Modelica Language Server

An experimental Modelica Language Server based on OpenModelica/tree-sitter-modelica.

For syntax highlighting install extension AnHeuermann.metamodelica in addition.

See CHANGELOG.md for the changes in 0.3.6.

Functionality

This Language Server works for Modelica files. It has the following language features:

• Document outline.

  

• Optional Modelica syntax diagnostics, off by default. Enable with "modelica.diagnostics.syntax": true in VS Code settings. The toggle takes effect without restarting; disabling cancels queued checks and clears errors. Other LSP clients can set initializationOptions.diagnostics.syntax or send settings.modelica.diagnostics.syntax in a configuration change. Diagnostics in open documents are updated after a short typing pause and cleared when fixed or closed. Errors come from the bundled tree-sitter grammar, with up to 100 reports per document. Missing tokens are marked at their insertion point. Grammar limitations can affect the results; these are not compiler/type checks and do not validate embedded HTML or XML. A shared queue coalesces edits for 150 ms and checks one document at a time, yielding at least 25 ms between files. Closing a document cancels queued work. Checks do not scan unopened libraries or retain additional syntax trees.

• Go to declaration and definition.

  

• Optional autocomplete, off by default. Enable with "modelica.completion.enabled": true; changes take effect without restarting. Other LSP clients can use initializationOptions.completion.enabled or settings.modelica.completion.enabled in a configuration change. Suggests direct declarations, built-in types, explicit imports, and qualified class/package members, including library files after a dot. Suggestions use unsaved text and replace the current word. Comments and strings are excluded. Only requested library paths are loaded; sibling filenames are listed without parsing their contents. Disabled requests do no completion parsing or loading. VS Code's independent word-based suggestions are controlled by editor.wordBasedSuggestions, not this setting. Results are limited to 200, with further requests when the prefix narrows.

  This is basic completion, not compiler-level semantic analysis. Broader scope, inheritance/redeclarations, aliases and instance-member resolution are tracked in #92, snippets in #93, and automatic imports in #94.

• Hover provider for declared symbols.

  

• Semantic highlighting for locally resolved classes and types, including their matching end names. Packages are classified as namespaces, records as structs, functions as functions, enumeration types as enums, other type declarations as types, and models/blocks/connectors/classes as classes. Declarations carry the declaration modifier; references and end names use the same token type.

  Tokens use the current unsaved document and do not load or scan libraries. Unknown external/imported/inherited names retain ordinary syntax highlighting. This complements the MetaModelica extension's syntax grammar. Colors depend on the theme; VS Code's editor.semanticHighlighting.enabled setting controls semantic coloring (set it to true to enable it regardless of theme). Other LSP clients can request textDocument/semanticTokens/full using the advertised legend. Range and delta token requests are not implemented.

• Optional document highlights, off by default. Enable "modelica.documentHighlights.enabled": true to highlight a symbol's declaration and references in the current document when placing the cursor on it. The setting changes live; other LSP clients can use initializationOptions.documentHighlights.enabled or settings.modelica.documentHighlights.enabled in a configuration change. Each request uses the latest unsaved buffer, without loading libraries or scanning other open documents. Disabled requests skip highlight parsing. Temporary syntax trees are released after each request.

  Supports local classes (including their end names), components, explicit import bindings, enumeration literals, and loop/comprehension indices. Local instance members are matched through locally declared types. Shadowed names, comments and strings are not merged. Unresolved external/inherited members, wildcard imports and type aliases are not guessed. Highlights use neutral Text ranges rather than assigning read/write meaning to Modelica equations. An editor may still show its own textual occurrence highlighting when the LSP feature is disabled.

• Format Document and Format Selection, using two-space Modelica indentation by default. Editor indentation options override this default. Formatting adjusts whitespace, spaces around operators and after commas, and wraps long argument lists at a target width of 100 columns (a soft limit). Section headings align with their class headers, as in the Modelica Standard Library.

  Selection formatting covers the selected lines and uses the surrounding code to determine indentation. Strings (including XML/HTML documentation) are preserved by default. Comments and declaration order are preserved. Inputs and outputs are not reordered, since that can change positional function calls. Files rejected by the bundled Modelica grammar are left untouched. Other LSP clients can supply printWidth as an additional formatting option.

  With modelica.formatting.formatDocumentation off (the default), embedded XML/HTML is preserved exactly, including whitespace, escaped quotes and line endings. Only the surrounding Modelica annotation syntax is formatted.

  To opt in to documentation formatting, add this to your VS Code settings:

  {
    "modelica.formatting.formatDocumentation": true
  }
  

  The setting applies to Format Document and Format Selection without restarting the server. Complete literal Documentation(info="...", revisions="...") values are delegated to the HTML language service for <html> documents (including an optional HTML doctype), or an XML formatter for other XML markup. Ordinary strings, concatenated documentation and partially selected string literals are left unchanged. XML that cannot be parsed is preserved. This is formatting, not syntax checking; diagnostics are tracked in #87 and #88.

  Other LSP clients can set initializationOptions.formatting.formatDocumentation, send settings.modelica.formatting.formatDocumentation in a configuration change, or pass formatDocumentation in a formatting request's options. An explicit per-request boolean overrides the server setting, so a client can disable markup formatting for an individual request even when it is enabled.

  

  To try it in VS Code:

  1. If the window is in Restricted Mode, open Manage Workspace Trust and trust the folder if you trust its contents.
  2. Open a .mo file and check that its language mode is Modelica.
  3. Press F1, type Format Document, and press Enter. If prompted, choose Modelica Language Server as the formatter.
  4. To format only part of a file, select the lines and run Format Selection.

  View or download the formatting GIF.

Configuration

Loading external Modelica libraries

To make the language server aware of libraries outside your workspace (such as the Modelica Standard Library), add their root directories to modelica.libraries in your VS Code settings.

Workspace settings (.vscode/settings.json):

{
  "modelica.libraries": [
    "/path/to/Modelica 4.0.0+maint.om"
  ]
}

User settings (via File → Preferences → Settings, search for modelica.libraries): click Add Item and enter the path to each library root directory — the folder that contains a package.mo file.

Typical paths:

The server registers configured library roots at startup, parsing each root package.mo. Other library files are loaded lazily when needed. The Modelica: Load Library command adds library roots to modelica.libraries. Adding or removing workspace folders or updating modelica.libraries takes effect without restarting. Libraries removed from the setting are retained if still needed as workspace libraries or supplied through modelicaPath.

Installation

Via Marketplace

• Visual Studio Marketplace
• Open VSX Registry

Via VSIX File

Download the .vsix asset from the release you want to install. For version 0.3.6, the filename is modelica-language-server-0.3.6.vsix.

Check the VS Code documentation on how to install a .vsix file. Use the Install from VSIX command or run

code --install-extension modelica-language-server-0.3.6.vsix

Standalone server

For npm installation, standalone binaries and configuration in other editors, see the server README.

Contributing ❤️

Contributions are very welcome!

We made the first tiny step but need help to add more features and refine the language server.

If you are searching for a good point to start check the good first issue. To see where the development is heading to check the Projects section. If you need more information start a discussion over at OpenModelica/OpenModelica.

Found a bug or having issues? Open a new issue.

Structure

.
├── client // Language Client
│   ├── src
│   │   ├── test // End to End tests for Language Client / Server
│   │   └── extension.ts // Language Client entry point
├── package.json // The extension manifest.
└── server // Modelica Language Server
    └── src
        └── server.ts // Language Server entry point

Building the Language Server

• Run npm ci in this folder. Its postinstall script installs the client and server dependencies. Node.js 24 is used in CI.
• Run npm run esbuild to build the extension and server bundles, or npm run esbuild-watch to rebuild as you edit.
• Open VS Code on this folder.
• Press Ctrl+Shift+B to start compiling the client and server in watch mode.
• Switch to the Run and Debug View in the Sidebar (Ctrl+Shift+D).
• Select Launch Client from the drop down (if it is not already).
• Press ▷ to run the launch config (F5).
• In the Extension Development Host instance of VSCode, open a document in 'modelica' language mode.
  • Check the Modelica Language Server output channel for server logs.

Semantic highlighting tests

npm run esbuild && npm run test:server runs the server and protocol tests; npm run test:e2e also checks token types and unsaved edits in VS Code. To repeat the editor tests with MetaModelica's syntax grammar installed, use a separate extension directory (replace /path/to/code with a VS Code CLI):

/path/to/code --extensions-dir /tmp/modelica-test-extensions --install-extension AnHeuermann.metamodelica@1.6.1
MODELICA_TEST_EXTENSIONS_DIR=/tmp/modelica-test-extensions MODELICA_TEST_METAMODELICA=1 npm run test:e2e

The coexistence run asserts that MetaModelica is installed and contributes the Modelica grammar, then verifies the same semantic tokens through VS Code. It does not assert theme-specific pixel colors. To use an already downloaded VS Code build, set VSCODE_TEST_EXECUTABLE_PATH to its executable.

OMEdit client compatibility

The separate OMEdit Qt client compatibility CI job runs OMEdit's production Qt LSP client against the standalone server built from this revision. It checks initialization, hover, cross-file definitions and unsaved document changes. This tests client/server compatibility without launching the OMEdit GUI or OMC. Release publication requires the job to pass. See the Qt smoke test instructions for local commands, client revision, coverage boundaries and test artifacts.

MSL sanity

The separate MSL sanity CI job checks every .mo file in the pinned MSL 4.1.0 release with the syntax diagnostic collector. This includes example models embedded inside larger package files, not just Examples/ directories. Any syntax diagnostic, parser failure or missing library fails the job; there is no allowlist. Files are checked sequentially and temporary trees are freed. This is a grammar sanity check, not compilation or simulation of the examples.

To run it locally after installing the server dependencies:

npm --prefix server run test:msl -- /path/to/ModelicaStandardLibrary/Modelica

Build and Install Extension

npx vsce package

License

modelica-language-server is licensed under the OSMC Public License v1.8, see OSMC-License.txt.

3rd Party Licenses

This extension is based on https://github.com/microsoft/vscode-extension-samples/tree/main/lsp-sample, licensed under MIT license.

Some parts of the source code are taken from bash-lsp/bash-language-server, licensed under the MIT license and adapted to the Modelica language server.

The bundled grammar comes from OpenModelica/tree-sitter-modelica and is licensed under the OSMC-PL v1.8.

Acknowledgments

This package was initially developed by Hochschule Bielefeld - University of Applied Sciences and Arts.