Add docs/rl-notes for nix hash convert / builtins.convertHash

https://github.com/NixOS/nix/issues/8876

doc/manual/rl-next/hash-format-nix32.md

@@ -0,0 +1,22 @@
+synopsis: Rename hash format `base32` to `nix32`
+prs: #9452
+description: {
+
+Hash format `base32` was renamed to `nix32` since it used a special nix-specific character set for 
+[Base32](https://en.wikipedia.org/wiki/Base32).
+
+## Deprecation: Use `nix32` instead of `base32` as `toHashFormat`
+
+For the builtin `convertHash`, the `toHashFormat` parameter now accepts the same hash formats as the `--to`/`--from`
+parameters of the `nix hash conert` command: `"base16"`, `"nix32"`, `"base64"`, and `"sri"`. The former `"base32"` value
+remains as a deprecated alias for `"base32"`. Please convert your code from:
+
+```nix
+builtins.convertHash { inherit hash hashAlgo; toHashFormat = "base32";}
+```
+
+to
+
+```nix
+builtins.convertHash { inherit hash hashAlgo; toHashFormat = "nix32";}
+```

doc/manual/rl-next/nix-hash-convert.md

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+synopsis: Add `nix hash convert`
+prs: #9452
+description: {
+
+New [`nix hash convert`](https://github.com/NixOS/nix/issues/8876) sub command with a fast track
+to stabilization! Examples:
+
+- Convert the hash to `nix32`.
+
+  ```bash
+  $ nix hash convert --algo "sha1" --to nix32 "800d59cfcd3c05e900cb4e214be48f6b886a08df"
+  vw46m23bizj4n8afrc0fj19wrp7mj3c0
+  ```
+  `nix32` is a base32 encoding with a nix-specific character set.
+  Explicitly specify the hashing algorithm (optional with SRI hashes) but detect hash format by the length of the input
+  hash.
+- Convert the hash to the `sri` format that includes an algorithm specification:
+  ```bash
+  nix hash convert --algo "sha1" "800d59cfcd3c05e900cb4e214be48f6b886a08df"
+  sha1-gA1Zz808BekAy04hS+SPa4hqCN8=
+  ```
+  or with an explicit `-to` format:
+  ```bash
+  nix hash convert --algo "sha1" --to sri "800d59cfcd3c05e900cb4e214be48f6b886a08df"
+  sha1-gA1Zz808BekAy04hS+SPa4hqCN8=
+  ```
+- Assert the input format of the hash:
+  ```bash
+  nix hash convert --algo "sha256" --from nix32 "ungWv48Bz+pBQUDeXa4iI7ADYaOWF3qctBD/YfIAFa0="
+  error: input hash 'ungWv48Bz+pBQUDeXa4iI7ADYaOWF3qctBD/YfIAFa0=' does not have the expected format '--from nix32'
+  nix hash convert --algo "sha256" --from nix32 "1b8m03r63zqhnjf7l5wnldhh7c134ap5vpj0850ymkq1iyzicy5s"
+  sha256-ungWv48Bz+pBQUDeXa4iI7ADYaOWF3qctBD/YfIAFa0=
+  ```
+
+The `--to`/`--from`/`--algo` parameters have context-sensitive auto-completion.
+
+## Related Deprecations
+
+The following commands are still available but will emit a deprecation warning. Please convert your code to
+`nix hash convert`:
+
+- `nix hash to-base16 $hash1 $hash2`: Use `nix hash convert --to base16 $hash1 $hash2` instead.
+- `nix hash to-base32 $hash1 $hash2`: Use `nix hash convert --to nix32 $hash1 $hash2` instead.
+- `nix hash to-base64 $hash1 $hash2`: Use `nix hash convert --to base64 $hash1 $hash2` instead.
+- `nix hash to-sri $hash1 $hash2`: : Use `nix hash convert --to sri $hash1 $hash2`
+  or even just `nix hash convert $hash1 $hash2` instead.
+}