vitessio/vitess · error

unexpected TrackedBuffer type %T

Error message

unexpected TrackedBuffer type %T

What it means

TrackedBuffer's astPrintf implements a custom printf engine. The %s (case-insensitive string) verb received a value whose Go type is not string/[]byte, so it cannot render it, and panics to surface the AST-format-string mismatch immediately during development.

Source

Thrown at go/vt/sqlparser/tracked_buffer.go:189

		i++ // '%'

		caseSensitive := false
		if format[i] == '#' {
			caseSensitive = true
			i++
		}

		switch format[i] {
		case 's':
			switch v := values[fieldnum].(type) {
			case string:
				if caseSensitive {
					buf.WriteString(v)
				} else {
					_, _ = buf.literal(v)
				}
			default:
				panic(fmt.Sprintf("unexpected TrackedBuffer type %T", v))
			}
		case 'l', 'r', 'v':
			left := format[i] != 'r'
			value := values[fieldnum]
			expr := getExpressionForParensEval(checkParens, value)

			if expr == nil {
				buf.formatter(value.(SQLNode))
			} else {
				needParens := needParens(currentExpr, expr, left)
				if needParens {
					buf.WriteByte('(')
				}
				buf.formatter(expr)
				if needParens {
					buf.WriteByte(')')
				}
			}

View on GitHub (pinned to 01a25a7d17)

Solutions

1. Fix the Format method to pass a string-typed value to %s (use v.ToString() or the String() of the field)
2. Use %v for SQLNode values instead of %s
3. Add/adjust unit tests that call ToString() on the affected node to catch regressions

Example fix

// before
buf.Myprintf("%s", node.Name)
// after
buf.Myprintf("%s", node.Name.String())

switch v := value.(type) {
case string:
    buf.Myprintf("%s", v)
default:
    return fmt.Errorf("%%s requires string, got %T", v)
}

defer func() {
    if r := recover(); r != nil {
        t.Fatalf("AST formatting panicked (check Format %%s argument types): %v\n%s", r, debug.Stack())
    }
}()

When it happens

Trigger: An AST node's Format() calls buf.Myprintf("%s", v) where v is not a string (e.g. passing a Token ID, struct, or []IdentifierCI); format/value count mismatches in a hand-written Format method.

Common situations: Writing or editing a new AST node's Format method and passing the wrong field for the %s verb; changing a field's type from string to a struct without updating Format.

Related errors

• unexepcted TrackedBuffer type %T
• unexpected format:
• input is not a slice
• element does not implement SQLNode
• invalid IntervalDateExpr syntax

AI-assisted analysis of vitessio/vitess@01a25a7d17 (2026-09-01). Data as JSON: /api/errors/fe1c1ecc1865697e. Report an issue: GitHub.