docs(lsp): add capability inventory, gaps, and next steps (issue #3)
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# PgTidy LSP Status & Roadmap
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This document describes the current state of the PgTidy LSP server (`pkg/lsp`,
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`cmd/pgtidy/lsp.go`), what it actually provides today, and concrete next steps.
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It was written as part of issue #3 ("See what we can provide for LSP").
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> Note: The V3 milestone is already implemented and shipping (`docs/todo.md` marks
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> V3 done), so this is an inventory + gap analysis, not a greenfield proposal.
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## What the server provides today
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Verified by hand against the built binary (`pgtidy lsp`, JSON-RPC 2.0 over stdio,
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`Content-Length` framing) — no external LSP library, all wire types hand-rolled.
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### Advertised capabilities (`initialize` → `capabilities`)
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| Capability | Value | Where |
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|---|---|---|
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| `textDocumentSync` | `1` (full sync) | `serverCaps` |
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| `documentFormattingProvider` | `true` | `handle("initialize")` |
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| `documentRangeFormattingProvider` | `true` | `handle("initialize")` |
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| `codeActionProvider` | `true` | `handle("initialize")` |
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### Supported methods
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| Method | Direction | Behavior |
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|---|---|---|
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| `initialize` / `shutdown` / `exit` / `initialized` | req/resp + notif | Lifecycle. `exit`/`shutdown` acknowledged with `null` result. |
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| `textDocument/didOpen` | notif | Stores document text; triggers `publishDiagnostics`. |
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| `textDocument/didChange` | notif | Stores latest content version; triggers `publishDiagnostics`. |
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| `textDocument/didClose` | notif | Drops text + fix cache; clears diagnostics with empty list. |
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| `textDocument/formatting` | req/resp | Full-doc format via `pkg/format`; returns one `fullReplace` `TextEdit`. |
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| `textDocument/rangeFormatting` | req/resp | Formats doc, returns minimal edit over the selected line range. |
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| `textDocument/codeAction` | req/resp | Returns quick-fix `WorkspaceEdit`s for fixable diagnostics overlapping the range. |
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| `textDocument/publishDiagnostics` | notif | Sent on every open/change; diagnostic code = `RuleID`, source = `pgtidy`. |
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| `$/cancelRequest` | req | Ignored (per LSP, no response). |
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| unknown | req/resp | `-32601 method not found` (when the request has an `id`). |
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### Verified at runtime (e2e smoke test)
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- `initialize` returns the capability block above.
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- `didOpen` on `select * from t;` → `publishDiagnostics` with `COR001`
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("SELECT * is fragile…", severity 4 = hint, code `COR001`).
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- `textDocument/formatting` on that input → edit replacing with
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`SELECT *\nFROM t;\n` (keyword casing + clause-per-line applied).
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- `textDocument/hover` → `-32601 method not found` (not implemented — correct).
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## What the server does NOT provide (gaps)
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These are the most useful, well-scoped gaps to fill next. None are blockers for the
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current shipping state.
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1. **No `hover`.** `textDocument/hover` is unimplemented and returns `-32601`.
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A natural first add: return the `RuleID` + a short explanation for diagnostics
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on the hovered range, or a keyword/type doc for `hover` on SQL identifiers.
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2. **No `documentSymbol` / `documentLink`.** No outline/symbol tree. For a formatter
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that already parses `CREATE FUNCTION`/`PROCEDURE` headers into a CST, a symbol
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provider listing functions/procedures would be low-cost and high-value in large
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schema files.
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3. **`hover`-style diagnostics shape.** Diagnostics currently use a `Range` whose
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`end.character` is `start.character + 1` (a 1-char caret), not the actual
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offending span. A real highlight range would improve editor UX.
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4. **`textDocument/willSave` / `willSaveWaitUntil` / `didSave`.** No save hooks —
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"format-on-save" must currently be driven by the client binding
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`textDocument/formatting` to the editor's save event. A `willSaveWaitUntil`
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handler would let the server own format-on-save.
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5. **No `completion`.** `textDocument/completion` is not implemented. Not urgent for
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a formatter/linter, but relevant if PL/pgSQL autocompletion (keywords, types) is
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ever in scope.
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6. **No diagnostics debounce/coalescing beyond full-sync.** Every `didChange`
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re-runs the full lint engine. Fine for now; a debounce + incremental re-check
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becomes relevant on large files.
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7. **`initializationOptions` / workspace config.** `initialize` params are parsed
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nowhere — no way to pass style overrides or a config path over the protocol.
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8. **No `textDocument/prepareRename`, `rename`, `references`, `foldingRange`.**
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Low priority; would be natural extensions once symbol info exists.
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## Conventions to keep consistent
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- **One core, many frontends.** The LSP reuses `pkg/diagnostics.Diagnostic` and
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`pkg/lint` directly — no parallel diagnostic model. New LSP features should reuse
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these, not fork them.
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- **Safety gate is non-negotiable.** Both `formatting` and `rangeFormatting` call
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`format.SemanticallyEqual(src, out)` before returning edits; on failure they return
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an empty edit (keep original). Any new code path that formats must honor this
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invariant (invariant #5 in `AGENTS.md`).
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- **No new external deps.** The wire layer is intentionally dependency-free. New
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protocol types should be added as local structs, not pulled in from an LSP library.
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## Concrete next steps (recommended, smallest-first)
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Ranked by effort/value for the smallest useful delta:
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1. **Add a real diagnostic highlight range** (swap the 1-char caret for the actual
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offending span) — ~1 file, no new method, immediate UX win. Reuses existing
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`RuleID`/severity data.
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2. **Add `textDocument/hover`** returning the rule explanation for the hovered
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diagnostic, or a keyword/type glossary. Reuses `pkg/lint` rule metadata.
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3. **Add `documentSymbol`** listing `CREATE FUNCTION`/`PROCEDURE` signatures.
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Reuses the existing CST header parse in `pkg/format`.
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4. **Add `willSaveWaitUntil`** to own format-on-save instead of relying on client
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binding.
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> Do NOT: expand the LSP surface into a broad design (workspace features,
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incremental parsing, custom `textDocument/*` extensions) as part of this issue.
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Keep any change scoped to the above and evidence-backed by a `pkg/lsp` test
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(see `server_test.go` for the framed-request/response harness).
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## Verification
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- `go build ./cmd/pgtidy` succeeds.
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- `go test ./...` passes (LSP unit tests in `pkg/lsp/server_test.go` exercise
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`initialize`, formatting, range formatting, `didClose` diagnostics clearing).
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- Runtime e2e smoke test (framed JSON-RPC over stdio) confirmed `initialize`
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capabilities, `COR001` diagnostics, and a formatting edit; `hover` correctly
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returns `-32601`.
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@@ -119,6 +119,7 @@ Legend: ✅ done · 🚧 in progress · ⬜ not started
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- `cmd/pgtidy/lsp.go`: `pgtidy lsp` subcommand; config discovered from cwd.
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- `editors/vscode/`: TS extension using `vscode-languageclient`; launches `pgtidy lsp` via stdio; `.pgsql` mapped to `sql` language; `pgtidy.path` / `pgtidy.enable` settings.
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- _Range formatting: future._
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- Full capability inventory, runtime-verified gaps, and ranked next steps in `docs/lsp-status.md` (issue #3).
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## ✅ V4 — DataGrip
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- `editors/datagrip/`: Gradle-based JetBrains plugin targeting DataGrip 2024.3+ via LSP4IJ.
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