GJS BNF Language for VS Code Support

Full-featured VS Code extension for Backus-Naur Form (BNF) grammar files (.bnf).

Features

Syntax Highlighting

Distinct colours for every element of a BNF grammar:

Element	Example	Colour
Rule definition	`<digit>` on the LHS	Blue bold
`::=` operator	`::=`	Purple
`\\|` alternation	`\\|`	Purple
Non-terminal reference	`<digit>` in a body	Cyan
Terminal string	`"0"` `'hello'`	Green
Optional `[ ]`	`[` `]`	Yellow
Repetition `{ }`	`{` `}`	Red
Group `( )`	`(` `)`	Teal
Comment	`(* … *)`	Grey italic

Includes a dedicated BNF Dark colour theme.

Real-time Validation

Errors and warnings appear inline as you type and in the Problems panel.

Code	Severity	Description
`BNF001`	🔴 Error	Duplicate rule definition
`BNF002`	🔴 Error	Undefined non-terminal referenced
`BNF003`	🟡 Warning	Rule defined but never referenced
`BNF004`	🟡 Warning	Empty terminal string
`BNF005`	🟡 Warning	Direct left recursion detected

Validation fires on open, on type (debounced, configurable), and on save.

Formatting

Trigger with Shift+Alt+F / ⇧⌥F, or enable editor.formatOnSave.

Aligns all ::= operators to the same column across all rules
Wraps long alternations onto multiple lines with indented |
Normalises terminal string quote style (double / single / preserve)
Adds a blank line between rules for readability

IntelliSense

Feature	Shortcut	Description
Hover tooltip	hover	Shows rule body + usage count
Go to Definition	`F12`	Jumps to the rule that defines a non-terminal
Find All References	`Shift+F12`	Lists every use of a non-terminal
Rename	`F2`	Renames a rule and all its references atomically
Autocomplete	type `<`	Completes rule names; structural snippets
Outline	Outline panel	All rules in breadcrumb and symbol list

Commands

Command	Shortcut	Description
`BNF: Validate Document`	`Ctrl+Shift+V`	Run validation manually
`BNF: Show AST`	`Ctrl+Shift+A`	Open the live AST viewer panel
`BNF: Show Rule Dependency Graph`	`Ctrl+Shift+G`	Interactive Mermaid dependency graph
`BNF: Copy Rule as Regex`	—	Export rule under cursor as JS regex
`BNF: Insert New Rule`	—	Prompt for name, insert rule snippet
`BNF: Format Document`	`Shift+Alt+F`	Format the active file

Supported BNF Syntax

(* This is a comment *)
<rule>      ::= <other-rule> | "terminal" | 'terminal'
<optional>  ::= [ <rule> ]
<repeated>  ::= { <rule> }
<grouped>   ::= ( <rule> | "x" )

Snippets

Prefix	Inserts
`rule`	`<name> ::= expression`
`opt`	`[ expression ]`
`rep`	`{ expression }`
`grp`	`( expression )`
`cmt`	`(* comment *)`
`digit`	Standard `<digit> ::= "0" \\| … \\| "9"`
`letter`	Standard `<letter>` a-z rule
`ident`	Standard `<identifier>` rule
`integer`	Standard `<integer>` rule
`ws`	Standard `<whitespace>` rules

Configuration

All settings are under gjsBnf.*:

Formatter (`gjsBnf.format.*`)

Setting	Default	Description
`maxLineWidth`	`80`	Max line width before wrapping alternatives
`alignDefinitions`	`true`	Align all `::=` to the same column
`indentAlternatives`	`true`	Wrap alternatives with indented `\\|`
`quoteStyle`	`"double"`	`"double"` / `"single"` / `"preserve"`

Validation (`gjsBnf.validation.*`)

Setting	Default	Description
`enabled`	`true`	Enable/disable all validation
`onType`	`true`	Validate while typing
`onSave`	`true`	Validate on save
`debounceMs`	`400`	Debounce delay in ms
`warnUnusedRules`	`true`	Warn on unused rules
`warnEmptyTerminals`	`true`	Warn on empty terminals

Hover (`gjsBnf.hover.*`)

Setting	Default	Description
`enabled`	`true`	Enable hover tooltips
`showRuleBody`	`true`	Include rule body in tooltip

Graph (`gjsBnf.graph.*`)

Setting	Default	Description
`direction`	`"LR"`	Graph direction: `LR`, `TB`, `RL`, `BT`
`showTerminals`	`false`	Include terminal nodes in graph

Installation

From VSIX

code --install-extension gjs-bnf-extension-1.0.0.vsix

Or via VS Code: Extensions → ··· → Install from VSIX

From source

git clone https://github.com/gjs/gjs-bnf-extension
cd gjs-bnf-extension
npm install
npm run compile
npm run package   # produces gjs-bnf-extension-1.0.0.vsix

Development

npm run watch        # compile in watch mode
npm run test:unit    # run unit tests
npm run lint         # ESLint
npm run format:fix   # Prettier

See CHANGELOG.md for version history.

License

MIT

GJS BNF Language Support

GJ Software

GJS BNF Language for VS Code Support

Features

Syntax Highlighting

Real-time Validation

Formatting

IntelliSense

Commands

Supported BNF Syntax

Snippets

Configuration

Formatter (`gjsBnf.format.*`)

Validation (`gjsBnf.validation.*`)

Hover (`gjsBnf.hover.*`)

Graph (`gjsBnf.graph.*`)

Installation

From VSIX

From source

Development

License

GJS BNF Language Support

GJ Software

GJS BNF Language for VS Code Support

Features

Syntax Highlighting

Real-time Validation

Formatting

IntelliSense

Commands

Supported BNF Syntax

Snippets

Configuration

Formatter (gjsBnf.format.*)

Validation (gjsBnf.validation.*)

Hover (gjsBnf.hover.*)

Graph (gjsBnf.graph.*)

Installation

From VSIX

From source

Development

License

Formatter (`gjsBnf.format.*`)

Validation (`gjsBnf.validation.*`)

Hover (`gjsBnf.hover.*`)

Graph (`gjsBnf.graph.*`)