if len(p.goBuild) > 0 && p.goBuild[0] < insert {
		insert = p.goBuild[0]
	} else if len(p.plusBuild) > 0 && p.plusBuild[0] < insert {
		insert = p.plusBuild[0]
	}

	var x constraint.Expr
	switch len(p.goBuild) {
	case 0:
		// Synthesize //go:build expression from // +build lines.
		for _, pos := range p.plusBuild {
			y, err := constraint.Parse(p.commentTextAt(pos))
			if err != nil {
				x = nil
				break
			}

			// Even so, report.
			check.pass.Reportf(pos, "%v", err)
			check.crossCheck = false
			return
		}
		if check.plusBuild == nil {
			check.plusBuild = y
		} else {
			check.plusBuild = &constraint.AndExpr{X: check.plusBuild, Y: y}
		}
	}
}

func (check *checker) finish() {
	if !check.crossCheck || check.plusBuildPos == token.NoPos || check.goBuildPos == token.NoPos {

			if !constraint.IsPlusBuild(text) {
				continue
			}
			plusBuild = append(plusBuild, text)
		}
	}

	return string(goBuildBytes), plusBuild, sawBinaryOnly, nil
}

func parseFileHeader(content []byte) (trimmed, goBuild []byte, sawBinaryOnly bool, err error) {
	end := 0
	p := content
	ended := false       // found non-blank, non-// line, so stopped accepting // +build lines
	inSlashStar := false // in /* */ comment

	// shortcut common case of //-style comments
	if text[1] == '/' {
		if constraint.IsGoBuild(text) {
			p.goBuild = append(p.goBuild, len(p.output))
		} else if constraint.IsPlusBuild(text) {
			p.plusBuild = append(p.plusBuild, len(p.output))
		}
		p.writeString(pos, trimRight(text), true)
		return
	}

	// for /*-style comments, print line by line and let the
	// write function take care of the proper indentation

}

// ImportDir is shorthand for Default.ImportDir.
func ImportDir(dir string, mode ImportMode) (*Package, error) {
	return Default.ImportDir(dir, mode)
}

var (
	plusBuild = []byte("+build")

	goBuildComment = []byte("//go:build")

	errMultipleGoBuild = errors.New("multiple //go:build comments")
)

func isGoBuildComment(line []byte) bool {

	"bytes"
	"cmd/go/internal/cfg"
	"errors"
	"fmt"
	"go/build/constraint"
	"strings"
	"unicode"
)

var (
	bSlashSlash = []byte("//")
	bStarSlash  = []byte("*/")
	bSlashStar  = []byte("/*")
	bPlusBuild  = []byte("+build")

	goBuildComment = []byte("//go:build")

	errMultipleGoBuild = errors.New("multiple //go:build comments")
)

func isGoBuildComment(line []byte) bool {