October 5, 2026
Fission 0.15.0: portable files and production-ready UI
Fission 0.15.0 makes two everyday application needs substantially easier: working
with user-approved files across native and Web targets, and producing a polished,
coherent interface without rebuilding basic design and interaction behaviour in
each application.
The release also advances the renderer, charts, accessibility, retained identity,
LiveTest reliability, documentation, and the component catalogue. It is a minor
release because it adds public APIs and intentionally changes the default visual
language.
One filesystem contract, native authority
The new opt-in filesystem capability lets an application work with direct native
paths or provider-backed directory locations through one asynchronous effect API.
Applications can list directories, inspect metadata, stream reads, write bytes or
streams, create directories, remove entries, inspect permission state, and release
grants.
Native paths use the process's operating-system authority. Fission does not impose
an additional path sandbox. Platform pickers provide user-selected locations on
desktop, Android, iOS, and modern browsers. On Web, Fission uses the File System
Access API and can retain granted handles in IndexedDB for later restoration;
file contents remain in the user's filesystem.
Transfers are incremental on desktop and lazy on Web. The default stream chunk is
appropriate for ordinary interactive work, and applications handling different
latency or throughput profiles can tune it explicitly.
CLI-managed projects enable the capability with:
fission add-capability filesystem --project-dir .
Applications that do not enable it do not compile or package its providers.
A stronger interface before application styling begins
Tidewater is now Fission's default design system. It uses a calm teal palette,
clear surface hierarchy, compact controls, consistent type, and restrained depth.
Graphite and Ember ship as alternate presets, and applications can still install
their own DSP package.
The framework now carries the design decisions that previously leaked into each
application: compact, comfortable, and spacious density; minimum pointer and touch
targets; paired surface and content colours; responsive breakpoints; elevation and
layer roles; loading and busy states; and an optional platform-native look.
Every built-in component now reads its spacing, sizing, colour, radius, and motion
from design tokens or component recipes. Existing DSP packages remain usable:
new roles are optional and inherit compatible fallbacks when omitted.
This release also completes interaction paths that a visual example can easily
hide. Split views resize by dragging, editable fields submit and cancel from the
keyboard, file upload exposes an accessible error state, calendars use labelled
icon navigation, comboboxes show placeholders, date ranges follow theme spacing,
and table headers fill their surface.
Rendering and interaction fidelity
The Vello renderer moves to the sparse-strips pipeline and WGPU 29. The retained
render model adds per-corner radii, per-edge borders, sweep gradients, blend modes,
backdrop colour filters, stroke trim and dash animation, and placement along a
path. Text painting now consumes the same wrapping and alignment geometry that
layout measured, removing several first-frame and multiline mismatches.
Focus, hover, minimum hit targets, implicit identities, drag-and-drop, scrollbars,
selection handles, nested portals, and popup dismissal have all received targeted
correctness work. The result is less application code compensating for framework
behaviour and more consistent input across desktop, mobile, and Web.
Charts add interactive tooltips and axis pointers, hover emphasis, legend
selection, wheel and slider zoom, region brushing, keyboard navigation, assistive
descriptions, and animated value changes. Dense line and category data is reduced
at presentation time so crowded plots remain readable.
A catalogue that can be inspected, not imagined
The widget gallery now gives each supported component a dedicated page with
working state, responsive coverage, design-system and density controls, and
maintained visual baselines. The showcase uses framework widgets for its own
controls and applies selected design systems only to the previewed application.
The documentation site, crate directory, guides, and examples have been refreshed
to match the current APIs and to make the value of a capability clear before its
implementation details. Advanced widget authors can use the public
LoweringContext surface and lexical with_scope(...) identity scoping without
depending on private lowering internals.
Upgrade
Update the framework and CLI:
[dependencies]
fission = { version = "0.15.0", default-features = false, features = ["desktop"] }
cargo install cargo-fission --version 0.15.0 --locked
The default look is now Tidewater at compact density. Applications that need a
different visual default should install an explicit design system or density.
Several component sizing fields now use Option<f32> so None can inherit the
active design system: CircularProgress::size and thickness,
RefreshIndicator::stroke_width and indicator_size, and the sizing fields on
TimelineLayout. Public design, semantics, environment, slider, combobox, and
file-upload structs also gained optional fields; struct literals should use
..Default::default() unless they intentionally initialize every field.
The filesystem capability is not enabled by the version upgrade. Add it only to
applications that use it, with the CLI command above.
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