lib: add readPath

1 files changed, 41 insertions, 0 deletions

diff --git a/lib/pure.nix b/lib/pure.nix
index ab4be9a..50b9676 100644
--- a/lib/pure.nix
+++ b/lib/pure.nix
@@ -239,4 +239,45 @@ in
 
 stockholm.lib
 // { lib = stockholm.lib; }
+//
+rec {
 
+  # Reads a filesystem path into a Nix datum
+  # - regular files become strings containing their contents;
+  # - directories become attrsets recursively containing their entries;
+  # - symlinks to directories or regular files are dereferenced and read as their targets.
+  readPath =
+    let
+      readHandlers.regular = readRegular;
+      readHandlers.directory = readDirectory;
+      readHandlers.symlink = readSymlink;
+
+      readRegular = path:
+        builtins.readFile path;
+
+      readDirectory = path:
+        builtins.mapAttrs
+          (name: _type: readPath (path + "/${name}"))
+          (builtins.readDir path);
+
+      readSymlink = path:
+        if canBeTraversedAsDirectory path then
+          readDirectory path
+        else
+          readRegular path;
+
+      # The trailing "/." causes symlinks to be dereferenced.
+      canBeTraversedAsDirectory = path:
+        builtins.pathExists "${toString path}/.";
+
+    in
+      path:
+        let
+          type = builtins.readFileType path;
+        in
+          if builtins.hasAttr type readHandlers then
+            readHandlers.${type} path
+          else
+            throw "Unsupported file type: ${toString path} (type=${type})";
+
+}