Built-in Registry

OAM Built-in Registry

Package registry exports every built-in handler and lowering rule launcher implements, keyed by the type each one registers under, so a consumer registers the builtins from the library instead of keeping its own list. kurel build registers exactly these (pkg/cmd/kurel, newBuiltinTransformer).

Function	Holds	Register with
`ComponentHandlers()`	every kind component of `pkg/oam/builtin/components`	`oam.NewTransformer` or `RegisterComponent`
`ComponentLoweringRules()`	`webservice`, `worker`, `helm`, `postgresql`, `oci`	`RegisterComponentLowering`
`TraitHandlers()`	every trait of `pkg/oam/builtin/traits`	`RegisterBuiltinTrait`
`TraitLoweringRules()`	`expose`	`RegisterBuiltinTraitLowering`
`PolicyHandlers()`	`dependency`, `placement`	`RegisterPolicy`

Each function returns a new map on every call: a caller may delete, replace or add entries, and the change reaches no other caller. A type launcher adds later appears in the map of its kind without a change on the caller’s side. Adding one takes two lines in one commit: its entry in registry.go, at its position in the order sort.Strings gives the types (prometheus before prometheus-probe, which it prefixes), and its line in kurel’s testdata/builtin-registries.txt. The table names the maps, not the types: the kind components themselves, each with what it emits and refuses, are listed in pkg/oam/builtin/components, so a new kind changes nothing here but those two lines.

A type that is a lowering rule is never also a handler of the same position, and RegisterComponentLowering and RegisterTraitLowering panic on that collision. A consumer that replaces a handler sets its own under the same key; one that replaces a lowered type (say webservice) with a handler deletes the type from the lowering-rule map.

launcher has no handler for the app-dependency, reconciliation and health-checks policies or the fluxcd-patches and fluxcd-postbuild traits, so none of the maps holds them: a consumer that implements them registers its own.

See “Registering the builtins” in pkg/oam for the registration sequence.

Tests

TestRegistries_FreshMapEachCall: a caller’s change to one call’s map does not show in the next call’s.
TestRegistries_LoweringRulesClaimTheirKey: each lowering rule is keyed under the type it claims.
TestRegistries_RegisterTogether: every entry registers on one transformer without a collision.
In pkg/cmd/kurel, TestKindLists_InOrder holds the entries of ComponentHandlers in the order of their type, TestBuiltinRegistries_TypesUnchanged holds kurel’s registered set to testdata/builtin-registries.txt, and the handler-schema tests cover every entry.