Skip to content

Recomposition Blame

Recomposition Blame traces a recomposition back to its cause. Where the Recomposition Cascade walks downstream (what this composable affects), Blame walks upstream (what caused this composable to recompose) — in two complementary ways.

1. State Write-Site (runtime)

For composables annotated with @TraceRecomposition(traceStates = true), a Compose Snapshot write observer records where each internal state was mutated and appends it to the log:

[state] counter: Int changed (0 → 1) ← onClick (MainActivity.kt:97)

The ← method (File.kt:line) suffix tells you exactly which line of code wrote the state that triggered the recomposition — turning "why did this recompose?" guesswork into a precise pointer. The same suffix appears in the heatmap inlay's tooltip.

Prerequisites

  1. @TraceRecomposition(traceStates = true) on the composable.
  2. ComposeStabilityAnalyzer.setEnabled(true) in your Application.
  3. A running app on a connected device (Android/JVM).

Supported state

Write-site capture works for delegated scalar state — var x by remember { mutableStateOf(...) } (and mutableIntStateOf, etc.). derivedStateOf has no write site, and non-delegated state (val s = mutableStateOf(...)) is not tracked.

2. Parameter Provenance (static)

To trace where a parameter's value comes from, right-click any @Composable in the editor and choose "Blame this Recomposition":

blame-menu

The Blame tool-window tab opens with the reverse of the cascade — which composables call this one, and where each argument's value originates:

blame-window

Each caller node lists the arguments it passes, annotated with the static origin of each value:

Origin label Meaning
val property / var property The argument reads a property (e.g. viewModel.products).
parameter The argument is forwarded from the caller's own parameter.
call to foo() The argument is the result of a function call.
expression A literal, lambda, or other dynamic expression.

This view is fully static — it needs no running app, so you can trace provenance while reading code.

How to Use

  • Write-sites: add @TraceRecomposition(traceStates = true), run the app, and read the ← … suffix on [state] lines in Logcat (or the heatmap tooltip).
  • Provenance: right-click a composable in the editor → Blame this Recomposition → inspect the upstream tree. Double-click a node to jump to its source.

Best-effort provenance

Parameter provenance is a static estimate. It searches project-source callers only (library callers are not shown), maps arguments by name/position (which can be approximate for vararg or mixed named/positional calls), and resolves the outermost expression; dynamic origins are shown as expression.