nix: add dart2nix

We can use this to translate pubspec.lock files into deps.nix dependency
lists. This initial version is fragile, but works well enough to be
helpful.

Author: jtacoma

nix/dart2nix.sh

@@ -0,0 +1,51 @@
+#!/usr/bin/env bash
+
+# Copyright 2020 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+pubspec2nix() {
+  local pubspec_in="$1";
+  local nix_out="$2";
+  if [ -z "$pubspec_in" ] || [ -z "$nix_out" ]; then
+    echo "usage: dart2nix <pubspec.lock> <packages.nix>" >&2
+    exit 1
+  fi
+  local url_template='https://storage.googleapis.com/pub-packages/packages/{{description.name}}-{{version}}.tar.gz'
+  local grep_template='  { name = .{{lock.description.name}}.; version = .{{lock.version}}.; sha256 = '
+  local pkg_template='  { name = "{{lock.description.name}}"; version = "{{lock.version}}"; sha256 = "{{sha256}}"; }'
+  local PATH="$PATH:/nix/store/s8jfiwj2p6hn3ycj840naf2jkac4azx6-jq-1.6-bin/bin" # 'yq' doesn't work unless jq is in $PATH
+  local yq="/nix/store/0l1wva10sr2yyqj78pf4nbqkq1al61qr-python3.8-yq-2.11.1/bin/yq"
+  local mustache="/nix/store/q1lllkgf81rzpsf9lyhw1660q55zn3l7-mustache-go-1.2.0/bin/mustache"
+  [ -f "$nix_out" ] || echo '[' > "$nix_out"
+  $yq -c '.packages[]' "$pubspec_in" | while read dep ; do
+    match="$( echo '{"lock":'$dep'}' | $mustache <(echo "$grep_template") )"
+    if grep "$match" "$nix_out" ; then
+      #echo "already got this one, moving on: $dep"
+      #elif true; then
+      #echo "would download this one: $match"
+      true
+    else
+      url="$(
+        echo "$dep" \
+        | $mustache <(echo "$url_template")
+      )"
+      sha256="$(
+        /nix/store/ckl9rqyajn45crcyw3b743bcaqx1j2w1-nix-2.3.10/bin/nix-hash --flat --base32 --type sha256 <(curl -L "$url")
+      )"
+      echo '{"sha256":"'$sha256'","lock":'$dep'}' | $mustache <(echo "$pkg_template") >> "$nix_out"
+    fi
+  done
+  echo ']' >> "$nix_out"
+}
+pubspec2nix "$@"

nix/default.nix

@@ -49,7 +49,7 @@ let
   };
 
   gitignoreSource =
-    (import sources."gitignore.nix" { inherit (pkgs) lib; }).gitignoreSource;
+    (import sources.gitignore { inherit (pkgs) lib; }).gitignoreSource;
   src = gitignoreSource ./..;
 
   lib = pkgs.lib;
@@ -101,6 +101,8 @@ let
       "$@"
   '';
 
+  dart2nix = pkgs.writeShellScriptBin "dart2nix" (lib.strings.fileContents ./dart2nix.sh);
+
 in rec
 {
   inherit pkgs src;
@@ -118,6 +120,7 @@ in rec
   # Additional tools useful for code work and repository maintenance.
   devTools = buildTools // {
     inherit (pkgs) niv;
+    inherit dart2nix;
   };
 
   buildInputs = builtins.attrValues ciTools;