lsp

name	lsp
description	How the atopile Language Server works (pygls), how it builds per-document graphs for completion/hover/defs, and the invariants for keeping it fast and crash-proof. Use when this capability is needed.
metadata	{"author":"atopile"}

LSP Module

The lsp module (located in src/atopile/lsp/) implements the Language Server Protocol for atopile. It provides IDE features like autocomplete, go-to-definition, and diagnostics (error reporting) for ato files.

Quick Start

Run the server on stdio (what editors expect):

python -m atopile.lsp.lsp_server

Relevant Files

• Server implementation: src/atopile/lsp/lsp_server.py
  • owns global LSP_SERVER (pygls LanguageServer)
  • maintains per-document DocumentState (graph/typegraph/build_result)
  • implements completion/hover/definition/diagnostics handlers
• Utilities: src/atopile/lsp/lsp_utils.py
• Optional debugging helper: src/atopile/lsp/_debug_server.py

Dependants (Call Sites)

• VSCode Extension: The designated client for this server.
• Compiler: The LSP invokes the compiler (often in a partial or fault-tolerant mode) to understand the code structure.

How to Work With / Develop / Test

Core Concepts

• Partial Compilation: Unlike the CLI build, the LSP must handle broken or incomplete code without crashing.
• Latency: Features must be fast (<50ms for typing, <200ms for completion).
• Per-document graphs: each open document has an isolated GraphView + TypeGraph stored in DocumentState.
• Keep last good build: the server keeps the last successful BuildFileResult to power completion/hover even when the current edit has errors.

Development Workflow

1. Edit handlers/helpers in src/atopile/lsp/lsp_server.py.
2. Run completion tests (fast loop) and verify GraphView cleanup paths.

Testing

• Integration-style tests: ato dev test --llm test/test_lsp_completion.py -q

Best Practices

• Robustness: Never let the server crash. Catch all exceptions in handlers and log them.
• Debouncing: Don't trigger expensive operations on every keystroke.

Core Invariants (easy to regress)

• Always destroy old graphs on rebuild/reset (DocumentState.reset_graph calls GraphView.destroy()).
• Do not assume builds succeed; most features must handle:
  • syntax errors (ANTLR)
  • partial typegraphs
  • exceptions from linking/deferred execution

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