flowrs-engine/crates/flowrs-openui

flowrs-openui

OpenUI Lang 1.0 in pure Rust: the lexer, parser, streaming parser, evaluator, edit merge, serializer, validation rules, and a headless runtime (state, forms, actions, queries, mutations, host events). flowRS's app layer (flowrs-app) writes and checks apps in it; the renderer draws the tree this crate evaluates.

Licence

MIT OR Apache-2.0, at your option (LICENSE-MIT, LICENSE-APACHE; third-party material in NOTICE).

Attribution

OpenUI Lang and its reference implementation are by Thesys Inc. (https://github.com/thesysdev/openui), under the MIT licence (LICENSES/OpenUI-MIT.txt, "Copyright (c) 2011-2024 Thesys Inc.").

This crate is a port, not a fork. It follows the 1.0 specification (spec/language.md, spec/overview.md, spec/prompt.md) and ports the behaviour of @openuidev/lang-core 1.0.1 (packages/lang-core/src) to Rust; every source file names the files it was ported from. It does not depend on, or copy from, the openui crate (openui-rs). No @openuidev JavaScript is shipped or run.

The conformance fixtures in tests/fixtures/1.0 are copied unchanged from spec/fixtures/1.0 at upstream commit 9d73d17d2bbac565672a85e78f6eb7740cb0d9ca (2026-10-23), under the same MIT licence.

Conformance

cargo test -p flowrs-openui runs all 59 fixtures: every program case at level 1 (syntax, streaming, entry, references, evaluation, editing, errors, validation rules), and the 12 interactions.json cases at level 2 through Session. A property test feeds every fixture's text in thousands of chunkings and requires the same program a batch parse gives.

Where this follows the spec text over the reference

Each is noted in the file that does it.

• Fences open only at the start of a line, and quotes in prose do not shield one (§1.2). The reference finds an opener anywhere.
• Statement boundaries read brackets as a stack, so a mismatched closer does not close (§1.4 with §4 rule 2); the reference counts depth. Both batch and streaming use the stack, so they agree on malformed input too.
• Query and mutation arguments resolve references like any expression, so what they name is reachable (§2.3, §6.1).
• Stream end makes the pending tail final, a redefinition included (§4 rule 7), so a stream always equals a batch parse.
• The edit merge reads both texts with §1.2 and §1.4, multi-line ternaries included (§7).
• Data never becomes an action: only an action call makes a plan.

Extensions

• Library::data_refs: names a host binds as data (flowRS: graph ports, n7.mean). A reference to one that no statement defines reads Host::reference instead of being unresolved. A spec client without the extension sees an unresolved name and renders nothing there.
• Nesting is bounded (MAX_DEPTH), and pattern runs on a small matcher with a step budget: model output is untrusted.
• Tools are synchronous (Tools); an asynchronous host answers from what it holds and calls Session::refetch when a result arrives.