Test with Cabal and Stack, fix build with older snapshots

1. Fix code in order to be compatible with older Stack LTS and ‘nixpkgs’
   snapshots

2. Add few older ‘nixpkgs’ release version Niv pins and add ‘shell.nix’ argument
   to be able to simply use different version
   (e.g. ‘--argstr nixpkgs-release 19.04’)

3. Update Stack LTS snapshot to the latest stable one (17.6, GHC 8.10.4)

4. Add some code to ‘shell.nix’ for testing with older Stack LTS snapshots

5. Provide an example of how to test the application with older Stack LTS
   snapshot in the comments of ‘stack.yaml’

.gitignore

@@ -1,5 +1,6 @@
 build
 dist
+dist-newstyle
 result
 
 cabal.sandbox.config

nix/sources.json

@@ -34,5 +34,41 @@
         "type": "tarball",
         "url": "https://github.com/NixOS/nixpkgs/archive/a3fa481cb683d619ab9e1a64877f3c0c5fd24f40.tar.gz",
         "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
+    },
+    "nixpkgs-19.03": {
+        "branch": "release-19.03",
+        "description": "Nix Packages collection",
+        "homepage": "",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "27aaaa5ba6923104a23bae75d323dc975390195e",
+        "sha256": "1fdzc6psj369bi9bybgm9vwl5c7sa4z6k2sdz95ypcpgcg3s12ql",
+        "type": "tarball",
+        "url": "https://github.com/NixOS/nixpkgs/archive/27aaaa5ba6923104a23bae75d323dc975390195e.tar.gz",
+        "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
+    },
+    "nixpkgs-19.09": {
+        "branch": "release-19.09",
+        "description": "Nix Packages collection",
+        "homepage": "",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "75f4ba05c63be3f147bcc2f7bd4ba1f029cedcb1",
+        "sha256": "157c64220lf825ll4c0cxsdwg7cxqdx4z559fdp7kpz0g6p8fhhr",
+        "type": "tarball",
+        "url": "https://github.com/NixOS/nixpkgs/archive/75f4ba05c63be3f147bcc2f7bd4ba1f029cedcb1.tar.gz",
+        "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
+    },
+    "nixpkgs-20.03": {
+        "branch": "release-20.03",
+        "description": "Nix Packages collection",
+        "homepage": "",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "462c6fe4b115804ea4d5bee7103c0f46ff9f9cfb",
+        "sha256": "0a4bdaxjrds6kyw9s3r2vbc96f7glgy5n03jk4zr5z8h3j4v2s81",
+        "type": "tarball",
+        "url": "https://github.com/NixOS/nixpkgs/archive/462c6fe4b115804ea4d5bee7103c0f46ff9f9cfb.tar.gz",
+        "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
     }
 }

shell.nix

@@ -2,9 +2,17 @@
 # License: GNU/GPLv3 https://raw.githubusercontent.com/unclechu/place-cursor-at/master/LICENSE
 
 let sources = import nix/sources.nix; in
-# Forwarded arguments
 args@
-{ pkgs ? import sources.nixpkgs {}
+{ pkgs ?
+    import sources."nixpkgs${
+      if nixpkgs-release == "20.09" then "" else "-${nixpkgs-release}"
+    }" {}
+
+# Tested with lower 19.03 and upper 20.09 pins.
+, nixpkgs-release ? "20.09" # One of: '20.09', '20.03', '19.09', '19.03'
+
+# It’s not provided in 19.03 for instance
+, yq-go ? (import sources.nixpkgs { inherit (pkgs) config; }).yq-go
 
 # Forwarded build options
 , __src ? null
@@ -16,6 +24,7 @@ args@
 # Local arguments
 , withCabal ? false
 , withStack ? false
+, withStackNixDependencies ? false
 , withPackageRepl ? false # Adds package library modules into GHCi REPL
 , withHoogle ? true
 , buildExecutable ? true
@@ -28,7 +37,7 @@ let
   hp = pkg.haskellPackages;
   name = pkg.haskellPackage.pname;
 
-  inherit (nix-utils) wrapExecutable;
+  inherit (nix-utils) esc wrapExecutable;
   pkgReplGhc = hp.ghcWithPackages (p: [p.${name}]);
 
   # Produces ‘PACKAGE-NAME-ghc’ and ‘PACKAGE-NAME-ghci’ files.
@@ -43,6 +52,34 @@ let
       (exe "ghci")
       (exe "ghc")
     ];
+
+  stackNixDependencies =
+    let
+      stackYamlFile = "${./stack.yaml}";
+      path = "nix.packages";
+
+      nixModule = pkgs.runCommand "${name}-stack-yaml-nix-packages" {} ''
+        set -Eeuo pipefail || exit
+        JSON=$(${esc yq-go}/bin/yq r -j -- ${esc stackYamlFile} ${esc path})
+
+        if [[ -z $JSON ]]; then
+          >&2 printf 'Failed to extract "%s" from "%s"!\n' \
+            ${esc path} ${esc stackYamlFile}
+          exit 1
+        fi
+
+        printf '%s' "$JSON" > "$out"
+      '';
+
+      attrPathToDerivation = x:
+        pkgs.lib.attrsets.getAttrFromPath (pkgs.lib.splitString "." x) pkgs;
+
+      attrPaths = builtins.fromJSON (builtins.readFile nixModule);
+    in
+      assert builtins.isList attrPaths;
+      assert builtins.length attrPaths > 0;
+      assert builtins.all builtins.isString attrPaths;
+      map attrPathToDerivation attrPaths;
 in
 hp.shellFor {
   packages = p: [
@@ -54,6 +91,7 @@ hp.shellFor {
   buildInputs =
     (if withCabal then [ hp.cabal-install ] else []) ++
     (if withStack then [ hp.stack ] else []) ++
+    (if withStackNixDependencies then stackNixDependencies else []) ++
     (if buildExecutable then [ hp.${name} ] else []) ++
     (if withPackageRepl then pkgRepl else []);
 }

src/place-cursor-at.hs

@@ -9,7 +9,7 @@
 {-# LANGUAGE UnicodeSyntax, BangPatterns, MultiWayIf, ViewPatterns, ScopedTypeVariables, GADTs #-}
 {-# LANGUAGE LambdaCase, DerivingStrategies, GeneralizedNewtypeDeriving #-}
 
-import Prelude.Unicode
+import Prelude.Unicode ((∘), (÷), (≡), (⧺), (∧), (≥))
 
 import Data.Bifunctor (first)
 import Data.Bits ((.|.))
@@ -582,3 +582,10 @@ mkDoneHandler = newEmptyMVar <&> \mvar → DoneApi
 (•) = flip (∘)
 infixl 9 •
 {-# INLINE (•) #-}
+
+-- This operator is provided by newer version of ‘base-unicode-symbols’.
+-- This adds support for older snaphots.
+(×) ∷ Num a ⇒ a → a → a
+(×) = (Prelude.*)
+infixl 7 ×
+{-# INLINE (×) #-}

stack.yaml

@@ -1,5 +1,24 @@
-# also tested with lts-14.27 (ghc 8.6.5)
-resolver: lts-16.6 # ghc 8.8.3
+# Also tested with lts-13.19 (ghc 8.6.4).
+#
+# Test older one using Nix:
+#   nix-shell \
+#     --argstr nixpkgs-release 19.03 \
+#     --arg buildExecutable false \
+#     --arg withStack true \
+#     --arg withStackNixDependencies true \
+#     --run '[[ $(ghc --numeric-version) == 8.6.4 ]] && \
+#       stack build --system-ghc --no-nix --resolver=lts-13.19 && \
+#       stack exec --system-ghc --no-nix --resolver=lts-13.19 \
+#       place-cursor-at'
+#
+# Test current one using Nix:
+#   nix-shell \
+#     --arg buildExecutable false \
+#     --arg withStack true \
+#     --run 'stack build --system-ghc && \
+#       stack exec --system-ghc -- place-cursor-at'
+#
+resolver: lts-17.6 # ghc 8.10.4
 
 system-ghc: false
 packages: [.]

stack.yaml.lock

@@ -6,7 +6,7 @@
 packages: []
 snapshots:
 - completed:
-    size: 531718
-    url: https://raw.githubusercontent.com/commercialhaskell/stackage-snapshots/master/lts/16/6.yaml
-    sha256: 230a7266fc11f76222bd3bb68e9503ed11d553060a752f164bff6753ed03e271
-  original: lts-16.6
+    size: 565712
+    url: https://raw.githubusercontent.com/commercialhaskell/stackage-snapshots/master/lts/17/6.yaml
+    sha256: 4e5e581a709c88e3fe26a9ce8bf331435729bead762fb5c190064c6c5bb1b835
+  original: lts-17.6