(#) Mutable objects in Compose will break state !!! ERROR: Mutable objects in Compose will break state This is an error. Id : `ComposeMutableParameters` Summary : Mutable objects in Compose will break state Severity : Error Category : Productivity Platform : Any Vendor : slack Identifier : com.slack.lint.compose:compose-lints Feedback : https://github.com/slackhq/compose-lints/issues Min : Lint 8.7+ Compiled : Lint 8.7+ Artifact : [com.slack.lint.compose:compose-lint-checks](com_slack_lint_compose_compose-lint-checks.md.html) Since : 1.0.0 Affects : Kotlin and Java files and test sources Editing : This check runs on the fly in the IDE editor Implementation : [Source Code](https://github.com/slackhq/compose-lints/tree/main/compose-lint-checks/src/main/java/slack/lint/compose/MutableParametersDetector.kt) Tests : [Source Code](https://github.com/slackhq/compose-lints/tree/main/compose-lint-checks/src/test/java/slack/lint/compose/MutableParametersDetectorTest.kt) Copyright Year : 2023 Using mutable objects as state in Compose will cause your users to see incorrect or stale data in your app.Mutable objects that are not observable, such as `ArrayList` or a mutable data class, cannot be observed by Compose to trigger recomposition when they change.See https://slackhq.github.io/compose-lints/rules/#do-not-use-inherently-mutable-types-as-parameters for more information. (##) Example Here is an example of lint warnings produced by this check: ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~text src/test.kt:5:Error: Using mutable objects as state in Compose will cause your users to see incorrect or stale data in your app.Mutable objects that are not observable, such as ArrayList or a mutable data class, cannot be observed by Compose to trigger recomposition when they change.See https://slackhq.github.io/compose-lints/rules/#do-not-use-inherently-mutable-types-as-parameters for more information. [ComposeMutableParameters] fun Something(a: MutableState<String>) {} -------------------- src/test.kt:7:Error: Using mutable objects as state in Compose will cause your users to see incorrect or stale data in your app.Mutable objects that are not observable, such as ArrayList or a mutable data class, cannot be observed by Compose to trigger recomposition when they change.See https://slackhq.github.io/compose-lints/rules/#do-not-use-inherently-mutable-types-as-parameters for more information. [ComposeMutableParameters] fun Something(a: ArrayList<String>) {} ----------------- src/test.kt:9:Error: Using mutable objects as state in Compose will cause your users to see incorrect or stale data in your app.Mutable objects that are not observable, such as ArrayList or a mutable data class, cannot be observed by Compose to trigger recomposition when they change.See https://slackhq.github.io/compose-lints/rules/#do-not-use-inherently-mutable-types-as-parameters for more information. [ComposeMutableParameters] fun Something(a: HashSet<String>) {} --------------- src/test.kt:11:Error: Using mutable objects as state in Compose will cause your users to see incorrect or stale data in your app.Mutable objects that are not observable, such as ArrayList or a mutable data class, cannot be observed by Compose to trigger recomposition when they change.See https://slackhq.github.io/compose-lints/rules/#do-not-use-inherently-mutable-types-as-parameters for more information. [ComposeMutableParameters] fun Something(a: MutableMap<String, String>) {} -------------------------- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Here is the source file referenced above: `src/test.kt`: ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~kotlin linenumbers import androidx.compose.runtime.MutableState import androidx.compose.runtime.Composable @Composable fun Something(a: MutableState) {} @Composable fun Something(a: ArrayList) {} @Composable fun Something(a: HashSet) {} @Composable fun Something(a: MutableMap) {} ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ You can also visit the [source code](https://github.com/slackhq/compose-lints/tree/main/compose-lint-checks/src/test/java/slack/lint/compose/MutableParametersDetectorTest.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, `MutableParametersDetector.errors when a Composable has a mutable parameter`. To report a problem with this extracted sample, visit https://github.com/slackhq/compose-lints/issues. (##) Including !!! This is not a built-in check. To include it, add the below dependency to your project. This lint check is included in the lint documentation, but the Android team may or may not agree with its recommendations. ``` // build.gradle.kts lintChecks("com.slack.lint.compose:compose-lint-checks:1.4.2") // build.gradle lintChecks 'com.slack.lint.compose:compose-lint-checks:1.4.2' // build.gradle.kts with version catalogs: lintChecks(libs.compose.lint.checks) # libs.versions.toml [versions] compose-lint-checks = "1.4.2" [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: compose-lint-checks = { module = "com.slack.lint.compose:compose-lint-checks", version.ref = "compose-lint-checks" } ``` 1.4.2 is the version this documentation was generated from; there may be newer versions available. [Additional details about com.slack.lint.compose:compose-lint-checks](com_slack_lint_compose_compose-lint-checks.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("ComposeMutableParameters") fun method() { problematicStatement() } ``` or ```java // Java @SuppressWarnings("ComposeMutableParameters") void method() { problematicStatement(); } ``` * Using a suppression comment like this on the line above: ```kt //noinspection ComposeMutableParameters 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="ComposeMutableParameters" 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 'ComposeMutableParameters' } ``` In Android projects this should be nested inside an `android { }` block. * For manual invocations of `lint`, using the `--ignore` flag: ``` $ lint --ignore ComposeMutableParameters ...` ``` * Last, but not least, using baselines, as discussed [here](https://googlesamples.github.io/android-custom-lint-rules/usage/baselines.md.html).