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ST Language Server and VS Code

D1 adds diagnostics, completion, go-to-definition, and hover for PLCopen Structured Text. The C++ front end remains the language authority; a zero-third-party Python package exposes an LSP 3.18 stdio server, and a thin VS Code extension connects the official language client.

Source snapshot only

D1 is not part of the published pyplcopen==0.20.0 package and the VS Code extension is not published to a marketplace. Build the wheel and VSIX from the same repository checkout, or download the VSIX artifact from a successful Language Tools workflow.

Requirements

  • Python 3.10+ with a C++17 build toolchain and CMake
  • Node.js 20+ for local VSIX packaging
  • VS Code 1.91+

Build and install the server

Use an isolated interpreter, then build the wheel from the repository root:

python -m pip install build
python -m build --wheel --outdir dist
python -m pip install --force-reinstall --no-deps dist/pyplcopen-*.whl

On PowerShell, resolve the wheel without a shell glob:

$Wheel = Get-ChildItem dist -Filter 'pyplcopen-*.whl' | Select-Object -First 1
python -m pip install --force-reinstall --no-deps $Wheel.FullName

Verify that this interpreter contains both parts:

python -c "import pyplcopen, plcopen_lsp; print(pyplcopen.__file__)"

The server is normally launched by an editor. Its direct entry point is python -m plcopen_lsp; it communicates only through LSP Content-Length frames on stdin/stdout.

Build and install the VSIX

cd editors/vscode
npm ci --ignore-scripts
npm run verify:licenses
npm test
npm audit --omit=dev
npm run package
npm run verify:vsix

Install plcopen-st-language-tools.vsix with Extensions: Install from VSIX.... Set the machine-scoped plcopenSt.pythonPath setting to the exact interpreter used above. The extension deliberately does not discover or run a workspace .venv.

Open a .st file, or choose the PLCopen ST language mode for an untitled document. Both schemes connect to the same language client.

Trust and failure behavior

  • In an untrusted workspace, VS Code still registers .st, comments, and brackets, but the extension does not create a Python process.
  • After workspace trust is granted, the extension starts <python> -m plcopen_lsp.
  • A missing module or invalid interpreter is reported in the PLCopen ST output channel and an error notification, including the wheel-install command.
  • The server treats document URIs as opaque. It analyzes only text sent by the client and does not read unopened files, access the network, execute ST, or run workspace commands.

v1 scope

One open document may contain types, globals, functions, function blocks, programs, and SFC. Diagnostics remain available for incomplete source, while the tolerant index supplies the symbols it can still prove.

The first version does not provide cross-file projects, workspace symbols, references, rename, formatting, semantic tokens, a debugger, online PLC access, or a TextMate grammar. Definitions never leave the current URI.

The exact protocol, UTF-16 update, capacity, ambiguity, and dependency rules are recorded in the D1 semantics matrix.