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go/gcexportdata: a new simpler API for the deprecated go/gcimporter15

Fixes golang/go#15651

Change-Id: I7dc7ba731a22c677e3c01bf13e91ecfff9e46765
Reviewed-on: https://go-review.googlesource.com/30612
Reviewed-by: Robert Griesemer <gri@golang.org>
This commit is contained in:
Alan Donovan 2016-10-06 17:39:25 -04:00
parent 8b5a8a45ae
commit 1a954d519b
4 changed files with 276 additions and 0 deletions

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// Copyright 2016 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package gcexportdata_test
import (
"fmt"
"go/ast"
"go/parser"
"go/token"
"go/types"
"log"
"os"
"path/filepath"
"golang.org/x/tools/go/gcexportdata"
)
// ExampleRead uses gcexportdata.Read to load type information for the
// "fmt" package from the fmt.a file produced by the gc compiler.
func ExampleRead() {
// Find the export data file.
filename, path := gcexportdata.Find("fmt", "")
if filename == "" {
log.Fatalf("can't find export data for fmt")
}
fmt.Printf("Package path: %s\n", path)
fmt.Printf("Export data: %s\n", filepath.Base(filename))
// Open and read the file.
f, err := os.Open(filename)
if err != nil {
log.Fatal(err)
}
defer f.Close()
r, err := gcexportdata.NewReader(f)
if err != nil {
log.Fatalf("reading export data %s: %v", filename, err)
}
// Decode the export data.
fset := token.NewFileSet()
imports := make(map[string]*types.Package)
pkg, err := gcexportdata.Read(r, fset, imports, path)
if err != nil {
log.Fatal(err)
}
// Print package information.
fmt.Printf("Package members: %s...\n", pkg.Scope().Names()[:5])
println := pkg.Scope().Lookup("Println")
posn := fset.Position(println.Pos())
posn.Line = 123 // make example deterministic
fmt.Printf("Println type: %s\n", println.Type())
fmt.Printf("Println location: %s\n", posn)
// Output:
//
// Package path: fmt
// Export data: fmt.a
// Package members: [Errorf Formatter Fprint Fprintf Fprintln]...
// Println type: func(a ...interface{}) (n int, err error)
// Println location: $GOROOT/src/fmt/print.go:123:1
}
// ExampleNewImporter demonstrates usage of NewImporter to provide type
// information for dependencies when type-checking Go source code.
func ExampleNewImporter() {
const src = `package twopi
import "math"
const TwoPi = 2 * math.Pi
`
fset := token.NewFileSet()
f, err := parser.ParseFile(fset, "twopi.go", src, 0)
if err != nil {
log.Fatal(err)
}
packages := make(map[string]*types.Package)
imp := gcexportdata.NewImporter(fset, packages)
conf := types.Config{Importer: imp}
pkg, err := conf.Check("twopi", fset, []*ast.File{f}, nil)
if err != nil {
log.Fatal(err)
}
// object from imported package
pi := packages["math"].Scope().Lookup("Pi")
fmt.Printf("const %s.%s %s = %s // %s\n",
pi.Pkg().Path(),
pi.Name(),
pi.Type(),
pi.(*types.Const).Val(),
fset.Position(pi.Pos()))
// object in source package
twopi := pkg.Scope().Lookup("TwoPi")
fmt.Printf("const %s %s = %s // %s\n",
twopi.Name(),
twopi.Type(),
twopi.(*types.Const).Val(),
fset.Position(twopi.Pos()))
// Output:
//
// const math.Pi untyped float = 3.14159 // $GOROOT/src/math/const.go:11:1
// const TwoPi untyped float = 6.28319 // twopi.go:5:7
}

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// Copyright 2016 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Package gcexportdata provides functions for locating, reading, and
// writing export data files containing type information produced by the
// gc compiler. This package supports go1.7 export data format and all
// later versions.
//
// This package replaces the deprecated golang.org/x/tools/go/gcimporter15
// package, which will be deleted in October 2017.
//
// Although it might seem convenient for this package to live alongside
// go/types in the standard library, this would cause version skew
// problems for developer tools that use it, since they must be able to
// consume the outputs of the gc compiler both before and after a Go
// update such as from Go 1.7 to Go 1.8. Because this package lives in
// golang.org/x/tools, sites can update their version of this repo some
// time before the Go 1.8 release and rebuild and redeploy their
// developer tools, which will then be able to consume both Go 1.7 and
// Go 1.8 export data files, so they will work before and after the
// Go update. (See discussion at https://github.com/golang/go/issues/15651.)
//
package gcexportdata // import "golang.org/x/tools/go/gcexportdata"
import (
"bufio"
"fmt"
"go/token"
"go/types"
"io"
"io/ioutil"
gcimporter "golang.org/x/tools/go/gcimporter15"
)
// Find returns the name of an object (.o) or archive (.a) file
// containing type information for the specified import path,
// using the workspace layout conventions of go/build.
// If no file was found, an empty filename is returned.
//
// A relative srcDir is interpreted relative to the current working directory.
//
// Find also returns the package's resolved (canonical) import path,
// reflecting the effects of srcDir and vendoring on importPath.
func Find(importPath string, srcDir string) (filename, path string) {
return gcimporter.FindPkg(importPath, srcDir)
}
// NewReader returns a reader for the export data section of an object
// (.o) or archive (.a) file read from r. The new reader may provide
// additional trailing data beyond the end of the export data.
func NewReader(r io.Reader) (io.Reader, error) {
buf := bufio.NewReader(r)
_, err := gcimporter.FindExportData(buf)
// If we ever switch to a zip-like archive format with the ToC
// at the end, we can return the correct portion of export data,
// but for now we must return the entire rest of the file.
return buf, err
}
// Read reads export data from in, decodes it, and returns type
// information for the package.
// The package name is specified by path.
// File position information is added to fset.
//
// Read may inspect and add to the imports map to ensure that references
// within the export data to other packages are consistent. The caller
// must ensure that imports[path] does not exist, or exists but is
// incomplete (see types.Package.Complete), and Read inserts the
// resulting package into this map entry.
//
// On return, the state of the reader is undefined.
func Read(in io.Reader, fset *token.FileSet, imports map[string]*types.Package, path string) (*types.Package, error) {
data, err := ioutil.ReadAll(in)
if err != nil {
return nil, fmt.Errorf("reading export data for %q: %v", path, err)
}
_, pkg, err := gcimporter.BImportData(fset, imports, data, path)
return pkg, err
}
// Write writes encoded type information for the specified package to out.
// The FileSet provides file position information for named objects.
func Write(out io.Writer, fset *token.FileSet, pkg *types.Package) error {
_, err := out.Write(gcimporter.BExportData(fset, pkg))
return err
}

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// Copyright 2016 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package gcexportdata
import (
"fmt"
"go/token"
"go/types"
"os"
)
// NewImporter returns a new instance of the types.Importer interface
// that reads type information from export data files written by gc.
// The Importer also satisfies types.ImporterFrom.
//
// Export data files are located using "go build" workspace conventions
// and the build.Default context.
//
// Use this importer instead of go/importer.For("gc", ...) to avoid the
// version-skew problems described in the documentation of this package,
// or to control the FileSet or access the imports map populated during
// package loading.
//
func NewImporter(fset *token.FileSet, imports map[string]*types.Package) types.ImporterFrom {
return importer{fset, imports}
}
type importer struct {
fset *token.FileSet
imports map[string]*types.Package
}
func (imp importer) Import(importPath string) (*types.Package, error) {
return imp.ImportFrom(importPath, "", 0)
}
func (imp importer) ImportFrom(importPath, srcDir string, mode types.ImportMode) (_ *types.Package, err error) {
filename, path := Find(importPath, srcDir)
if filename == "" {
if importPath == "unsafe" {
// Even for unsafe, call Find first in case
// the package was vendored.
return types.Unsafe, nil
}
return nil, fmt.Errorf("can't find import: %s", importPath)
}
if pkg, ok := imp.imports[path]; ok && pkg.Complete() {
return pkg, nil // cache hit
}
// open file
f, err := os.Open(filename)
if err != nil {
return nil, err
}
defer func() {
f.Close()
if err != nil {
// add file name to error
err = fmt.Errorf("reading export data: %s: %v", filename, err)
}
}()
r, err := NewReader(f)
if err != nil {
return nil, err
}
return Read(r, imp.fset, imp.imports, path)
}

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// standard library's go/importer package, specifically customizable
// package data lookup. This package should be deleted once that
// functionality becomes available in the standard library.
//
// Deprecated: this package will be deleted in October 2017.
// New code should use golang.org/x/tools/go/gcexportdata.
//
package gcimporter // import "golang.org/x/tools/go/gcimporter15"
import (