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:
Open this repository in VS Code.
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.
