Aggregates: libraries and archives. Last updated May 2, 2022
OBazl makes a clear and firm distinction between the concepts
library and archive.
A library is just an aggregate - a collection of compiled modules,
interfaces, and possibly other resources, such as data files.
Libraries are expressed in OBazl using the ocaml_library rule. A
target using this rule lists its contents in a manifest attribute;
the content elements, being expressed as Bazel labels, can be located
anywhere in the project. An ocaml_library may contain
other libraries.
An ocaml_library does not execute an action. It does not build
anything; rather, it just collects the dependencies listed in its
manifest attribute and delivers them to its clients. Its power lies
in its ability to aggregate any collection of targets from anywhere in
the project workspace. For example, this makes it easy to organize
source code along conceptual lines. Instead of stuffing a lot of files
into a single directory, you can create a hierarchy of directories
where each corresponds to some concept. Each such directory can have
its own ocaml_library, which will depend on the ocaml_library
targets of whatever other directories it depends on,
An archive is a library packaged as an OCaml archive (.cma/.cmxa)
file. Like an ocaml_library, an ocaml_archive target lists its
contents in a manifest attribute, but unlike ocaml_library it
executes a build action that constructs an OCaml archive. An
ocaml_archive may contain ocaml_library targets, but may not contain
other ocaml_archive targets.
In contrast to other build systems, and the OCaml community in
general, OBazl makes a distinction between the concepts library and
archive.
An OBazl library is just an aggregate - a collection of
compiled modules, signatures. An ocaml_library target lists its
contents in a manifest attribute: it constructs nothing and delivers
its contents as a list in dependency order.
An archive is a library packaged as an OCaml archive (.cma/.cmxa)
file. Like an ocaml_library, an ocaml_archive target lists its
contents in a manifest attribute, but unlike ocaml_library it
executes a build action that constructs an OCaml archive. An
ocaml_archive may contain ocaml_library deps, but may not contain
other ocaml_archive deps (since the OCaml compiler will not accept
archives as input to an archive build command).