ComposableTarget.kt
/*
* Copyright 2021 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package androidx.compose.runtime
/**
* The [Composable] function is declared to expect an applier with the name [applier]. The [applier]
* name can be an arbitrary string but is expected to be a fully qualified name of a class that
* is annotated by [ComposableTargetMarker] containing a descriptive name to be used in diagnostic
* messages.
*
* The [applier] name is used in diagnostic messages but, if it refers to a marked annotation,
* [ComposableTargetMarker.description] is used instead of the class name.
*
* The Compose compiler plugin can, in most cases, infer this or an equivalent
* [ComposableInferredTarget], for composable functions. For example, if a composable function
* calls another composable function then both must be of the same group of composable functions
* (that is, have declared or inferred the same [applier] value). This means that, if the function
* called is already determined to be in a group, them the function that calls it must also be in
* the same group. If two functions are called of different groups then the Compose compiler plugin
* will generate an diagnostic message describing which group was received and which group was
* expected.
*
* The grouping of composable functions corresponds to the instance of [Applier] that is required to
* be used by the [Composer] to apply changes to the composition. The [Applier] is checked at
* runtime to ensure the [Applier] that is expected by a composable function is the one supplied at
* runtime. This annotation, and the corresponding validation performed by the Compose compiler
* plugin, can detect mismatches at compile time, and issue a diagnostic message when calling a
* [Composable] function will result in the [Applier] check failing.
*
* In most cases this annotation can be inferred. However, this annotation is required for
* [Composable] functions that call [ComposeNode] directly, for abstract methods, such as
* interfaces functions (which do not contain a body from which the plugin can infer the
* annotation), when using a composable lambda in sub-composition, or when a composable lambda is
* stored in a class field or global variable.
*
* Leaving the annotation off in such cases will result in the compiler ignoring the function and it
* will not emit the diagnostic when the function is called incorrectly.
*
* @param applier The applier name used during composable call checking. This is usually
* inferred by the compiler. This can be an arbitrary string value but is expected to be a fully
* qualified name of a class that is marked with [ComposableTargetMarker].
*/
@Retention(AnnotationRetention.BINARY)
@Target(
AnnotationTarget.FILE,
AnnotationTarget.CLASS,
AnnotationTarget.FUNCTION,
AnnotationTarget.PROPERTY_GETTER,
AnnotationTarget.TYPE,
AnnotationTarget.TYPE_PARAMETER,
)
annotation class ComposableTarget(val applier: String)