Dejavu

Wait... didn't we just compose this?

Lock in Compose performance. Catch recomposition regressions before your users do.

The Problem

Compose's recomposition behavior is an implicit contract — composables should recompose when their inputs change and stay stable otherwise. But that contract breaks silently, and today's options for catching it are limited:

• Layout Inspector — manual, requires a running app, can't automate, can't run in CI
• Manual tracking code — SideEffect counters, LaunchedEffect logging, wrapper composables; invasive, doesn't scale, and ships in your production code
• Neither gives you a testable, automatable contract you can enforce on every PR

What Dejavu Does

Dejavu is a test-only library that turns recomposition behavior into assertions. Tag your composables with standard Modifier.testTag(), write expectations against recomposition counts, and get structured diagnostics when something changes — whether from a teammate, a library upgrade, an AI agent rewriting your UI code, or a refactor that silently destabilizes a lambda.

• Zero production code changes — just Modifier.testTag()
• One-line test setup — createRecompositionTrackingRule<Activity>()
• Rich diagnostics — source location, recomposition timeline, parameter diffs, causality analysis
• Per-instance tracking — multiple instances of the same composable get independent counters

Next Steps

• Getting Started — add the dependency and write your first test
• Examples — test patterns for common scenarios
• API Reference — all assertions and utilities
• How It Works — internals, compatibility, and limitations