kotlin-tooling-native-build-performance

Kotlin/Native Build Performance

Turn "the iOS build is slow" into a measured diagnosis and a small set of safe fixes. Two rules apply throughout:

1. Never trade away required release behavior. A faster local loop must not

change what CI publishes.

1. Measure before and after with the same command and the same build state.

An unmeasured fix is a guess.

Step 0: Classify the Slow Scenario

Establish four facts before editing anything: where (local or CI), what (debug feedback loop or release/distribution artifact), state (first build, clean, warm, or no-op), and phase (which tasks dominate the log). Then match the dominant symptom:

Step 1: Audit and Measure

1. Run the static audit from the project root:

   scripts/audit-native-build.sh /path/to/project

It is read-only and prints file:line findings (disabled caches, broad local tasks, transitiveExport, broad KSP configuration, missing CI .konan cache), each pointing at the reference file with the fix. Findings are leads, not verdicts — confirm each against project policy.

1. Find the command the user actually waits for: a script, a CI step, or the

Gradle invocation inside an Xcode build phase. Optimize that command, not a task you picked yourself.

1. Run it twice when practical. The first build downloads Kotlin/Native

components and fills caches; only the second and later runs are representative. Attribute time per task before blaming the compiler:

   kotlin.build.report.output=file   # writes build/reports/kotlin-build/

Gradle's --scan or --profile work too.

1. If you cannot run the build (no macOS host, no Xcode), analyze logs, build

scans, or checked-in metrics instead — and state explicitly that the conclusion is static.

Step 2: Fix in Safe Order

Apply fixes one at a time, re-measuring as you go:

1. Restore healthy defaults — remove cache/daemon workarounds, enable

Gradle build and configuration caches, keep ~/.konan warm in CI, update Kotlin: references/caching-and-gradle.md

1. Build only what the feedback loop needs — one specific task per loop,

correct integration method, justified target matrix: references/artifacts-and-targets.md

1. Cut export and generated-code cost — drop transitiveExport, narrow

export(...), scope KSP work to the native compilations that need it: references/exports-and-generated-code.md

1. Experimental switches last, with the user's agreement:

references/experimental.md

Worked Example

A developer on an Apple Silicon Mac complains that "every shared-module change costs 12 minutes". Their loop runs ./gradlew :shared:assembleXCFramework. A build scan of the second (warm) run shows:

:shared:linkReleaseFrameworkIosArm64             348s
:shared:linkReleaseFrameworkIosX64               341s
:shared:compileKotlinIosX64                       96s
:shared:linkDebugFrameworkIosSimulatorArm64       41s
:shared:compileKotlinIosSimulatorArm64            38s
configuration phase                               64s

Reasoning chain:

• The loop is local + debug + warm, but ~690s goes to linkRelease* —

release linking is an order of magnitude slower than debug and only CI needs it. Replace the local command with :shared:linkDebugFrameworkIosSimulatorArm64 (or the Xcode embed task if Xcode drives the build). (artifacts-and-targets)

• All iosX64 work serves Intel simulators; ask whether the team still

supports them before removing the target. (artifacts-and-targets)

• 64s of configuration on every run disappears behind

org.gradle.configuration-cache=true once trialed. (caching-and-gradle)

• Expected loop after the change: ~40s compile + ~40s link on warm builds —

confirm by re-running the new command twice and comparing.

• CI keeps assembleXCFramework untouched; note that explicitly in the

report.

Verify

• [ ] Re-run the exact baseline command; compare warm build against warm

build, not warm against cold.

• [ ] Second run with the configuration cache reports it is being reused.
• [ ] The local development log no longer contains linkRelease*,

*ReleaseXCFramework, or removed generator tasks.

• [ ] CI still produces every required release artifact, unchanged.
• [ ] Tests pass and the app still runs from Xcode.
• [ ] scripts/audit-native-build.sh reports no findings you have not

consciously accepted and documented.

Report Your Changes

Close with a short performance note:

• The slow scenario (local/CI, debug/release, cold/warm) and the measured

evidence — or a statement that the analysis was static.

• Each change, and why it is safe for release behavior.
• The before/after commands the user can run to confirm the win.
• Remaining tradeoffs: experimental flags enabled, targets removed under a

policy assumption, worker limits, or generated-code work deferred.

• Links to the relevant official documentation below.

Official Documentation