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We are very pleased to announce the release of opam 2.2.0, and encourage all users to upgrade. Please read on for installation and upgrade instructions.

Try it!

In case you plan a possible rollback, you may want to first backup your ~/.opam or $env:LOCALAPPDATA\opam directory.

The upgrade instructions are unchanged:

  1. Either from binaries: run

For Unix systems

bash -c "sh <(curl -fsSL --version 2.2.0"

or from PowerShell for Windows systems

Invoke-Expression "& { $(Invoke-RestMethod }"

or download manually from the Github "Releases" page to your PATH.

  1. Or from source, manually: see the instructions in the README.

You should then run:

opam init --reinit -ni


Major change: Windows support

After 8 years' effort, opam and opam-repository now have official native Windows support! A big thank you is due to Andreas Hauptmann (@fdopen), whose WODI and OCaml for Windows projects were for many years the principal downstream way to obtain OCaml on Windows, Jun Furuse (@camlspotter) whose initial experimentation with OPAM from Cygwin formed the basis of opam-repository-mingw, and, most recently, Jonah Beckford (@jonahbeckford) whose DkML distribution kept - and keeps - a full development experience for OCaml available on Windows.

OCaml when used on native Windows requires certain tools from the Unix world which are provided by either Cygwin or MSYS2. We have engineered opam init so that it is possible for a user not to need to worry about this, with opam managing the Unix world, and the user being able to use OCaml from either the Command Prompt or PowerShell. However, for the Unix user coming over to Windows to test their software, it is also possible to have your own Cygwin/MSYS2 installation and use native Windows opam from that. Please see the previous blog post for more information.

There are two "ports" of OCaml on native Windows, referred to by the name of provider of the C compiler. The mingw-w64 port is GCC-based. opam's external dependency (depext) system works for this port (including providing GCC itself), and many packages are already well-supported in opam-repository, thanks to the previous efforts in opam-repository-mingw. The MSVC port is Visual Studio-based. At present, there is less support in this ecosystem for external dependencies, though this is something we expect to work on both in opam-repository and in subsequent opam releases. In particular, it is necessary to install Visual Studio or Visual Studio BuildTools separately, but opam will then automatically find and use the C compiler from Visual Studio.

Major change: opam tree / opam why

opam tree is a new command showing packages and their dependencies with a tree view. It is very helpful to determine which packages bring which dependencies in your installed switch.

$ opam tree cppo
├── base-unix.base
├── dune.3.8.2 (>= 1.10)
│   ├── base-threads.base
│   ├── base-unix.base [*]
│   └── ocaml.4.14.1 (>= 4.08)
│       ├── ocaml-base-compiler.4.14.1 (>= 4.14.1~ & < 4.14.2~)
│       └── ocaml-config.2 (>= 2)
│           └── ocaml-base-compiler.4.14.1 (>= 4.12.0~) [*]
└── ocaml.4.14.1 (>= 4.02.3) [*]

Reverse-dependencies can also be displayed using the new opam why command. This is useful to examine how dependency versions get constrained.

$ opam why cmdliner
├── (>= 1.1.0) b0.0.0.5
│   └── (= 0.0.5) odig.0.0.9
├── (>= 1.1.0) ocp-browser.1.3.4
├── (>= 1.0.0) ocp-indent.1.8.1
│   └── (>= 1.4.2) ocp-index.1.3.4
│       └── (= version) ocp-browser.1.3.4 [*]
├── (>= 1.1.0) ocp-index.1.3.4 [*]
├── (>= 1.1.0) odig.0.0.9 [*]
├── (>= 1.0.0) odoc.2.2.0
│   └── (>= 2.0.0) odig.0.0.9 [*]
├── (>= 1.1.0) opam-client.2.2.0~alpha
│   ├── (= version) opam.2.2.0~alpha
│   └── (= version) opam-devel.2.2.0~alpha
├── (>= 1.1.0) opam-devel.2.2.0~alpha [*]
├── (>= 0.9.8) opam-installer.2.2.0~alpha
└── user-setup.0.7

Special thanks to @cannorin for contributing this feature.

Major change: with-dev-setup

There is now a way for a project maintainer to share their project development tools: the with-dev-setup dependency flag. It is used in the same way as with-doc and with-test: by adding a {with-dev-setup} filter after a dependency. It will be ignored when installing normally, but it's pulled in when the package is explicitly installed with the --with-dev-setup flag specified on the command line.

For example

opam-version: "2.0"
depends: [
  "ocp-indent" {with-dev-setup}
build: [make]
install: [make "install"]
[ "Thanks for installing the package"
  "as well as its development setup. It will help with your future contributions" {with-dev-setup} ]

Major change: opam pin --recursive

When pinning a package using opam pin, opam looks for opam files in the root directory only. With recursive pinning, you can now instruct opam to look for .opam files in subdirectories as well, while maintaining the correct relationship between the .opam files and the package root for versioning and build purposes.

Recursive pinning is enabled by the following options to opam pin and opam install:

  • With --recursive, opam will look for .opam files recursively in all subdirectories.
  • With --subpath <path>, opam will only look for .opam files in the subdirectory <path>.

The two options can be combined: for instance, if your opam packages are stored as a deep hierarchy in the mylib subdirectory of your project you can try opam pin . --recursive --subpath mylib.

These options are useful when dealing with a large monorepo-type repository with many opam libraries spread about.

New Options

  • opam switch -, inspired by git switch -, makes opam switch back to the previously selected global switch.

  • opam pin --current fixes a package to its current state (disabling pending reinstallations or removals from the repository). The installed package will be pinned to its current installed state, i.e. the pinned opam file is the one installed.

  • opam pin remove --all removes all the pinned packages from a switch.

  • opam exec --no-switch removes the opam environment when running a command. It is useful when you want to launch a command without opam environment changes.

  • opam clean --untracked removes untracked files interactively remaining from previous packages removal.

  • opam admin add-constraint <cst> --packages pkg1,pkg2,pkg3 applies the given constraint to a given set of packages

  • opam list --base has been renamed into --invariant, reflecting the fact that since opam 2.1 the "base" packages of a switch are instead expressed using a switch invariant.

  • opam install --formula <formula> installs a formula instead of a list of packages. This can be useful if you would like to install one package or another one. For example opam install --formula '"extlib" |"extlib-compat"' will install either extlib or extlib-compat depending on what's best for the current switch.

Miscellaneous changes

  • The UI now displays a status when extracting an archive or reloading a repository
  • Overhauled the implementation of opam env, fixing many corner cases for environment updates and making the reverting of package environment variables precise. As a result, using setenv in an opam file no longer triggers a lint warning.
  • Fix parsing pre-opam 2.1.4 switch import files containing extra-files
  • Add a new sys-ocaml-system default global eval variable
  • Hijack the "%{var?string-if-true:string-if-false-or-undefined}%" syntax to support extending the variables of packages with + in their name (conf-c++ and conf-g++ already exist) using "%{?pgkname:var:}%"
  • Fix issues when using fish as shell
  • Sandbox: Mark the user temporary directory (as returned by getconf DARWIN_USER_TEMP_DIR) as writable when TMPDIR is not defined on macOS
  • Add Warning 69: Warn for new syntax when package name in variable in string interpolation contains several '+' (this is related to the "hijack" item above)
  • Add support for Wolfi OS, treating it like Alpine family as it also uses apk
  • Sandbox: /tmp is now writable again, restoring POSIX compliance
  • Add a new opam admin: new add-extrafiles command to add/check/update the extra-files: field according to the files present in the files/ directory
  • Add a new opam lint -W @1..9 syntax to allow marking a set of warnings as errors
  • Fix bugs in the handling of the OPAMCURL, OPAMFETCH and OPAMVERBOSE environment variables
  • Fix bugs in the handling of the --assume-built argument
  • Software Heritage fallbacks is now supported, but is disabled-by-default for now. For more information you can read one of our previous blog post

And many other general and performance improvements were made and bugs were fixed. You can take a look to previous blog posts. API changes and a more detailed description of the changes are listed in:

This release also includes PRs improving the documentation and improving and extending the tests.

Please report any issues to the bug-tracker.

We hope you will enjoy the new features of opam 2.2! 📯