(#) Flow operator functions should not be invoked within composition !!! ERROR: Flow operator functions should not be invoked within composition This is an error. Id : `FlowOperatorInvokedInComposition` Summary : Flow operator functions should not be invoked within composition Severity : Error Category : Correctness Platform : Any Vendor : Jetpack Compose Identifier : androidx.compose.runtime Feedback : https://issuetracker.google.com/issues/new?component=612128 Min : Lint 8.7+ Compiled : Lint 8.7+ Artifact : [androidx.compose.runtime:runtime-android](androidx_compose_runtime_runtime-android.md.html) Since : 1.5.0 Affects : Kotlin and Java files and test sources Editing : This check runs on the fly in the IDE editor Implementation : [Source Code](https://cs.android.com/androidx/platform/frameworks/support/+/androidx-main:/compose/runtime/runtime-lint/src/main/java/androidx/compose/runtime/lint/ComposableFlowOperatorDetector.kt) Tests : [Source Code](https://cs.android.com/androidx/platform/frameworks/support/+/androidx-main:/compose/runtime/runtime-lint/src/test/java/androidx/compose/runtime/lint/ComposableFlowOperatorDetectorTest.kt) Copyright Year : 2021 Calling a Flow operator function within composition will result in a new Flow being created every recomposition, which will reset collectAsState() and cause other related problems. Instead Flow operators should be called inside `remember`, or a side effect such as LaunchedEffect. (##) Example Here is an example of lint warnings produced by this check: ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~text src/androidx/compose/runtime/foo/test.kt:15:Error: Flow operator functions should not be invoked within composition [FlowOperatorInvokedInComposition] .customOperator(true) -------------- src/androidx/compose/runtime/foo/test.kt:16:Error: Flow operator functions should not be invoked within composition [FlowOperatorInvokedInComposition] .drop(0) ---- src/androidx/compose/runtime/foo/test.kt:21:Error: Flow operator functions should not be invoked within composition [FlowOperatorInvokedInComposition] .map { true } --- src/androidx/compose/runtime/foo/test.kt:22:Error: Flow operator functions should not be invoked within composition [FlowOperatorInvokedInComposition] .customOperator(true) -------------- src/androidx/compose/runtime/foo/test.kt:23:Error: Flow operator functions should not be invoked within composition [FlowOperatorInvokedInComposition] .drop(0) ---- src/androidx/compose/runtime/foo/test.kt:28:Error: Flow operator functions should not be invoked within composition [FlowOperatorInvokedInComposition] .map { true } --- src/androidx/compose/runtime/foo/test.kt:29:Error: Flow operator functions should not be invoked within composition [FlowOperatorInvokedInComposition] .customOperator(true) -------------- src/androidx/compose/runtime/foo/test.kt:30:Error: Flow operator functions should not be invoked within composition [FlowOperatorInvokedInComposition] .drop(0) ---- src/androidx/compose/runtime/foo/test.kt:40:Error: Flow operator functions should not be invoked within composition [FlowOperatorInvokedInComposition] .map { true } --- src/androidx/compose/runtime/foo/test.kt:41:Error: Flow operator functions should not be invoked within composition [FlowOperatorInvokedInComposition] .customOperator(true) -------------- src/androidx/compose/runtime/foo/test.kt:42:Error: Flow operator functions should not be invoked within composition [FlowOperatorInvokedInComposition] .drop(0) ---- src/androidx/compose/runtime/foo/test.kt:46:Error: Flow operator functions should not be invoked within composition [FlowOperatorInvokedInComposition] .map { true } --- src/androidx/compose/runtime/foo/test.kt:47:Error: Flow operator functions should not be invoked within composition [FlowOperatorInvokedInComposition] .customOperator(true) -------------- src/androidx/compose/runtime/foo/test.kt:48:Error: Flow operator functions should not be invoked within composition [FlowOperatorInvokedInComposition] .drop(0) ---- src/androidx/compose/runtime/foo/test.kt:55:Error: Flow operator functions should not be invoked within composition [FlowOperatorInvokedInComposition] .map { true } --- src/androidx/compose/runtime/foo/test.kt:56:Error: Flow operator functions should not be invoked within composition [FlowOperatorInvokedInComposition] .customOperator(true) -------------- src/androidx/compose/runtime/foo/test.kt:57:Error: Flow operator functions should not be invoked within composition [FlowOperatorInvokedInComposition] .drop(0) ---- src/androidx/compose/runtime/foo/test.kt:62:Error: Flow operator functions should not be invoked within composition [FlowOperatorInvokedInComposition] .map { true } --- src/androidx/compose/runtime/foo/test.kt:63:Error: Flow operator functions should not be invoked within composition [FlowOperatorInvokedInComposition] .customOperator(true) -------------- src/androidx/compose/runtime/foo/test.kt:64:Error: Flow operator functions should not be invoked within composition [FlowOperatorInvokedInComposition] .drop(0) ---- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Here is the source file referenced above: `src/androidx/compose/runtime/foo/test.kt`: ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~kotlin linenumbers package androidx.compose.runtime.foo import androidx.compose.runtime.Composable import kotlinx.coroutines.flow.* val emptyFlow: Flow = object : Flow {} fun Flow.customOperator(param: Boolean): Flow = this @Composable fun Test() { emptyFlow .map { true } .customOperator(true) .drop(0) } val lambda = @Composable { emptyFlow .map { true } .customOperator(true) .drop(0) } val lambda2: @Composable () -> Unit = { emptyFlow .map { true } .customOperator(true) .drop(0) } @Composable fun LambdaParameter(content: @Composable () -> Unit) {} @Composable fun Test2() { LambdaParameter(content = { emptyFlow .map { true } .customOperator(true) .drop(0) }) LambdaParameter { emptyFlow .map { true } .customOperator(true) .drop(0) } } fun test3() { val localLambda1 = @Composable { emptyFlow .map { true } .customOperator(true) .drop(0) } val localLambda2: @Composable () -> Unit = { emptyFlow .map { true } .customOperator(true) .drop(0) } } ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ You can also visit the [source code](https://cs.android.com/androidx/platform/frameworks/support/+/androidx-main:/compose/runtime/runtime-lint/src/test/java/androidx/compose/runtime/lint/ComposableFlowOperatorDetectorTest.kt) for the unit tests for this check to see additional scenarios. The above example was automatically extracted from the first unit test found for this lint check, `ComposableFlowOperatorDetector.errors`. To report a problem with this extracted sample, visit https://issuetracker.google.com/issues/new?component=612128. (##) Including !!! This is not a built-in check. To include it, add the below dependency to your project. ``` // build.gradle.kts implementation("androidx.compose.runtime:runtime-android:1.9.0-alpha01") // build.gradle implementation 'androidx.compose.runtime:runtime-android:1.9.0-alpha01' // build.gradle.kts with version catalogs: implementation(libs.runtime.android) # libs.versions.toml [versions] runtime-android = "1.9.0-alpha01" [libraries] # For clarity and text wrapping purposes the following declaration is # shown split up across lines, but in TOML it needs to be on a single # line (see https://github.com/toml-lang/toml/issues/516) so adjust # when pasting into libs.versions.toml: runtime-android = { module = "androidx.compose.runtime:runtime-android", version.ref = "runtime-android" } ``` 1.9.0-alpha01 is the version this documentation was generated from; there may be newer versions available. NOTE: These lint checks are **also** made available separate from the main library. You can also use `androidx.compose.runtime:runtime-lint:1.9.0-alpha01`. [Additional details about androidx.compose.runtime:runtime-android](androidx_compose_runtime_runtime-android.md.html). (##) Suppressing You can suppress false positives using one of the following mechanisms: * Using a suppression annotation like this on the enclosing element: ```kt // Kotlin @Suppress("FlowOperatorInvokedInComposition") fun method() { problematicStatement() } ``` or ```java // Java @SuppressWarnings("FlowOperatorInvokedInComposition") void method() { problematicStatement(); } ``` * Using a suppression comment like this on the line above: ```kt //noinspection FlowOperatorInvokedInComposition problematicStatement() ``` * Using a special `lint.xml` file in the source tree which turns off the check in that folder and any sub folder. A simple file might look like this: ```xml <?xml version="1.0" encoding="UTF-8"?> <lint> <issue id="FlowOperatorInvokedInComposition" severity="ignore" /> </lint> ``` Instead of `ignore` you can also change the severity here, for example from `error` to `warning`. You can find additional documentation on how to filter issues by path, regular expression and so on [here](https://googlesamples.github.io/android-custom-lint-rules/usage/lintxml.md.html). * In Gradle projects, using the DSL syntax to configure lint. For example, you can use something like ```gradle lintOptions { disable 'FlowOperatorInvokedInComposition' } ``` In Android projects this should be nested inside an `android { }` block. * For manual invocations of `lint`, using the `--ignore` flag: ``` $ lint --ignore FlowOperatorInvokedInComposition ...` ``` * Last, but not least, using baselines, as discussed [here](https://googlesamples.github.io/android-custom-lint-rules/usage/baselines.md.html).