Migrate rust-overlay patch to an overlay

Towards TraceMachina#1512

flake.nix

@@ -379,19 +379,13 @@
               ./tools/nixpkgs_disable_ratehammering_pulumi_tests.diff
             ];
           };
-          rust-overlay-patched = (import self.inputs.nixpkgs {inherit system;}).applyPatches {
-            name = "rust-overlay-patched";
-            src = self.inputs.rust-overlay;
-            patches = [
-              # This dependency has a giant dependency chain and we don't need
-              # it for our usecases.
-              ./tools/rust-overlay_cut_libsecret.diff
-            ];
-          };
         in
           import nixpkgs-patched {
             inherit system;
-            overlays = [(import rust-overlay-patched)];
+            overlays = [
+              (import rust-overlay)
+              (import ./tools/rust-overlay-cut-libsecret.nix)
+            ];
           };
         apps = {
           default = {

tools/rust-overlay-cut-libsecret.nix

@@ -0,0 +1,15 @@
+final: _prev: {
+  rust-overlay =
+    final.rust-overlay
+    // {
+      mkComponent = args @ {lib, ...}:
+        (final.rust-overlay.mkComponent args)
+        // {
+          postFixup =
+            lib.replaceStrings
+            ["patchelf --add-needed ${args.pkgsHostHost.libsecret}/lib/libsecret-1.so.0 $out/bin/cargo"]
+            ["# patchelf --add-needed ${args.pkgsHostHost.libsecret}/lib/libsecret-1.so.0 $out/bin/cargo"]
+            ((final.rust-overlay.mkComponent args).postFixup or "");
+        };
+    };
+}