Add the changelog for opam 2.4.0~alpha1

data/changelog/opam/2025-04-18-opam-2-4-0-alpha1.md

@@ -0,0 +1,50 @@
+---
+title: "opam 2.4.0~alpha1"
+authors: [
+  "Raja Boujbel",
+  "Kate Deplaix",
+  "David Allsopp",
+]
+description: "Release of opam 2.4.0~alpha1"
+tags: [opam, platform]
+---
+
+We are happy to announce the first alpha release of opam 2.4.0.
+
+This version is an alpha, we invite users to test it to spot previously unnoticed bugs as we head towards the stable release.
+
+## What’s new? Some highlights:
+
+* 🐲 **On `opam init` the compiler** chosen for the default switch will **no longer be `ocaml-system`** ([#3509](https://github.com/ocaml/opam/issues/3509))
+  This was done because the system compiler (as-is your ocaml installed system wide, e.g. /usr/bin/ocaml) is known to be under-tested and prone to a variety of bugs and configuration issues.
+  Removing it from the default compiler allows new-comers a more smooth experience.
+  *Note: if you wish to use it anyway, you are always able to do it explicitly using `opam init --compiler=ocaml-system`*
+
+* 🐪 GNU **`patch`** and the **`diff`** command are **no longer runtime dependencies**. Instead the OCaml `patch` library is used ([#6019](https://github.com/ocaml/opam/issues/6019), [#6052](https://github.com/ocaml/opam/issues/6052), [#3782](https://github.com/ocaml/opam/issues/3782), [ocaml/setup-ocaml#933](https://github.com/ocaml/setup-ocaml/pull/933))
+  Doing this we've removed some rarely used features of GNU Patch such as the support of [Context diffs](https://www.gnu.org/software/diffutils/manual/html_node/Example-Context.html).
+  The new implementation only supports [Unified diffs](https://www.gnu.org/software/diffutils/manual/html_node/Example-Unified.html) including the [git extended headers](https://git-scm.com/docs/diff-format), however file permission changes via said extended headers have no effect.
+
+* ❄️ Add **Nix support** for **external dependencies (depexts)** by adding support for stateless package managers ([#5982](https://github.com/ocaml/opam/issues/5982)). *Thanks to [@RyanGibb](https://github.com/RyanGibb) for this contribution*
+
+* 🪳 **Fix `opam install <local_dir>`** with and without options like `--deps-only` or `--show-action` having **unexpected behaviours** ([#6248](https://github.com/ocaml/opam/issues/6248), [#5567](https://github.com/ocaml/opam/issues/5567)) such as:
+  * reporting `Nothing to do` despite dependencies or package not being up-to-date
+  * asking to install the wrong dependencies
+
+* 🌊 Many more UI additions and improvements, bug fixes, performance improvements, …
+
+
+📖 You can read our [blog post](https://opam.ocaml.org/blog/opam-2-4-0-alpha1/) for more information about these changes and more, and for even more details you can take a look at the [release note](https://github.com/ocaml/opam/releases/tag/2.4.0-alpha1) or the [changelog](https://github.com/ocaml/opam/blob/2.4.0-alpha1/CHANGES).
+
+## Try it!
+
+The upgrade instructions are unchanged:
+
+For Unix systems
+```sh
+bash -c "sh <(curl -fsSL https://opam.ocaml.org/install.sh) --version 2.4.0~alpha1"
+```
+or from PowerShell for Windows systems
+```sh
+Invoke-Expression "& { $(Invoke-RestMethod https://opam.ocaml.org/install.ps1) } -Version 2.4.0~alpha1"
+```
+Please report any issues to the [bug-tracker](https://github.com/ocaml/opam/issues).