Pinning Projects

When Dune is looking up packages to lock, it uses the (pre)configured OCaml package repositories. However it is also possible to manually specify the sources of packages; for example, if the package is not released in a package repository. This is called “pinning”.

Installing Packages From a Pin

To pin a package, a new pin has to be declared in the dune-project file.

dune-project

(lang dune 3.17)
(name test)

(pin
 (url "git+https://github.com/dbuenzli/fmt.git")
 (package (name fmt)))

(package
 (name test)
 (depends
  (ocaml (>= 4.14))
  fmt))

This will create a pin on the fmt package and use the specified Git repository URL to retrieve the sources. For more information refer to the pin stanza reference.

Don’t forget to remove the version constraints from fmt in the list of dependencies.

The next time the project is built, Dune will use this repository instead of the information from the selected package repositories. Thus the fmt package will be built from the source in the specified Git repository rather than from the source tarball released in the opam-repository.

dune build

will find a new solution, quoting _build/log:

...

# Dependency solution for
# _build/.sandbox/<sandbox-hash>/_private/default/.lock/dune.lock:
# - base-unix.base
# - fmt.dev
# - ocaml.5.4.0
# - ocaml-base-compiler.5.4.0
# - ocaml-compiler.5.4.0
# - ocaml-config.3
# - ocamlbuild.0.16.1+dune
# - ocamlfind.1.9.8+dune
# - topkg.1.1.1
...

Unlike previously, the version of the fmt library that is picked is dev, to signify a development version.

$ dune exec ./test.exe
Hello, OCaml, Rust!