go objectpath 源码
golang objectpath 代码
文件路径：/src/cmd/vendor/golang.org/x/tools/go/types/objectpath/objectpath.go
// Copyright 2018 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 objectpath defines a naming scheme for types.Objects
// (that is, named entities in Go programs) relative to their enclosing
// package.
//
// Type-checker objects are canonical, so they are usually identified by
// their address in memory (a pointer), but a pointer has meaning only
// within one address space. By contrast, objectpath names allow the
// identity of an object to be sent from one program to another,
// establishing a correspondence between types.Object variables that are
// distinct but logically equivalent.
//
// A single object may have multiple paths. In this example,
//
// type A struct{ X int }
// type B A
//
// the field X has two paths due to its membership of both A and B.
// The For(obj) function always returns one of these paths, arbitrarily
// but consistently.
package objectpath
import (
"fmt"
"go/types"
"sort"
"strconv"
"strings"
"golang.org/x/tools/internal/typeparams"
)
// A Path is an opaque name that identifies a types.Object
// relative to its package. Conceptually, the name consists of a
// sequence of destructuring operations applied to the package scope
// to obtain the original object.
// The name does not include the package itself.
type Path string
// Encoding
//
// An object path is a textual and (with training) human-readable encoding
// of a sequence of destructuring operators, starting from a types.Package.
// The sequences represent a path through the package/object/type graph.
// We classify these operators by their type:
//
// PO package->object Package.Scope.Lookup
// OT object->type Object.Type
// TT type->type Type.{Elem,Key,Params,Results,Underlying} [EKPRU]
// TO type->object Type.{At,Field,Method,Obj} [AFMO]
//
// All valid paths start with a package and end at an object
// and thus may be defined by the regular language:
//
// objectpath = PO (OT TT* TO)*
//
// The concrete encoding follows directly:
// - The only PO operator is Package.Scope.Lookup, which requires an identifier.
// - The only OT operator is Object.Type,
// which we encode as '.' because dot cannot appear in an identifier.
// - The TT operators are encoded as [EKPRUTC];
// one of these (TypeParam) requires an integer operand,
// which is encoded as a string of decimal digits.
// - The TO operators are encoded as [AFMO];
// three of these (At,Field,Method) require an integer operand,
// which is encoded as a string of decimal digits.
// These indices are stable across different representations
// of the same package, even source and export data.
// The indices used are implementation specific and may not correspond to
// the argument to the go/types function.
//
// In the example below,
//
// package p
//
// type T interface {
// f() (a string, b struct{ X int })
// }
//
// field X has the path "T.UM0.RA1.F0",
// representing the following sequence of operations:
//
// p.Lookup("T") T
// .Type().Underlying().Method(0). f
// .Type().Results().At(1) b
// .Type().Field(0) X
//
// The encoding is not maximally compact---every R or P is
// followed by an A, for example---but this simplifies the
// encoder and decoder.
const (
// object->type operators
opType = '.' // .Type() (Object)
// type->type operators
opElem = 'E' // .Elem() (Pointer, Slice, Array, Chan, Map)
opKey = 'K' // .Key() (Map)
opParams = 'P' // .Params() (Signature)
opResults = 'R' // .Results() (Signature)
opUnderlying = 'U' // .Underlying() (Named)
opTypeParam = 'T' // .TypeParams.At(i) (Named, Signature)
opConstraint = 'C' // .Constraint() (TypeParam)
// type->object operators
opAt = 'A' // .At(i) (Tuple)
opField = 'F' // .Field(i) (Struct)
opMethod = 'M' // .Method(i) (Named or Interface; not Struct: "promoted" names are ignored)
opObj = 'O' // .Obj() (Named, TypeParam)
)
// The For function returns the path to an object relative to its package,
// or an error if the object is not accessible from the package's Scope.
//
// The For function guarantees to return a path only for the following objects:
// - package-level types
// - exported package-level non-types
// - methods
// - parameter and result variables
// - struct fields
// These objects are sufficient to define the API of their package.
// The objects described by a package's export data are drawn from this set.
//
// For does not return a path for predeclared names, imported package
// names, local names, and unexported package-level names (except
// types).
//
// Example: given this definition,
//
// package p
//
// type T interface {
// f() (a string, b struct{ X int })
// }
//
// For(X) would return a path that denotes the following sequence of operations:
//
// p.Scope().Lookup("T") (TypeName T)
// .Type().Underlying().Method(0). (method Func f)
// .Type().Results().At(1) (field Var b)
// .Type().Field(0) (field Var X)
//
// where p is the package (*types.Package) to which X belongs.
func For(obj types.Object) (Path, error) {
pkg := obj.Pkg()
// This table lists the cases of interest.
//
// Object Action
// ------ ------
// nil reject
// builtin reject
// pkgname reject
// label reject
// var
// package-level accept
// func param/result accept
// local reject
// struct field accept
// const
// package-level accept
// local reject
// func
// package-level accept
// init functions reject
// concrete method accept
// interface method accept
// type
// package-level accept
// local reject
//
// The only accessible package-level objects are members of pkg itself.
//
// The cases are handled in four steps:
//
// 1. reject nil and builtin
// 2. accept package-level objects
// 3. reject obviously invalid objects
// 4. search the API for the path to the param/result/field/method.
// 1. reference to nil or builtin?
if pkg == nil {
return "", fmt.Errorf("predeclared %s has no path", obj)
}
scope := pkg.Scope()
// 2. package-level object?
if scope.Lookup(obj.Name()) == obj {
// Only exported objects (and non-exported types) have a path.
// Non-exported types may be referenced by other objects.
if _, ok := obj.(*types.TypeName); !ok && !obj.Exported() {
return "", fmt.Errorf("no path for non-exported %v", obj)
}
return Path(obj.Name()), nil
}
// 3. Not a package-level object.
// Reject obviously non-viable cases.
switch obj := obj.(type) {
case *types.TypeName:
if _, ok := obj.Type().(*typeparams.TypeParam); !ok {
// With the exception of type parameters, only package-level type names
// have a path.
return "", fmt.Errorf("no path for %v", obj)
}
case *types.Const, // Only package-level constants have a path.
*types.Label, // Labels are function-local.
*types.PkgName: // PkgNames are file-local.
return "", fmt.Errorf("no path for %v", obj)
case *types.Var:
// Could be:
// - a field (obj.IsField())
// - a func parameter or result
// - a local var.
// Sadly there is no way to distinguish
// a param/result from a local
// so we must proceed to the find.
case *types.Func:
// A func, if not package-level, must be a method.
if recv := obj.Type().(*types.Signature).Recv(); recv == nil {
return "", fmt.Errorf("func is not a method: %v", obj)
}
if path, ok := concreteMethod(obj); ok {
// Fast path for concrete methods that avoids looping over scope.
return path, nil
}
default:
panic(obj)
}
// 4. Search the API for the path to the var (field/param/result) or method.
// First inspect package-level named types.
// In the presence of path aliases, these give
// the best paths because non-types may
// refer to types, but not the reverse.
empty := make([]byte, 0, 48) // initial space
names := scope.Names()
for _, name := range names {
o := scope.Lookup(name)
tname, ok := o.(*types.TypeName)
if !ok {
continue // handle non-types in second pass
}
path := append(empty, name...)
path = append(path, opType)
T := o.Type()
if tname.IsAlias() {
// type alias
if r := find(obj, T, path, nil); r != nil {
return Path(r), nil
}
} else {
if named, _ := T.(*types.Named); named != nil {
if r := findTypeParam(obj, typeparams.ForNamed(named), path, nil); r != nil {
// generic named type
return Path(r), nil
}
}
// defined (named) type
if r := find(obj, T.Underlying(), append(path, opUnderlying), nil); r != nil {
return Path(r), nil
}
}
}
// Then inspect everything else:
// non-types, and declared methods of defined types.
for _, name := range names {
o := scope.Lookup(name)
path := append(empty, name...)
if _, ok := o.(*types.TypeName); !ok {
if o.Exported() {
// exported non-type (const, var, func)
if r := find(obj, o.Type(), append(path, opType), nil); r != nil {
return Path(r), nil
}
}
continue
}
// Inspect declared methods of defined types.
if T, ok := o.Type().(*types.Named); ok {
path = append(path, opType)
// Note that method index here is always with respect
// to canonical ordering of methods, regardless of how
// they appear in the underlying type.
canonical := canonicalize(T)
for i := 0; i < len(canonical); i++ {
m := canonical[i]
path2 := appendOpArg(path, opMethod, i)
if m == obj {
return Path(path2), nil // found declared method
}
if r := find(obj, m.Type(), append(path2, opType), nil); r != nil {
return Path(r), nil
}
}
}
}
return "", fmt.Errorf("can't find path for %v in %s", obj, pkg.Path())
}
func appendOpArg(path []byte, op byte, arg int) []byte {
path = append(path, op)
path = strconv.AppendInt(path, int64(arg), 10)
return path
}
// concreteMethod returns the path for meth, which must have a non-nil receiver.
// The second return value indicates success and may be false if the method is
// an interface method or if it is an instantiated method.
//
// This function is just an optimization that avoids the general scope walking
// approach. You are expected to fall back to the general approach if this
// function fails.
func concreteMethod(meth *types.Func) (Path, bool) {
// Concrete methods can only be declared on package-scoped named types. For
// that reason we can skip the expensive walk over the package scope: the
// path will always be package -> named type -> method. We can trivially get
// the type name from the receiver, and only have to look over the type's
// methods to find the method index.
//
// Methods on generic types require special consideration, however. Consider
// the following package:
//
// L1: type S[T any] struct{}
// L2: func (recv S[A]) Foo() { recv.Bar() }
// L3: func (recv S[B]) Bar() { }
// L4: type Alias = S[int]
// L5: func _[T any]() { var s S[int]; s.Foo() }
//
// The receivers of methods on generic types are instantiations. L2 and L3
// instantiate S with the type-parameters A and B, which are scoped to the
// respective methods. L4 and L5 each instantiate S with int. Each of these
// instantiations has its own method set, full of methods (and thus objects)
// with receivers whose types are the respective instantiations. In other
// words, we have
//
// S[A].Foo, S[A].Bar
// S[B].Foo, S[B].Bar
// S[int].Foo, S[int].Bar
//
// We may thus be trying to produce object paths for any of these objects.
//
// S[A].Foo and S[B].Bar are the origin methods, and their paths are S.Foo
// and S.Bar, which are the paths that this function naturally produces.
//
// S[A].Bar, S[B].Foo, and both methods on S[int] are instantiations that
// don't correspond to the origin methods. For S[int], this is significant.
// The most precise object path for S[int].Foo, for example, is Alias.Foo,
// not S.Foo. Our function, however, would produce S.Foo, which would
// resolve to a different object.
//
// For S[A].Bar and S[B].Foo it could be argued that S.Bar and S.Foo are
// still the correct paths, since only the origin methods have meaningful
// paths. But this is likely only true for trivial cases and has edge cases.
// Since this function is only an optimization, we err on the side of giving
// up, deferring to the slower but definitely correct algorithm. Most users
// of objectpath will only be giving us origin methods, anyway, as referring
// to instantiated methods is usually not useful.
if typeparams.OriginMethod(meth) != meth {
return "", false
}
recvT := meth.Type().(*types.Signature).Recv().Type()
if ptr, ok := recvT.(*types.Pointer); ok {
recvT = ptr.Elem()
}
named, ok := recvT.(*types.Named)
if !ok {
return "", false
}
if types.IsInterface(named) {
// Named interfaces don't have to be package-scoped
//
// TODO(dominikh): opt: if scope.Lookup(name) == named, then we can apply this optimization to interface
// methods, too, I think.
return "", false
}
// Preallocate space for the name, opType, opMethod, and some digits.
name := named.Obj().Name()
path := make([]byte, 0, len(name)+8)
path = append(path, name...)
path = append(path, opType)
canonical := canonicalize(named)
for i, m := range canonical {
if m == meth {
path = appendOpArg(path, opMethod, i)
return Path(path), true
}
}
panic(fmt.Sprintf("couldn't find method %s on type %s", meth, named))
}
// find finds obj within type T, returning the path to it, or nil if not found.
//
// The seen map is used to short circuit cycles through type parameters. If
// nil, it will be allocated as necessary.
func find(obj types.Object, T types.Type, path []byte, seen map[*types.TypeName]bool) []byte {
switch T := T.(type) {
case *types.Basic, *types.Named:
// Named types belonging to pkg were handled already,
// so T must belong to another package. No path.
return nil
case *types.Pointer:
return find(obj, T.Elem(), append(path, opElem), seen)
case *types.Slice:
return find(obj, T.Elem(), append(path, opElem), seen)
case *types.Array:
return find(obj, T.Elem(), append(path, opElem), seen)
case *types.Chan:
return find(obj, T.Elem(), append(path, opElem), seen)
case *types.Map:
if r := find(obj, T.Key(), append(path, opKey), seen); r != nil {
return r
}
return find(obj, T.Elem(), append(path, opElem), seen)
case *types.Signature:
if r := findTypeParam(obj, typeparams.ForSignature(T), path, seen); r != nil {
return r
}
if r := find(obj, T.Params(), append(path, opParams), seen); r != nil {
return r
}
return find(obj, T.Results(), append(path, opResults), seen)
case *types.Struct:
for i := 0; i < T.NumFields(); i++ {
fld := T.Field(i)
path2 := appendOpArg(path, opField, i)
if fld == obj {
return path2 // found field var
}
if r := find(obj, fld.Type(), append(path2, opType), seen); r != nil {
return r
}
}
return nil
case *types.Tuple:
for i := 0; i < T.Len(); i++ {
v := T.At(i)
path2 := appendOpArg(path, opAt, i)
if v == obj {
return path2 // found param/result var
}
if r := find(obj, v.Type(), append(path2, opType), seen); r != nil {
return r
}
}
return nil
case *types.Interface:
for i := 0; i < T.NumMethods(); i++ {
m := T.Method(i)
path2 := appendOpArg(path, opMethod, i)
if m == obj {
return path2 // found interface method
}
if r := find(obj, m.Type(), append(path2, opType), seen); r != nil {
return r
}
}
return nil
case *typeparams.TypeParam:
name := T.Obj()
if name == obj {
return append(path, opObj)
}
if seen[name] {
return nil
}
if seen == nil {
seen = make(map[*types.TypeName]bool)
}
seen[name] = true
if r := find(obj, T.Constraint(), append(path, opConstraint), seen); r != nil {
return r
}
return nil
}
panic(T)
}
func findTypeParam(obj types.Object, list *typeparams.TypeParamList, path []byte, seen map[*types.TypeName]bool) []byte {
for i := 0; i < list.Len(); i++ {
tparam := list.At(i)
path2 := appendOpArg(path, opTypeParam, i)
if r := find(obj, tparam, path2, seen); r != nil {
return r
}
}
return nil
}
// Object returns the object denoted by path p within the package pkg.
func Object(pkg *types.Package, p Path) (types.Object, error) {
if p == "" {
return nil, fmt.Errorf("empty path")
}
pathstr := string(p)
var pkgobj, suffix string
if dot := strings.IndexByte(pathstr, opType); dot < 0 {
pkgobj = pathstr
} else {
pkgobj = pathstr[:dot]
suffix = pathstr[dot:] // suffix starts with "."
}
obj := pkg.Scope().Lookup(pkgobj)
if obj == nil {
return nil, fmt.Errorf("package %s does not contain %q", pkg.Path(), pkgobj)
}
// abstraction of *types.{Pointer,Slice,Array,Chan,Map}
type hasElem interface {
Elem() types.Type
}
// abstraction of *types.{Named,Signature}
type hasTypeParams interface {
TypeParams() *typeparams.TypeParamList
}
// abstraction of *types.{Named,TypeParam}
type hasObj interface {
Obj() *types.TypeName
}
// The loop state is the pair (t, obj),
// exactly one of which is non-nil, initially obj.
// All suffixes start with '.' (the only object->type operation),
// followed by optional type->type operations,
// then a type->object operation.
// The cycle then repeats.
var t types.Type
for suffix != "" {
code := suffix[0]
suffix = suffix[1:]
// Codes [AFM] have an integer operand.
var index int
switch code {
case opAt, opField, opMethod, opTypeParam:
rest := strings.TrimLeft(suffix, "0123456789")
numerals := suffix[:len(suffix)-len(rest)]
suffix = rest
i, err := strconv.Atoi(numerals)
if err != nil {
return nil, fmt.Errorf("invalid path: bad numeric operand %q for code %q", numerals, code)
}
index = int(i)
case opObj:
// no operand
default:
// The suffix must end with a type->object operation.
if suffix == "" {
return nil, fmt.Errorf("invalid path: ends with %q, want [AFMO]", code)
}
}
if code == opType {
if t != nil {
return nil, fmt.Errorf("invalid path: unexpected %q in type context", opType)
}
t = obj.Type()
obj = nil
continue
}
if t == nil {
return nil, fmt.Errorf("invalid path: code %q in object context", code)
}
// Inv: t != nil, obj == nil
switch code {
case opElem:
hasElem, ok := t.(hasElem) // Pointer, Slice, Array, Chan, Map
if !ok {
return nil, fmt.Errorf("cannot apply %q to %s (got %T, want pointer, slice, array, chan or map)", code, t, t)
}
t = hasElem.Elem()
case opKey:
mapType, ok := t.(*types.Map)
if !ok {
return nil, fmt.Errorf("cannot apply %q to %s (got %T, want map)", code, t, t)
}
t = mapType.Key()
case opParams:
sig, ok := t.(*types.Signature)
if !ok {
return nil, fmt.Errorf("cannot apply %q to %s (got %T, want signature)", code, t, t)
}
t = sig.Params()
case opResults:
sig, ok := t.(*types.Signature)
if !ok {
return nil, fmt.Errorf("cannot apply %q to %s (got %T, want signature)", code, t, t)
}
t = sig.Results()
case opUnderlying:
named, ok := t.(*types.Named)
if !ok {
return nil, fmt.Errorf("cannot apply %q to %s (got %T, want named)", code, t, t)
}
t = named.Underlying()
case opTypeParam:
hasTypeParams, ok := t.(hasTypeParams) // Named, Signature
if !ok {
return nil, fmt.Errorf("cannot apply %q to %s (got %T, want named or signature)", code, t, t)
}
tparams := hasTypeParams.TypeParams()
if n := tparams.Len(); index >= n {
return nil, fmt.Errorf("tuple index %d out of range [0-%d)", index, n)
}
t = tparams.At(index)
case opConstraint:
tparam, ok := t.(*typeparams.TypeParam)
if !ok {
return nil, fmt.Errorf("cannot apply %q to %s (got %T, want type parameter)", code, t, t)
}
t = tparam.Constraint()
case opAt:
tuple, ok := t.(*types.Tuple)
if !ok {
return nil, fmt.Errorf("cannot apply %q to %s (got %T, want tuple)", code, t, t)
}
if n := tuple.Len(); index >= n {
return nil, fmt.Errorf("tuple index %d out of range [0-%d)", index, n)
}
obj = tuple.At(index)
t = nil
case opField:
structType, ok := t.(*types.Struct)
if !ok {
return nil, fmt.Errorf("cannot apply %q to %s (got %T, want struct)", code, t, t)
}
if n := structType.NumFields(); index >= n {
return nil, fmt.Errorf("field index %d out of range [0-%d)", index, n)
}
obj = structType.Field(index)
t = nil
case opMethod:
hasMethods, ok := t.(hasMethods) // Interface or Named
if !ok {
return nil, fmt.Errorf("cannot apply %q to %s (got %T, want interface or named)", code, t, t)
}
canonical := canonicalize(hasMethods)
if n := len(canonical); index >= n {
return nil, fmt.Errorf("method index %d out of range [0-%d)", index, n)
}
obj = canonical[index]
t = nil
case opObj:
hasObj, ok := t.(hasObj)
if !ok {
return nil, fmt.Errorf("cannot apply %q to %s (got %T, want named or type param)", code, t, t)
}
obj = hasObj.Obj()
t = nil
default:
return nil, fmt.Errorf("invalid path: unknown code %q", code)
}
}
if obj.Pkg() != pkg {
return nil, fmt.Errorf("path denotes %s, which belongs to a different package", obj)
}
return obj, nil // success
}
// hasMethods is an abstraction of *types.{Interface,Named}. This is pulled up
// because it is used by methodOrdering, which is in turn used by both encoding
// and decoding.
type hasMethods interface {
Method(int) *types.Func
NumMethods() int
}
// canonicalize returns a canonical order for the methods in a hasMethod.
func canonicalize(hm hasMethods) []*types.Func {
count := hm.NumMethods()
if count <= 0 {
return nil
}
canon := make([]*types.Func, count)
for i := 0; i < count; i++ {
canon[i] = hm.Method(i)
}
less := func(i, j int) bool {
return canon[i].Id() < canon[j].Id()
}
sort.Slice(canon, less)
return canon
}
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