LibreMediaConverter/CLAUDE.md

CLAUDE.md

This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.

LibreMediaConverter is an Android media converter (Kotlin, Jetpack Compose, Material 3) with two conversion engines: Media3 Transformer for the hardware path and FFmpeg for everything the platform cannot do. See @README.md for the architecture and @LICENSES/README.md for the split license — this file covers only what is not obvious from the code.

Build, test, lint

Everything is on Java 25 — daemon, CI, IDE, and the app's own bytecode. Four places say so and they must not drift apart:

Where	What sets it
Gradle daemon	gradle/gradle-daemon-jvm.properties → toolchainVersion=25
CI	java-version: '25' in both workflows
IDE	.idea/misc.xml
App bytecode	compileOptions in app/build.gradle.kts

Do not pick a JDK for the daemon — the repo does. gradle-daemon-jvm.properties carries foojay download URLs per platform, so Gradle provisions and runs the daemon on Java 25 regardless of what JAVA_HOME says (that only sets the launcher — ./gradlew --version prints both). Change it with ./gradlew updateDaemonJvm --jvm-version=NN, never by hand.

Reaching 25 in the bytecode row took a deliberate build change. AGP 9's built-in Kotlin compiles with the KGP it bundles — 2.2.10 for AGP 9.3.1 — and that caps jvmTarget at 24. The root build.gradle.kts puts KGP (and the lockstep Compose compiler plugin) on the buildscript classpath so AGP picks up 2.4.10 instead, which supports up to 26. That is why the module applies com.android.application and the Compose plugin by id() rather than from the catalog. Verified end to end, not assumed: compiled classes report major version 69, D8 dexes them, and R8 minifies them.

Consequences worth knowing before touching any of it:

• Raising kotlin requires a matching compose-compiler-gradle-plugin; they are one version.
• Still do not apply org.jetbrains.kotlin.android — incompatible with AGP 9's DSL.
• Java 24 is not an option even though Kotlin allows it: Adoptium dropped the EOL non-LTS, so there is no installable temurin-24. 25 is LTS and in the repo.

The Gradle wrapper does not float and cannot: distributionUrl names one archive and distributionSha256Sum is that file's checksum. Bump it with ./gradlew wrapper --gradle-version X --gradle-distribution-sha256-sum <sha> so the two stay consistent.

./gradlew :app:assembleDebug          # build debug APK
./gradlew :app:testDebugUnitTest      # JVM unit tests
./gradlew :app:ktlintCheck            # formatting
./gradlew :app:ktlintFormat           # fix formatting in place
./gradlew :app:detekt                 # static analysis
./gradlew :app:lintDebug              # Android lint
./gradlew :app:jacocoTestReport       # coverage (XML+HTML under app/build/reports/jacoco/)
# single unit test:
./gradlew :app:testDebugUnitTest --tests "org.libremediaconverter.model.ConversionRouterTest"

CI's "Static analysis" gate is exactly ./gradlew :app:ktlintCheck :app:detekt :app:lintDebug --continue. Run it with --continue locally too: one round trip gives you all three lists instead of the first one that fails.

Before treating a change as done, run: assembleDebug + testDebugUnitTest + compileDebugAndroidTestKotlin + ktlintCheck + detekt + lintDebug. compileDebugAndroidTestKotlin matters more here than it looks — the instrumented suite cannot run on this machine (below), so without it an androidTest compile error is not discovered until CI. ktlint and detekt also cover the test/androidTest source sets that lintDebug skips.

Instrumented tests: where they actually run

This section said the opposite until 2026-08-24, and both of its claims had been false for two days. Read it as the current answer, and see the git history if you need the old one.

• Local emulators work, for API 33-36. tools/local-emulator/run-e2e.sh runs them on this host. The segfault that made this look impossible was not a broken machine: SwiftShader's Reactor JIT writes generated shader code onto the heap and executes it, Fedora's SELinux policy denies execheap, and qemu dies. Choosing a different renderer avoids it entirely — -gpu host, angle_indirect and swangle_indirect all boot, while auto, off, guest and swiftshader_indirect do not. docs/local-emulator.md has the evidence and the per-API renderer table.
• CI runs API 37, and it gates. The matrix is 33/34/35/36/37. Two Media3 hardware-transcode tests fail inside the emulator's own c2.goldfish.h264.decoder rather than on anything this app does; they carry @FailsOnEmulatorApi37 and run in a separate continue-on-error job, E2E API 37 Media3 hardware transcode (advisory). The gating leg runs the other 55. That advisory job is red on every PR, by design — do not read it as your change breaking something, and do not read a green run as evidence those two tests pass. docs/api-37-emulator-crash.md has the measurements.

Still true, and the reason the advisory job is not simply deleted: API 37 needs a manual check on the Pixel 10 Pro XL before each release. The advisory pair is the one thing CI cannot answer for.

On a device or emulator, build only the ABI it can execute:

./gradlew :app:connectedDebugAndroidTest -PabiFilters=x86_64

FFmpeg's native libraries dominate the APK, so shipping arm64 to an x86_64 emulator doubles the install for code that can never run — and on API 37 the full APK does not fit at all.

Conventions

• ktlint owns formatting, detekt owns static analysis. detekt's formatting ruleset is off, so the two can never disagree about the same line. Never hand-fix a formatting complaint — run ktlintFormat. Style is intellij_idea at 120 columns, set in .editorconfig.

• detekt config is config/detekt/detekt.yml, merged onto detekt's defaults (buildUponDefaultConfig = true), so it carries only the rules this codebase legitimately breaks — each with the reason written next to it. Relax a rule that way or fix the code; never a bare @Suppress. Do not invent config keys: unknown ones are rejected.

• The model package is excluded from ReturnCount and CyclomaticComplexMethod only. It is the decision layer, where one branch is one documented user-visible outcome and the metric counts answers rather than complexity. Every other rule still applies there.

• Coverage is reported, not gated — 69.2% of lines (1519/2194), 53.2% of branches, measured 2026-08-24 with ./gradlew :app:jacocoTestReport.

  Every figure this file carried before that date was an artifact, roughly half the real one. Robolectric loads classes through its own sandbox classloader with no source location, JaCoCo skips no-location classes by default, and nothing told it otherwise — so not one Robolectric test counted, and Robolectric is what exercises the framework edge here. The isIncludeNoLocationClasses block in app/build.gradle.kts is what fixes it; do not delete it as stray config, and re-run the numbers if you ever touch it. Same commit, same 335 tests: 29.7% -> 69.2% with that block alone.

  The old entry also explained the wrong thing. It said coverage fell as the suite grew from 11 test files to 43 because "the denominator outran the numerator" on framework-edge code "the JVM cannot reach". The JVM reaches that code fine. What actually happened is that the new tests were disproportionately Robolectric, so each one added denominator and no numerator — the measurement was punishing exactly the tests that were hardest to write.

  Two things still hold. A floor needs a baseline that has settled, and this one has now moved by 39 points in a single build change, so it has not. And re-measure before quoting — that instruction is the only reason this was caught.

• Testable code is not done until it is tested. If a piece is unit testable, it gets unit tests before it counts as done. If it is e2e testable, it gets e2e tests. Both clauses apply — a change that is both needs both.

  Three things make that a real bar rather than a slogan here:

  • Unit-testable is broader than it looks. The pure-seam pattern — work/FailureOutcome.kt documents the reasoning — turns "needs a device" into "a pure function plus a thin edge". Robolectric is in the JVM source set, compose-ui-test-junit4 with it, so Compose screens are unit testable too. Reach for the seam before concluding something cannot be unit tested.
  • E2E is runnable locally, API 33-36, via tools/local-emulator/run-e2e.sh — see "Instrumented tests: where they actually run" above. That was believed impossible until the SELinux/renderer cause was found, and it is what makes the e2e half of this norm enforceable.
  • A test has to bite. Revert the line it covers, confirm it goes red, restore. A review of this codebase ran 46 mutations against a 257-test suite and 9 were vacuous — five of them passing the whole suite over a completely unguarded code path. Green is not evidence.

  Name what you did not cover and why. Genuine exemptions exist; implied coverage is the problem.

• kotlin.code.style=official. Gradle stays Kotlin DSL.

• File one-off issues with tools/github/file-issue.sh, not gh issue create. gh issue create does not touch the project board, so the issue exists, carries its labels, and is invisible in the Kanban — indistinguishable from never having been filed. Measured 2026-08-24: eight issues filed as a scripted batch all reached the board; one filed as a one-off minutes later did not. A batch carries the board step in its loop; one-offs are where it slips, which is what the script is for. It resolves the project and Status ids by name rather than caching them, and it reads the item back — a mutation returning 200 is not evidence the board shows what was asked for. Exit 3 means the issue was created but did not reach the board, and prints the number so it cannot be lost quietly.

  above-cut and backlog are labels from the 2026-08-22 triage pass — "worked autonomously overnight" and "held for manual review". They are not board columns. Status carries board state; do not put a cut label on a newly filed ticket.

• shellcheck runs in CI, inside the Static analysis job, over git ls-files '*.sh' so a new script is covered without editing the workflow. It runs at full severity, info included: the two findings that raises today are answered with targeted disable directives carrying their reason, exactly as config/detekt/detekt.yml carries only the rules this codebase legitimately breaks. Do not silence it with --severity=warning — that hides the next real finding too. It is pinned by image digest, and joins ktlint/detekt/JaCoCo in the "Dependency versions" rule above — for exactly the reason stated there, demonstrated the day it was added. The first cut used the runner's ambient shellcheck. That is 0.9.0, while the container used to check locally was 0.11.0, and the two disagree about how to report a trap handler: 0.11.0 says SC2329 once on the declaration, 0.9.0 says SC2317 on each of seven lines in the body. Same script, same directive, one green and one red. Directives that must survive both name both codes.

  Locally, use the same pin rather than whatever is installed: podman run --rm -v "$PWD:/mnt:z" docker.io/koalaman/shellcheck@sha256:61862eba... <files> (the digest is in status_check.yml; there is no shellcheck system package on this host).

  It does not cover inline run: blocks in the workflows, and a good deal of this repo's bash lives there. actionlint does cover them — it runs shellcheck over each run: — and reports one pre-existing info finding in build.yml. It is not wired in because every action here is pinned by SHA, and actionlint's usual installer is a curl | bash off a moving branch; doing it properly means pinning a container digest. Tracked separately rather than bolted on.

Dependency versions

Libraries float on minor + patch (coreKtx = "1.+"). Three groups deliberately do not:

• agp, kotlin, ksp are version-locked to each other. AGP 9.3.1's POM declares kotlin-gradle-plugin 2.2.10, and that is what AGP's built-in Kotlin compiles with. Android lint will suggest Kotlin 2.4.10; taking it breaks the Compose compiler unless KGP is also forced onto the root buildscript classpath. Move all three together, by hand, or none.
• ktlint, detekt and JaCoCo are pinned. A new rule in a linter makes files nobody touched stop passing, so CI goes red on a PR whose diff cannot explain it. Upgrading them is its own commit: run the tool, read the new findings, fix or relax them.
• The FFmpeg AAR is a committed file, not a coordinate.

+ does not mean "newest stable" on its own — Gradle will happily resolve it to an alpha, and androidx routinely publishes alphas numbered above the current stable (at last check: lifecycle, navigation, work, datastore and annotation all did). The componentSelection block in app/build.gradle.kts rejects prereleases, which is the only reason 2.+ means 2.11.0 rather than 2.12.0-alpha01. Do not remove it. To try a prerelease, name the exact version in the catalog — that pins it, which is the right way round.

Because versions float, a build can change without a commit. ./gradlew :app:dependencies --configuration debugRuntimeClasspath shows what actually resolved.

Traps

• Do not apply org.jetbrains.kotlin.android. AGP 9 has built-in Kotlin; applying the legacy plugin fails the build. This is why libs.versions.toml pins kotlin to AGP's bundled KGP version rather than the newest Kotlin release — the Compose compiler plugin must match it.
• The FFmpeg AAR is committed under bin/, deliberately. It is not on any Maven repo (ffmpeg-kit was archived and delisted). Rebuilding per CI run made red builds ambiguous: broken code, or a cross-compile that hiccuped? bin/README.md has provenance and how to regenerate it.
• Anything touching Media3 carries @UnstableApi rather than swallowing the marker with @OptIn. Android lint's UnsafeOptInUsageError catches a missed one.
• Release builds ship both ABIs. -PabiFilters is a test-run override only; build.yml verifies the released APK carries every ABI and that all native libraries are 16 KB aligned.