elm: add instructions for versions.dat and elm-elm.nix

(cherry picked from commit fcabcb2e41a89b2249d24e68355866979e961f8a)
Signed-off-by: Domen Kožar <[e-mail]>

pkgs/development/compilers/elm/default.nix

···
 # To update:
 
 # 1) Modify ./update.sh and run it
-# 2) XXX: generate packages/elm-elm.nix
-# 3) XXX: versions.dat
+
+# 2) to generate versions.dat:
+# 2.1) git clone https://github.com/elm/compiler.git
+# 2.2) cd compiler
+# 2.3) cabal2nix --shell . | sed 's/"default",/"ghc822",/' > shell.nix
+# 2.4) nix-shell
+# 2.5) mkdir .elm
+# 2.6) export ELM_HOME=$(pwd)/.elm
+# 2.7) cabal build
+# 2.8) cp .elm/0.19.0/package/versions.dat ...
+
+# 3) generate a template for elm-elm.nix with:
+# (
+#   echo "{";
+#   jq '.dependencies | .direct, .indirect | to_entries | .[] | { (.key) : { version : .value, sha256:  "" } } ' \
+#   < ui/browser/elm.json \
+#   | sed 's/:/ =/' \
+#   | sed 's/^[{}]//' \
+#   | sed -E 's/(["}]),?$/\1;/' \
+#   | sed -E 's/"(version|sha256)"/\1/' \
+#   | grep -v '^$';
+#   echo "}"
+# )
+#
+# ... then fill in the sha256s
 
 # Notes:
 

pkgs/development/compilers/elm/packages/elm-elm.nix

···
 {
-  "elm/time" = {
-    version = "1.0.0";
-    sha256 = "0vch7i86vn0x8b850w1p69vplll1bnbkp8s383z7pinyg94cm2z1";
-  };
-  "elm/url" = {
+  "elm/browser" = {
     version = "1.0.0";
-    sha256 = "0av8x5syid40sgpl5vd7pry2rq0q4pga28b4yykn9gd9v12rs3l4";
+    sha256 = "1apmvyax93nvmagwj00y16zx10kfv640cxpi64xgqbgy7d2wphy4";
   };
-  "elm/json" = {
+  "elm/core" = {
     version = "1.0.0";
-    sha256 = "1g0hafkqf2q633r7ir9wxpb1lnlzskhpsyi0h5bkzj0gl072zfnb";
+    sha256 = "10kr86h4v5h4p0586q406a5wbl8xvr1jyrf6097zp2wb8sv21ylw";
   };
   "elm/html" = {
     version = "1.0.0";
     sha256 = "1n3gpzmpqqdsldys4ipgyl1zacn0kbpc3g4v3hdpiyfjlgh8bf3k";
   };
-  "elm/parser" = {
-    version = "1.0.0";
-    sha256 = "0k4zlq30lrvawqvzwbvsl0hrmwf9s832mb41z7fdspm4549dj7wc";
-  };
   "elm/http" = {
     version = "1.0.0";
     sha256 = "1igmm89ialzrjib1j8xagkxalq1x2gj4l0hfxcd66mpwmvg7psl8";
   };
-  "elm/virtual-dom" = {
-    version = "1.0.0";
-    sha256 = "0hm8g92h7z39km325dlnhk8n00nlyjkqp3r3jppr37k2k13md6aq";
-  };
-  "elm/browser" = {
+  "elm/json" = {
     version = "1.0.0";
-    sha256 = "1apmvyax93nvmagwj00y16zx10kfv640cxpi64xgqbgy7d2wphy4";
+    sha256 = "1g0hafkqf2q633r7ir9wxpb1lnlzskhpsyi0h5bkzj0gl072zfnb";
   };
-  "elm/core" = {
+  "elm/project-metadata-utils" = {
     version = "1.0.0";
-    sha256 = "10kr86h4v5h4p0586q406a5wbl8xvr1jyrf6097zp2wb8sv21ylw";
+    sha256 = "1d4rd4grrnbdvj9gf00h7dr6hbkjzawgkzpizfrkp1z1pyr3mvq9";
   };
   "elm/svg" = {
     version = "1.0.0";
     sha256 = "08x0v8p9wm699jjmsnbq69pxv3jh60j4f6fg7y6hyr7xxj85y390";
   };
-  "elm/project-metadata-utils" = {
-    version = "1.0.0";
-    sha256 = "1d4rd4grrnbdvj9gf00h7dr6hbkjzawgkzpizfrkp1z1pyr3mvq9";
-  };
   "elm-explorations/markdown" = {
     version = "1.0.0";
     sha256 = "0k3110ixa4wwf3vkkdplagwah9ypr965qxr1y147rnsc1xsxmr6y";
+  };
+  "elm/parser" = {
+    version = "1.0.0";
+    sha256 = "0k4zlq30lrvawqvzwbvsl0hrmwf9s832mb41z7fdspm4549dj7wc";
+  };
+  "elm/time" = {
+    version = "1.0.0";
+    sha256 = "0vch7i86vn0x8b850w1p69vplll1bnbkp8s383z7pinyg94cm2z1";
+  };
+  "elm/url" = {
+    version = "1.0.0";
+    sha256 = "0av8x5syid40sgpl5vd7pry2rq0q4pga28b4yykn9gd9v12rs3l4";
+  };
+  "elm/virtual-dom" = {
+    version = "1.0.0";
+    sha256 = "0hm8g92h7z39km325dlnhk8n00nlyjkqp3r3jppr37k2k13md6aq";
   };
 }