Transitive Version Pinning

A transitive pin beats your version choice

You declared a version. A library you added declares a strict constraint on some shared lower-level artifact — a rendering backend, a serialization core, a native binding — and strict wins: it overrides a plain version, and it overrides the platform/BOM you thought was in charge. Nothing warns you. The build compiles, because every module still compiles against whatever headers it was built with.

The failure arrives later and somewhere else.

The shape of the failure

A concrete run of it: adding a glass-effect UI library pinned the rendering backend strictly several minor versions up. The UI runtime, a vector-animation renderer and the image loader had all been built against the older one, and the newer backend had removed a matrix helper method. Result: a missing-method failure at runtime, thrown inside the animation renderer's draw pass — a component with no relationship to the library that had been added, and only when an animation actually rendered.

Note every property that made this hard:

• Not a build failure. Compilation and packaging were green.
• Not near the cause. The stack trace names the victim, never the pinner.
• Not deterministic on startup. It fires when that draw path first runs.
• Not visible on the platform that mattered. At the time, the library that forced the bump was never rendered on the affected target at all, so the cost of the constraint was pure.

Three versions of the shared backend appear below, and keeping them apart is the whole point: A.B.C is the older one the app had been built against, A.D.E is the newer one the strict constraint demanded, and A.D.F is the one a later alignment settled on — newer than A.B.C, but not the version the constraint had asked for.

Traps

Find out who pinned it before doing anything else. Guessing costs build cycles; the resolution report answers in one command and names the constraint and the module that declared it:

./gradlew :<module>:dependencyInsight \
  --configuration <runtimeClasspathConfiguration> \
  --dependency <group>:<artifact>

Read the selection-reason lines it prints for the artifact. A strict constraint shows up as a constraint from a specific module rather than as a plain requested version, and that module is your culprit — check your build's own report wording rather than grepping for a fixed heading. Run it per configuration — desktop, Android and test configurations resolve independently, and a pin can be present in one and absent in another, which is exactly why "it works on the other platform" is not evidence of anything.

Force back when the pinning library is not exercised on that target — and say so in the comment. Justify by scope, not by preference: if the feature that wanted the newer version never renders on this platform, pinning back costs nothing and that fact is the whole argument. When the shared artifact is not a direct dependency (so a version-catalog entry cannot reach it), rewrite it during resolution:

// adapted — <glass-lib> pins <render-backend> `strictly A.D.E`, dragging the whole desktop tree
// up. The UI runtime, the animation renderer and the image loader all compile against A.B.C, and
// A.D.E removed Matrix33.makeTranslate(float, float) — the animation renderer dies with a
// missing-method failure. Desktop did not render the glass effect at the time, so pin the backend
// back to what the UI runtime actually ships with.
configurations.configureEach {
    resolutionStrategy.eachDependency {
        if (requested.group == "<render-backend-group>") useVersion("A.B.C")
    }
}

For the simpler case — two libraries depending on different builds of the same artifact — a project-wide force is enough:

// adapted
subprojects {
    configurations.all {
        resolutionStrategy { force("<group>:<artifact>:<version>") }
    }
}

Align instead of forcing when your own UI runtime genuinely needs the newer version. Forcing back is a holding action; it becomes wrong the moment you upgrade the runtime for an unrelated reason. That is exactly what happened here — the effect later did reach the target that had been assumed never to render it, and the force had to be replaced by an alignment. Aligning means choosing the runtime build whose transitive backend version every other library can also live with — which in practice can mean taking a pre-release or snapshot build of one of the other libraries, because it is the first one compiled against the new backend. Note where that landed: the force-back had pinned A.B.C, while the alignment settled on A.D.F, a third version that satisfies everyone without being the one the strict constraint demanded. Then delete the force, or it will silently drag you back down.

The pin runs in both directions. Once the runtime version is fixed, a library compiled against a different signature of the same backend fails the same way — a call inside its effect path throws a missing-method failure. If that effect is optional, guard the call site by platform and let that target lose the effect; if it is not, you are back to alignment. Either way the guard needs a comment saying which version pair it is protecting, or it looks like dead code.

The shrinker sees this before your users do. An unresolvable method reference makes a bytecode shrinker abort the build with an unresolved-reference error. That abort is a free early warning for exactly this class of mismatch — treat it as a version-alignment signal first. Suppressing it is correct only when the code path is genuinely unreachable on that target, which is the same judgement call as forcing back, and it deserves the same written reason.

Document why the version is pinned, on the line with the pin, including what the next version breaks. A commit message does not survive contact with a dependency-update bot; a comment in the version catalog does. Say the version, the transitive consequence, and the failure the next version causes:

# adapted
ui-runtime = "1.12.0-alpha01"  # alpha01 → <render-backend> A.D.F (still has Matrix33.makeTranslate);
                               # alpha02 bumps to A.D.E which removed it → animation renderer crashes
anim-renderer = "2.2.2-ui-1.12-SNAPSHOT"  # snapshot built against A.D.F; the stable build needs the
                                          # old A.B.C and crashes against the runtime pinned above

Without those two comments, the pair reads as "someone was lazy and left a snapshot in", and the first tidy-up upgrade reintroduces the crash.

Verifying it

After any change to a pin or an alignment:

1. Re-run dependencyInsight for the shared artifact in every configuration you ship — the desktop runtime classpath and the mobile one resolve separately.
2. Build a release/shrunk artifact, not a development run: the shrinker's unresolved-reference pass is one of the few checks that catches a signature mismatch statically.
3. Exercise the drawing paths by hand — an animation, a blurred or layered surface, an image load. These are the ones that only fail when they paint, so no automated smoke test that skips rendering will tell you anything.