@default

This alias corresponds to the default argument for dune build: dune build is equivalent to dune build @@default (@@ indicates a non-recursive alias). Similarly, dune build dir is equivalent to dune build @@dir/default.

When a directory doesn’t explicitly define what the default alias means via an alias stanza, the following implicit definition is assumed:

(alias
 (name default)
 (deps (alias_rec all)))

But if such a stanza is present in the dune file in a directory, it will be used instead. For example, if the following is present in tests/dune, dune build tests will run tests there:

(alias
 (name default)
 (deps (alias_rec runtest)))