# `MishkaCmsCore.Runtime.Resources.Validations.InterfaceDeclaration`
[🔗](https://github.com/mishka-group/mishka_cms_core/blob/v0.0.1/lib/mishka_cms_core/runtime/resources/__validations/interface_declaration.ex#L5)

Refuses a component whose declared attributes or slots could not compile.

## Why this is on the resource and not in the editor

A component's `attrs` and `slots` reach the database from three places — the Components table's
form, the builder's Interface tab, and any script or import that writes the columns — and the rule
is the same everywhere: a name becomes an atom and is written into a `def`, so `Size` and
`my-size` are not names, one name may not be declared twice, and Phoenix refuses `required: true`
together with a default ("attributes should not have a default value if they are required").

Enforced in the editor alone, each of those surfaces would have needed its own copy, and the two
that are not the editor would have had none. Here it is one answer at the action boundary, which is
where `MishkaCmsCore.Runtime.Resources.Validations.CodeChange` and `TemplateCompiles` already sit
for the same reason.

`MishkaCmsCore.Runtime.PageBuilder.Interface.validate/2` holds the rules themselves, because the
editor also wants them BEFORE a save — to mark the offending row while somebody is still typing in
it. This is the half that makes them true of the record.

## What it does not do

It says nothing about whether the template AGREES with the declaration. A component may legitimately
be saved with an attribute its markup does not read yet, and a template that reads `@size` with no
`attr :size` is advice the editor gives — see `Interface.undeclared/3` — rather than a write to
refuse. Half-finished work has to be storable.

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*Consult [api-reference.md](api-reference.md) for complete listing*