+++ /dev/null
-// 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"
- "strconv"
- "strings"
-
- "go/types"
-)
-
-// 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 [EKPRU].
-// - The OT 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.
-//
-// 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)
-
- // 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)
-)
-
-// 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.Const, // Only package-level constants have a path.
- *types.TypeName, // Only package-level types 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)
- }
- // TODO(adonovan): opt: if the method is concrete,
- // do a specialized version of the rest of this function so
- // that it's O(1) not O(|scope|). Basically 'find' is needed
- // only for struct fields and interface methods.
-
- 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); r != nil {
- return Path(r), nil
- }
- } else {
- // defined (named) type
- if r := find(obj, T.Underlying(), append(path, opUnderlying)); 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)); 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)
- for i := 0; i < T.NumMethods(); i++ {
- m := T.Method(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)); 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
-}
-
-// find finds obj within type T, returning the path to it, or nil if not found.
-func find(obj types.Object, T types.Type, path []byte) []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))
- case *types.Slice:
- return find(obj, T.Elem(), append(path, opElem))
- case *types.Array:
- return find(obj, T.Elem(), append(path, opElem))
- case *types.Chan:
- return find(obj, T.Elem(), append(path, opElem))
- case *types.Map:
- if r := find(obj, T.Key(), append(path, opKey)); r != nil {
- return r
- }
- return find(obj, T.Elem(), append(path, opElem))
- case *types.Signature:
- if r := find(obj, T.Params(), append(path, opParams)); r != nil {
- return r
- }
- return find(obj, T.Results(), append(path, opResults))
- case *types.Struct:
- for i := 0; i < T.NumFields(); i++ {
- f := T.Field(i)
- path2 := appendOpArg(path, opField, i)
- if f == obj {
- return path2 // found field var
- }
- if r := find(obj, f.Type(), append(path2, opType)); 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)); 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)); r != nil {
- return r
- }
- }
- return nil
- }
- panic(T)
-}
-
-// 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.{Interface,Named}
- type hasMethods interface {
- Method(int) *types.Func
- NumMethods() int
- }
-
- // 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:
- 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 %s, want named)", code, t, t)
- }
- t = named.Underlying()
-
- case opAt:
- tuple, ok := t.(*types.Tuple)
- if !ok {
- return nil, fmt.Errorf("cannot apply %q to %s (got %s, 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 %s, want interface or named)", code, t, t)
- }
- if n := hasMethods.NumMethods(); index >= n {
- return nil, fmt.Errorf("method index %d out of range [0-%d)", index, n)
- }
- obj = hasMethods.Method(index)
- t = nil
-
- case opObj:
- named, ok := t.(*types.Named)
- if !ok {
- return nil, fmt.Errorf("cannot apply %q to %s (got %s, want named)", code, t, t)
- }
- obj = named.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
-}
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