---
id: SLICE-0005
type: slice
status: ready
parent: NS-0002
title: Prove LSP diagnostics parity with hemx-build
refs:
  - REQUIREMENTS.md
  - docs/diagnostics.md
  - docs/editor-support.md
  - hemx-lsp/src/main.rs
  - hemx-build/src/lib.rs
---

## Objective

Make LSP diagnostics a faithful editor transport for `hemx-build` diagnostics across open, change, save, close, and CLI file checks.

## Authority

`docs/diagnostics.md` and `REQUIREMENTS.md` `diagnostics/004`, `diagnostics/005`, and `check/001` require editor overlays to share compiler authority and preserve useful spans.

## Close when

- A focused LSP test opens an invalid `.heml` document and observes the same diagnostic code/severity/range as the `hemx-lsp diagnostics FILE.heml` path.
- `didChange` updates diagnostics from in-memory text.
- `didSave` with and without text uses the documented source of truth.
- `didClose` clears diagnostics.

## Verification

- `cargo test -p hemx-lsp`
- `cargo run -p hemx-lsp -- diagnostics <fixture>.heml`
- `cargo check --workspace` if public LSP/build types change.

## Non-goals

- Do not implement a second `.heml` parser in the LSP.
- Do not add provider-specific VS Code/Neovim behavior in this slice.

## Evidence

`hemx-lsp/src/main.rs` already has diagnostics CLI and LSP publish paths that can be covered with protocol tests.