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// Copyright 2019 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 apidiff
import (
"go/types"
"sort"
)
// Two types are correspond if they are identical except for defined types,
// which must correspond.
//
// Two defined types correspond if they can be interchanged in the old and new APIs,
// possibly after a renaming.
//
// This is not a pure function. If we come across named types while traversing,
// we establish correspondence.
func (d *differ) correspond(old, new types.Type) bool {
return d.corr(old, new, nil)
}
// corr determines whether old and new correspond. The argument p is a list of
// known interface identities, to avoid infinite recursion.
//
// corr calls itself recursively as much as possible, to establish more
// correspondences and so check more of the API. E.g. if the new function has more
// parameters than the old, compare all the old ones before returning false.
//
// Compare this to the implementation of go/types.Identical.
func (d *differ) corr(old, new types.Type, p *ifacePair) bool {
// Structure copied from types.Identical.
old = types.Unalias(old)
new = types.Unalias(new)
switch old := old.(type) {
case *types.Basic:
return types.Identical(old, new)
case *types.Array:
if new, ok := new.(*types.Array); ok {
return d.corr(old.Elem(), new.Elem(), p) && old.Len() == new.Len()
}
case *types.Slice:
if new, ok := new.(*types.Slice); ok {
return d.corr(old.Elem(), new.Elem(), p)
}
case *types.Map:
if new, ok := new.(*types.Map); ok {
return d.corr(old.Key(), new.Key(), p) && d.corr(old.Elem(), new.Elem(), p)
}
case *types.Chan:
if new, ok := new.(*types.Chan); ok {
return d.corr(old.Elem(), new.Elem(), p) && old.Dir() == new.Dir()
}
case *types.Pointer:
if new, ok := new.(*types.Pointer); ok {
return d.corr(old.Elem(), new.Elem(), p)
}
case *types.Signature:
if new, ok := new.(*types.Signature); ok {
pe := d.corr(old.Params(), new.Params(), p)
re := d.corr(old.Results(), new.Results(), p)
return old.Variadic() == new.Variadic() && pe && re
}
case *types.Tuple:
if new, ok := new.(*types.Tuple); ok {
for i := 0; i < old.Len(); i++ {
if i >= new.Len() || !d.corr(old.At(i).Type(), new.At(i).Type(), p) {
return false
}
}
return old.Len() == new.Len()
}
case *types.Struct:
if new, ok := new.(*types.Struct); ok {
for i := 0; i < old.NumFields(); i++ {
if i >= new.NumFields() {
return false
}
of := old.Field(i)
nf := new.Field(i)
if of.Anonymous() != nf.Anonymous() ||
old.Tag(i) != new.Tag(i) ||
!d.corr(of.Type(), nf.Type(), p) ||
!d.corrFieldNames(of, nf) {
return false
}
}
return old.NumFields() == new.NumFields()
}
case *types.Interface:
if new, ok := new.(*types.Interface); ok {
// Deal with circularity. See the comment in types.Identical.
q := &ifacePair{old, new, p}
for p != nil {
if p.identical(q) {
return true // same pair was compared before
}
p = p.prev
}
oldms := d.sortedMethods(old)
newms := d.sortedMethods(new)
for i, om := range oldms {
if i >= len(newms) {
return false
}
nm := newms[i]
if d.methodID(om) != d.methodID(nm) || !d.corr(om.Type(), nm.Type(), q) {
return false
}
}
return old.NumMethods() == new.NumMethods()
}
case *types.Named:
if new, ok := new.(*types.Named); ok {
return d.establishCorrespondence(old, new)
}
if new, ok := new.(*types.Basic); ok {
// Basic types are defined types, too, so we have to support them.
return d.establishCorrespondence(old, new)
}
default:
panic("unknown type kind")
}
return false
}
// Compare old and new field names. We are determining correspondence across packages,
// so just compare names, not packages. For an unexported, embedded field of named
// type (non-named embedded fields are possible with aliases), we check that the type
// names correspond. We check the types for correspondence before this is called, so
// we've established correspondence.
func (d *differ) corrFieldNames(of, nf *types.Var) bool {
if of.Anonymous() && nf.Anonymous() && !of.Exported() && !nf.Exported() {
if on, ok := of.Type().(*types.Named); ok {
nn := nf.Type().(*types.Named)
return d.establishCorrespondence(on, nn)
}
}
return of.Name() == nf.Name()
}
// Establish that old corresponds with new if it does not already
// correspond to something else.
func (d *differ) establishCorrespondence(old *types.Named, new types.Type) bool {
oldname := old.Obj()
oldc := d.correspondMap[oldname]
if oldc == nil {
// For now, assume the types don't correspond unless they are from the old
// and new packages, respectively.
//
// This is too conservative. For instance,
// [old] type A = q.B; [new] type A q.C
// could be OK if in package q, B is an alias for C.
// Or, using p as the name of the current old/new packages:
// [old] type A = q.B; [new] type A int
// could be OK if in q,
// [old] type B int; [new] type B = p.A
// In this case, p.A and q.B name the same type in both old and new worlds.
// Note that this case doesn't imply circular package imports: it's possible
// that in the old world, p imports q, but in the new, q imports p.
//
// However, if we didn't do something here, then we'd incorrectly allow cases
// like the first one above in which q.B is not an alias for q.C
//
// What we should do is check that the old type, in the new world's package
// of the same path, doesn't correspond to something other than the new type.
// That is a bit hard, because there is no easy way to find a new package
// matching an old one.
if newn, ok := new.(*types.Named); ok {
if old.Obj().Pkg() != d.old || newn.Obj().Pkg() != d.new {
return old.Obj().Id() == newn.Obj().Id()
}
}
// If there is no correspondence, create one.
d.correspondMap[oldname] = new
// Check that the corresponding types are compatible.
d.checkCompatibleDefined(oldname, old, new)
return true
}
return types.Identical(oldc, new)
}
func (d *differ) sortedMethods(iface *types.Interface) []*types.Func {
ms := make([]*types.Func, iface.NumMethods())
for i := 0; i < iface.NumMethods(); i++ {
ms[i] = iface.Method(i)
}
sort.Slice(ms, func(i, j int) bool { return d.methodID(ms[i]) < d.methodID(ms[j]) })
return ms
}
func (d *differ) methodID(m *types.Func) string {
// If the method belongs to one of the two packages being compared, use
// just its name even if it's unexported. That lets us treat unexported names
// from the old and new packages as equal.
if m.Pkg() == d.old || m.Pkg() == d.new {
return m.Name()
}
return m.Id()
}
// Copied from the go/types package:
// An ifacePair is a node in a stack of interface type pairs compared for identity.
type ifacePair struct {
x, y *types.Interface
prev *ifacePair
}
func (p *ifacePair) identical(q *ifacePair) bool {
return p.x == q.x && p.y == q.y || p.x == q.y && p.y == q.x
}