Add support for component private pipes or pure method calls from templates

Which @angular/* package(s) are relevant/related to the feature request?

core

Description

Currently pipes must be declared at module level. Sometimes a pipe is only used on a single component. The power of pipes being by default pure is that they are only invoked when the input changes. Using a local component function force Angular to always run the function because it has no way to know if the function is pure or not.

Proposed solution

Add a declarations setting to the Component decorator that allows declaring pipes locally for the component. Another option could be to add a new Pure decorator that can be added to the component method in order to tell Angular that the function invocation from the template gives pure results.

Alternatives considered

Declaring pipes on the module level, this still add too much boilerplate when the pipe is used on a single place.

[alxhub]

Nope, there is no additional overhead for a pipe that’s only used on one component - in fact it will probably be less overhead.

[pkozlowski-opensource]

Add a declarations setting to the Component decorator that allows declaring pipes locally for the component

You can achieve this today with standalone components.