parser: merge nested dynamic attributes

Fixes https://github.com/NixOS/nix/issues/7115

1 files changed, 19 insertions, 0 deletions

diff --git a/doc/manual/src/release-notes/rl-next.md b/doc/manual/src/release-notes/rl-next.md
index 139d07188..160245a31 100644
--- a/doc/manual/src/release-notes/rl-next.md
+++ b/doc/manual/src/release-notes/rl-next.md
@@ -6,3 +6,22 @@
 
 - Nix now allows unprivileged/[`allowed-users`](../command-ref/conf-file.md#conf-allowed-users) to sign paths.
   Previously, only [`trusted-users`](../command-ref/conf-file.md#conf-trusted-users) users could sign paths.
+
+- Nested dynamic attributes are now merged correctly by the parser. For example:
+
+  ```nix
+  {
+    nested = { foo = 1; };
+    nested = { ${"ba" + "r"} = 2; };
+  }
+  ```
+
+  This used to silently discard `nested.bar`, but now behaves as one would expect and evaluates to:
+
+  ```nix
+  { nested = { bar = 2; foo = 1; }; }
+  ```
+
+  Note that the feature of merging multiple attribute set declarations is of questionable value.
+  It allows writing expressions that are very hard to read, for instance when there are many lines of code between two declarations of the same attribute.
+  This has been around for a long time and is therefore supported for backwards compatibility, but should not be relied upon.