Add the announcement for opam 2.3.0~alpha1

opam-2-3-0-alpha1.md

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+title: "opam 2.3.0 alpha1 release"
+authors: [
+  "Raja Boujbel - OCamlPro" {"mailto:raja.boujbel(à)ocamlpro.com"}
+  "Kate Deplaix - Ahrefs" {"mailto:kit-ty-kate(à)outlook.com"}
+  "David Allsopp - Tarides" {"mailto:david(à)tarides.com"}
+]
+date: "2024-09-19"
+--BODY--
+
+_Feedback on this post is welcomed on [Discuss](https://discuss.ocaml.org/t/ann-opam-2-3-0-alpha1/XXXXX)!_
+
+As mentioned in [our talk at the OCaml Workshop 2024](https://icfp24.sigplan.org/details/ocaml-2024-papers/10/Opam-2-2-and-beyond),
+we decided to switch to a time-based release cycle (every 6 months), starting with opam 2.3.
+
+As promised, we are happy to announce the first alpha release of opam 2.3.0.
+You can view the full list of changes in the
+[release note](https://github.com/ocaml/opam/releases/tag/2.3.0-alpha1).
+
+This version is an alpha, we invite users to test it to spot previously
+unnoticed bugs as we head towards the stable release.
+
+## Major breaking change
+
+When loading a repository, opam now ignores files in packages' `files/` directories which aren't listed in the `extra-files` field of the opam file.
+This was done to simplify the opam specification where we hope the opam file to be the only thing that you have to look at when reading a package specification. The optionality of the `extra-files:` field goes against that principle. This change also reduces the surface area for potential file corruption as it ensures that extra-files are checked against their checksums.
+
+This is a breaking change and means that if you are using the `files/` directory without the `extra-files:` field, you need to make sure that all files in that directory are listed in the `extra-files` field.
+Once done, the resulting opam file is backward-compatible and you don't need to worry about anything else.
+
+If you have an opam repository, you should make sure all files are listed so every packages continues to work without any issue, which can be done automatically using the `opam admin update-extrafiles` command.
+
+## Major changes
+
+* Packages requiring an unsupported version of opam are now marked unavailable, instead of causing a repository error. This means an opam repository can now allow smoother upgrade in the future where some packages can require a newer version of opam without having to fork the repository to upgrade every package to that version as was done for the upgrade from opam 1.2 to 2.0
+
+* Add a new `opam list --latests-only` option to list only the latest versions of packages. Note that this option is respects the order options were given on the command line. For example: `--available --latests-only` will first list all the available packages, then choose only the latest packages in that set; while `--latests-only --available` will first list all the latest packages, then only show the ones that are available in that set
+
+* Fix and improve `opam install --check`, which now checks if the whole dependency tree of the package is installed instead of only the root dependencies
+
+* Add a new `--verbose-on` option to enable verbose output for specified package names. *Thanks to [@desumn](https://github.com/desumn) for this contribution*
+
+* Add a new `opam switch import --deps-only` option to install only the dependencies of the root packages listed in the opam switch export file
+
+* `opam switch list-available` will now not display compilers flagged with `avoid-version`/`deprecated` unless `--all` is given, meaning that the "trunk" build of OCaml no longer appears to be the latest version
+
+* `opam switch create --repos` now accepts git URLs suffixed with `.git` instead of requiring the `git+https://` protocol prefix. This is consistant with other commands such as `opam repository add`. *Thanks to [@Keryan-dev](https://github.com/Keryan-dev) for this contribution*
+
+* `opam switch set-invariant` now displays the switch invariant using the same syntax as the `--invariant` flag
+
+* The `builtin-0install` solver was improved and should now be capable of being your default solver instead of `builtin-mccs+glpk`. It was previously mostly only suited for automated tasks such as Continuous Integration. If you wish to give it a try, simply call `opam option solver=builtin-0install`
+
+* Most of the unhelpful conflict messages were fixed
+
+* Fix the value of the `arch` variable when the current OS is 32bit on a 64bit machine (e.g. Raspberry Pi OS)
+
+* opam now fails when git submodules fail to update instead of ignoring the error and just showing a warning
+
+* opam's libraries now compile with OCaml >= 5.0 on Windows
+
+Various performance and other improvements were made and bugs were fixed.
+API changes are denoted in the release note linked above.
+This release also includes a handful of PRs improving the documentation and more two dozen PRs improving and extending the tests.
+
+## Try it!
+
+The upgrade instructions are unchanged:
+
+1. Either from binaries: run
+
+For Unix systems
+```
+bash -c "sh <(curl -fsSL https://raw.githubusercontent.com/ocaml/opam/master/shell/install.sh) --version 2.3.0~alpha1"
+```
+or from PowerShell for Windows systems
+```
+Invoke-Expression "& { $(Invoke-RestMethod https://raw.githubusercontent.com/ocaml/opam/master/shell/install.ps1) } -Version 2.3.0~alpha1"
+```
+or download manually from [the Github "Releases" page](https://github.com/ocaml/opam/releases/tag/2.3.0-alpha1) to your PATH.
+
+2. Or from source, manually: see the instructions in the [README](https://github.com/ocaml/opam/tree/2.3.0-alpha1#compiling-this-repo).
+
+
+You should then run:
+```
+opam init --reinit -ni
+```
+
+
+Please report any issues to [the bug-tracker](https://github.com/ocaml/opam/issues).
+
+Happy hacking!