github.com/sbinet/go@v0.0.0-20160827155028-54d7de7dd62b/src/go/internal/gcimporter/gcimporter.go (about)

     1  // Copyright 2011 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  // Package gcimporter implements Import for gc-generated object files.
     6  package gcimporter // import "go/internal/gcimporter"
     7  
     8  import (
     9  	"bufio"
    10  	"fmt"
    11  	"go/build"
    12  	"go/types"
    13  	"io/ioutil"
    14  	"os"
    15  	"path/filepath"
    16  	"strings"
    17  )
    18  
    19  // debugging/development support
    20  const debug = false
    21  
    22  var pkgExts = [...]string{".a", ".o"}
    23  
    24  // FindPkg returns the filename and unique package id for an import
    25  // path based on package information provided by build.Import (using
    26  // the build.Default build.Context). A relative srcDir is interpreted
    27  // relative to the current working directory.
    28  // If no file was found, an empty filename is returned.
    29  //
    30  func FindPkg(path, srcDir string) (filename, id string) {
    31  	if path == "" {
    32  		return
    33  	}
    34  
    35  	var noext string
    36  	switch {
    37  	default:
    38  		// "x" -> "$GOPATH/pkg/$GOOS_$GOARCH/x.ext", "x"
    39  		// Don't require the source files to be present.
    40  		if abs, err := filepath.Abs(srcDir); err == nil { // see issue 14282
    41  			srcDir = abs
    42  		}
    43  		bp, _ := build.Import(path, srcDir, build.FindOnly|build.AllowBinary)
    44  		if bp.PkgObj == "" {
    45  			return
    46  		}
    47  		noext = strings.TrimSuffix(bp.PkgObj, ".a")
    48  		id = bp.ImportPath
    49  
    50  	case build.IsLocalImport(path):
    51  		// "./x" -> "/this/directory/x.ext", "/this/directory/x"
    52  		noext = filepath.Join(srcDir, path)
    53  		id = noext
    54  
    55  	case filepath.IsAbs(path):
    56  		// for completeness only - go/build.Import
    57  		// does not support absolute imports
    58  		// "/x" -> "/x.ext", "/x"
    59  		noext = path
    60  		id = path
    61  	}
    62  
    63  	if false { // for debugging
    64  		if path != id {
    65  			fmt.Printf("%s -> %s\n", path, id)
    66  		}
    67  	}
    68  
    69  	// try extensions
    70  	for _, ext := range pkgExts {
    71  		filename = noext + ext
    72  		if f, err := os.Stat(filename); err == nil && !f.IsDir() {
    73  			return
    74  		}
    75  	}
    76  
    77  	filename = "" // not found
    78  	return
    79  }
    80  
    81  // Import imports a gc-generated package given its import path and srcDir, adds
    82  // the corresponding package object to the packages map, and returns the object.
    83  // The packages map must contain all packages already imported.
    84  //
    85  func Import(packages map[string]*types.Package, path, srcDir string) (pkg *types.Package, err error) {
    86  	filename, id := FindPkg(path, srcDir)
    87  	if filename == "" {
    88  		if path == "unsafe" {
    89  			return types.Unsafe, nil
    90  		}
    91  		err = fmt.Errorf("can't find import: %s", id)
    92  		return
    93  	}
    94  
    95  	// no need to re-import if the package was imported completely before
    96  	if pkg = packages[id]; pkg != nil && pkg.Complete() {
    97  		return
    98  	}
    99  
   100  	// open file
   101  	f, err := os.Open(filename)
   102  	if err != nil {
   103  		return
   104  	}
   105  	defer func() {
   106  		f.Close()
   107  		if err != nil {
   108  			// add file name to error
   109  			err = fmt.Errorf("%s: %v", filename, err)
   110  		}
   111  	}()
   112  
   113  	var hdr string
   114  	buf := bufio.NewReader(f)
   115  	if hdr, err = FindExportData(buf); err != nil {
   116  		return
   117  	}
   118  
   119  	switch hdr {
   120  	case "$$\n":
   121  		err = fmt.Errorf("import %q: old export format no longer supported (recompile library)", path)
   122  	case "$$B\n":
   123  		var data []byte
   124  		data, err = ioutil.ReadAll(buf)
   125  		if err == nil {
   126  			_, pkg, err = BImportData(packages, data, id)
   127  			return
   128  		}
   129  	default:
   130  		err = fmt.Errorf("unknown export data header: %q", hdr)
   131  	}
   132  
   133  	return
   134  }
   135  
   136  func deref(typ types.Type) types.Type {
   137  	if p, _ := typ.(*types.Pointer); p != nil {
   138  		return p.Elem()
   139  	}
   140  	return typ
   141  }
   142  
   143  type byPath []*types.Package
   144  
   145  func (a byPath) Len() int           { return len(a) }
   146  func (a byPath) Swap(i, j int)      { a[i], a[j] = a[j], a[i] }
   147  func (a byPath) Less(i, j int) bool { return a[i].Path() < a[j].Path() }