NextCapture return inaccurate index

[smacker]

NextCapture return inaccurate index

[sluongng]

Changed it to

			cap, _, ok := qc.NextCapture()
			if !ok {
				break
			}

			name := q.CaptureNameForId(cap.Captures[0].Index)

which worked ok... But feels like a hack, especially around cap.Captures[0] part.

Am I wrong to expect NextCapture to return the index of the capture?

[didroe]

The NextCapture API returns the index within the match (always zero in your case), not within the query. This is the same behaviour as the underlying C API. I've not used this before, but it looks like the intention is to allow iterating over multiple captures in order, when they might not be in order in the Captures slice.

For your use case I would just use NextMatch and use .Captures[0] as you are doing.

[vipmax]

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

func TestTreeSitterQueries(t *testing.T) {
	code := []byte(`
function hello() { 
	// comment line 
	console.log('hello') 
	if (true) { console.log('true') }
	return "value"
}
`)

	query := `
[
  "function"
  "if"
  "return"
] @keyword

(comment) @comment
`

	// Parse source code
	lang := javascript.GetLanguage()
	n, _ := sitter.ParseCtx(context.Background(), code, lang)

	// Execute the query
	q, _ := sitter.NewQuery([]byte(query), lang)
	qc := sitter.NewQueryCursor()
	qc.Exec(q, n)

	for {
		m, ok := qc.NextMatch()
		if !ok { break }
		m = qc.FilterPredicates(m, code)
		for _, c := range m.Captures {
			name := q.CaptureNameForId(c.Index)
			content := c.Node.Content(code)
			fmt.Println(c.Node.StartPoint(), c.Node.EndPoint(), name, c.Node.Type(), content)
		}
	}
}

output

{1 0} {1 8} keyword function function
{2 1} {2 17} comment comment // comment line 
{4 1} {4 3} keyword if if
{5 1} {5 7} keyword return return

example