(#) Using Modifier.then with a Modifier factory function with an implicit receiver !!! ERROR: Using Modifier.then with a Modifier factory function with an implicit receiver This is an error. Id : `SuspiciousModifierThen` Summary : Using Modifier.then with a Modifier factory function with an implicit receiver Severity : Error Category : Correctness Platform : Any Vendor : Jetpack Compose Identifier : androidx.compose.ui Feedback : https://issuetracker.google.com/issues/new?component=612128 Min : Lint 8.7+ Compiled : Lint 8.7+ Artifact : [androidx.compose.ui:ui-android](androidx_compose_ui_ui-android.md.html) Since : 1.7.0 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/ui/ui-lint/src/main/java/androidx/compose/ui/lint/SuspiciousModifierThenDetector.kt) Tests : [Source Code](https://cs.android.com/androidx/platform/frameworks/support/+/androidx-main:/compose/ui/ui-lint/src/test/java/androidx/compose/ui/lint/SuspiciousModifierThenDetectorTest.kt) Copyright Year : 2024 Calling a Modifier factory function with an implicit receiver inside Modifier.then will result in the receiver (`this`) being added twice to the chain. For example, fun Modifier.myModifier() = this.then(otherModifier()) - the implementation of factory functions such as Modifier.otherModifier() will internally call this.then(...) to chain the provided modifier with their implementation. When you expand this.then(otherModifier()), it becomes: this.then(this.then(OtherModifierImplementation)) - so you can see that `this` is included twice in the chain, which results in modifiers such as padding being applied twice, for example. Instead, you should either remove the then() and directly chain the factory function on the receiver, this.otherModifier(), or add the empty Modifier as the receiver for the factory, such as this.then(Modifier.otherModifier()) (##) Example Here is an example of lint warnings produced by this check: ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~text src/test/TestModifier.kt:10:Error: Using Modifier.then with a Modifier factory function with an implicit receiver [SuspiciousModifierThen] fun Modifier.test2() = this.then(test()) ---- src/test/TestModifier.kt:12:Error: Using Modifier.then with a Modifier factory function with an implicit receiver [SuspiciousModifierThen] fun Modifier.test3() = this.then(with(1) { test() }) ---- src/test/TestModifier.kt:14:Error: Using Modifier.then with a Modifier factory function with an implicit receiver [SuspiciousModifierThen] fun Modifier.test4() = this.then(if (true) test() else TestModifier) ---- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Here is the source file referenced above: `src/test/TestModifier.kt`: ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~kotlin linenumbers package test import androidx.compose.ui.Modifier object TestModifier : Modifier.Element fun Modifier.test(): Modifier = this.then(TestModifier) fun Modifier.test2() = this.then(test()) fun Modifier.test3() = this.then(with(1) { test() }) fun Modifier.test4() = this.then(if (true) test() else TestModifier) ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ You can also visit the [source code](https://cs.android.com/androidx/platform/frameworks/support/+/androidx-main:/compose/ui/ui-lint/src/test/java/androidx/compose/ui/lint/SuspiciousModifierThenDetectorTest.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, `SuspiciousModifierThenDetector.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.ui:ui-android:1.9.0-alpha01") // build.gradle implementation 'androidx.compose.ui:ui-android:1.9.0-alpha01' // build.gradle.kts with version catalogs: implementation(libs.ui.android) # libs.versions.toml [versions] ui-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: ui-android = { module = "androidx.compose.ui:ui-android", version.ref = "ui-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.ui:ui-lint:1.9.0-alpha01`. [Additional details about androidx.compose.ui:ui-android](androidx_compose_ui_ui-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("SuspiciousModifierThen") fun method() { then(...) } ``` or ```java // Java @SuppressWarnings("SuspiciousModifierThen") void method() { then(...); } ``` * Using a suppression comment like this on the line above: ```kt //noinspection SuspiciousModifierThen 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="SuspiciousModifierThen" 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 'SuspiciousModifierThen' } ``` In Android projects this should be nested inside an `android { }` block. * For manual invocations of `lint`, using the `--ignore` flag: ``` $ lint --ignore SuspiciousModifierThen ...` ``` * Last, but not least, using baselines, as discussed [here](https://googlesamples.github.io/android-custom-lint-rules/usage/baselines.md.html).