diff --git a/boot.nix b/boot.nix
new file mode 100644
index 0000000..a2d4f48
--- /dev/null
+++ b/boot.nix
@@ -0,0 +1,24 @@
+# This is a tentative public interface.
+#
+# We may decide to stablize it, but for now it is still UNSTABLE.
+
+let
+  inherit (import ./private.nix)
+    contentsMatch
+    isThunkWithThunkNix
+    ;
+
+in {
+  # This only works with newer thunks, and is intended for the
+  # bootstrapping usecase where:
+  #
+  #  - We don't yet have a `lib,` `pkgs`, or `gitignoreSource`
+  #
+  #  - We just need the repo in question for Nix code, and not source
+  #  files to copy to the store.
+  thunkSourceNoFilter = p:
+    let
+      contents = builtins.readDir p;
+    in if isThunkWithThunkNix contents then import (p + "/thunk.nix")
+    else p;
+}
diff --git a/default.nix b/default.nix
index f1f31aa..f3002e5 100644
--- a/default.nix
+++ b/default.nix
@@ -15,9 +15,17 @@ let defaultInputs = import ./defaultInputs.nix; in
     (import ./dep/gitignore.nix { inherit lib; }).gitignoreSource,
 }:
 
-let myLib = import ./lib.nix { inherit haskell-nix pkgs; }; in
+let
+
+  myLib = import ./lib.nix { inherit haskell-nix pkgs; }; in
+
+  inherit (import ./private.nix)
+    contentsMatch
+    isThunkWithThunkNix
+    ;
+
+in rec {
 
-rec {
   command = (myLib.perGhc {}).command;
 
   # Retrieve source that is controlled by the hack-* scripts; it may be either a
@@ -25,32 +33,19 @@ rec {
   thunkSource = p:
     let
       contents = builtins.readDir p;
-
-      contentsMatch = { required, optional }:
-           (let all = required // optional; in all // contents == all)
-        && builtins.intersectAttrs required contents == required;
-
-      # Newer obelisk thunks include the feature of hackGet with a thunk.nix file in the thunk.
-      isObeliskThunkWithThunkNix =
-        let
-          packed = jsonFileName: {
-            required = { ${jsonFileName} = "regular"; "default.nix" = "regular"; "thunk.nix" = "regular"; };
-            optional = { ".attr-cache" = "directory"; };
-          };
-        in builtins.any (n: contentsMatch (packed n)) [ "git.json" "github.json" ];
-
+    in if isThunkWithThunkNix contents then import (p + "/thunk.nix")
+    else let # legacy cases
       filterArgs = x: removeAttrs x [ "branch" ];
       hasValidThunk = name: if builtins.pathExists (p + ("/" + name))
         then
-          contentsMatch {
+          contentsMatch contents {
             required = { ${name} = "regular"; };
             optional = { "default.nix" = "regular"; ".attr-cache" = "directory"; };
           }
           || throw "Thunk at ${toString p} has files in addition to ${name} and optionally default.nix and .attr-cache. Remove either ${name} or those other files to continue (check for leftover .git too)."
         else false;
     in
-      if isObeliskThunkWithThunkNix then import (p + "/thunk.nix")
-      else if hasValidThunk "git.json" then (
+      if hasValidThunk "git.json" then (
         let gitArgs = filterArgs (builtins.fromJSON (builtins.readFile (p + "/git.json")));
         in if builtins.elem "@" (lib.stringToCharacters gitArgs.url)
           then pkgs.fetchgitPrivate gitArgs
diff --git a/lib.nix b/packaging.nix
similarity index 100%
rename from lib.nix
rename to packaging.nix
diff --git a/private.nix b/private.nix
new file mode 100644
index 0000000..4ea4f7f
--- /dev/null
+++ b/private.nix
@@ -0,0 +1,17 @@
+# Private library functions.
+#
+# UNSTABLE, do not rely on this in external repos.
+rec {
+  contentsMatch = contents: { required, optional }:
+       (let all = required // optional; in all // contents == all)
+    && builtins.intersectAttrs required contents == required;
+
+  # Newer obelisk thunks include the feature of hackGet with a thunk.nix file in the thunk.
+  isThunkWithThunkNix = contents:
+    let
+      packed = jsonFileName: {
+        required = { ${jsonFileName} = "regular"; "default.nix" = "regular"; "thunk.nix" = "regular"; };
+        optional = { ".attr-cache" = "directory"; };
+      };
+    in builtins.any (n: contentsMatch contents (packed n)) [ "git.json" "github.json" ];
+}
diff --git a/release.nix b/release.nix
index 845be2b..92c337a 100644
--- a/release.nix
+++ b/release.nix
@@ -1,5 +1,5 @@
 let versions = import ./versions.nix;
-    nix-thunk = import ./lib.nix {};
+    nix-thunk = import ./packaging.nix {};
     instances = builtins.listToAttrs (map (ghcVersion: {
       name = ghcVersion;
       value = nix-thunk.perGhc { ghc = ghcVersion; };