DuckDB Grammar Support

A VS Code extension for DuckDB's PEG grammar files (.gram), built to mirror the CLion extension as closely as VS Code APIs allow.

Features

• Syntax highlighting for rule names, separators (<-), literals, references, operators, choices, quantifiers, regex patterns, parameters, and comments
• Go to Definition for grammar rule references across workspace .gram files
• Find References for grammar rules across the workspace
• Hover previews on grammar rule references and Transform<Rule> methods to show the matching grammar rule body
• Child index inlay hints in .gram files so each direct parse-result child is labeled with its node.children[i] index
• Transformer child cheat sheets and hovers that show clickable CodeLens child entries above each Transform<Rule> method while still resolving node.children[i], list_pr.Child<T>(i), and list_pr.GetChild(i) on hover
• Keyword-backed rule resolution for pseudo-rules like UnreservedKeyword, with both grammar/keywords/*.list and inlined_grammar.gram exposed when available
• Grammar → Transformer navigation with CodeLens on grammar rules that have matching PEGTransformerFactory::Transform<Rule> methods in transform_*.cpp
• Transformer → Grammar navigation with CodeLens and Go to Definition on matching Transform<Rule> methods
• Outline / Document Symbols listing all grammar rules in the current file
• Code folding for multi-line rule bodies
• Comment toggling with # line comments
• Rule name completions sourced from workspace grammar files

Building from Source

npm install
npm run compile
npm test

To run the extension in a VS Code Extension Development Host:

1. Open this repository in VS Code.
2. Press F5.

Usage

• Open a .gram file to activate the language support.
• Hover a grammar rule reference or matching Transform<Rule> method to preview the corresponding grammar rule.
• Use the inlay hints in .gram files to see the direct child index DuckDB assigns to each top-level rule element.
• Use the CodeLens child entries above each transformer method as a child-index quick reference, and click any entry to jump to that exact child in the grammar.
• Use F12 or Cmd+Click on a rule reference to jump to its definition.
• Use Shift+F12 on a rule definition or reference to find usages.
• Use the Outline view to browse rule definitions in the current file.
• Use the CodeLens links above grammar rules and transformer methods to jump between .gram and transform_*.cpp files.
• For keyword-backed pseudo-rules, VS Code will surface multiple definitions when both the generated inlined_grammar.gram rule and the source grammar/keywords/*.list file are present, so you can choose either target.

Parity Notes

• VS Code does not expose JetBrains-style custom gutter icons for this workflow, so grammar/C++ navigation is implemented with CodeLens.
• VS Code folding uses standard line-based folding ranges and does not support CLion's custom folding placeholder text.
• inlined_grammar.gram remains excluded from general workspace indexing to avoid duplicate generated definitions, but keyword-backed pseudo-rules intentionally surface both generated and source-list targets.