Update to sentencepiece 0.3

This also requires us to update to nixpkgs-unstable, since the
sentencepiece crate now requires sentencepiece 0.1.90.

nix/sources.json

@@ -55,15 +55,15 @@
         "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
     },
     "nixpkgs": {
-        "branch": "nixos-20.03",
+        "branch": "nixos-unstable",
         "description": "A read-only mirror of NixOS/nixpkgs tracking the released channels. Send issues and PRs to",
         "homepage": "https://github.com/NixOS/nixpkgs",
         "owner": "nixos",
         "repo": "nixpkgs-channels",
-        "rev": "025deb80b2412e5b7e88ea1de631d1bd65af1840",
-        "sha256": "09mp6vqs0h71g27w004yrz1jxla31ihf18phw69wj61ix74ac4m0",
+        "rev": "dc80d7bc4a244120b3d766746c41c0d9c5f81dfa",
+        "sha256": "0dy0mp7alc7m34zxall14x42qx9yjm7b0m6psgmw0lb6j1iy1pla",
         "type": "tarball",
-        "url": "https://github.com/nixos/nixpkgs-channels/archive/025deb80b2412e5b7e88ea1de631d1bd65af1840.tar.gz",
+        "url": "https://github.com/nixos/nixpkgs-channels/archive/dc80d7bc4a244120b3d766746c41c0d9c5f81dfa.tar.gz",
         "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
     },
     "xlm-roberta-base-sentencepiece": {

nix/sources.nix

@@ -49,26 +49,22 @@ let
 
   # The set of packages used when specs are fetched using non-builtins.
   mkPkgs = sources:
-    if hasNixpkgsPath
-    then
-      if hasThisAsNixpkgsPath
-      then import (builtins_fetchTarball { inherit (mkNixpkgs sources) url sha256; }) {}
-      else import <nixpkgs> {}
-    else
-      import (builtins_fetchTarball { inherit (mkNixpkgs sources) url sha256; }) {};
-
-  mkNixpkgs = sources:
-    if builtins.hasAttr "nixpkgs" sources
-    then sources.nixpkgs
-    else abort
-      ''
-        Please specify either <nixpkgs> (through -I or NIX_PATH=nixpkgs=...) or
-        add a package called "nixpkgs" to your sources.json.
-      '';
-
-  hasNixpkgsPath = (builtins.tryEval <nixpkgs>).success;
-  hasThisAsNixpkgsPath =
-    (builtins.tryEval <nixpkgs>).success && <nixpkgs> == ./.;
+    let
+      sourcesNixpkgs =
+        import (builtins_fetchTarball { inherit (sources.nixpkgs) url sha256; }) {};
+      hasNixpkgsPath = builtins.any (x: x.prefix == "nixpkgs") builtins.nixPath;
+      hasThisAsNixpkgsPath = <nixpkgs> == ./.;
+    in
+      if builtins.hasAttr "nixpkgs" sources
+      then sourcesNixpkgs
+      else if hasNixpkgsPath && ! hasThisAsNixpkgsPath then
+        import <nixpkgs> {}
+      else
+        abort
+          ''
+            Please specify either <nixpkgs> (through -I or NIX_PATH=nixpkgs=...) or
+            add a package called "nixpkgs" to your sources.json.
+          '';
 
   # The actual fetching function.
   fetch = pkgs: name: spec:

sticker2/Cargo.toml

@@ -21,7 +21,7 @@ numberer = "0.2"
 ordered-float = "1"
 rand = "0.7"
 rand_xorshift = "0.2"
-sentencepiece = "0.2"
+sentencepiece = "0.3"
 serde = { version = "1", features = [ "derive" ] }
 serde_json = "1"
 sticker-encoders = "0.5.1"