feat(android): render intrinsic sheets and box semantics - #39
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Four findings from an adversarial pass, one of them a hard crash. All verified
on a physical Moto G power (2021), including a negative control.
1. CRASH — an intrinsic sheet containing a scrollable child killed the app.
The content-detent path wrapped the sheet body in verticalScroll
unconditionally. Compose's checkScrollableContainerConstraints THROWS when
a scrollable is measured with an infinite max height, so a `scroll` or
`lazy_list` inside `detents: [:content]` — the most natural use of an
intrinsic sheet — died at first measure with
FATAL EXCEPTION: java.lang.IllegalStateException: Vertically scrollable
component was measured with an infinity maximum height constraints
iOS survives the equivalent nesting because SwiftUI tolerates it; Compose
does not. The sheet now only adds its own scroll when the content has none
(isScrollableNode walks the subtree); the height cap applies either way and
the child keeps owning its scrolling.
Proven, not assumed: with the guard disabled the app dies with that
exception; with it, the same screen reports 40 rows and stays alive.
2. A disabled box still dispatched taps unless it also carried
accessibility_role: :button. The non-button `when` arm had no `enabled`
check while the semantics block below emitted disabled() — TalkBack
announced it as disabled and it kept firing. iOS disables every box
regardless of role, so this was also a platform split.
3. A box declared `accessibility_role: :button` whose tap is handled by an
ancestor was announced as "…, button, disabled". Compose publishes
disabled() semantics whenever clickable's `enabled` is false, so encoding
"no handler" as enabled = false mislabelled a live control. The branch now
requires a handler and falls through to semantics-only otherwise.
4. The height cap sat outside the node's own padding, so a padded sheet
overshot max_height by the padding amount and disagreed with iOS, which
caps the already-padded body. Modifier order corrected.
Also: merge descendants on label OR button role, matching the iOS fix — role
without merging leaves children as separate nodes inside a "button".
Device results (Moto G power): short content hugs (3 rows), max_height 320 caps
and scrolls internally (40 rows), scrollable child renders and survives (40
rows), app alive across all cases.
340 tests, format, credo --strict, ktlint generate-then-lint, and a real Gradle
build all clean.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
GenericJam
added a commit
that referenced
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Aug 28, 2026
…crash fix Pairs with mob 0.7.32, published first. Ships #39: the generated Android renderer parses typed content detents, hugs short content, caps against max_height and the parent constraint, scrolls overflow internally, and honours composite Box accessibility (label as contentDescription, explicit button role preserved without a tap handle, disabled semantics, no dispatch when disabled, passive labelled boxes stay non-buttons). Plus four fixes from an adversarial review, one of them a hard crash: - A content Sheet containing a scroll/lazy_list child KILLED THE APP. The content-detent path wrapped the body in verticalScroll unconditionally, and Compose throws when a scrollable is measured with infinite max height. Proven on a Moto G with a negative control: guard disabled, the app dies with IllegalStateException; guard enabled, the same screen renders 40 rows and survives. - A disabled Box dispatched taps unless it also had a button role, while reporting disabled() semantics — announced disabled, still firing, and a split from iOS which disables every Box regardless of role. - A Box declared a button whose tap is handled by an ancestor was announced as "button, disabled", because Compose publishes disabled semantics whenever clickable's enabled is false. - The height cap sat outside the node's padding, so a padded sheet overshot max_height; iOS caps the already-padded body. Generated dependency floor raised to {:mob, "~> 0.7.32"}. The comment now records both reasons a floor exists here — mob_send_dismiss since 0.7.31, and 0.7.32's validation/encoding of detents and accessibility props, without which the Kotlin silently renders a default sheet and drops the semantics rather than erroring. Preflight: format, credo --strict, compile --warnings-as-errors, 340 tests, git diff --check, ktlint generate-then-lint, and a real Gradle build + device deploy all clean. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
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Summary
Ownership
This is the generated Android half of the coordinated Mob renderer change. The downstream UI library remains responsible for Select/BottomSheet composition and visual styling; the generated host owns Material Sheet mechanics and generic Box semantics.
The matching runtime/iOS implementation is GenericJam/mob#94.
Verification
mix format --check-formattedmix credo --strictmix compile --warnings-as-errorsMOB_DIRandMOB_DEV_DIR(339 total behavior checks green)mix test --only lint— generated Kotlin lint passedgit diff --check origin/master..HEADThis PR intentionally does not bump the archive version or generated Mob dependency floor. Release bookkeeping follows after the matching Mob release is approved.