Esempio n. 1
0
// lookupMethod returns the method set for type typ, which may be one
// of the interpreter's fake types.
func lookupMethod(i *interpreter, typ types.Type, meth *types.Func) *ssa.Function {
	switch typ {
	case rtypeType:
		return i.rtypeMethods[meth.Id()]
	case errorType:
		return i.errorMethods[meth.Id()]
	}
	return i.prog.LookupMethod(typ, meth.Pkg(), meth.Name())
}
Esempio n. 2
0
// checkMethod performs safety checks for renaming a method.
// There are three hazards:
// - declaration conflicts
// - selection ambiguity/changes
// - entailed renamings of assignable concrete/interface types.
//   We reject renamings initiated at concrete methods if it would
//   change the assignability relation.  For renamings of abstract
//   methods, we rename all methods transitively coupled to it via
//   assignability.
func (r *Unexporter) checkMethod(objsToUpdate map[types.Object]string, from *types.Func, to string) {
	// e.g. error.Error
	if from.Pkg() == nil {
		r.warn(from, r.errorf(from.Pos(), "you cannot rename built-in method %s", from))
		return
	}

	// ASSIGNABILITY: We reject renamings of concrete methods that
	// would break a 'satisfy' constraint; but renamings of abstract
	// methods are allowed to proceed, and we rename affected
	// concrete and abstract methods as necessary.  It is the
	// initial method that determines the policy.

	// Check for conflict at point of declaration.
	// Check to ensure preservation of assignability requirements.
	R := recv(from).Type()
	if isInterface(R) {
		// Abstract method

		// declaration
		prev, _, _ := types.LookupFieldOrMethod(R, false, from.Pkg(), to)
		if prev != nil {
			r.warn(from,
				r.errorf(from.Pos(), "renaming this interface method %q to %q",
					from.Name(), to),
				r.errorf(prev.Pos(), "\twould conflict with this method"))
			return
		}

		// Check all interfaces that embed this one for
		// declaration conflicts too.
		for _, info := range r.packages {
			// Start with named interface types (better errors)
			for _, obj := range info.Defs {
				if obj, ok := obj.(*types.TypeName); ok && isInterface(obj.Type()) {
					f, _, _ := types.LookupFieldOrMethod(
						obj.Type(), false, from.Pkg(), from.Name())
					if f == nil {
						continue
					}
					t, _, _ := types.LookupFieldOrMethod(
						obj.Type(), false, from.Pkg(), to)
					if t == nil {
						continue
					}
					r.warn(from,
						r.errorf(from.Pos(), "renaming this interface method %q to %q",
							from.Name(), to),
						r.errorf(t.Pos(), "\twould conflict with this method"),
						r.errorf(obj.Pos(), "\tin named interface type %q", obj.Name()))
				}
			}

			// Now look at all literal interface types (includes named ones again).
			for e, tv := range info.Types {
				if e, ok := e.(*ast.InterfaceType); ok {
					_ = e
					_ = tv.Type.(*types.Interface)
					// TODO(adonovan): implement same check as above.
				}
			}
		}

		// assignability
		//
		// Find the set of concrete or abstract methods directly
		// coupled to abstract method 'from' by some
		// satisfy.Constraint, and rename them too.
		for key := range r.satisfy() {
			// key = (lhs, rhs) where lhs is always an interface.

			lsel := r.msets.MethodSet(key.LHS).Lookup(from.Pkg(), from.Name())
			if lsel == nil {
				continue
			}
			rmethods := r.msets.MethodSet(key.RHS)
			rsel := rmethods.Lookup(from.Pkg(), from.Name())
			if rsel == nil {
				continue
			}

			// If both sides have a method of this name,
			// and one of them is m, the other must be coupled.
			var coupled *types.Func
			switch from {
			case lsel.Obj():
				coupled = rsel.Obj().(*types.Func)
			case rsel.Obj():
				coupled = lsel.Obj().(*types.Func)
			default:
				continue
			}

			// We must treat concrete-to-interface
			// constraints like an implicit selection C.f of
			// each interface method I.f, and check that the
			// renaming leaves the selection unchanged and
			// unambiguous.
			//
			// Fun fact: the implicit selection of C.f
			// 	type I interface{f()}
			// 	type C struct{I}
			// 	func (C) g()
			//      var _ I = C{} // here
			// yields abstract method I.f.  This can make error
			// messages less than obvious.
			//
			if !isInterface(key.RHS) {
				// The logic below was derived from checkSelections.

				rtosel := rmethods.Lookup(from.Pkg(), to)
				if rtosel != nil {
					rto := rtosel.Obj().(*types.Func)
					delta := len(rsel.Index()) - len(rtosel.Index())
					if delta < 0 {
						continue // no ambiguity
					}

					// TODO(adonovan): record the constraint's position.
					keyPos := token.NoPos

					rename := r.errorf(from.Pos(), "renaming this method %q to %q",
						from.Name(), to)
					if delta == 0 {
						// analogous to same-block conflict
						r.warn(from, rename,
							r.errorf(keyPos, "\twould make the %s method of %s invoked via interface %s ambiguous",
								to, key.RHS, key.LHS),
							r.errorf(rto.Pos(), "\twith (%s).%s",
								recv(rto).Type(), to))
					} else {
						// analogous to super-block conflict
						r.warn(from, rename,
							r.errorf(keyPos, "\twould change the %s method of %s invoked via interface %s",
								to, key.RHS, key.LHS),
							r.errorf(coupled.Pos(), "\tfrom (%s).%s",
								recv(coupled).Type(), to),
							r.errorf(rto.Pos(), "\tto (%s).%s",
								recv(rto).Type(), to))
					}
					return // one error is enough
				}
			}

			if !r.changeMethods {
				// This should be unreachable.
				r.warn(from,
					r.errorf(from.Pos(), "internal error: during renaming of abstract method %s", from),
					r.errorf(coupled.Pos(), "\tchangedMethods=false, coupled method=%s", coupled),
					r.errorf(from.Pos(), "\tPlease file a bug report"))
				return
			}

			// Rename the coupled method to preserve assignability.
			r.check(objsToUpdate, coupled, to)
		}
	} else {
		// Concrete method

		// declaration
		prev, indices, _ := types.LookupFieldOrMethod(R, true, from.Pkg(), to)
		if prev != nil && len(indices) == 1 {
			r.warn(from,
				r.errorf(from.Pos(), "renaming this method %q to %q",
					from.Name(), to),
				r.errorf(prev.Pos(), "\twould conflict with this %s",
					objectKind(prev)))
			return
		}

		// assignability
		//
		// Find the set of abstract methods coupled to concrete
		// method 'from' by some satisfy.Constraint, and rename
		// them too.
		//
		// Coupling may be indirect, e.g. I.f <-> C.f via type D.
		//
		// 	type I interface {f()}
		//	type C int
		//	type (C) f()
		//	type D struct{C}
		//	var _ I = D{}
		//
		for key := range r.satisfy() {
			// key = (lhs, rhs) where lhs is always an interface.
			if isInterface(key.RHS) {
				continue
			}
			rsel := r.msets.MethodSet(key.RHS).Lookup(from.Pkg(), from.Name())
			if rsel == nil || rsel.Obj() != from {
				continue // rhs does not have the method
			}
			lsel := r.msets.MethodSet(key.LHS).Lookup(from.Pkg(), from.Name())
			if lsel == nil {
				continue
			}
			imeth := lsel.Obj().(*types.Func)

			// imeth is the abstract method (e.g. I.f)
			// and key.RHS is the concrete coupling type (e.g. D).
			if !r.changeMethods {
				rename := r.errorf(from.Pos(), "renaming this method %q to %q",
					from.Name(), to)
				var pos token.Pos
				var iface string

				i := recv(imeth).Type()
				if named, ok := i.(*types.Named); ok {
					pos = named.Obj().Pos()
					iface = "interface " + named.Obj().Name()
				} else {
					pos = from.Pos()
					iface = i.String()
				}
				r.warn(from, rename,
					r.errorf(pos, "\twould make %s no longer assignable to %s",
						key.RHS, iface),
					r.errorf(imeth.Pos(), "\t(rename %s.%s if you intend to change both types)",
						i, from.Name()))
				return // one error is enough
			}

			// Rename the coupled interface method to preserve assignability.
			r.check(objsToUpdate, imeth, to)
		}
	}

	// Check integrity of existing (field and method) selections.
	// We skip this if there were errors above, to avoid redundant errors.
	r.checkSelections(objsToUpdate, from, to)
}
Esempio n. 3
0
func (e *Export) checkMethod(from *types.Func, to string) {
	// e.g. error.Error
	if from.Pkg() == nil {
		e.Conflicting = true
		return
	}

	// ASSIGNABILITY: We reject renamings of concrete methods that
	// would break a 'satisfy' constraint; but renamings of abstract
	// methods are allowed to proceed, and we rename affected
	// concrete and abstract methods as necessary.  It is the
	// initial method that determines the policy.

	// Check for conflict at point of declaration.
	// Check to ensure preservation of assignability requirements.
	R := recv(from).Type()
	if isInterface(R) {
		// Abstract method

		// declaration
		prev, _, _ := types.LookupFieldOrMethod(R, false, from.Pkg(), to)
		if prev != nil {
			e.Conflicting = true
			return
		}

		// Check all interfaces that embed this one for
		// declaration conflicts too.
		for _, info := range e.u.prog.AllPackages {
			// Start with named interface types (better errors)
			for _, obj := range info.Defs {
				if obj, ok := obj.(*types.TypeName); ok && isInterface(obj.Type()) {
					f, _, _ := types.LookupFieldOrMethod(
						obj.Type(), false, from.Pkg(), from.Name())
					if f == nil {
						continue
					}
					t, _, _ := types.LookupFieldOrMethod(obj.Type(), false, from.Pkg(), to)
					if t == nil {
						continue
					}
					e.Conflicting = true
					return
				}
			}
		}

		// assignability
		//
		// Find the set of concrete or abstract methods directly
		// coupled to abstract method 'from' by some
		// satisfy.Constraint, and rename them too.
		for key := range e.u.satisfy() {
			// key = (lhs, rhs) where lhs is always an interface.

			lsel := e.u.msets.MethodSet(key.LHS).Lookup(from.Pkg(), from.Name())
			if lsel == nil {
				continue
			}
			rmethods := e.u.msets.MethodSet(key.RHS)
			rsel := rmethods.Lookup(from.Pkg(), from.Name())
			if rsel == nil {
				continue
			}

			// If both sides have a method of this name,
			// and one of them is m, the other must be coupled.
			var coupled *types.Func
			switch from {
			case lsel.Obj():
				coupled = rsel.Obj().(*types.Func)
			case rsel.Obj():
				coupled = lsel.Obj().(*types.Func)
			default:
				continue
			}

			// We must treat concrete-to-interface
			// constraints like an implicit selection C.f of
			// each interface method I.f, and check that the
			// renaming leaves the selection unchanged and
			// unambiguous.
			//
			// Fun fact: the implicit selection of C.f
			// 	type I interface{f()}
			// 	type C struct{I}
			// 	func (C) g()
			//      var _ I = C{} // here
			// yields abstract method I.f.  This can make error
			// messages less than obvious.
			//
			if !isInterface(key.RHS) {
				// The logic below was derived from checkSelections.

				rtosel := rmethods.Lookup(from.Pkg(), to)
				if rtosel != nil {
					delta := len(rsel.Index()) - len(rtosel.Index())
					if delta < 0 {
						continue // no ambiguity
					}
					e.Conflicting = true
					return
				}
			}

			// Rename the coupled method to preserve assignability.
			e.check(coupled, to)
		}
	}

	// Concrete method

	// declaration
	prev, indices, _ := types.LookupFieldOrMethod(R, true, from.Pkg(), to)
	if prev != nil && len(indices) == 1 {
		e.Conflicting = true
		return
	}

	// assignability
	//
	// Find the set of abstract methods coupled to concrete
	// method 'from' by some satisfy.Constraint, and rename
	// them too.
	//
	// Coupling may be indirect, e.g. I.f <-> C.f via type D.
	//
	// 	type I interface {f()}
	//	type C int
	//	type (C) f()
	//	type D struct{C}
	//	var _ I = D{}
	//
	for key := range e.u.satisfy() {
		// key = (lhs, rhs) where lhs is always an interface.
		if isInterface(key.RHS) {
			continue
		}
		rsel := e.u.msets.MethodSet(key.RHS).Lookup(from.Pkg(), from.Name())
		if rsel == nil || rsel.Obj() != from {
			continue // rhs does not have the method
		}
		lsel := e.u.msets.MethodSet(key.LHS).Lookup(from.Pkg(), from.Name())
		if lsel == nil {
			continue
		}
		imeth := lsel.Obj().(*types.Func)
		e.check(imeth, to)
	}

	// Check integrity of existing (field and method) selections.
	// We skip this if there were errors above, to avoid redundant errors.
	e.checkSelections(from, to)
}
Esempio n. 4
0
// Implements displays the "implements" relation as it pertains to the
// selected type.  If the selection is a method, 'implements' displays
// the corresponding methods of the types that would have been reported
// by an implements query on the receiver type.
//
func implements(o *Oracle, qpos *QueryPos) (queryResult, error) {
	// Find the selected type.
	path, action := findInterestingNode(qpos.info, qpos.path)

	var method *types.Func
	var T types.Type // selected type (receiver if method != nil)

	switch action {
	case actionExpr:
		// method?
		if id, ok := path[0].(*ast.Ident); ok {
			if obj, ok := qpos.info.ObjectOf(id).(*types.Func); ok {
				recv := obj.Type().(*types.Signature).Recv()
				if recv == nil {
					return nil, fmt.Errorf("this function is not a method")
				}
				method = obj
				T = recv.Type()
			}
		}
	case actionType:
		T = qpos.info.TypeOf(path[0].(ast.Expr))
	}
	if T == nil {
		return nil, fmt.Errorf("no type or method here")
	}

	// Find all named types, even local types (which can have
	// methods via promotion) and the built-in "error".
	//
	// TODO(adonovan): include all packages in PTA scope too?
	// i.e. don't reduceScope?
	//
	var allNamed []types.Type
	for _, info := range o.typeInfo {
		for _, obj := range info.Defs {
			if obj, ok := obj.(*types.TypeName); ok {
				allNamed = append(allNamed, obj.Type())
			}
		}
	}
	allNamed = append(allNamed, types.Universe.Lookup("error").Type())

	var msets types.MethodSetCache

	// Test each named type.
	var to, from, fromPtr []types.Type
	for _, U := range allNamed {
		if isInterface(T) {
			if msets.MethodSet(T).Len() == 0 {
				continue // empty interface
			}
			if isInterface(U) {
				if msets.MethodSet(U).Len() == 0 {
					continue // empty interface
				}

				// T interface, U interface
				if !types.Identical(T, U) {
					if types.AssignableTo(U, T) {
						to = append(to, U)
					}
					if types.AssignableTo(T, U) {
						from = append(from, U)
					}
				}
			} else {
				// T interface, U concrete
				if types.AssignableTo(U, T) {
					to = append(to, U)
				} else if pU := types.NewPointer(U); types.AssignableTo(pU, T) {
					to = append(to, pU)
				}
			}
		} else if isInterface(U) {
			if msets.MethodSet(U).Len() == 0 {
				continue // empty interface
			}

			// T concrete, U interface
			if types.AssignableTo(T, U) {
				from = append(from, U)
			} else if pT := types.NewPointer(T); types.AssignableTo(pT, U) {
				fromPtr = append(fromPtr, U)
			}
		}
	}

	var pos interface{} = qpos
	if nt, ok := deref(T).(*types.Named); ok {
		pos = nt.Obj()
	}

	// Sort types (arbitrarily) to ensure test determinism.
	sort.Sort(typesByString(to))
	sort.Sort(typesByString(from))
	sort.Sort(typesByString(fromPtr))

	var toMethod, fromMethod, fromPtrMethod []*types.Selection // contain nils
	if method != nil {
		for _, t := range to {
			toMethod = append(toMethod,
				types.NewMethodSet(t).Lookup(method.Pkg(), method.Name()))
		}
		for _, t := range from {
			fromMethod = append(fromMethod,
				types.NewMethodSet(t).Lookup(method.Pkg(), method.Name()))
		}
		for _, t := range fromPtr {
			fromPtrMethod = append(fromPtrMethod,
				types.NewMethodSet(t).Lookup(method.Pkg(), method.Name()))
		}
	}

	return &implementsResult{qpos, T, pos, to, from, fromPtr, method, toMethod, fromMethod, fromPtrMethod}, nil
}
Esempio n. 5
0
// Implements displays the "implements" relation as it pertains to the
// selected type.
// If the selection is a method, 'implements' displays
// the corresponding methods of the types that would have been reported
// by an implements query on the receiver type.
//
func implements(q *Query) error {
	lconf := loader.Config{Build: q.Build}
	allowErrors(&lconf)

	qpkg, err := importQueryPackage(q.Pos, &lconf)
	if err != nil {
		return err
	}

	// Set the packages to search.
	if len(q.Scope) > 0 {
		// Inspect all packages in the analysis scope, if specified.
		if err := setPTAScope(&lconf, q.Scope); err != nil {
			return err
		}
	} else {
		// Otherwise inspect the forward and reverse
		// transitive closure of the selected package.
		// (In theory even this is incomplete.)
		_, rev, _ := importgraph.Build(q.Build)
		for path := range rev.Search(qpkg) {
			lconf.ImportWithTests(path)
		}

		// TODO(adonovan): for completeness, we should also
		// type-check and inspect function bodies in all
		// imported packages.  This would be expensive, but we
		// could optimize by skipping functions that do not
		// contain type declarations.  This would require
		// changing the loader's TypeCheckFuncBodies hook to
		// provide the []*ast.File.
	}

	// Load/parse/type-check the program.
	lprog, err := lconf.Load()
	if err != nil {
		return err
	}
	q.Fset = lprog.Fset

	qpos, err := parseQueryPos(lprog, q.Pos, false)
	if err != nil {
		return err
	}

	// Find the selected type.
	path, action := findInterestingNode(qpos.info, qpos.path)

	var method *types.Func
	var T types.Type // selected type (receiver if method != nil)

	switch action {
	case actionExpr:
		// method?
		if id, ok := path[0].(*ast.Ident); ok {
			if obj, ok := qpos.info.ObjectOf(id).(*types.Func); ok {
				recv := obj.Type().(*types.Signature).Recv()
				if recv == nil {
					return fmt.Errorf("this function is not a method")
				}
				method = obj
				T = recv.Type()
			}
		}
	case actionType:
		T = qpos.info.TypeOf(path[0].(ast.Expr))
	}
	if T == nil {
		return fmt.Errorf("no type or method here")
	}

	// Find all named types, even local types (which can have
	// methods via promotion) and the built-in "error".
	var allNamed []types.Type
	for _, info := range lprog.AllPackages {
		for _, obj := range info.Defs {
			if obj, ok := obj.(*types.TypeName); ok {
				allNamed = append(allNamed, obj.Type())
			}
		}
	}
	allNamed = append(allNamed, types.Universe.Lookup("error").Type())

	var msets typeutil.MethodSetCache

	// Test each named type.
	var to, from, fromPtr []types.Type
	for _, U := range allNamed {
		if isInterface(T) {
			if msets.MethodSet(T).Len() == 0 {
				continue // empty interface
			}
			if isInterface(U) {
				if msets.MethodSet(U).Len() == 0 {
					continue // empty interface
				}

				// T interface, U interface
				if !types.Identical(T, U) {
					if types.AssignableTo(U, T) {
						to = append(to, U)
					}
					if types.AssignableTo(T, U) {
						from = append(from, U)
					}
				}
			} else {
				// T interface, U concrete
				if types.AssignableTo(U, T) {
					to = append(to, U)
				} else if pU := types.NewPointer(U); types.AssignableTo(pU, T) {
					to = append(to, pU)
				}
			}
		} else if isInterface(U) {
			if msets.MethodSet(U).Len() == 0 {
				continue // empty interface
			}

			// T concrete, U interface
			if types.AssignableTo(T, U) {
				from = append(from, U)
			} else if pT := types.NewPointer(T); types.AssignableTo(pT, U) {
				fromPtr = append(fromPtr, U)
			}
		}
	}

	var pos interface{} = qpos
	if nt, ok := deref(T).(*types.Named); ok {
		pos = nt.Obj()
	}

	// Sort types (arbitrarily) to ensure test determinism.
	sort.Sort(typesByString(to))
	sort.Sort(typesByString(from))
	sort.Sort(typesByString(fromPtr))

	var toMethod, fromMethod, fromPtrMethod []*types.Selection // contain nils
	if method != nil {
		for _, t := range to {
			toMethod = append(toMethod,
				types.NewMethodSet(t).Lookup(method.Pkg(), method.Name()))
		}
		for _, t := range from {
			fromMethod = append(fromMethod,
				types.NewMethodSet(t).Lookup(method.Pkg(), method.Name()))
		}
		for _, t := range fromPtr {
			fromPtrMethod = append(fromPtrMethod,
				types.NewMethodSet(t).Lookup(method.Pkg(), method.Name()))
		}
	}

	q.result = &implementsResult{
		qpos, T, pos, to, from, fromPtr, method, toMethod, fromMethod, fromPtrMethod,
	}
	return nil
}
Esempio n. 6
0
// checkMethod performs safety checks for renaming a method.
// There are three hazards:
// - declaration conflicts
// - selection ambiguity/changes
// - entailed renamings of assignable concrete/interface types (for now, just reject)
func (r *renamer) checkMethod(from *types.Func) {
	// e.g. error.Error
	if from.Pkg() == nil {
		r.errorf(from.Pos(), "you cannot rename built-in method %s", from)
		return
	}

	// As always, having to support concrete methods with pointer
	// and non-pointer receivers, and named vs unnamed types with
	// methods, makes tooling fun.

	// ASSIGNABILITY
	//
	// For now, if any method renaming breaks a required
	// assignability to another type, we reject it.
	//
	// TODO(adonovan): probably we should compute the entailed
	// renamings so that an interface method renaming causes
	// concrete methods to change too.  But which ones?
	//
	// There is no correct answer, only heuristics, because Go's
	// "duck typing" doesn't distinguish intentional from contingent
	// assignability.  There are two obvious approaches:
	//
	// (1) Update the minimum set of types to preserve the
	//     assignability of types all syntactic assignments
	//     (incl. implicit ones in calls, returns, sends, etc).
	//     The satisfy.Finder enumerates these.
	//     This is likely to be an underapproximation.
	//
	// (2) Update all types that are assignable to/from the changed
	//     type.  This requires computing the "implements" relation
	//     for all pairs of types (as godoc and oracle do).
	//     This is likely to be an overapproximation.
	//
	// If a concrete type is renamed, we probably do not want to
	// rename corresponding interfaces; interface renamings should
	// probably be initiated at the interface.  (But what if a
	// concrete type implements multiple interfaces with the same
	// method?  Then the user is stuck.)
	//
	// We need some experience before we decide how to implement this.

	// Check for conflict at point of declaration.
	// Check to ensure preservation of assignability requirements.
	recv := from.Type().(*types.Signature).Recv().Type()
	if isInterface(recv) {
		// Abstract method

		// declaration
		prev, _, _ := types.LookupFieldOrMethod(recv, false, from.Pkg(), r.to)
		if prev != nil {
			r.errorf(from.Pos(), "renaming this interface method %q to %q",
				from.Name(), r.to)
			r.errorf(prev.Pos(), "\twould conflict with this method")
			return
		}

		// Check all interfaces that embed this one for
		// declaration conflicts too.
		for _, info := range r.packages {
			// Start with named interface types (better errors)
			for _, obj := range info.Defs {
				if obj, ok := obj.(*types.TypeName); ok && isInterface(obj.Type()) {
					f, _, _ := types.LookupFieldOrMethod(
						obj.Type(), false, from.Pkg(), from.Name())
					if f == nil {
						continue
					}
					t, _, _ := types.LookupFieldOrMethod(
						obj.Type(), false, from.Pkg(), r.to)
					if t == nil {
						continue
					}
					r.errorf(from.Pos(), "renaming this interface method %q to %q",
						from.Name(), r.to)
					r.errorf(t.Pos(), "\twould conflict with this method")
					r.errorf(obj.Pos(), "\tin named interface type %q", obj.Name())
				}
			}

			// Now look at all literal interface types (includes named ones again).
			for e, tv := range info.Types {
				if e, ok := e.(*ast.InterfaceType); ok {
					_ = e
					_ = tv.Type.(*types.Interface)
					// TODO(adonovan): implement same check as above.
				}
			}
		}

		// assignability
		for T := range r.findAssignments(recv) {
			if obj, _, _ := types.LookupFieldOrMethod(T, false, from.Pkg(), from.Name()); obj == nil {
				continue
			}

			r.errorf(from.Pos(), "renaming this method %q to %q",
				from.Name(), r.to)
			var pos token.Pos
			var other string
			if named, ok := T.(*types.Named); ok {
				pos = named.Obj().Pos()
				other = named.Obj().Name()
			} else {
				pos = from.Pos()
				other = T.String()
			}
			r.errorf(pos, "\twould make %s no longer assignable to it", other)
			return
		}
	} else {
		// Concrete method

		// declaration
		prev, indices, _ := types.LookupFieldOrMethod(recv, true, from.Pkg(), r.to)
		if prev != nil && len(indices) == 1 {
			r.errorf(from.Pos(), "renaming this method %q to %q",
				from.Name(), r.to)
			r.errorf(prev.Pos(), "\twould conflict with this %s",
				objectKind(prev))
			return
		}

		// assignability (of both T and *T)
		recvBase := deref(recv)
		for _, R := range []types.Type{recvBase, types.NewPointer(recvBase)} {
			for I := range r.findAssignments(R) {
				if obj, _, _ := types.LookupFieldOrMethod(I, true, from.Pkg(), from.Name()); obj == nil {
					continue
				}
				r.errorf(from.Pos(), "renaming this method %q to %q",
					from.Name(), r.to)
				var pos token.Pos
				var iface string
				if named, ok := I.(*types.Named); ok {
					pos = named.Obj().Pos()
					iface = "interface " + named.Obj().Name()
				} else {
					pos = from.Pos()
					iface = I.String()
				}
				r.errorf(pos, "\twould make it no longer assignable to %s", iface)
				return // one is enough
			}
		}
	}

	// Check integrity of existing (field and method) selections.
	// We skip this if there were errors above, to avoid redundant errors.
	r.checkSelections(from)
}