Add cabalProjectToNix

Author: hamishmack

default.nix

@@ -6,6 +6,8 @@
 # It's also possible to override these sources with NIX_PATH.
 , hackageSourceJSON ? ./hackage-src.json
 , stackageSourceJSON ? ./stackage-src.json
+, hackageIndexState ? null
+, recentNixpkgs ? import <nixpkgs> {}
 }:
 
 let
@@ -38,12 +40,24 @@ let
   # overridden with NIX_PATH.
   fetchExternal = import ./lib/fetch-external.nix;
 
+  hackageIndex = import ./lib/hackageIndex.nix {
+    inherit (pkgs) runCommand;
+    inherit (recentNixpkgs) cabal-install;
+    indexState = hackageIndexState;
+  };
+  
   # All packages from Hackage as Nix expressions
-  hackage = import (fetchExternal {
-    name     = "hackage-exprs-source";
-    specJSON = hackageSourceJSON;
-    override = "hackage";
-  });
+  hackage = if hackageIndexState == null
+    then import (fetchExternal {
+        name     = "hackage-exprs-source";
+        specJSON = hackageSourceJSON;
+        override = "hackage";
+      })
+    else import (import ./lib/callHackageToNix.nix {
+        inherit (pkgs) runCommand;
+        inherit (import ./. {}) nix-tools;
+        inherit hackageIndex;
+      });
 
   # The set of all Stackage snapshots
   stackage = import (fetchExternal {
@@ -118,6 +132,19 @@ let
       update-stackage = self.callPackage ./scripts/update-stackage.nix {};
       update-pins = self.callPackage ./scripts/update-pins.nix {};
     };
+
+    # Make this handy overridable fetch function available.
+    inherit fetchExternal;
+
+    # Takes a haskell src directory runs cabal new-configure and plan-to-nix.
+    # Resulting nix files are added to nix-plan subdirectory.
+    cabalProjectToNix = import ./lib/cabalProjectToNix.nix {
+      inherit pkgs hackageIndex;
+      inherit (pkgs) runCommand;
+      inherit (recentNixpkgs) cabal-install ghc;
+      inherit (recentNixpkgs.haskellPackages) hpack;
+      inherit (import ./. {}) nix-tools;
+    };
   });
 
 in

lib/cabalProjectToNix.nix

@@ -0,0 +1,28 @@
+{ pkgs, runCommand, nix-tools, cabal-install
+, hackageIndex, ghc, hpack
+} :
+{src} :
+let
+  cabalFiles =
+    builtins.filterSource (path: type:
+      type == "directory" ||
+      pkgs.lib.any (i: (pkgs.lib.hasSuffix i path)) [ ".project" ".cabal" "package.yaml" ])
+      src;
+  plan = runCommand "plan" {
+    buildInputs = [ ghc hpack ];
+  } ''
+    tmp=$(mktemp -d)
+    cd $tmp
+    cp -r ${cabalFiles}/* .
+    chmod +w -R .
+    find . -name package.yaml -exec hpack "{}" \;
+    HOME=${hackageIndex} ${cabal-install}/bin/cabal new-configure
+    HOME=$out ${nix-tools}/bin/plan-to-nix --plan-json dist-newstyle/cache/plan.json -o nix-plan
+    cp -r nix-plan $out
+  '';
+in
+  runCommand "plan-and-src" {} ''
+    mkdir $out
+    cp -r ${src}/* $out
+    ln -sf ${plan} $out/nix-plan
+  ''

lib/callHackageToNix.nix

@@ -0,0 +1,5 @@
+{ runCommand, nix-tools
+, hackageIndex
+} : runCommand "hackage-nix" {} ''
+    HOME=${hackageIndex} ${nix-tools}/bin/hackage-to-nix $out
+  ''

lib/hackageIndex.nix

@@ -0,0 +1,16 @@
+{ runCommand, cabal-install
+, indexState ? "2019-04-24T21:34:04Z"
+} :
+let
+  # To avoid downloading more data than necessary this will provide a base.
+  cachedState = runCommand "hackage-${builtins.substring 0 4 indexState}" {} ''
+    mkdir -p $out
+    HOME=$out ${cabal-install}/bin/cabal new-update 'hackage.haskell.org,${builtins.substring 0 4 indexState}-01-01T00:00:00Z'
+  '';
+in runCommand "hackage-${builtins.replaceStrings [":"] [""] indexState}" {} ''
+    mkdir -p $out
+    cp -r ${cachedState}/.cabal $out
+    chmod +w -R $out/.cabal
+    sed -i.back -e "s|${cachedState}|$out|g" $out/.cabal/config
+    HOME=$out ${cabal-install}/bin/cabal new-update 'hackage.haskell.org,${indexState}'
+  ''