Improve dev tools in the Nix environment (#1666)

* Improve dev tools in the nix environment

Added postgrest-build, postgrest-run, postgrest-clean, postgrest-check
and postgrest-watch tools. Changed order of postgrest-test-spec-all to
run backwards from pg13 to pg9.5. Added shellcheck to lint shell scripts
in nix environment.

Co-authored-by: monacoremo <monacoremo>

nix/style.nix

@@ -0,0 +1,49 @@
+{ buildEnv
+, checkedShellScript
+, git
+, hlint
+, nixpkgs-fmt
+, silver-searcher
+, stylish-haskell
+}:
+let
+  style =
+    checkedShellScript "postgrest-style"
+      ''
+        rootdir="$(${git}/bin/git rev-parse --show-toplevel)"
+
+        # Format Nix files
+        ${nixpkgs-fmt}/bin/nixpkgs-fmt "$rootdir" > /dev/null 2> /dev/null
+
+        # Format Haskell files
+        ${silver-searcher}/bin/ag -l -g '\.l?hs$' . "$rootdir" \
+          | xargs ${stylish-haskell}/bin/stylish-haskell -i
+      '';
+
+  # Script to check whether any uncommited changes result from postgrest-style
+  styleCheck =
+    checkedShellScript "postgrest-style-check"
+      ''
+        ${style}
+
+        ${git}/bin/git diff-index --exit-code HEAD -- '*.hs' '*.lhs' '*.nix'
+      '';
+
+  lint =
+    checkedShellScript "postgrest-lint"
+      ''
+        rootdir="$(${git}/bin/git rev-parse --show-toplevel)"
+
+        # Lint Haskell files
+        ${silver-searcher}/bin/ag -l -g '\.l?hs$' "$rootdir" \
+          | xargs ${hlint}/bin/hlint -X QuasiQuotes -X NoPatternSynonyms
+      '';
+in
+buildEnv {
+  name = "postgrest-devtools";
+  paths = [
+    style.bin
+    styleCheck.bin
+    lint.bin
+  ];
+}