Syntax Highlighting and Diagnostics

The VS Code extension provides three layers of language feedback: syntax highlighting, parse diagnostics, and semantic diagnostics.

Syntax Highlighting

MDL files (.mdl) receive full syntax coloring based on a TextMate grammar:

Highlighting works immediately on file open – no project or language server connection is required.

Parse Diagnostics (Real-Time)

As you type, the extension sends the file content to the MDL language server, which runs the ANTLR4 parser and reports syntax errors in real time. These appear as:

• Red underlines on the offending tokens
• Error entries in the Problems panel (Ctrl+Shift+M)
• Inline hover messages when you point at the underlined text

Parse diagnostics catch issues like:

• Missing semicolons
• Unmatched parentheses or braces
• Invalid keyword combinations
• Malformed qualified names

Example error:

Line 3, Col 42: mismatched input ')' expecting ','

Parse diagnostics run on every keystroke (debounced) and do not require a Mendix project file.

Semantic Diagnostics (On Save)

When you save a .mdl file, the language server performs deeper validation against the actual Mendix project (.mpr file). Semantic diagnostics check:

• Entity references – does MyModule.Customer actually exist?
• Attribute references – does the entity have the named attribute?
• Microflow references – do called microflows exist with correct signatures?
• Association references – are FROM/TO entities valid?
• Module existence – does the referenced module exist in the project?

Semantic diagnostics require:

1. A valid mdl.mprPath setting (or auto-discovered .mpr file)
2. The mxcli lsp server to be running

These diagnostics appear as warnings or errors in the Problems panel, identical in appearance to parse errors but typically with more descriptive messages referencing the project state.

Diagnostic Severity Levels

Equivalent CLI Commands

The same checks available in the extension can be run from the command line:

# Syntax check only (no project needed)
mxcli check script.mdl

# Syntax + reference validation
mxcli check script.mdl -p app.mpr --references