github.com/smacker/go-tree-sitter

go tree-sitter

Golang bindings for tree-sitter

Usage

Create a parser with a grammar:

import (
	sitter "github.com/smacker/go-tree-sitter"
	"github.com/smacker/go-tree-sitter/javascript"
)

parser := sitter.NewParser()
parser.SetLanguage(javascript.GetLanguage())

Parse some code:

sourceCode := []byte("let a = 1")
tree := parser.Parse(nil, sourceCode)

Inspect the syntax tree:

n := tree.RootNode()

fmt.Println(n) // (program (lexical_declaration (variable_declarator (identifier) (number))))

child := n.NamedChild(0)
fmt.Println(child.Type()) // lexical_declaration
fmt.Println(child.StartByte()) // 0
fmt.Println(child.EndByte()) // 9

Custom grammars

This repository provides grammars for many common languages out of the box.

But if you need support for any other language you can keep it inside your own project or publish it as a separate repository to share with the community.

See explanation on how to create a grammar for go-tree-sitter here.

Known external grammars:

• Salesforce grammars - including Apex, SOQL, and SOSL languages.
• Ruby - Deprecated, grammar is provided by main repo instead
• Go Template - Used for helm

Editing

If your source code changes, you can update the syntax tree. This will take less time than the first parse.

// change 1 -> true
newText := []byte("let a = true")
tree.Edit(sitter.EditInput{
    StartIndex:  8,
    OldEndIndex: 9,
    NewEndIndex: 12,
    StartPoint: sitter.Point{
        Row:    0,
        Column: 8,
    },
    OldEndPoint: sitter.Point{
        Row:    0,
        Column: 9,
    },
    NewEndPoint: sitter.Point{
        Row:    0,
        Column: 12,
    },
})

// check that it changed tree
assert.True(n.HasChanges())
assert.True(n.Child(0).HasChanges())
assert.False(n.Child(0).Child(0).HasChanges()) // left side of the tree didn't change
assert.True(n.Child(0).Child(1).HasChanges())

// generate new tree
newTree := parser.Parse(tree, newText)

Predicates

You can filter AST by using predicate S-expressions.

Similar to Rust or WebAssembly bindings we support filtering on a few common predicates:

• eq?, not-eq?
• match?, not-match?

Usage example:

func main() {
	// Javascript code
	sourceCode := []byte(`
		const camelCaseConst = 1;
		const SCREAMING_SNAKE_CASE_CONST = 2;
		const lower_snake_case_const = 3;`)
	// Query with predicates
	screamingSnakeCasePattern := `(
		(identifier) @constant
		(#match? @constant "^[A-Z][A-Z_]+")
	)`

	// Parse source code
	lang := javascript.GetLanguage()
	n, _ := sitter.ParseCtx(context.Background(), sourceCode, lang)
	// Execute the query
	q, _ := sitter.NewQuery([]byte(screamingSnakeCasePattern), lang)
	qc := sitter.NewQueryCursor()
	qc.Exec(q, n)
	// Iterate over query results
	for {
		m, ok := qc.NextMatch()
		if !ok {
			break
		}
		// Apply predicates filtering
		m = qc.FilterPredicates(m, sourceCode)
		for _, c := range m.Captures {
			fmt.Println(c.Node.Content(sourceCode))
		}
	}
}

// Output of this program:
// SCREAMING_SNAKE_CASE_CONST

Development

Updating a grammar

Check if any updates for vendored files are available:

go run _automation/main.go check-updates

Update vendor files:

• open _automation/grammars.json
• modify reference (for tagged grammars) or revision (for grammars from a branch)
• run go run _automation/main.go update <grammar-name>

It is also possible to update all grammars in one go using

go run _automation/main.go update-all