Dependencies¶

Important

This section focuses on adding dependencies to EPICS top packages. Adding dependencies to other types of Nix packages is different because of how EPICS handles cross-compilation.

For a general explanation, read Nix dependency types.

Adding dependencies¶

Tip

When changing the dependencies of your IOC, remember to exit and re-enter your development shell and run epicsConfigurePhase.

Adding EPICS support modules¶

To add an EPICS support module as a dependency, add it to propagatedBuildInputs:

ioc.nix — Adding an EPICS support module as a dependency¶

{
  mkEpicsPackage,
  lib,
  epnix,
}:
mkEpicsPackage {
  # ...

  propagatedBuildInputs = [ epnix.support.StreamDevice ];

  # ...
}

Adding libraries¶

If your IOC depends on a system library, add it to both nativeBuildInputs and buildInputs:

ioc.nix — Adding a system library as a dependency¶

{
  mkEpicsPackage,
  lib,
  epnix,
  libpcre,
}:
mkEpicsPackage {
  # ...

  nativeBuildInputs = [ libpcre ];
  buildInputs = [ libpcre ];

  # ...
}

Adding build tools¶

If your IOC needs to run a tool during compilation, add it to nativeBuildInputs:

ioc.nix — Adding a build tool as a dependency¶

{
  mkEpicsPackage,
  lib,
  epnix,
  python3,
}:
mkEpicsPackage {
  # ...

  # If you need to run a Python script during the build
  nativeBuildInputs = [ python3 ];

  # ...
}

Special cases¶

If the build tool you want to add generates native code or searches for system libraries (such as pkg-config), add it to both depsBuildBuild and nativeBuildInputs:

ioc.nix — Adding a special build tool as a dependency¶

{
  mkEpicsPackage,
  lib,
  epnix,
  pkg-config,
}:
mkEpicsPackage {
  # ...

  # pkg-config searches for system libraries
  depsBuildBuild = [ pkg-config ];
  nativeBuildInputs = [ pkg-config ];

  # ...
}

Listing dependencies¶

To list all the dependencies of your EPICS top package, build your top package and run:

Listing all dependencies of a Nix package¶

nix path-info -rsSh ./result

This command shows all the dependencies of your package recursively.

For more information, see the nix path-info manual.

Finding a dependency chain¶

To find why your package depends on a specific dependency, copy the dependency path shown in the Listing all dependencies of a Nix package output and run:

Finding a dependency chain with Nix¶

nix why-depends ./result /nix/store/...-my-dependency

For more information, see the nix why-depends manual.