Trait LexHandler 

pub trait LexHandler: Send + Sync {
    // Provided methods
    fn on_label(&self, _ctx: &LabelCtx) { ... }
    fn on_validate(
        &self,
        _ctx: &LabelCtx,
    ) -> Result<Vec<Diagnostic>, HandlerError> { ... }
    fn on_resolve(
        &self,
        _ctx: &LabelCtx,
    ) -> Result<Option<WireNode>, HandlerError> { ... }
    fn on_render(
        &self,
        _ctx: &LabelCtx,
        _fmt: Format,
    ) -> Result<Option<RenderOut>, HandlerError> { ... }
    fn on_hover(&self, _ctx: &LabelCtx) -> Result<Option<Hover>, HandlerError> { ... }
    fn on_completion(
        &self,
        _ctx: &LabelCtx,
    ) -> Result<Vec<Completion>, HandlerError> { ... }
    fn on_code_action(
        &self,
        _ctx: &LabelCtx,
    ) -> Result<Vec<CodeAction>, HandlerError> { ... }
    fn on_format(
        &self,
        _ctx: &FormatCtx,
    ) -> Result<Option<LexAnnotationOut>, HandlerError> { ... }
}

The hook-event interface a Lex extension implements.

Every method has a default implementation that returns the identity (Ok(None), Ok(Vec::new()), ()), so an extension only needs to override the methods it cares about. An empty impl LexHandler for Foo {} is a no-op handler that compiles and runs.

Provided Methods

fn on_label(&self, _ctx: &LabelCtx)

Informational notification fired during the analyse phase. No response is expected. Use this for handlers that maintain external state (caches, indices, link graphs).

fn on_validate(&self, _ctx: &LabelCtx) -> Result<Vec<Diagnostic>, HandlerError>

Returns diagnostics for a labelled node. Fires during analyse, after resolve.

fn on_resolve(&self, _ctx: &LabelCtx) -> Result<Option<WireNode>, HandlerError>

Returns an AST replacement subtree, which the host splices into the parent in place of the labelled node. Fires during the resolve phase, before analyse. Ok(None) leaves the original node in place.

fn on_render( &self, _ctx: &LabelCtx, _fmt: Format, ) -> Result<Option<RenderOut>, HandlerError>

Returns the labelled node’s representation in a target format. Fires during lexd convert or library-driven rendering. Ok(None) falls back to default rendering of the underlying node.

fn on_hover(&self, _ctx: &LabelCtx) -> Result<Option<Hover>, HandlerError>

Returns hover content for a labelled node. Fires in response to textDocument/hover LSP requests.

fn on_completion( &self, _ctx: &LabelCtx, ) -> Result<Vec<Completion>, HandlerError>

Returns completion items for a position inside a labelled node’s params or body. Fires in response to textDocument/completion.

fn on_code_action( &self, _ctx: &LabelCtx, ) -> Result<Vec<CodeAction>, HandlerError>

Returns code actions for a labelled node. Fires in response to textDocument/codeAction.

fn on_format( &self, _ctx: &FormatCtx, ) -> Result<Option<LexAnnotationOut>, HandlerError>

Returns the Lex-source representation of a typed AST subtree owned by this handler’s namespace — the inverse of on_resolve, and the reverse-direction sibling of on_render for the Lex target format.

Phase 4a of #570 ships this trait method, the FormatCtx / LexAnnotationOut wire types, and the Registry::dispatch_format entry point. Phase 4b implements on_format in the built-in lex.tabular.* / lex.media.* handlers. Production call sites in to_lex.rs and lexd format get wired in a Phase 4b follow-up — until that lands, the hook is invocable through the registry (tests + library embedders use it) but no built-in pass dispatches through it yet, so a handler implementing on_format will be exercised by direct Registry::dispatch_format callers only.

Ok(None) lets the host fall back to its built-in formatter for the underlying node kind — there is no separate “not handled” error code. See comms/specs/proposals/lex-extension-wire.lex §4.8 for the full wire contract.

Implementors