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: importer.go
    path of file: ./repos/moby/vendor/golang.org/x/tools/go/gcexportdata
    
    the code of the file until where you have to start completion: // Copyright 2016 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 gcexportdata

import (
	"fmt"
	"go/token"
	"go/types"
	"os"
)

// NewImporter returns a new instance of the types.Importer interface
// that reads type information from export data files written by gc.
// The Importer also satisfies types.ImporterFrom.
//
// Export data files are located using "go build" workspace conventions
// and the build.Default context.
//
// Use this importer instead of go/import
    
func (imp importer) ImportFrom(importPath, srcDir string, mode types.ImportMode) (_ *types.Package, err error) {
	filename, path := Find(importPath, srcDir)
	if filename == "" {
		if importPath == "unsafe" {
			// Even for unsafe, call Find first in case
			// the package was vendored.
			return types.Unsafe, nil
		}
		return nil, fmt.Errorf("can't find import: %s", importPath)
	}

	if pkg, ok := imp.imports[path]; ok && pkg.Complete() {
		return pkg, nil // cache hit
	}

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

	r, err := NewReader(f)
	if err != nil {
		return nil, err
	}

	return Read(r, imp.fset, imp.imports, path)
}