East Diagnostics

East-aware diagnostic rules over the TypeScript checker

East Diagnostics is the shared rule engine that catches East-specific mistakes which plain TypeScript can't — the same checks surfaced to the agent at write-time (the Claude plugin daemon) and to developers in the editor and CI (@elaraai/eslint-plugin-east). The rules run against a real ts.Program, so they are type-aware, not regex heuristics.

Features

• Shared rule set - One engine, runEastRules(ts, program, sourceFile, checker), reused across every surface.
• Type-aware - Rules consult the TypeScript checker (e.g. resolving BlockBuilder, variant contextual types).
• No bundled compiler - typescript is a peer dependency; the host's version is injected.
• Diagnostics service - createDiagnosticsService() resolves the nearest tsconfig, holds a warm LanguageService, and merges native type errors with the East rules for a file. Supports in-memory overlays for unsaved buffers.
• Readable East type errors - native TS assignability errors on East types are rewritten via east's structural type diff (diffTypes), so a mismatch deep inside a recursive type reads as one localized line instead of pages of restated generics. The project's own @elaraai/east is resolved at runtime, so the diff always matches the project's type semantics.
• LSP server - runEastLsp() serves the same diagnostics over the Language Server Protocol (stdio, zero dependencies), usable by Claude Code plugin lspServers, Neovim, or any LSP client.
• tsserver plugin - the @elaraai/east-diagnostics/tsserver-plugin entry decorates the editor's existing TypeScript language service (no second program), shipped to VS Code via the East UI Preview extension's typescriptServerPlugins contribution.

Rules

• no-redundant-east-cast - A TypeScript cast on the value of $.let/$.const when the East type argument is present.
• prefer-explicit-east-type - One-arg $.let/$.const on an under-determined value ([], {}, new Map()).
• prefer-some-none - variant("some"/"none", …) instead of some() / none.
• no-handrolled-variant - A plain object literal where an East variant/option is expected.
• no-east-namespaced-type - East.IntegerType etc. instead of a bare import.
• prefer-let-const-over-east-value - East.value(…) declared or returned inside an East.function block.
• no-relative-src-import - Importing ../src/… instead of the published package name.
• no-let-const-in-expression - Using $.let/$.const inline in an expression instead of binding to a const.
• no-unexecuted-east-expression - A bare East expression statement that is never executed with $( … ) or bound.
• no-reinlined-east-binding - An East Expr bound to a JS const/let and reused inside a block is re-inlined per use — bind it once with $.let/$.const.
• no-east-data-builder-helper - A TS helper whose only job is to return a hand-built East value — inline it or make it a real East.function.
• prefer-jsx-over-factory-call - In a .tsx file, a factory's Foo.Root(...) whose result is a JSX element — author it with the <Foo> tag instead.

Usage

import * as ts from "typescript";
import { runEastRules, createDiagnosticsService } from "@elaraai/east-diagnostics";

// Pure: run the rules over one source file you already have a program + checker for.
const diagnostics = runEastRules(ts, program, sourceFile, checker, { disabled: ["prefer-some-none"] });

// Or let the service resolve the project and merge native + rule diagnostics.
const service = createDiagnosticsService();
const text = service.diagnoseText("/path/to/file.ts"); // "" when clean

Claude Code plugin

The East ecosystem also ships a Claude Code plugin — East language skills, example search, and preemptive diagnostics for East code — installed separately from the elaraai marketplace:

# Inside Claude Code
/plugin marketplace add elaraai/east-workspace
/plugin install east@elaraai

# From a terminal
claude plugin marketplace add elaraai/east-workspace
claude plugin install east@elaraai

License

Dual-licensed:

• Open Source: AGPL-3.0 - Free for open source use
• Commercial: Available for proprietary use - contact [email protected]

Developed by Elara AI Pty Ltd