github.com/zebozhuang/go@v0.0.0-20200207033046-f8a98f6f5c5d/src/go/importer/importer.go (about)

     1  // Copyright 2015 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 importer provides access to export data importers.
     6  package importer
     7  
     8  import (
     9  	"go/build"
    10  	"go/internal/gccgoimporter"
    11  	"go/internal/gcimporter"
    12  	"go/internal/srcimporter"
    13  	"go/token"
    14  	"go/types"
    15  	"io"
    16  	"runtime"
    17  )
    18  
    19  // A Lookup function returns a reader to access package data for
    20  // a given import path, or an error if no matching package is found.
    21  type Lookup func(path string) (io.ReadCloser, error)
    22  
    23  // For returns an Importer for importing from installed packages
    24  // for the compilers "gc" and "gccgo", or for importing directly
    25  // from the source if the compiler argument is "source". In this
    26  // latter case, importing may fail under circumstances where the
    27  // exported API is not entirely defined in pure Go source code
    28  // (if the package API depends on cgo-defined entities, the type
    29  // checker won't have access to those).
    30  //
    31  // If lookup is nil, the default package lookup mechanism for the
    32  // given compiler is used.
    33  //
    34  // BUG(issue13847): For does not support non-nil lookup functions.
    35  func For(compiler string, lookup Lookup) types.Importer {
    36  	switch compiler {
    37  	case "gc":
    38  		if lookup != nil {
    39  			panic("gc importer for custom import path lookup not supported (issue #13847).")
    40  		}
    41  
    42  		return make(gcimports)
    43  
    44  	case "gccgo":
    45  		if lookup != nil {
    46  			panic("gccgo importer for custom import path lookup not supported (issue #13847).")
    47  		}
    48  
    49  		var inst gccgoimporter.GccgoInstallation
    50  		if err := inst.InitFromDriver("gccgo"); err != nil {
    51  			return nil
    52  		}
    53  		return &gccgoimports{
    54  			packages: make(map[string]*types.Package),
    55  			importer: inst.GetImporter(nil, nil),
    56  		}
    57  
    58  	case "source":
    59  		if lookup != nil {
    60  			panic("source importer for custom import path lookup not supported (issue #13847).")
    61  		}
    62  
    63  		return srcimporter.New(&build.Default, token.NewFileSet(), make(map[string]*types.Package))
    64  	}
    65  
    66  	// compiler not supported
    67  	return nil
    68  }
    69  
    70  // Default returns an Importer for the compiler that built the running binary.
    71  // If available, the result implements types.ImporterFrom.
    72  func Default() types.Importer {
    73  	return For(runtime.Compiler, nil)
    74  }
    75  
    76  // gc importer
    77  
    78  type gcimports map[string]*types.Package
    79  
    80  func (m gcimports) Import(path string) (*types.Package, error) {
    81  	return m.ImportFrom(path, "" /* no vendoring */, 0)
    82  }
    83  
    84  func (m gcimports) ImportFrom(path, srcDir string, mode types.ImportMode) (*types.Package, error) {
    85  	if mode != 0 {
    86  		panic("mode must be 0")
    87  	}
    88  	return gcimporter.Import(m, path, srcDir)
    89  }
    90  
    91  // gccgo importer
    92  
    93  type gccgoimports struct {
    94  	packages map[string]*types.Package
    95  	importer gccgoimporter.Importer
    96  }
    97  
    98  func (m *gccgoimports) Import(path string) (*types.Package, error) {
    99  	return m.ImportFrom(path, "" /* no vendoring */, 0)
   100  }
   101  
   102  func (m *gccgoimports) ImportFrom(path, srcDir string, mode types.ImportMode) (*types.Package, error) {
   103  	if mode != 0 {
   104  		panic("mode must be 0")
   105  	}
   106  	// TODO(gri) pass srcDir
   107  	return m.importer(m.packages, path)
   108  }