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Source file src/go/importer/importer.go

Documentation: go/importer

     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, and the resulting importer attempts
    33  // to resolve relative and absolute import paths to canonical
    34  // import path IDs before finding the imported file.
    35  //
    36  // If lookup is non-nil, then the returned importer calls lookup
    37  // each time it needs to resolve an import path. In this mode
    38  // the importer can only be invoked with canonical import paths
    39  // (not relative or absolute ones); it is assumed that the translation
    40  // to canonical import paths is being done by the client of the
    41  // importer.
    42  func For(compiler string, lookup Lookup) types.Importer {
    43  	switch compiler {
    44  	case "gc":
    45  		return &gcimports{
    46  			packages: make(map[string]*types.Package),
    47  			lookup:   lookup,
    48  		}
    49  
    50  	case "gccgo":
    51  		var inst gccgoimporter.GccgoInstallation
    52  		if err := inst.InitFromDriver("gccgo"); err != nil {
    53  			return nil
    54  		}
    55  		return &gccgoimports{
    56  			packages: make(map[string]*types.Package),
    57  			importer: inst.GetImporter(nil, nil),
    58  			lookup:   lookup,
    59  		}
    60  
    61  	case "source":
    62  		if lookup != nil {
    63  			panic("source importer for custom import path lookup not supported (issue #13847).")
    64  		}
    65  
    66  		return srcimporter.New(&build.Default, token.NewFileSet(), make(map[string]*types.Package))
    67  	}
    68  
    69  	// compiler not supported
    70  	return nil
    71  }
    72  
    73  // Default returns an Importer for the compiler that built the running binary.
    74  // If available, the result implements types.ImporterFrom.
    75  func Default() types.Importer {
    76  	return For(runtime.Compiler, nil)
    77  }
    78  
    79  // gc importer
    80  
    81  type gcimports struct {
    82  	packages map[string]*types.Package
    83  	lookup   Lookup
    84  }
    85  
    86  func (m *gcimports) Import(path string) (*types.Package, error) {
    87  	return m.ImportFrom(path, "" /* no vendoring */, 0)
    88  }
    89  
    90  func (m *gcimports) ImportFrom(path, srcDir string, mode types.ImportMode) (*types.Package, error) {
    91  	if mode != 0 {
    92  		panic("mode must be 0")
    93  	}
    94  	return gcimporter.Import(m.packages, path, srcDir, m.lookup)
    95  }
    96  
    97  // gccgo importer
    98  
    99  type gccgoimports struct {
   100  	packages map[string]*types.Package
   101  	importer gccgoimporter.Importer
   102  	lookup   Lookup
   103  }
   104  
   105  func (m *gccgoimports) Import(path string) (*types.Package, error) {
   106  	return m.ImportFrom(path, "" /* no vendoring */, 0)
   107  }
   108  
   109  func (m *gccgoimports) ImportFrom(path, srcDir string, mode types.ImportMode) (*types.Package, error) {
   110  	if mode != 0 {
   111  		panic("mode must be 0")
   112  	}
   113  	return m.importer(m.packages, path, srcDir, m.lookup)
   114  }
   115  

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