2020-04-05 06:20:50 +00:00
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// Copyright 2018 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Package objectpath defines a naming scheme for types.Objects
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// (that is, named entities in Go programs) relative to their enclosing
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// package.
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//
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// Type-checker objects are canonical, so they are usually identified by
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// their address in memory (a pointer), but a pointer has meaning only
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// within one address space. By contrast, objectpath names allow the
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// identity of an object to be sent from one program to another,
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// establishing a correspondence between types.Object variables that are
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// distinct but logically equivalent.
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//
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// A single object may have multiple paths. In this example,
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// type A struct{ X int }
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// type B A
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// the field X has two paths due to its membership of both A and B.
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// The For(obj) function always returns one of these paths, arbitrarily
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// but consistently.
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package objectpath
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import (
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"fmt"
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"strconv"
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"strings"
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"go/types"
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)
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// A Path is an opaque name that identifies a types.Object
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// relative to its package. Conceptually, the name consists of a
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// sequence of destructuring operations applied to the package scope
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// to obtain the original object.
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// The name does not include the package itself.
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type Path string
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// Encoding
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//
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// An object path is a textual and (with training) human-readable encoding
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// of a sequence of destructuring operators, starting from a types.Package.
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// The sequences represent a path through the package/object/type graph.
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// We classify these operators by their type:
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//
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// PO package->object Package.Scope.Lookup
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// OT object->type Object.Type
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// TT type->type Type.{Elem,Key,Params,Results,Underlying} [EKPRU]
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// TO type->object Type.{At,Field,Method,Obj} [AFMO]
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//
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// All valid paths start with a package and end at an object
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// and thus may be defined by the regular language:
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//
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// objectpath = PO (OT TT* TO)*
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//
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// The concrete encoding follows directly:
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// - The only PO operator is Package.Scope.Lookup, which requires an identifier.
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// - The only OT operator is Object.Type,
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// which we encode as '.' because dot cannot appear in an identifier.
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// - The TT operators are encoded as [EKPRU].
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// - The OT operators are encoded as [AFMO];
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// three of these (At,Field,Method) require an integer operand,
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// which is encoded as a string of decimal digits.
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// These indices are stable across different representations
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// of the same package, even source and export data.
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//
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// In the example below,
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//
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// package p
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//
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// type T interface {
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// f() (a string, b struct{ X int })
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// }
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//
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// field X has the path "T.UM0.RA1.F0",
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// representing the following sequence of operations:
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//
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// p.Lookup("T") T
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// .Type().Underlying().Method(0). f
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// .Type().Results().At(1) b
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// .Type().Field(0) X
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//
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// The encoding is not maximally compact---every R or P is
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// followed by an A, for example---but this simplifies the
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// encoder and decoder.
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//
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const (
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// object->type operators
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opType = '.' // .Type() (Object)
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// type->type operators
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opElem = 'E' // .Elem() (Pointer, Slice, Array, Chan, Map)
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opKey = 'K' // .Key() (Map)
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opParams = 'P' // .Params() (Signature)
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opResults = 'R' // .Results() (Signature)
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opUnderlying = 'U' // .Underlying() (Named)
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// type->object operators
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opAt = 'A' // .At(i) (Tuple)
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opField = 'F' // .Field(i) (Struct)
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opMethod = 'M' // .Method(i) (Named or Interface; not Struct: "promoted" names are ignored)
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opObj = 'O' // .Obj() (Named)
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)
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// The For function returns the path to an object relative to its package,
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// or an error if the object is not accessible from the package's Scope.
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//
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// The For function guarantees to return a path only for the following objects:
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// - package-level types
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// - exported package-level non-types
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// - methods
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// - parameter and result variables
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// - struct fields
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// These objects are sufficient to define the API of their package.
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// The objects described by a package's export data are drawn from this set.
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//
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// For does not return a path for predeclared names, imported package
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// names, local names, and unexported package-level names (except
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// types).
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//
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// Example: given this definition,
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//
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// package p
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//
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// type T interface {
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// f() (a string, b struct{ X int })
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// }
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//
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// For(X) would return a path that denotes the following sequence of operations:
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//
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// p.Scope().Lookup("T") (TypeName T)
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// .Type().Underlying().Method(0). (method Func f)
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// .Type().Results().At(1) (field Var b)
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// .Type().Field(0) (field Var X)
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//
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// where p is the package (*types.Package) to which X belongs.
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func For(obj types.Object) (Path, error) {
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pkg := obj.Pkg()
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// This table lists the cases of interest.
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//
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// Object Action
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// ------ ------
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// nil reject
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// builtin reject
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// pkgname reject
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// label reject
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// var
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// package-level accept
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// func param/result accept
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// local reject
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// struct field accept
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// const
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// package-level accept
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// local reject
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// func
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// package-level accept
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// init functions reject
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// concrete method accept
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// interface method accept
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// type
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// package-level accept
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// local reject
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//
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// The only accessible package-level objects are members of pkg itself.
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//
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// The cases are handled in four steps:
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//
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// 1. reject nil and builtin
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// 2. accept package-level objects
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// 3. reject obviously invalid objects
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// 4. search the API for the path to the param/result/field/method.
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// 1. reference to nil or builtin?
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if pkg == nil {
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return "", fmt.Errorf("predeclared %s has no path", obj)
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}
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scope := pkg.Scope()
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// 2. package-level object?
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if scope.Lookup(obj.Name()) == obj {
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// Only exported objects (and non-exported types) have a path.
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// Non-exported types may be referenced by other objects.
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if _, ok := obj.(*types.TypeName); !ok && !obj.Exported() {
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return "", fmt.Errorf("no path for non-exported %v", obj)
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}
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return Path(obj.Name()), nil
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}
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// 3. Not a package-level object.
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// Reject obviously non-viable cases.
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switch obj := obj.(type) {
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case *types.Const, // Only package-level constants have a path.
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*types.TypeName, // Only package-level types have a path.
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*types.Label, // Labels are function-local.
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*types.PkgName: // PkgNames are file-local.
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return "", fmt.Errorf("no path for %v", obj)
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case *types.Var:
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// Could be:
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// - a field (obj.IsField())
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// - a func parameter or result
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// - a local var.
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// Sadly there is no way to distinguish
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// a param/result from a local
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// so we must proceed to the find.
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case *types.Func:
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// A func, if not package-level, must be a method.
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if recv := obj.Type().(*types.Signature).Recv(); recv == nil {
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return "", fmt.Errorf("func is not a method: %v", obj)
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}
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// TODO(adonovan): opt: if the method is concrete,
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// do a specialized version of the rest of this function so
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// that it's O(1) not O(|scope|). Basically 'find' is needed
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// only for struct fields and interface methods.
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default:
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panic(obj)
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}
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// 4. Search the API for the path to the var (field/param/result) or method.
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// First inspect package-level named types.
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// In the presence of path aliases, these give
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// the best paths because non-types may
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// refer to types, but not the reverse.
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empty := make([]byte, 0, 48) // initial space
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2020-08-15 17:13:07 +00:00
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names := scope.Names()
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for _, name := range names {
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2020-04-05 06:20:50 +00:00
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o := scope.Lookup(name)
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tname, ok := o.(*types.TypeName)
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if !ok {
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continue // handle non-types in second pass
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}
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path := append(empty, name...)
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path = append(path, opType)
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T := o.Type()
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if tname.IsAlias() {
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// type alias
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if r := find(obj, T, path); r != nil {
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return Path(r), nil
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}
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} else {
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// defined (named) type
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if r := find(obj, T.Underlying(), append(path, opUnderlying)); r != nil {
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return Path(r), nil
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}
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}
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}
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// Then inspect everything else:
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// non-types, and declared methods of defined types.
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2020-08-15 17:13:07 +00:00
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for _, name := range names {
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2020-04-05 06:20:50 +00:00
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o := scope.Lookup(name)
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path := append(empty, name...)
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if _, ok := o.(*types.TypeName); !ok {
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if o.Exported() {
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// exported non-type (const, var, func)
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if r := find(obj, o.Type(), append(path, opType)); r != nil {
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return Path(r), nil
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}
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}
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continue
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}
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// Inspect declared methods of defined types.
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if T, ok := o.Type().(*types.Named); ok {
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path = append(path, opType)
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for i := 0; i < T.NumMethods(); i++ {
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m := T.Method(i)
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path2 := appendOpArg(path, opMethod, i)
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if m == obj {
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return Path(path2), nil // found declared method
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}
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if r := find(obj, m.Type(), append(path2, opType)); r != nil {
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return Path(r), nil
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}
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}
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}
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}
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return "", fmt.Errorf("can't find path for %v in %s", obj, pkg.Path())
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}
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func appendOpArg(path []byte, op byte, arg int) []byte {
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path = append(path, op)
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path = strconv.AppendInt(path, int64(arg), 10)
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return path
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}
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// find finds obj within type T, returning the path to it, or nil if not found.
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func find(obj types.Object, T types.Type, path []byte) []byte {
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switch T := T.(type) {
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case *types.Basic, *types.Named:
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// Named types belonging to pkg were handled already,
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// so T must belong to another package. No path.
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return nil
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case *types.Pointer:
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return find(obj, T.Elem(), append(path, opElem))
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case *types.Slice:
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return find(obj, T.Elem(), append(path, opElem))
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case *types.Array:
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return find(obj, T.Elem(), append(path, opElem))
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case *types.Chan:
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return find(obj, T.Elem(), append(path, opElem))
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case *types.Map:
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if r := find(obj, T.Key(), append(path, opKey)); r != nil {
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return r
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}
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return find(obj, T.Elem(), append(path, opElem))
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case *types.Signature:
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if r := find(obj, T.Params(), append(path, opParams)); r != nil {
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return r
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}
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return find(obj, T.Results(), append(path, opResults))
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case *types.Struct:
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for i := 0; i < T.NumFields(); i++ {
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f := T.Field(i)
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path2 := appendOpArg(path, opField, i)
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if f == obj {
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return path2 // found field var
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}
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if r := find(obj, f.Type(), append(path2, opType)); r != nil {
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return r
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}
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}
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return nil
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case *types.Tuple:
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for i := 0; i < T.Len(); i++ {
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v := T.At(i)
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path2 := appendOpArg(path, opAt, i)
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if v == obj {
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return path2 // found param/result var
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}
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if r := find(obj, v.Type(), append(path2, opType)); r != nil {
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return r
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}
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}
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return nil
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case *types.Interface:
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for i := 0; i < T.NumMethods(); i++ {
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m := T.Method(i)
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path2 := appendOpArg(path, opMethod, i)
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if m == obj {
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return path2 // found interface method
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}
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if r := find(obj, m.Type(), append(path2, opType)); r != nil {
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return r
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}
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}
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return nil
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}
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panic(T)
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}
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// Object returns the object denoted by path p within the package pkg.
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func Object(pkg *types.Package, p Path) (types.Object, error) {
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if p == "" {
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return nil, fmt.Errorf("empty path")
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}
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pathstr := string(p)
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var pkgobj, suffix string
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if dot := strings.IndexByte(pathstr, opType); dot < 0 {
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pkgobj = pathstr
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} else {
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pkgobj = pathstr[:dot]
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suffix = pathstr[dot:] // suffix starts with "."
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}
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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
|
|
|
|
}
|