block = append(block, "//go:build "...)
		block = append(block, x.String()...)
		block = append(block, tabwriter.Escape, '\n')
		if len(p.plusBuild) > 0 {
			lines, err := constraint.PlusBuildLines(x)
			if err != nil {
				lines = []string{"// +build error: " + err.Error()}
			}
			for _, line := range lines {
				block = append(block, tabwriter.Escape)
				block = append(block, line...)

		return
	}

	// Have both //go:build and // +build,
	// with no errors found (crossCheck still true).
	// Check they match.
	var want constraint.Expr
	lines, err := constraint.PlusBuildLines(check.goBuild)
	if err != nil {
		check.pass.Reportf(check.goBuildPos, "%v", err)
		return
	}
	for _, line := range lines {
		y, err := constraint.Parse(line)
		if err != nil {

		{"IsPlusBuild", Func, 16},
		{"NotExpr", Type, 16},
		{"NotExpr.X", Field, 16},
		{"OrExpr", Type, 16},
		{"OrExpr.X", Field, 16},
		{"OrExpr.Y", Field, 16},
		{"Parse", Func, 16},
		{"PlusBuildLines", Func, 16},
		{"SyntaxError", Type, 16},
		{"SyntaxError.Err", Field, 16},
		{"SyntaxError.Offset", Field, 16},
		{"TagExpr", Type, 16},
		{"TagExpr.Tag", Field, 16},
	},
	"go/constant": {