Documentation
¶
Overview ¶
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.
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 github.com/peske/golang-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://golang.org/issue/15651.)
Index ¶
- func Find(importPath, srcDir string) (filename, path string)deprecated
- func NewImporter(fset *token.FileSet, imports map[string]*types.Package) types.ImporterFromdeprecated
- func NewReader(r io.Reader) (io.Reader, error)
- func Read(in io.Reader, fset *token.FileSet, imports map[string]*types.Package, ...) (*types.Package, error)
- func ReadBundle(in io.Reader, fset *token.FileSet, imports map[string]*types.Package) ([]*types.Package, error)
- func Write(out io.Writer, fset *token.FileSet, pkg *types.Package) error
- func WriteBundle(out io.Writer, fset *token.FileSet, pkgs []*types.Package) error
Examples ¶
Constants ¶
This section is empty.
Variables ¶
This section is empty.
Functions ¶
func Find
deprecated
Find returns the name of an object (.o) or archive (.a) file containing type information for the specified import path, using the go command. 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.
Deprecated: Use the higher-level API in github.com/peske/golang-x-tools/go/packages, which is more efficient.
func NewImporter
deprecated
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.
Deprecated: Use the higher-level API in github.com/peske/golang-x-tools/go/packages, which is more efficient.
Example ¶
ExampleNewImporter demonstrates usage of NewImporter to provide type information for dependencies when type-checking Go source code.
package main
import (
"fmt"
"go/ast"
"go/parser"
"go/token"
"go/types"
"log"
"path/filepath"
"github.com/peske/golang-x-tools/go/gcexportdata"
)
func main() {
const src = `package myrpc
// choosing a package that doesn't change across releases
import "net/rpc"
const serverError rpc.ServerError = ""
`
fset := token.NewFileSet()
f, err := parser.ParseFile(fset, "myrpc.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("myrpc", fset, []*ast.File{f}, nil)
if err != nil {
log.Fatal(err)
}
// object from imported package
pi := packages["net/rpc"].Scope().Lookup("ServerError")
fmt.Printf("type %s.%s %s // %s\n",
pi.Pkg().Path(),
pi.Name(),
pi.Type().Underlying(),
slashify(fset.Position(pi.Pos())),
)
// object in source package
twopi := pkg.Scope().Lookup("serverError")
fmt.Printf("const %s %s = %s // %s\n",
twopi.Name(),
twopi.Type(),
twopi.(*types.Const).Val(),
slashify(fset.Position(twopi.Pos())),
)
}
func slashify(posn token.Position) token.Position {
posn.Filename = filepath.ToSlash(posn.Filename)
return posn
}
Output: type net/rpc.ServerError string // $GOROOT/src/net/rpc/client.go:20:1 const serverError net/rpc.ServerError = "" // myrpc.go:6:7
func NewReader ¶
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 Read ¶
func Read(in io.Reader, fset *token.FileSet, imports map[string]*types.Package, path string) (*types.Package, error)
Read reads export data from in, decodes it, and returns type information for the package.
The package path (effectively its linker symbol prefix) is specified by path, since unlike the package name, this information may not be recorded in the export data.
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.
Example ¶
ExampleRead uses gcexportdata.Read to load type information for the "fmt" package from the fmt.a file produced by the gc compiler.
package main
import (
"fmt"
"go/token"
"go/types"
"log"
"os"
"path/filepath"
"strings"
"github.com/peske/golang-x-tools/go/gcexportdata"
)
func main() {
// 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)
// 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)
}
// We can see all the names in Names.
members := pkg.Scope().Names()
foundPrintln := false
for _, member := range members {
if member == "Println" {
foundPrintln = true
break
}
}
fmt.Print("Package members: ")
if foundPrintln {
fmt.Println("Println found")
} else {
fmt.Println("Println not found")
}
// We can also look up a name directly using Lookup.
println := pkg.Scope().Lookup("Println")
// go 1.18+ uses the 'any' alias
typ := strings.ReplaceAll(println.Type().String(), "interface{}", "any")
fmt.Printf("Println type: %s\n", typ)
posn := fset.Position(println.Pos())
// make example deterministic
posn.Line = 123
fmt.Printf("Println location: %s\n", slashify(posn))
}
func slashify(posn token.Position) token.Position {
posn.Filename = filepath.ToSlash(posn.Filename)
return posn
}
Output: Package path: fmt Package members: Println found Println type: func(a ...any) (n int, err error) Println location: $GOROOT/src/fmt/print.go:123:1
func ReadBundle ¶
func ReadBundle(in io.Reader, fset *token.FileSet, imports map[string]*types.Package) ([]*types.Package, error)
ReadBundle reads an export bundle from in, decodes it, and returns type information for the packages. File position information is added to fset.
ReadBundle may inspect and add to the imports map to ensure that references within the export bundle to other packages are consistent.
On return, the state of the reader is undefined.
Experimental: This API is experimental and may change in the future.
func Write ¶
Write writes encoded type information for the specified package to out. The FileSet provides file position information for named objects.
func WriteBundle ¶
WriteBundle writes encoded type information for the specified packages to out. The FileSet provides file position information for named objects.
Experimental: This API is experimental and may change in the future.
Types ¶
This section is empty.
Source Files