add better diff ignores

hosts/juni/impermanence-tools.nix

@@ -7,9 +7,64 @@
 let
   cfg = config.impermanence.tools;
 
-  bcacheImpermanenceBin = pkgs.writeShellScriptBin "bcache-impermanence" (
+  persistence = config.environment.persistence or { };
+
+  normalizePath = v:
+    if builtins.isString v then
+      v
+    else if v ? dirPath then
+      v.dirPath
+    else if v ? filePath then
+      v.filePath
+    else
+      null;
+
+  pathsFromList = f: xs: lib.filter (p: p != null) (map f xs);
+
+  userPersistencePaths = users:
+    lib.flatten (
+      lib.mapAttrsToList (
+        userName: userCfg:
+        let
+          home = (config.users.users.${userName} or { }).home or "/home/${userName}";
+          normalizeUserPath = v:
+            if builtins.isString v then
+              if lib.hasPrefix "/" v then v else "${home}/${v}"
+            else
+              normalizePath v;
+        in
+        (pathsFromList normalizeUserPath (userCfg.directories or [ ]))
+        ++ (pathsFromList normalizeUserPath (userCfg.files or [ ]))
+      ) users
+    );
+
+  ignorePaths =
+    lib.unique (
+      lib.filter (p: p != null && p != "" && p != "/") (
+        lib.flatten (
+          lib.mapAttrsToList (
+            persistRoot: persistCfg:
+            [ persistRoot ]
+            ++ (pathsFromList normalizePath (persistCfg.directories or [ ]))
+            ++ (pathsFromList normalizePath (persistCfg.files or [ ]))
+            ++ (userPersistencePaths (persistCfg.users or { }))
+          ) persistence
+        )
+      )
+    );
+
+  ignoreFile = pkgs.writeText "bcache-impermanence-ignore-paths" (
+    lib.concatStringsSep "\n" ignorePaths + "\n"
+  );
+
+  scriptFile = pkgs.writeText "bcache-impermanence.sh" (
     builtins.readFile ./impermanence-tools.sh
   );
+
+  bcacheImpermanenceBin = pkgs.writeShellScriptBin "bcache-impermanence" ''
+    export BCACHE_IMPERMANENCE_IGNORE_FILE="${ignoreFile}"
+    exec ${pkgs.bash}/bin/bash "${scriptFile}" "$@"
+  '';
 in
 {
   options.impermanence.tools = {

hosts/juni/impermanence-tools.sh

@@ -7,6 +7,7 @@ KEEP_RECENT_WEEKS=4
 KEEP_RECENT_COUNT=5
 DRY_RUN=0
 DIFF_MAX_DEPTH=0
+IGNORE_FILE="${BCACHE_IMPERMANENCE_IGNORE_FILE-}"
 
 usage() {
   cat <<EOF
@@ -466,6 +467,13 @@ cmd_diff() {
   local persist_mounts
   persist_mounts=$(awk '$2 ~ "^/persist(/|$)" { print $2 }' /proc/self/mounts || true)
 
+  # Optional ignore list file generated from `environment.persistence`.
+  local ignore_list
+  ignore_list=""
+  if [ -n "$IGNORE_FILE" ] && [ -f "$IGNORE_FILE" ]; then
+    ignore_list=$(grep -vE '^[[:space:]]*($|#)' "$IGNORE_FILE" | sed 's/[[:space:]]*$//' || true)
+  fi
+
   is_persist_backed() {
     local p
     p="$1"
@@ -484,6 +492,34 @@ cmd_diff() {
     return 1
   }
 
+  is_ignored_path() {
+    local p
+    p="$1"
+
+    if [ -z "$p" ] || [ "$p" = "/" ]; then
+      return 1
+    fi
+
+    if [ -z "$ignore_list" ]; then
+      return 1
+    fi
+
+    local ign
+    while read -r ign; do
+      [ -n "$ign" ] || continue
+      case "$ign" in
+        /*) : ;;
+        *) continue ;;
+      esac
+
+      case "$p" in
+        "$ign"|"$ign"/*) return 0 ;;
+      esac
+    done <<<"$ignore_list"
+
+    return 1
+  }
+
   local prefixes
   prefixes=("$@")
 
@@ -504,6 +540,11 @@ cmd_diff() {
       continue
     fi
 
+    # Skip prefixes explicitly persisted via `environment.persistence`.
+    if is_ignored_path "$prefix"; then
+      continue
+    fi
+
     local rel
     rel="${prefix#/}"
     [ -z "$rel" ] && rel="."
@@ -550,6 +591,11 @@ cmd_diff() {
       continue
     fi
 
+    # Skip paths explicitly persisted via `environment.persistence`.
+    if is_ignored_path "$b_path"; then
+      continue
+    fi
+
     local status
     if [ ! -e "$a_path" ] && [ -e "$b_path" ]; then
       status="added"