importer.go

     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  //
     7  // These functions, which are mostly deprecated, date from before the
     8  // introduction of modules in release Go 1.11. They should no longer
     9  // be relied on except for use in test cases using small programs that
    10  // depend only on the standard library. For reliable module-aware
    11  // loading of type information, use the packages.Load function from
    12  // golang.org/x/tools/go/packages.
    13  package importer
    14  
    15  import (
    16  	"go/build"
    17  	"go/internal/gccgoimporter"
    18  	"go/internal/gcimporter"
    19  	"go/internal/srcimporter"
    20  	"go/token"
    21  	"go/types"
    22  	"io"
    23  	"runtime"
    24  )
    25  
    26  // A Lookup function returns a reader to access package data for
    27  // a given import path, or an error if no matching package is found.
    28  type Lookup func(path string) (io.ReadCloser, error)
    29  
    30  // ForCompiler returns an Importer for importing from installed packages
    31  // for the compilers "gc" and "gccgo", or for importing directly
    32  // from the source if the compiler argument is "source". In this
    33  // latter case, importing may fail under circumstances where the
    34  // exported API is not entirely defined in pure Go source code
    35  // (if the package API depends on cgo-defined entities, the type
    36  // checker won't have access to those).
    37  //
    38  // The lookup function is called each time the resulting importer needs
    39  // to resolve an import path. In this mode the importer can only be
    40  // invoked with canonical import paths (not relative or absolute ones);
    41  // it is assumed that the translation to canonical import paths is being
    42  // done by the client of the importer.
    43  //
    44  // A lookup function must be provided for correct module-aware operation.
    45  // Deprecated: If lookup is nil, for backwards-compatibility, the importer
    46  // will attempt to resolve imports in the $GOPATH workspace.
    47  func ForCompiler(fset *token.FileSet, compiler string, lookup Lookup) types.Importer {
    48  	switch compiler {
    49  	case "gc":
    50  		return &gcimports{
    51  			fset:     fset,
    52  			packages: make(map[string]*types.Package),
    53  			lookup:   lookup,
    54  		}
    55  
    56  	case "gccgo":
    57  		var inst gccgoimporter.GccgoInstallation
    58  		if err := inst.InitFromDriver("gccgo"); err != nil {
    59  			return nil
    60  		}
    61  		return &gccgoimports{
    62  			packages: make(map[string]*types.Package),
    63  			importer: inst.GetImporter(nil, nil),
    64  			lookup:   lookup,
    65  		}
    66  
    67  	case "source":
    68  		if lookup != nil {
    69  			panic("source importer for custom import path lookup not supported (issue #13847).")
    70  		}
    71  
    72  		return srcimporter.New(&build.Default, fset, make(map[string]*types.Package))
    73  	}
    74  
    75  	// compiler not supported
    76  	return nil
    77  }
    78  
    79  // For calls [ForCompiler] with a new FileSet.
    80  //
    81  // Deprecated: Use [ForCompiler], which populates a FileSet
    82  // with the positions of objects created by the importer.
    83  func For(compiler string, lookup Lookup) types.Importer {
    84  	return ForCompiler(token.NewFileSet(), compiler, lookup)
    85  }
    86  
    87  // Default returns an Importer for the compiler that built the running binary.
    88  // If available, the result implements [types.ImporterFrom].
    89  //
    90  // Default may be convenient for use in the simplest of cases, but
    91  // most clients should instead use [ForCompiler], which accepts a
    92  // [token.FileSet] from the caller; without it, all position
    93  // information derived from the Importer will be incorrect and
    94  // misleading. See also the package documentation.
    95  func Default() types.Importer {
    96  	return For(runtime.Compiler, nil)
    97  }
    98  
    99  // gc importer
   100  
   101  type gcimports struct {
   102  	fset     *token.FileSet
   103  	packages map[string]*types.Package
   104  	lookup   Lookup
   105  }
   106  
   107  func (m *gcimports) Import(path string) (*types.Package, error) {
   108  	return m.ImportFrom(path, "" /* no vendoring */, 0)
   109  }
   110  
   111  func (m *gcimports) ImportFrom(path, srcDir string, mode types.ImportMode) (*types.Package, error) {
   112  	if mode != 0 {
   113  		panic("mode must be 0")
   114  	}
   115  	return gcimporter.Import(m.fset, m.packages, path, srcDir, m.lookup)
   116  }
   117  
   118  // gccgo importer
   119  
   120  type gccgoimports struct {
   121  	packages map[string]*types.Package
   122  	importer gccgoimporter.Importer
   123  	lookup   Lookup
   124  }
   125  
   126  func (m *gccgoimports) Import(path string) (*types.Package, error) {
   127  	return m.ImportFrom(path, "" /* no vendoring */, 0)
   128  }
   129  
   130  func (m *gccgoimports) ImportFrom(path, srcDir string, mode types.ImportMode) (*types.Package, error) {
   131  	if mode != 0 {
   132  		panic("mode must be 0")
   133  	}
   134  	return m.importer(m.packages, path, srcDir, m.lookup)
   135  }
   136
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