Selector reference

Selectors are conditions evaluated against the resolved enabled feature set. They are accepted as values of a public function's named WHEN argument. Selector evaluation is available only after besa_configure_complete() has frozen configuration.

ALL_OF

WHEN ALL_OF feature-a feature-b ~feature-c

Every atom must match. A normal atom matches when that feature is enabled; a ~feature atom matches when that feature is disabled. The same underlying feature must not appear twice in one selector.

ANY_OF

WHEN ANY_OF toolchain-cuda toolchain-hip

At least one atom must match. Negated atoms use the same semantics as ALL_OF.

REGEX

WHEN REGEX "^project-"

The selector succeeds when at least one enabled feature matches the CMake regular expression. This is intentionally regex syntax, not glob syntax. It is useful for namespace-like feature families such as project-* and showcase-* without introducing wildcard parsing rules into BESA.

FUNCTION

WHEN FUNCTION my_selector

BESA invokes the named CMake command using this contract:

my_selector(
  OUTPUT_VARIABLE <variable-to-set>
  ERROR_VARIABLE  <variable-to-set>
  NAME            <object-name>
  FEATURES        <resolved-feature>...
)

Use the public parser helper rather than duplicating callback argument parsing:

function(my_selector)
  besa_selector_arguments_parse(
    PREFIX ARG
    ARGUMENTS ${ARGN}
  )

  # ARG_NAME is the object being considered.
  # ARG_FEATURES is the resolved enabled feature list.

  set("${ARG_OUTPUT_VARIABLE}" TRUE PARENT_SCOPE)
  set("${ARG_ERROR_VARIABLE}" "" PARENT_SCOPE)
endfunction()

Set the output to FALSE with an empty error to mean "not selected". Set ERROR_VARIABLE to a non-empty string only when evaluation itself is invalid; BESA reports that text as a fatal configuration error.