You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: gcimporter.go
    path of file: ./repos/gccrs/libgo/go/go/internal/gcimporter
    
    the code of the file until where you have to start completion: // Copyright 2011 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// Package gcimporter implements Import for gc-generated object files.
package gcimporter // import "go/internal/gcimporter"

import (
	"bufio"
	"fmt"
	"go/build"
	"go/token"
	"go/types"
	"io"
	"os"
	"path/filepath"
	"strings"
)

// debugging/development support
const debug = false

var pkgExts = [...]string{".a", ".o"}

// FindPkg returns the filename and unique package id for an import
// path based on package information provided by build.Import (using
// the build.Default build.Context). A relative srcDir is interpreted
// relative to the current working directory.
// If no file was found, an empty filename is returned.
//
func FindPkg(path, srcDir string) (filename, id string) {
	if path == "" {
		return
	}

	var noext string
	switch {
	default:
		// "x" -> "$GOPATH/pkg/$GOOS_$GOARCH/x.ext", "x"
		// Don't require the source files to be present.
		if abs, err := filepath.Abs(srcDir); err == nil { // see issue 14282
			srcDir = abs
		}
		bp, _ := build.Import(path, srcDir, build.FindOnly|build.AllowBinary)
		if bp.PkgObj == "" {
			id = path // make sure we have an id to print in error message
			ret
    
func Import(fset *token.FileSet, packages map[string]*types.Package, path, srcDir string, lookup func(path string) (io.ReadCloser, error)) (pkg *types.Package, err error) {
	var rc io.ReadCloser
	var id string
	if lookup != nil {
		// With custom lookup specified, assume that caller has
		// converted path to a canonical import path for use in the map.
		if path == "unsafe" {
			return types.Unsafe, nil
		}
		id = path

		// No need to re-import if the package was imported completely before.
		if pkg = packages[id]; pkg != nil && pkg.Complete() {
			return
		}
		f, err := lookup(path)
		if err != nil {
			return nil, err
		}
		rc = f
	} else {
		var filename string
		filename, id = FindPkg(path, srcDir)
		if filename == "" {
			if path == "unsafe" {
				return types.Unsafe, nil
			}
			return nil, fmt.Errorf("can't find import: %q", id)
		}

		// no need to re-import if the package was imported completely before
		if pkg = packages[id]; pkg != nil && pkg.Complete() {
			return
		}

		// open file
		f, err := os.Open(filename)
		if err != nil {
			return nil, err
		}
		defer func() {
			if err != nil {
				// add file name to error
				err = fmt.Errorf("%s: %v", filename, err)
			}
		}()
		rc = f
	}
	defer rc.Close()

	var hdr string
	buf := bufio.NewReader(rc)
	if hdr, err = FindExportData(buf); err != nil {
		return
	}

	switch hdr {
	case "$$\n":
		err = fmt.Errorf("import %q: old textual export format no longer supported (recompile library)", path)

	case "$$B\n":
		var exportFormat byte
		exportFormat, err = buf.ReadByte()

		// The indexed export format starts with an 'i'; the older
		// binary export format starts with a 'c', 'd', or 'v'
		// (from "version"). Select appropriate importer.
		if err == nil && exportFormat == 'i' {
			pkg, err = iImportData(fset, packages, buf, id)
		} else {
			err = fmt.Errorf("import %q: old binary export format no longer supported (recompile library)", path)
		}

	default:
		err = fmt.Errorf("import %q: unknown export data header: %q", path, hdr)
	}

	return
}