improve deno cache FOD

shelf/deno-workspace.nix

@@ -1,4 +1,4 @@
-{ pkgs, system }:
+{ pkgs, system, knownDenoHashes }:
 
 let
   target =
@@ -18,8 +18,38 @@ let
   scrollsDir = ./deno;
   lib = pkgs.lib;
   packageDirs = builtins.attrNames (builtins.readDir scrollsDir);
-  
-  # Separate FOD for cache only
+
+  # hash only dependency-relevant files (lock files and configs)
+  hashDependencyFiles = dir:
+    let
+      entries = builtins.readDir dir;
+
+      # Only process directories and dependency-relevant files
+      relevantEntry = name: type:
+        if type == "directory"
+        then hashDependencyFiles (dir + "/${name}")
+        else if (lib.hasSuffix ".lock" name ||
+                 lib.hasSuffix ".json" name ||
+                 lib.hasSuffix ".jsonc" name)
+        then builtins.readFile (dir + "/${name}")
+        else null;
+
+      contentMap = lib.filterAttrs (_: v: v != null)
+        (builtins.mapAttrs relevantEntry entries);
+    in builtins.toJSON contentMap;
+
+  sourceContentHash = builtins.convertHash {
+    hash = "sha1:${builtins.hashString "sha1" (hashDependencyFiles scrollsDir)}";
+    toHashFormat = "base64";
+  };
+
+  # we assume that same lock+config files yield same deno caches here
+  # however, jsons need to be sorted and some sqlite files deleted
+
+  # jsr gentlemen specifically require their package metadata
+  # to have multiple timestamps, so they can fuck off
+  outputHash = knownDenoHashes.${sourceContentHash} or lib.fakeSha256;
+
   unifiedCache = pkgs.stdenv.mkDerivation {
     name = "deno-scrolls-cache";
     src = scrollsDir;
@@ -50,13 +80,21 @@ let
           ${pkgs.jq}/bin/jq -S . "$file" > "$file.tmp" && mv "$file.tmp" "$file"
         fi
       done
+
+      echo 'sourceContentHash: ${sourceContentHash}'
+      echo ""
+      echo "add me to knownHashes if you see a fake sha256 error ^"
+      echo "DON'T USE JSR DEPS UNLESS YOU MAKE THEM REPRODUCIBLE SOMEHOW"
+      echo ""
     '';
     
     installPhase = "true";
     
     outputHashMode = "recursive";
     outputHashAlgo = "sha256";
-    outputHash = "sha256-maP/JMY6n95A9FQx72YFwRtnprGXc97v1ZdPgt2GB8s=";
+    # this is basically FOD on steroids cause it
+    # deliberately breaks on relevant source changes
+    inherit outputHash;
   };
   
 in