tech(nix): update niv and remove allowbroken (#350)

https://github.com/haskell/haskell-language-server/issues/325
retrie is no longer appears to be marked broken:
https://github.com/NixOS/nixpkgs/blob/master/pkgs/development/haskell-modules/hackage-packages.nix#L215948

nix/sources.json

@@ -5,10 +5,10 @@
         "homepage": "https://github.com/nmattia/niv",
         "owner": "nmattia",
         "repo": "niv",
-        "rev": "ab9cc41caf44d1f1d465d8028e4bc0096fd73238",
-        "sha256": "17k52n8zwp832cqifsc4458mhy4044wmk22f807171hf6p7l4xvr",
+        "rev": "89ae775e9dfc2571f912156dd2f8627e14d4d507",
+        "sha256": "0ssw6byyn79fpyzswi28s5b85x66xh4xsfhmcfl5mkdxxpmyy0ns",
         "type": "tarball",
-        "url": "https://github.com/nmattia/niv/archive/ab9cc41caf44d1f1d465d8028e4bc0096fd73238.tar.gz",
+        "url": "https://github.com/nmattia/niv/archive/89ae775e9dfc2571f912156dd2f8627e14d4d507.tar.gz",
         "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
     },
     "nixpkgs": {
@@ -17,10 +17,10 @@
         "homepage": "https://github.com/NixOS/nixpkgs",
         "owner": "NixOS",
         "repo": "nixpkgs-channels",
-        "rev": "2c4e0f37a6d5d33666b550a1b85daf46b37f1b25",
-        "sha256": "0hqr6ci0rgg1fyfg7w2182vgbi0cq472p2j8r7mcmkbpdwwi6i69",
+        "rev": "a332da8588aeea4feb9359d23f58d95520899e3c",
+        "sha256": "18hlja5syv3xpi14c07h9lrn1cchq2azmj06fyalq52vl064nx75",
         "type": "tarball",
-        "url": "https://github.com/NixOS/nixpkgs-channels/archive/2c4e0f37a6d5d33666b550a1b85daf46b37f1b25.tar.gz",
+        "url": "https://github.com/NixOS/nixpkgs-channels/archive/a332da8588aeea4feb9359d23f58d95520899e3c.tar.gz",
         "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
     }
 }

nix/sources.nix

@@ -12,36 +12,29 @@ let
     else
       pkgs.fetchurl { inherit (spec) url sha256; };
 
-  fetch_tarball = pkgs: spec:
-    if spec.builtin or true then
-      builtins_fetchTarball { inherit (spec) url sha256; }
-    else
-      pkgs.fetchzip { inherit (spec) url sha256; };
+  fetch_tarball = pkgs: name: spec:
+    let
+      ok = str: ! builtins.isNull (builtins.match "[a-zA-Z0-9+-._?=]" str);
+      # sanitize the name, though nix will still fail if name starts with period
+      name' = stringAsChars (x: if ! ok x then "-" else x) "${name}-src";
+    in
+      if spec.builtin or true then
+        builtins_fetchTarball { name = name'; inherit (spec) url sha256; }
+      else
+        pkgs.fetchzip { name = name'; inherit (spec) url sha256; };
 
   fetch_git = spec:
     builtins.fetchGit { url = spec.repo; inherit (spec) rev ref; };
 
-  fetch_builtin-tarball = spec:
-    builtins.trace
-      ''
-        WARNING:
-          The niv type "builtin-tarball" will soon be deprecated. You should
-          instead use `builtin = true`.
+  fetch_local = spec: spec.path;
 
-          $ niv modify <package> -a type=tarball -a builtin=true
-      ''
-      builtins_fetchTarball { inherit (spec) url sha256; };
+  fetch_builtin-tarball = name: throw
+    ''[${name}] The niv type "builtin-tarball" is deprecated. You should instead use `builtin = true`.
+        $ niv modify ${name} -a type=tarball -a builtin=true'';
 
-  fetch_builtin-url = spec:
-    builtins.trace
-      ''
-        WARNING:
-          The niv type "builtin-url" will soon be deprecated. You should
-          instead use `builtin = true`.
-
-          $ niv modify <package> -a type=file -a builtin=true
-      ''
-      (builtins_fetchurl { inherit (spec) url sha256; });
+  fetch_builtin-url = name: throw
+    ''[${name}] The niv type "builtin-url" will soon be deprecated. You should instead use `builtin = true`.
+        $ niv modify ${name} -a type=file -a builtin=true'';
 
   #
   # Various helpers
@@ -72,13 +65,23 @@ let
     if ! builtins.hasAttr "type" spec then
       abort "ERROR: niv spec ${name} does not have a 'type' attribute"
     else if spec.type == "file" then fetch_file pkgs spec
-    else if spec.type == "tarball" then fetch_tarball pkgs spec
+    else if spec.type == "tarball" then fetch_tarball pkgs name spec
     else if spec.type == "git" then fetch_git spec
-    else if spec.type == "builtin-tarball" then fetch_builtin-tarball spec
-    else if spec.type == "builtin-url" then fetch_builtin-url spec
+    else if spec.type == "local" then fetch_local spec
+    else if spec.type == "builtin-tarball" then fetch_builtin-tarball name
+    else if spec.type == "builtin-url" then fetch_builtin-url name
     else
       abort "ERROR: niv spec ${name} has unknown type ${builtins.toJSON spec.type}";
 
+  # If the environment variable NIV_OVERRIDE_${name} is set, then use
+  # the path directly as opposed to the fetched source.
+  replace = name: drv:
+    let
+      saneName = stringAsChars (c: if isNull (builtins.match "[a-zA-Z0-9]" c) then "_" else c) name;
+      ersatz = builtins.getEnv "NIV_OVERRIDE_${saneName}";
+    in
+      if ersatz == "" then drv else ersatz;
+
   # Ports of functions for older nix versions
 
   # a Nix version of mapAttrs if the built-in doesn't exist
@@ -87,13 +90,23 @@ let
     listToAttrs (map (attr: { name = attr; value = f attr set.${attr}; }) (attrNames set))
   );
 
+  # https://github.com/NixOS/nixpkgs/blob/0258808f5744ca980b9a1f24fe0b1e6f0fecee9c/lib/lists.nix#L295
+  range = first: last: if first > last then [] else builtins.genList (n: first + n) (last - first + 1);
+
+  # https://github.com/NixOS/nixpkgs/blob/0258808f5744ca980b9a1f24fe0b1e6f0fecee9c/lib/strings.nix#L257
+  stringToCharacters = s: map (p: builtins.substring p 1 s) (range 0 (builtins.stringLength s - 1));
+
+  # https://github.com/NixOS/nixpkgs/blob/0258808f5744ca980b9a1f24fe0b1e6f0fecee9c/lib/strings.nix#L269
+  stringAsChars = f: s: concatStrings (map f (stringToCharacters s));
+  concatStrings = builtins.concatStringsSep "";
+
   # fetchTarball version that is compatible between all the versions of Nix
-  builtins_fetchTarball = { url, sha256 }@attrs:
+  builtins_fetchTarball = { url, name, sha256 }@attrs:
     let
       inherit (builtins) lessThan nixVersion fetchTarball;
     in
       if lessThan nixVersion "1.12" then
-        fetchTarball { inherit url; }
+        fetchTarball { inherit name url; }
       else
         fetchTarball attrs;
 
@@ -115,13 +128,13 @@ let
         then abort
           "The values in sources.json should not have an 'outPath' attribute"
         else
-          spec // { outPath = fetch config.pkgs name spec; }
+          spec // { outPath = replace name (fetch config.pkgs name spec); }
     ) config.sources;
 
   # The "config" used by the fetchers
   mkConfig =
-    { sourcesFile ? ./sources.json
-    , sources ? builtins.fromJSON (builtins.readFile sourcesFile)
+    { sourcesFile ? if builtins.pathExists ./sources.json then ./sources.json else null
+    , sources ? if isNull sourcesFile then {} else builtins.fromJSON (builtins.readFile sourcesFile)
     , pkgs ? mkPkgs sources
     }: rec {
       # The sources, i.e. the attribute set of spec name to spec
@@ -130,5 +143,6 @@ let
       # The "pkgs" (evaluated nixpkgs) to use for e.g. non-builtin fetchers
       inherit pkgs;
     };
+
 in
 mkSources (mkConfig {}) // { __functor = _: settings: mkSources (mkConfig settings); }

shell.nix

@@ -16,9 +16,7 @@
 #    assuming that cabal new-build does succeed outside nix-shell
 
 { sources ? import nix/sources.nix,
-  # TODO Remove allowBroken once retrie is no longer marked as broken in Nixpkgs
-  # See https://github.com/haskell/haskell-language-server/issues/325
-  nixpkgs ? import sources.nixpkgs { config.allowBroken = true; },
+  nixpkgs ? import sources.nixpkgs { },
   compiler ? "default",
   hoogle ? false
  }: