Add haskell-nix.project (and project') (input-output-hk#703)

Generalized version of the `cabalProject` and `stackProject`
functions.

Automatically selects the correct project type based on the
`projectFileName` argument if provided or what files exist in
the `src` directory if no `projectFileName` was specified.

If it cannot be determined which it should use the following
error message is given:

```
error: haskell-nix.project : both `stack.yaml` and `cabal.project` files exist set `projectFileName = "stack.yaml;"` or `projectFileName = "cabal.project";`
```

Author: hamishmack

docs/tutorials/clean-git.md

@@ -75,7 +75,7 @@ packages:
 Then in `repoA/default.nix` we can use:
 
 ```
-haskell-nix.cabalProject {
+haskell-nix.project {
   src = haskell-nix.haskellLib.cleanSourceWith {
     src = haskell-nix.haskellLib.cleanGits {
       name = "root";

docs/tutorials/getting-started.md

@@ -18,16 +18,19 @@ $ cachix use iohk
 
 ## Scaffolding
 
-The following configuration will use `stack.yaml` if it exists,
-otherwise fallback to `cabal.project`.
+The following work with `stack.yaml` and `cabal.project` based
+projects.
 
 Add `default.nix`:
 
 ```nix
-{ haskellCompiler ? "ghc865"
+{ # Default version of GHC to use (when not otherwise specified)
+  defaultCompilerNixName ? "ghc865"
 
 # Fetch the latest haskell.nix and import its default.nix
-, haskellNix ? import (builtins.fetchTarball https://github.com/input-output-hk/haskell.nix/archive/master.tar.gz) {}
+, haskellNix ? import (builtins.fetchTarball https://github.com/input-output-hk/haskell.nix/archive/master.tar.gz) {
+  inherit defaultCompilerNixName;
+}
 
 # haskell.nix provides access to the nixpkgs pins which are used by our CI, hence
 # you will be more likely to get cache hits when using these.
@@ -40,26 +43,26 @@ Add `default.nix`:
 
 # import nixpkgs with overlays
 , pkgs ? import nixpkgsSrc nixpkgsArgs
+}: pkgs.haskell-nix.project {
+  # 'cleanGit' cleans a source directory based on the files known by git
+  src = pkgs.haskell-nix.haskellLib.cleanGit {
+    name = "haskell-nix-project";
+    src = ./.;
+  };
+}
+```
+
+Or a shorter `default.nix` that uses the default nixpkgs and default GHC:
 
-# 'cleanGit' cleans a source directory based on the files known by git
-, src ? pkgs.haskell-nix.haskellLib.cleanGit {
+```nix
+{ haskellNix ? import (builtins.fetchTarball https://github.com/input-output-hk/haskell.nix/archive/master.tar.gz) {}
+, pkgs ? haskellNix.pkgs
+}: pkgs.haskell-nix.project {
+  src = pkgs.haskell-nix.haskellLib.cleanGit {
     name = "haskell-nix-project";
     src = ./.;
-  }
-, hasStack ? builtins.pathExists (./. + "/cabal.project")
-, hasCabalProject ? builtins.pathExists (./. + "/stack.yaml")
-}:
-
-assert (if hasStack && hasCabalProject then throw "This project has both stack.yaml and cabal.project. Edit default.nix to pick the one you'd like to use." else true);
-
-if hasStack
-then pkgs.haskell-nix.stackProject
-  { inherit src;
-  }
-else pkgs.haskell-nix.cabalProject
-  { inherit src;
-    compiler-nix-name = haskellCompiler;
-  }
+  };
+}
 ```
 
 !!! note "git dependencies"

docs/tutorials/materialization.md

@@ -8,9 +8,9 @@ of an IFD (import from derviation).
 
 ## Why use materialization?
 
-Using functions like `cabalProject`, `stackProject` and `hackage-package`
-results in a lot of dependencies (all the dependencies of nix-tools
-for instance).
+Using functions like `project`, `cabalProject`, `stackProject`
+and `hackage-package` results in a lot of dependencies (all the
+dependencies of nix-tools for instance).
 
 * They can be slow to calculate (even if no work needs to be done it
   is not unusual for it to take 5 seconds per project).
@@ -59,8 +59,8 @@ trace: Using index-state: 2020-04-15T00:00:00Z for hlint
 ```
 
 To materialize the nix files we need to take care to pin down the
-inputs.  For `cabalProject` and `hackage-package` this means
-we must specify the `index-state` of hackage we want to use:
+inputs.  For cabal projects this means we must specify the
+`index-state` of hackage we want to use:
 
 ```nix
 let inherit (import ./. {}) sources nixpkgsArgs;
@@ -88,7 +88,7 @@ $ nix-hash --base32 --type sha256 /nix/store/8z6p4237rin3c6c1lmjwshmj8rdqrhw2-hl
 ```
 
 We can add the hash as `plan-sha256` or (`stack-sha256` for
-`stackProject`)
+stack projects)
 
 ```nix
 let inherit (import ./. {}) sources nixpkgsArgs;
@@ -191,10 +191,10 @@ the time, we would be better off just removing `materialized` and `plan-sha256`.
 
 ## How can we update the nix files with a script?
 
-There are versions of the functions (`cabalProject'`, `stackProject'`
-and `hackage-project`) that also return the nix as `plan-nix` or
-`stack-nix`.  By calling one of these functions without the
-hash and materialized nix we can find out what nix files should be.
+There are versions of the functions (`project'`, `cabalProject'`,
+`stackProject'` and `hackage-project`) that also return the nix as
+`plan-nix` or `stack-nix`.  By calling one of these functions without
+the hash and materialized nix we can find out what nix files should be.
 For instance:
 
 ```nix

docs/tutorials/source-repository-hashes.md

@@ -7,8 +7,8 @@ that we wish to use.  This is mostly handled automatically by
 system that is configured to use restricted mode (typically hydra)
 it will need an aditionaly hash.
 
-When using `cabalProject` or `stackProject` functions you can include
-the hash needed in a comment.
+When using `project`, `cabalProject` or `stackProject` functions
+you can include the hash needed in a comment.
 
 To calculate the hash use `nix-prefetch-git`:
 
@@ -24,7 +24,7 @@ $ nix-prefetch-git https://github.com/input-output-hk/haskell.nix.git bc01ebc05a
 }
 ```
 
-If you are using `cabalProject` add a `--sha256` comment to the
+If you have a cabal project add a `--sha256` comment to the
 `cabal.project` file:
 
 ```
@@ -36,7 +36,7 @@ source-repository-package
   --sha256: 003lm3pm024vhbfmii7xcdd9v2rczpflxf7gdl2pyxia7p014i8z
 ```
 
-If you are using `stackProject` add a `# nix-sha256` comment to the
+If you have a stack project add a `# nix-sha256` comment to the
 `stack.yaml` file:
 
 ```
@@ -48,12 +48,12 @@ extra-deps:
   # nix-sha256: 003lm3pm024vhbfmii7xcdd9v2rczpflxf7gdl2pyxia7p014i8z
 ```
 
-## lookupSha256
+## sha256map
 
-In some cases we cannot modify the `cabal.project` file to add the
-`--sha256` comments. As an alternative we can pass in a `lookupSha256`
-function to get them.  For instance pandoc includes a `cabal.project`
-file in hackage includes a `source-package-reference` to `pandoc-citeproc`:
+In some cases we cannot modify the `cabal.project` or `stack.yaml` file
+to add sha256 comments. As an alternative we can pass in a `sha256map`
+For instance pandoc includes a `cabal.project` file in hackage includes a
+`source-package-reference` to `pandoc-citeproc`:
 
 ```
 { haskell-nix, testSrc } :
@@ -64,10 +64,9 @@ let
     index-state  = "2020-04-15T00:00:00Z"; 
     # Function that returns a sha256 string by looking up the location
     # and tag in a nested attrset
-    lookupSha256 = { location, tag, ... }:
+    sha256map =
       { "https://github.com/jgm/pandoc-citeproc"."0.17"
-          = "0dxx8cp2xndpw3jwiawch2dkrkp15mil7pyx7dvd810pwc22pm2q"; }
-        ."${location}"."${tag}";
+          = "0dxx8cp2xndpw3jwiawch2dkrkp15mil7pyx7dvd810pwc22pm2q"; };
   };
 in
   pandoc.components.exes.pandoc

overlays/haskell.nix

@@ -541,6 +541,47 @@ final: prev: {
               shells.ghc = p.hsPkgs.shellFor {};
             };
 
+        # `project'` and `project` automatically select between `cabalProject`
+        # and `stackProject` (when possible) by looking for `stack.yaml` or
+        # `cabal.project` files.  If both exist we can pass in one of:
+        #     `projectFileName = "stack.yaml;"`
+        #     `projectFileName = "cabal.project";`
+        # to let it know which to choose (or pick another name).  If the
+        # selected file ends in a `.yaml` it is assumed to be for `stackProject`.
+        # If niether `stack.yaml` nor `cabal.project` exist `cabalProject` is
+        # used (as it will use a default `cabal.project`).
+        project' = { src, projectFileName ? null, ... }@args: 
+          let
+            dir = __readDir (src.origSrcSubDir or src);
+            exists = fileName: builtins.elem (dir.${fileName} or "") ["regular" "symlink"];
+            stackYamlExists    = exists "stack.yaml";
+            cabalProjectExists = exists "cabal.project";
+            selectedFileName =
+              if projectFileName != null
+                then projectFileName  # Prefer the user selected project file name
+                else
+                  if stackYamlExists && cabalProjectExists
+                    then throw ("haskell-nix.project : both `stack.yaml` and `cabal.project` files exist "
+                      + "set `projectFileName = \"stack.yaml\";` or `projectFileName = \"cabal.project\";`")
+                    else
+                      if stackYamlExists
+                        then "stack.yaml"      # stack needs a stack.yaml
+                        else "cabal.project";  # the cabal.project file is optional
+          in
+            if final.lib.hasSuffix ".yaml" selectedFileName
+              then stackProject' (args // { stackYaml            = selectedFileName; })
+              else cabalProject' (args // { cabalProjectFileName = selectedFileName; });
+
+        # This is the same as the `cabalPackage` and `stackPackage` wrappers
+        # for `cabalPackage` and `stackPackage`.
+        project = args: let p = project' args;
+            in p.hsPkgs // {
+              # Provide `nix-shell -A shells.ghc` for users migrating from the reflex-platform.
+              # But we should encourage use of `nix-shell -A shellFor`
+              shells.ghc = p.hsPkgs.shellFor {};
+            } // final.lib.optionalAttrs (p ? stack-nix) { inherit (p) stack-nix; }
+              // final.lib.optionalAttrs (p ? plan-nix ) { inherit (p) plan-nix;  };
+
         # Like `cabalProject'`, but for building the GHCJS compiler.
         # This is exposed to allow GHCJS developers to work on the GHCJS
         # code in a nix-shell with `shellFor`.

test/cabal-simple/default.nix

@@ -1,5 +1,5 @@
 # Test a package set
-{ stdenv, util, mkCabalProjectPkgSet, cabalProject', haskellLib, recurseIntoAttrs, testSrc }:
+{ stdenv, util, mkCabalProjectPkgSet, project', haskellLib, recurseIntoAttrs, testSrc }:
 
 with stdenv.lib;
 
@@ -12,7 +12,7 @@ let
      }
   ];
 
-  project = cabalProject' {
+  project = project' {
     src = testSrc "cabal-simple";
     inherit modules;
   };

test/haskell-language-server/cabal.nix

@@ -1,12 +1,13 @@
 { testSrc, evalPackages, buildPackages }:
 
-(buildPackages.haskell-nix.cabalProject {
+(buildPackages.haskell-nix.project {
   src = evalPackages.fetchgit {
     url = "https://github.com/haskell/haskell-language-server.git";
     fetchSubmodules = true;
     rev = "d2654185eef1b0d703cebc694e85438e20600e37";
     sha256 = "0s0k2i0imkcn9zykhrlqq0r4ssv25mwbpdyc675xkzgl1vj1l8kd";
   };
+  projectFileName = "cabal.project";
   sha256map = {
     "https://github.com/wz1000/shake"."fb3859dca2e54d1bbb2c873e68ed225fa179fbef" = "0sa0jiwgyvjsmjwpfcpvzg2p7277aa0dgra1mm6afh2rfnjphz8z";
     "https://github.com/peti/cabal-plan"."894b76c0b6bf8f7d2f881431df1f13959a8fce87" = "06iklj51d9kh9bhc42lrayypcpgkjrjvna59w920ln41rskhjr4y";

test/haskell-language-server/stack.nix

@@ -1,13 +1,13 @@
 { testSrc, haskell-nix, evalPackages, buildPackages }:
 
-(buildPackages.haskell-nix.stackProject {
+(buildPackages.haskell-nix.project {
   src = evalPackages.fetchgit {
     url = "https://github.com/haskell/haskell-language-server.git";
     fetchSubmodules = true;
     rev = "d2654185eef1b0d703cebc694e85438e20600e37";
     sha256 = "0s0k2i0imkcn9zykhrlqq0r4ssv25mwbpdyc675xkzgl1vj1l8kd";
   };
-  stackYaml = "stack-${haskell-nix.ghc.version}.yaml";
+  projectFileName = "stack-${haskell-nix.ghc.version}.yaml";
   sha256map = {
     "https://github.com/wz1000/shake.git"."fb3859dca2e54d1bbb2c873e68ed225fa179fbef" = "0sa0jiwgyvjsmjwpfcpvzg2p7277aa0dgra1mm6afh2rfnjphz8z";
     "https://github.com/peti/cabal-plan.git"."894b76c0b6bf8f7d2f881431df1f13959a8fce87" = "06iklj51d9kh9bhc42lrayypcpgkjrjvna59w920ln41rskhjr4y";

test/stack-local-resolver/default.nix

@@ -1,7 +1,7 @@
-{ stackProject', recurseIntoAttrs, testSrc }:
+{ project', recurseIntoAttrs, testSrc }:
 
 let
-  project = stackProject' {
+  project = project' {
     src = testSrc "stack-local-resolver";
   };
   packages = project.hsPkgs;