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command lsp
summary Run a Language Server Protocol server on stdio for editor integrations.

mdsmith lsp

Run an LSP server that speaks the Language Server Protocol over stdio. The server reuses the same lint and fix pipelines as check and fix, surfaces diagnostics, and exposes per-rule quick fixes plus a whole-file source.fixAll.mdsmith action.

mdsmith lsp [--stdio]

The subcommand is designed to be spawned by an LSP client (VS Code, Neovim, Helix, JetBrains LSP plugin), not run interactively. It reads JSON-RPC frames on stdin and writes responses and notifications on stdout.

--stdio is accepted as a no-op for clients (notably vscode-languageclient) that always append it when selecting stdio transport. The server uses stdio either way.

Capabilities advertised

Capability Behavior
textDocumentSync = Full Full-document sync; lint trigger gated by mdsmith.run
publishDiagnostics One push after each lint
codeActionProvider quickfix per fixable diagnostic, source.fixAll.mdsmith
hoverProvider Rule docs on hover over a diagnostic; directive docs on hover inside <?…?>
documentSymbolProvider Hierarchical outline (headings, link refs, front matter, directives)
definitionProvider Jump-to-definition for anchor / file / ref-style links and directive arguments
implementationProvider Multi-target jump for kind: values and headings (every link target)
referencesProvider Workspace links pointing at the symbol under the cursor
workspaceSymbolProvider Substring search across headings, link refs, front-matter title:, and kind names
callHierarchyProvider File-level call graph over <?include?>, <?catalog?>, <?build?>, and links
completionProvider Heading anchors, link-ref labels, kind names, and directive file paths
renameProvider Heading + link-reference label renames, with prepareProvider: true
workspace/didChangeWatchedFiles Re-lint open buffers on .mdsmith.yml change; index refresh on Markdown changes

mdsmith.run controls when the server actually re-lints:

  • onSave (default): lint on didOpen, didSave, and config changes. didChange events update the buffer but do not trigger a lint pass.
  • onType: lint on every didChange (debounced 200 ms) plus the same triggers as onSave.
  • off: never lint automatically. Code actions still work when invoked explicitly.

Hover

textDocument/hover resolves in two passes:

  1. Diagnostic-first. If the cursor falls inside an active diagnostic range, the server returns a MarkupContent (kind markdown). The body begins with the diagnostic message followed by the rule's full help text — the same text mdsmith help rule <id> prints.

  2. Directive fallback. If no diagnostic covers the cursor, the server checks whether the cursor is inside a <?directive …?> block. If so, it returns the directive's guide page from docs/guides/directives/. The documented directives are catalog, include, build, allow-empty-section, and require.

If neither pass finds a match, the server returns null (no hover). Each hover response includes a range field set to the matched span — the diagnostic range or the full directive block range — so clients can anchor the popup to the right span.

mdsmith/rulePatterns returns rule maintainability metadata; hover adds "Suggested remediation" only when for-diagnostic: true.

Diagnostic mapping

LSP Diagnostic fields map from the same JSON shape check prints:

mdsmith LSP
rule + name code (e.g. MDS001); source = mdsmith
severity severity (error → 1, warning → 2)
line, column range.start; end is the line's UTF-16 length (squiggle → end-of-line)
message message
rule name data.rule (echoed back on codeAction)

Code actions

  • quickfix — one per fixable diagnostic. Each edit replaces the whole document with the output of running the single rule, so it covers every occurrence of that rule (the action title reads "Fix all <rule> with mdsmith"). Within one request all quick-fix actions for the same rule share one WorkspaceEdit; the fix is run once regardless of how many diagnostics carry that rule. Generated-section rules (catalog, toc, include) regenerate the section in their fix; the action surfaces normally and the title ("Fix all <rule> with mdsmith") is explicit about the whole-file scope.
  • source.fixAll.mdsmith — runs mdsmith fix on the current buffer; produces the same bytes the on-disk fixer would write.

Symbol navigation

The server indexes the workspace into a symbol graph. The graph is built lazily on the first symbol-navigation request and is kept in sync via:

  • didOpen / didChange re-parse the open buffer and swap its slice of the index.
  • **/*.md watcher events refresh one file from disk when it changes outside any open buffer.
  • .mdsmith.yml changes invalidate the whole index because ignore:, kind-assignment:, and follow-symlinks: all shift what the index sees. Open buffers bypass ignore: (the user editing a file always wants it visible).

Symbol kinds

Concept LSP SymbolKind Container
Heading (H1–H6) String (15) parent heading
Link-reference definition Key (20) file
Front-matter field Property (7) file
Directive (<?name … ?>) Event (24) enclosing heading or file

Headings drive the outline; the others hang off the synthetic file-root entry. The cross-document key is (file, anchor) for headings (slug from mdtext.CollectTOCItems) and (file, label) for link refs.

Definition and implementation

Cursor on… Definition Implementation adds
[text](#anchor) heading in this file —
[text](./other.md) line 1 of other.md —
[text](./other.md#anchor) heading in other.md —
[text][label] matching [label]: url —
<?include file: "x.md"?> arg x.md line 1 —
<?build source: "x.md"?> arg x.md line 1 —
kind: value in front matter kind block in .mdsmith.yml every file with that kind
Heading line the heading every link target matching

References

Cursor on… References returned
Heading every workspace link to (file, anchor)
[label]: url definition every [text][label] and shortcut in the file
File line 1 every link target with this path (no anchor)
kind: value every file with that kind assignment
Directive arg (file: / source:) every directive whose file: / source: = this

includeDeclaration: false excludes the heading or definition itself.

Workspace symbol

The query is a case-insensitive substring. It matches heading text, link-ref labels, front-matter title:, and kind names. The relative path goes in containerName.

Call hierarchy

A Markdown file is the unit of "function"; an outbound reference is a "call". incomingCalls answers "who depends on this runbook?", outgoingCalls answers "what does this overview embed?".

prepareCallHierarchy accepts three cursor positions:

  • File root → the item is the file.
  • Heading line → the item is that heading section.
  • Directive arg → the item is the target file.

incomingCalls returns every edge into the item, with sources from cross-file links, <?include?>, <?catalog?> matches, and <?build?>. Each entry carries the source file and the reference line. outgoingCalls returns every edge out of the item; catalog matches collapse to one entry per directive (expansion would inflate large globs into noise).

Completion

The server handles textDocument/completion and advertises:

"completionProvider": {
  "triggerCharacters": ["#", "[", ":", "/", "\""],
  "resolveProvider": false
}

Completion items are fully computed in one pass from the workspace symbol index (resolveProvider: false). Items are returned sorted with same-file matches first for anchor completion.

Supported contexts

Cursor on… Items returned kind
[text](#prefix Heading anchors in current file Reference
[text](./other.md#prefix Heading anchors in other.md Reference
[text][prefix Link-ref labels in current file Reference
Front-matter kind: prefix Kind names from .mdsmith.yml EnumMember
Front-matter kinds: list item Kind names from .mdsmith.yml EnumMember
<?include file: "prefix"?> arg Workspace Markdown paths File
<?build source: "prefix"?> arg Workspace Markdown paths File
<?catalog glob: "prefix"?> entry Workspace Markdown paths File
Any other position Empty list (no error) —

The detail field carries the source file path for headings and link-ref labels, and .mdsmith.yml for kind names.

Duplicate-slug anchors (foo, foo-1, foo-2, …) are each returned as separate items.

Directive-arg paths are relative to the open buffer's directory. This matches how ResolveRelTarget resolves them at lint time. Both .md and .markdown files appear as candidates.

Image links (![alt](#…) do not trigger anchor completion. Completion inside fenced or indented code blocks returns an empty list.

Rename

prepareRename returns the text range for ATX heading text (without #s), setext heading text lines, [label]: url defs, the trailing […] of a full reference, and the leading […] of a shortcut or collapsed reference. The placeholder pre-fills the popup; other positions return null.

Heading rename rewrites the heading and every workspace anchor link to its slug. Duplicate-name disambiguator shifts emit follow-up edits. Link-ref rename rewrites the [label]: url def plus every same-file use. InvalidParams fires on a new duplicate base slug, a colliding def, an empty slug, or a [ / ] / newline in a label. The error's data.conflict names the colliding symbol.

Configuration discovery

The server uses workspace-wide discovery. It starts at the workspace root supplied at initialize (rootUri or the first workspaceFolders entry) and walks upward until it finds a .mdsmith.yml or hits a .git boundary — the same walk mdsmith check uses from its CWD. Every open buffer shares the resolved config; the server does not re-discover per file.

Clients override the walk with mdsmith.config, which the server pulls via workspace/configuration. Edits to .mdsmith.yml invalidate the cached config. The server then re-lints every open document immediately.

Example

For client setup and troubleshooting see the VS Code guide or the Claude Code plugin README. Other LSP clients can spawn the binary directly:

mdsmith lsp

Performance

The squiggle-update path is benchmarked under internal/lsp/. Plan 121 sets a p95 budget of 150 ms on a 1 000-line buffer and 500 ms on a 5 000-line buffer. Run the benchmark locally with:

go test -run=^$ -bench=. ./internal/lsp/...

Exit codes

Code Meaning
0 Server exited cleanly
2 Runtime or transport error

See also