasty-hunit, tasty-quickcheck, temporary, text
+, time, transformers, tree-diff, unix
+}:
+mkDerivation {
+  pname = "Cabal";
+  version = "3.0.0.0";
+  sha256 = "5143ec26d740c1a508c93a8860e64407e7546c29b9817db20ff1595c1968d287";
+  setupHaskellDepends = [ mtl parsec ];
+  libraryHaskellDepends = [
+    array base binary bytestring containers deepseq directory filepath
+    mtl parsec pretty process text time transformers unix
+  ];
+  testHaskellDepends = [
+    array base base-compat base-orphans binary bytestring containers
+    deepseq Diff directory filepath integer-logarithms
+    optparse-applicative pretty process QuickCheck stm tagged tar tasty
+    tasty-golden tasty-hunit tasty-quickcheck temporary text tree-diff
+  ];
+  doCheck = false;
+  homepage = "http://www.haskell.org/cabal/";
+  description = "A framework for packaging Haskell software";
+  license = stdenv.lib.licenses.bsd3;
+}

nix/static.nix → nix/static/default.nix

@@ -28,18 +28,17 @@ let
           final: prev:
             {
               # Add our source package.
-              "${name}" =
-                #prev.callPackage ./postgrest.nix { inherit name src; };
-                prev.callCabal2nix name src {};
+              "${name}" = prev.callCabal2nix name src {};
 
-              Cabal = prev.Cabal_3_2_0_0;
+              # cabal2nix depends on Cabal 3.0.*, while our pinned version of Nixpkgs 
+              # only provides 2.4 or 3.2. So we pinned 3.0.0.0 in ./Cabal.nix
+              cabal2nix =
+                prev.cabal2nix.overrideScope 
+                  (self: super: { Cabal = self.callPackage ./Cabal.nix {}; });
 
               # The tests for the packages below took a long time on static
               # builds, so we disable them for now - to be investigated.
               happy = self.haskell.lib.dontCheck prev.happy;
-              text-short = self.haskell.lib.dontCheck prev.text-short;
-              jose = self.haskell.lib.dontCheck prev.jose;
-              tls = self.haskell.lib.dontCheck prev.tls;
             };
       in
         # Override the set of Haskell packages at