[davidschachterADFA]

ADFA-6822: D8 "Unexpected error during rewriting of Kotlin metadata"

AGP 8.8.2 bundles D8 8.8.34, which predates Kotlin 2.3 metadata (mv=[2,3,0]) and throws Should never be called while rewriting it. D8 logged this once per class, burying every real diagnostic in the CI log.

This PR puts com.android.tools:r8:8.13.25 first on the root buildscript classpath so it wins over the R8 shaded in AGP's builder jar, and adds a CI guard so a Kotlin bump can't silently bring the problem back. Dropping the pin needs an AGP upgrade, tracked separately.

Changes

• gradle/libs.versions.toml: r8 = "8.13.25" and android-r8, plus a comment next to kotlin that a Kotlin minor bump may need a newer r8.
• build.gradle.kts: classpath(libs.android.r8) first in the root buildscript. It resolves from the repositories the build already declares, so the buildscript has no repositories block of its own.
• .github/workflows/debug.yml: the Assemble step now tees the Gradle output and fails with an ::error:: if it contains Unexpected error during rewriting of Kotlin metadata.

Results (local :app:clean :app:assembleV8Debug --no-build-cache)

	Before	After
D8 version in use (temporary probe)	8.8.34	8.13.25
"Unexpected error during rewriting of Kotlin metadata"	21,546	0
Build log	~2.3M lines	~2.5k lines
APK size	114,628,533 B	114,710,453 B (+0.07%)
Dex files	37	37
NoSuchMethodError / NoClassDefFoundError	n/a	0

An earlier baseline run counted 25,416; the ticket's 2,743 came from the CI log and undercounts.

Verified

• :app:assembleV8Release, assembleV8Profileable, assembleV7Debug, :app:testV8DebugUnitTest and spotlessCheck all pass (BUILD SUCCESSFUL in 14m 14s, 0 metadata warnings).
• Pixel 6 Pro (Android 17, arm64): the app launches, opens a project, Quick Build and the normal build both produce an APK and reach the installer. No FATAL EXCEPTION in logcat.

Not verified

• That D8 now keeps valid Kotlin metadata on a given class. dexdump doesn't show annotation values; the Lkotlin/Metadata; reference counts match before and after (207), and runtime impact was probably nil to begin with (kotlin-reflect is not on :app's runtime classpath).
• Installing the built app and attaching the debugger (needs the Play Protect prompt approved by hand).

Notes

• The CI guard changes how the Assemble step captures output (2>&1 | tee). ADFA-6818, which merges the Gradle invocations, will need to preserve it.
• This pin affects only this project's build classpath. The IDE's bundled on-device toolchain (agp-tooling 9.3.1) is untouched.
• Rollback: revert the classpath line and the catalog entry.

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Summary

• Pin com.android.tools:r8:8.13.25 first on the root buildscript classpath to address reported D8 errors rewriting Kotlin 2.3 metadata.
• Add a CI guard that fails the V8 debug assembly if its Gradle log contains Unexpected error during rewriting of Kotlin metadata. The workflow captures the output and preserves Gradle’s exit status.
• The author reports successful local V8 and V7 builds, V8 unit tests, and spotlessCheck, with zero metadata warnings. The author also reports launching the app and building APKs on a Pixel 6 Pro running Android 17.
• Risk: The author did not verify that valid Kotlin metadata remains intact on individual classes. Installing the built app and attaching the debugger were also not verified.
• Maintenance note: The R8 pin applies to the project’s build classpath, not the IDE’s bundled on-device toolchain. The version catalog says to update the pin with Kotlin and remove it after an AGP upgrade.

The buildscript adds R8 version 8.13.25 before the Kotlin Gradle plugin. The debug workflow captures APK assembly output and fails if it detects the specified D8 Kotlin metadata rewriting error.

Changes: R8 metadata build handling

Layer / File(s)	Summary
Register the R8 dependency build.gradle.kts, gradle/libs.versions.toml	The version catalog defines R8 8.13.25 and its library alias. The buildscript adds R8 to the classpath before the Kotlin Gradle plugin.
Capture and check assembly output .github/workflows/debug.yml	The debug workflow logs Gradle assembly output and fails if the log contains Unexpected error during rewriting of Kotlin metadata.

Estimated code review effort: 2 (Simple) | ~10 minutes

Change: Bug fix

Suggested reviewers: daniel-adfa, itsaky-adfa

Merge Risk: Minimal · previous review a9e9a

No actionable merge-blocking issue is established; the change is mergeable after normal checks.

Pre-merge checks: 5

Check name	Status	Explanation
Title check		The title names the main change: pinning R8 to 8.13.25 so D8 can rewrite Kotlin 2.3 metadata. The raw summary and objectives both describe the R8 classpath pin and the Kotlin metadata error, so the ti…
Description check		The description states the problem (D8 8.8.34 throws errors rewriting Kotlin 2.3 metadata), the fix (R8 8.13.25 placed first on the root buildscript classpath), and the CI guard in the Assemble step. …
Docstring Coverage		No eligible functions found in the changed files. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff with cyclomatic complexity of at least 2. Documentat…
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.

Full details: Title check

Explanation

The title names the main change: pinning R8 to 8.13.25 so D8 can rewrite Kotlin 2.3 metadata. The raw summary and objectives both describe the R8 classpath pin and the Kotlin metadata error, so the title matches the changeset.

Full details: Description check

Explanation

The description states the problem (D8 8.8.34 throws errors rewriting Kotlin 2.3 metadata), the fix (R8 8.13.25 placed first on the root buildscript classpath), and the CI guard in the Assemble step. It also lists the changed files and verification results. This matches the changeset.

Full details: Docstring Coverage

Explanation

No eligible functions found in the changed files. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff with cyclomatic complexity of at least 2. Documentation-only edits and deletions within surviving functions are included; unchanged diff context and fully deleted functions are excluded. Analyzed 0 functions across 1 files. (1 skipped: 1 unsupported.)

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_{A rabbit checks the build log bright,
Then pins R8 in place just right.
Gradle’s output leaves a trace,
D8 errors meet a guarded gate.
The bunny hops beneath the moon,
And hopes the build completes quite soon.}

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