Fix RUM-13135: Compose Instrumentation modifying expected layout#3249
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Fix RUM-13135: Compose Instrumentation modifying expected layout#3249
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Root cause: The Datadog Kotlin Compiler Plugin prepends Modifier.semantics {}
to every composable call's modifier chain. In certain Compose versions, the
CoreSemanticsModifierNode implementation may participate in the layout
measurement chain, causing constraint propagation issues in SubcomposeLayout-
based components (e.g., Coil SubcomposeAsyncImage) inside LazyRow/LazyColumn.
Changes:
- Replace Modifier.semantics {} with custom DatadogSemanticsElement/Node
- DatadogSemanticsNode explicitly implements only SemanticsModifierNode
- Node is guaranteed to never interfere with layout constraints
- DatadogSemanticsPropertyKey and public API remain unchanged
Tests: 7 unit
Apply ktlint standard:class-signature and standard:function-signature rules to DatadogSemanticsElement, DatadogSemanticsNode, and test methods.
…shCode Convert DatadogSemanticsElement from data class to regular class to avoid detekt DataClassContainsFunctions violation. Manually implement equals() and hashCode() to maintain the same behavior for Compose modifier reuse.
Revert ktlint auto-format to use multi-line class and function signatures that match the existing project style conventions (parameters on separate lines when there are 2+ parameters).
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Summary
Fixes layout constraint propagation issue caused by Datadog Compose auto-instrumentation. When the compiler plugin prepends
Modifier.semantics {}to composable modifier chains, it can interfere withSubcomposeLayout-based components (e.g., Coil'sSubcomposeAsyncImage) insideLazyRow/LazyColumn, causinghasBoundedHeightto becomefalseandminHeightto become0.RUM-13135
Root Cause
The Datadog Kotlin Compiler Plugin (
ComposeTagTransformer) auto-instruments composable functions by insertinginstrumentedDatadog(name).then(originalModifier)at every composable call site. TheinstrumentedDatadog()function previously usedModifier.semantics {}(fromCoreSemanticsModifierNode), which in certain Compose framework versions may participate in the layout measurement chain, modifying constraint propagation.Changes
DatadogModifier.kt: ReplacedModifier.semantics {}with customDatadogSemanticsElement/DatadogSemanticsNodeusing theModifierNodeElementAPIDatadogSemanticsNodeexplicitly implements onlySemanticsModifierNode(NOTLayoutModifierNode)DatadogSemanticsPropertyKeyand publicModifier.datadog()API remain unchangedDatadogSemanticsElementTest.kt: 7 unit tests for the new element/nodeCompanion Change (separate repo)
dd-sdk-android-gradle-plugin:ComposeTagTransformer.buildIrExpression()should change modifier order fromdatadogTag.then(original)tooriginal.then(datadogTag), placing semantics INNER instead of OUTER so layout modifiers process constraints first.Test Plan
DatadogSemanticsElementandDatadogSemanticsNodeGenerated by rum:fix-jira-issues