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  // ForCompiler 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  // The lookup function is called each time the resulting importer needs
		32  // to resolve an import path. In this mode the importer can only be
		33  // invoked with canonical import paths (not relative or absolute ones);
		34  // it is assumed that the translation to canonical import paths is being
		35  // done by the client of the importer.
		36  //
		37  // A lookup function must be provided for correct module-aware operation.
		38  // Deprecated: If lookup is nil, for backwards-compatibility, the importer
		39  // will attempt to resolve imports in the $GOPATH workspace.
		40  func ForCompiler(fset *token.FileSet, compiler string, lookup Lookup) types.Importer {
		41  	switch compiler {
		42  	case "gc":
		43  		return &gcimports{
		44  			fset:		 fset,
		45  			packages: make(map[string]*types.Package),
		46  			lookup:	 lookup,
		47  		}
		48  
		49  	case "gccgo":
		50  		var inst gccgoimporter.GccgoInstallation
		51  		if err := inst.InitFromDriver("gccgo"); err != nil {
		52  			return nil
		53  		}
		54  		return &gccgoimports{
		55  			packages: make(map[string]*types.Package),
		56  			importer: inst.GetImporter(nil, nil),
		57  			lookup:	 lookup,
		58  		}
		59  
		60  	case "source":
		61  		if lookup != nil {
		62  			panic("source importer for custom import path lookup not supported (issue #13847).")
		63  		}
		64  
		65  		return srcimporter.New(&build.Default, fset, make(map[string]*types.Package))
		66  	}
		67  
		68  	// compiler not supported
		69  	return nil
		70  }
		71  
		72  // For calls ForCompiler with a new FileSet.
		73  //
		74  // Deprecated: Use ForCompiler, which populates a FileSet
		75  // with the positions of objects created by the importer.
		76  func For(compiler string, lookup Lookup) types.Importer {
		77  	return ForCompiler(token.NewFileSet(), compiler, lookup)
		78  }
		79  
		80  // Default returns an Importer for the compiler that built the running binary.
		81  // If available, the result implements types.ImporterFrom.
		82  func Default() types.Importer {
		83  	return For(runtime.Compiler, nil)
		84  }
		85  
		86  // gc importer
		87  
		88  type gcimports struct {
		89  	fset		 *token.FileSet
		90  	packages map[string]*types.Package
		91  	lookup	 Lookup
		92  }
		93  
		94  func (m *gcimports) Import(path string) (*types.Package, error) {
		95  	return m.ImportFrom(path, "" /* no vendoring */, 0)
		96  }
		97  
		98  func (m *gcimports) ImportFrom(path, srcDir string, mode types.ImportMode) (*types.Package, error) {
		99  	if mode != 0 {
	 100  		panic("mode must be 0")
	 101  	}
	 102  	return gcimporter.Import(m.fset, m.packages, path, srcDir, m.lookup)
	 103  }
	 104  
	 105  // gccgo importer
	 106  
	 107  type gccgoimports struct {
	 108  	packages map[string]*types.Package
	 109  	importer gccgoimporter.Importer
	 110  	lookup	 Lookup
	 111  }
	 112  
	 113  func (m *gccgoimports) Import(path string) (*types.Package, error) {
	 114  	return m.ImportFrom(path, "" /* no vendoring */, 0)
	 115  }
	 116  
	 117  func (m *gccgoimports) ImportFrom(path, srcDir string, mode types.ImportMode) (*types.Package, error) {
	 118  	if mode != 0 {
	 119  		panic("mode must be 0")
	 120  	}
	 121  	return m.importer(m.packages, path, srcDir, m.lookup)
	 122  }
	 123
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