Add release notes for "Functions are printed with more detail"

doc/manual/rl-next/lambda-printing.md

@@ -0,0 +1,50 @@
+---
+synopsis: Functions are printed with more detail
+prs: 9606
+issues: 7145
+---
+
+Functions and `builtins` are printed with more detail in `nix repl`, `nix
+eval`, `builtins.trace`, and most other places values are printed.
+
+Before:
+
+```
+$ nix repl nixpkgs
+nix-repl> builtins.map
+«primop»
+
+nix-repl> builtins.map lib.id
+«primop-app»
+
+nix-repl> builtins.trace lib.id "my-value"
+trace: <LAMBDA>
+"my-value"
+
+$ nix eval --file functions.nix
+{ id = <LAMBDA>; primop = <PRIMOP>; primop-app = <PRIMOP-APP>; }
+```
+
+After:
+
+```
+$ nix repl nixpkgs
+nix-repl> builtins.map
+«primop map»
+
+nix-repl> builtins.map lib.id
+«partially applied primop map»
+
+nix-repl> builtins.trace lib.id "my-value"
+trace: «lambda id @ /nix/store/8rrzq23h2zq7sv5l2vhw44kls5w0f654-source/lib/trivial.nix:26:5»
+"my-value"
+
+$ nix eval --file functions.nix
+{ id = «lambda id @ /Users/wiggles/nix/functions.nix:2:8»; primop = «primop map»; primop-app = «partially applied primop map»; }
+```
+
+This was actually released in Nix 2.20, but wasn't added to the release notes
+so we're announcing it here. The historical release notes have been updated as well.
+
+[type-error]: https://github.com/NixOS/nix/pull/9753
+[coercion-error]: https://github.com/NixOS/nix/pull/9754

doc/manual/src/release-notes/rl-2.20.md

@@ -167,6 +167,25 @@
 
          error: expected a set but found an integer
   ```
+
+- Functions are printed with more detail [#7145](https://github.com/NixOS/nix/issues/7145) [#9606](https://github.com/NixOS/nix/pull/9606)
+
+  `nix repl`, `nix eval`, `builtins.trace`, and most other places values are
+  printed will now include function names and source location information:
+
+  ```
+  $ nix repl nixpkgs
+  nix-repl> builtins.map
+  «primop map»
+
+  nix-repl> builtins.map lib.id
+  «partially applied primop map»
+
+  nix-repl> builtins.trace lib.id "my-value"
+  trace: «lambda id @ /nix/store/8rrzq23h2zq7sv5l2vhw44kls5w0f654-source/lib/trivial.nix:26:5»
+  "my-value"
+  ```
+
 - Flake operations like `nix develop` will no longer fail when run in a Git
   repository where the `flake.lock` file is `.gitignore`d
   [#8854](https://github.com/NixOS/nix/issues/8854)