Create `nemo-lsp` language server

[geoffjay]

Summary

Create a new nemo-lsp binary crate that implements the Language Server Protocol over stdio using tower-lsp. The server reuses nemo-config for parsing and nemo-registry for schema access, providing autocomplete, hover documentation, diagnostics, and go-to-definition for Nemo XML files.

Context

Authors currently write Nemo XML with no editor assistance beyond basic XML syntax. The existing schema/nemo.xsd provides XML structure validation but cannot encode component-specific property constraints. The LSP bridges this gap by using the live ComponentRegistry and ConfigSchema data.

The LSP reuses existing infrastructure — no new parsing logic needed:

• nemo-config::XmlParser — parse XML into Value trees
• nemo-config::ConfigValidator — schema-based validation with error locations
• nemo-config::ConfigSchema / PropertySchema — property types, defaults, constraints
• nemo-registry::ComponentRegistry — component list, search, category grouping
• nemo-config::ConfigResolver — expression evaluation for ${} syntax

Acceptance Criteria

• New crate at crates/nemo-lsp/ with tower-lsp dependency

• LSP capabilities implemented:

  Completion — component element names

  • Triggered when typing inside <layout> or as a child element
  • Source: ComponentRegistry.list_components() → XML tag names

  Completion — attribute names

  • Triggered on existing component elements
  • Source: ComponentDescriptor.schema.properties keys
  • Include common attributes from schema/nemo.xsd attribute groups (layout-attrs, border-attrs, decoration-attrs, event-attrs, binding-attrs)

  Completion — enum values

  • Triggered on string-typed attributes with OneOf validation rule
  • Source: PropertySchema.rules → ValidationRule::OneOf(values)
  • Depends on Enrich builtin component schemas with property descriptions and enum constraints #70 for rich enum data in builtin schemas

  Hover documentation

  • Source: PropertySchema.description formatted as Markdown
  • Include type, default value, required status
  • Depends on Enrich builtin component schemas with property descriptions and enum constraints #70 for per-property descriptions in builtin schemas

  Diagnostics

  • Run ConfigValidator on the document
  • Map ValidationError to LSP Diagnostic with range information
  • Source location from nemo-config::SourceLocation (line/column)
  • Depends on Add source location tracking to XML parser and validator for LSP diagnostics #69 for source location tracking in parser/validator

  Completion — data binding paths

  • <binding source="..."> and bind-* attributes
  • Source: <data> source definitions in current file

  Completion — template references

  • template="..." attribute values
  • Source: <templates> block in current file

  Completion — handler names

  • on-click="...", on-change="...", etc.
  • Source: .rhai file function names from configured script directory

  Go-to-definition

  • template="name" → jump to <template name="name">
  • source="datasource" → jump to <source name="datasource">

• LSP activated for files containing a <nemo> root element (via workspace/didChangeWatchedFiles or content-based detection)

• Server starts with reasonable defaults (no config file required for basic operation)

• Logging to file (not stdout, which is the LSP transport) via tracing

• Cargo workspace member added to root Cargo.toml

Relevant Files

• schema/nemo.xsd — existing XML schema with attribute groups
• crates/nemo-config/src/xml_parser.rs — XML parser
• crates/nemo-config/src/validator.rs — ConfigValidator, ValidationResult
• crates/nemo-config/src/resolver.rs — ConfigResolver, expression evaluation
• crates/nemo-config/src/schema.rs — ConfigSchema, PropertySchema
• crates/nemo-registry/src/registry.rs — ComponentRegistry
• crates/nemo-registry/src/builtins.rs — component registration
• crates/nemo-registry/src/descriptor.rs — ComponentDescriptor
• crates/nemo-config/src/error.rs — ValidationError
• Cargo.toml — workspace members

Stack Base

• Stack on: main
• Blocked by: Add source location tracking to XML parser and validator for LSP diagnostics #69 (source location tracking), Enrich builtin component schemas with property descriptions and enum constraints #70 (schema enrichment)