applyPatches: simplify src attribute inheritance.

This fixes the potential mismatch between a `applyPatches` with and without patches, as the latter would not merge the `meta` or `passthru` args.
This is technically a breaking change to the `applyPatches` interface, but there are no instances of this in nixpkgs.

pkgs/build-support/trivial-builders/default.nix

@@ -1022,6 +1022,12 @@ rec {
       postPatch ? "",
       ...
     }@args:
+    assert lib.assertMsg (
+      !args ? meta
+    ) "applyPatches will not merge 'meta', change it in 'src' instead";
+    assert lib.assertMsg (
+      !args ? passthru
+    ) "applyPatches will not merge 'passthru', change it in 'src' instead";
     if patches == [ ] && prePatch == "" && postPatch == "" then
       src # nothing to do, so use original src to avoid additional drv
     else
@@ -1051,19 +1057,17 @@ rec {
           phases = "unpackPhase patchPhase installPhase";
           installPhase = "cp -R ./ $out";
         }
-        # Carry and merge information from the underlying `src` if present.
-        // (optionalAttrs (src ? meta || args ? meta) {
-          meta = src.meta or { } // args.meta or { };
+        # Carry (and merge) information from the underlying `src` if present.
+        // (optionalAttrs (src ? meta) {
+          inherit (src) meta;
         })
-        // (optionalAttrs (extraPassthru != { } || src ? passthru || args ? passthru) {
-          passthru = extraPassthru // src.passthru or { } // args.passthru or { };
+        // (optionalAttrs (extraPassthru != { } || src ? passthru) {
+          passthru = extraPassthru // src.passthru or { };
         })
         # Forward any additional arguments to the derviation
         // (removeAttrs args [
           "src"
           "name"
-          "meta"
-          "passthru"
           "patches"
           "prePatch"
           "postPatch"