1 files changed, 364 insertions, 0 deletions
diff --git a/dependencies/pkg/mod/golang.org/x/exp@v0.0.0-20220613132600-b0d781184e0d/apidiff/compatibility.go b/dependencies/pkg/mod/golang.org/x/exp@v0.0.0-20220613132600-b0d781184e0d/apidiff/compatibility.go
new file mode 100644
index 0000000..44238fb
--- /dev/null
+++ b/dependencies/pkg/mod/golang.org/x/exp@v0.0.0-20220613132600-b0d781184e0d/apidiff/compatibility.go
@@ -0,0 +1,364 @@
+package apidiff
+
+import (
+	"fmt"
+	"go/types"
+	"reflect"
+)
+
+func (d *differ) checkCompatible(otn *types.TypeName, old, new types.Type) {
+	switch old := old.(type) {
+	case *types.Interface:
+		if new, ok := new.(*types.Interface); ok {
+			d.checkCompatibleInterface(otn, old, new)
+			return
+		}
+
+	case *types.Struct:
+		if new, ok := new.(*types.Struct); ok {
+			d.checkCompatibleStruct(otn, old, new)
+			return
+		}
+
+	case *types.Chan:
+		if new, ok := new.(*types.Chan); ok {
+			d.checkCompatibleChan(otn, old, new)
+			return
+		}
+
+	case *types.Basic:
+		if new, ok := new.(*types.Basic); ok {
+			d.checkCompatibleBasic(otn, old, new)
+			return
+		}
+
+	case *types.Named:
+		panic("unreachable")
+
+	default:
+		d.checkCorrespondence(otn, "", old, new)
+		return
+
+	}
+	// Here if old and new are different kinds of types.
+	d.typeChanged(otn, "", old, new)
+}
+
+func (d *differ) checkCompatibleChan(otn *types.TypeName, old, new *types.Chan) {
+	d.checkCorrespondence(otn, ", element type", old.Elem(), new.Elem())
+	if old.Dir() != new.Dir() {
+		if new.Dir() == types.SendRecv {
+			d.compatible(otn, "", "removed direction")
+		} else {
+			d.incompatible(otn, "", "changed direction")
+		}
+	}
+}
+
+func (d *differ) checkCompatibleBasic(otn *types.TypeName, old, new *types.Basic) {
+	// Certain changes to numeric types are compatible. Approximately, the info must
+	// be the same, and the new values must be a superset of the old.
+	if old.Kind() == new.Kind() {
+		// old and new are identical
+		return
+	}
+	if compatibleBasics[[2]types.BasicKind{old.Kind(), new.Kind()}] {
+		d.compatible(otn, "", "changed from %s to %s", old, new)
+	} else {
+		d.typeChanged(otn, "", old, new)
+	}
+}
+
+// All pairs (old, new) of compatible basic types.
+var compatibleBasics = map[[2]types.BasicKind]bool{
+	{types.Uint8, types.Uint16}:         true,
+	{types.Uint8, types.Uint32}:         true,
+	{types.Uint8, types.Uint}:           true,
+	{types.Uint8, types.Uint64}:         true,
+	{types.Uint16, types.Uint32}:        true,
+	{types.Uint16, types.Uint}:          true,
+	{types.Uint16, types.Uint64}:        true,
+	{types.Uint32, types.Uint}:          true,
+	{types.Uint32, types.Uint64}:        true,
+	{types.Uint, types.Uint64}:          true,
+	{types.Int8, types.Int16}:           true,
+	{types.Int8, types.Int32}:           true,
+	{types.Int8, types.Int}:             true,
+	{types.Int8, types.Int64}:           true,
+	{types.Int16, types.Int32}:          true,
+	{types.Int16, types.Int}:            true,
+	{types.Int16, types.Int64}:          true,
+	{types.Int32, types.Int}:            true,
+	{types.Int32, types.Int64}:          true,
+	{types.Int, types.Int64}:            true,
+	{types.Float32, types.Float64}:      true,
+	{types.Complex64, types.Complex128}: true,
+}
+
+// Interface compatibility:
+// If the old interface has an unexported method, the new interface is compatible
+// if its exported method set is a superset of the old. (Users could not implement,
+// only embed.)
+//
+// If the old interface did not have an unexported method, the new interface is
+// compatible if its exported method set is the same as the old, and it has no
+// unexported methods. (Adding an unexported method makes the interface
+// unimplementable outside the package.)
+//
+// TODO: must also check that if any methods were added or removed, every exposed
+// type in the package that implemented the interface in old still implements it in
+// new. Otherwise external assignments could fail.
+func (d *differ) checkCompatibleInterface(otn *types.TypeName, old, new *types.Interface) {
+	// Method sets are checked in checkCompatibleDefined.
+
+	// Does the old interface have an unexported method?
+	if unexportedMethod(old) != nil {
+		d.checkMethodSet(otn, old, new, additionsCompatible)
+	} else {
+		// Perform an equivalence check, but with more information.
+		d.checkMethodSet(otn, old, new, additionsIncompatible)
+		if u := unexportedMethod(new); u != nil {
+			d.incompatible(otn, u.Name(), "added unexported method")
+		}
+	}
+}
+
+// Return an unexported method from the method set of t, or nil if there are none.
+func unexportedMethod(t *types.Interface) *types.Func {
+	for i := 0; i < t.NumMethods(); i++ {
+		if m := t.Method(i); !m.Exported() {
+			return m
+		}
+	}
+	return nil
+}
+
+// We need to check three things for structs:
+//
+//  1. The set of exported fields must be compatible. This ensures that keyed struct
+//     literals continue to compile. (There is no compatibility guarantee for unkeyed
+//     struct literals.)
+//
+//  2. The set of exported *selectable* fields must be compatible. This includes the exported
+//     fields of all embedded structs. This ensures that selections continue to compile.
+//
+//  3. If the old struct is comparable, so must the new one be. This ensures that equality
+//     expressions and uses of struct values as map keys continue to compile.
+//
+// An unexported embedded struct can't appear in a struct literal outside the
+// package, so it doesn't have to be present, or have the same name, in the new
+// struct.
+//
+// Field tags are ignored: they have no compile-time implications.
+func (d *differ) checkCompatibleStruct(obj types.Object, old, new *types.Struct) {
+	d.checkCompatibleObjectSets(obj, exportedFields(old), exportedFields(new))
+	d.checkCompatibleObjectSets(obj, exportedSelectableFields(old), exportedSelectableFields(new))
+	// Removing comparability from a struct is an incompatible change.
+	if types.Comparable(old) && !types.Comparable(new) {
+		d.incompatible(obj, "", "old is comparable, new is not")
+	}
+}
+
+// exportedFields collects all the immediate fields of the struct that are exported.
+// This is also the set of exported keys for keyed struct literals.
+func exportedFields(s *types.Struct) map[string]types.Object {
+	m := map[string]types.Object{}
+	for i := 0; i < s.NumFields(); i++ {
+		f := s.Field(i)
+		if f.Exported() {
+			m[f.Name()] = f
+		}
+	}
+	return m
+}
+
+// exportedSelectableFields collects all the exported fields of the struct, including
+// exported fields of embedded structs.
+//
+// We traverse the struct breadth-first, because of the rule that a lower-depth field
+// shadows one at a higher depth.
+func exportedSelectableFields(s *types.Struct) map[string]types.Object {
+	var (
+		m    = map[string]types.Object{}
+		next []*types.Struct // embedded structs at the next depth
+		seen []*types.Struct // to handle recursive embedding
+	)
+	for cur := []*types.Struct{s}; len(cur) > 0; cur, next = next, nil {
+		seen = append(seen, cur...)
+		// We only want to consider unambiguous fields. Ambiguous fields (where there
+		// is more than one field of the same name at the same level) are legal, but
+		// cannot be selected.
+		for name, f := range unambiguousFields(cur) {
+			// Record an exported field we haven't seen before. If we have seen it,
+			// it occurred a lower depth, so it shadows this field.
+			if f.Exported() && m[name] == nil {
+				m[name] = f
+			}
+			// Remember embedded structs for processing at the next depth,
+			// but only if we haven't seen the struct at this depth or above.
+			if !f.Anonymous() {
+				continue
+			}
+			t := f.Type().Underlying()
+			if p, ok := t.(*types.Pointer); ok {
+				t = p.Elem().Underlying()
+			}
+			if t, ok := t.(*types.Struct); ok && !contains(seen, t) {
+				next = append(next, t)
+			}
+		}
+	}
+	return m
+}
+
+func contains(ts []*types.Struct, t *types.Struct) bool {
+	for _, s := range ts {
+		if types.Identical(s, t) {
+			return true
+		}
+	}
+	return false
+}
+
+// Given a set of structs at the same depth, the unambiguous fields are the ones whose
+// names appear exactly once.
+func unambiguousFields(structs []*types.Struct) map[string]*types.Var {
+	fields := map[string]*types.Var{}
+	seen := map[string]bool{}
+	for _, s := range structs {
+		for i := 0; i < s.NumFields(); i++ {
+			f := s.Field(i)
+			name := f.Name()
+			if seen[name] {
+				delete(fields, name)
+			} else {
+				seen[name] = true
+				fields[name] = f
+			}
+		}
+	}
+	return fields
+}
+
+// Anything removed or change from the old set is an incompatible change.
+// Anything added to the new set is a compatible change.
+func (d *differ) checkCompatibleObjectSets(obj types.Object, old, new map[string]types.Object) {
+	for name, oldo := range old {
+		newo := new[name]
+		if newo == nil {
+			d.incompatible(obj, name, "removed")
+		} else {
+			d.checkCorrespondence(obj, name, oldo.Type(), newo.Type())
+		}
+	}
+	for name := range new {
+		if old[name] == nil {
+			d.compatible(obj, name, "added")
+		}
+	}
+}
+
+func (d *differ) checkCompatibleDefined(otn *types.TypeName, old *types.Named, new types.Type) {
+	// We've already checked that old and new correspond.
+	d.checkCompatible(otn, old.Underlying(), new.Underlying())
+	// If there are different kinds of types (e.g. struct and interface), don't bother checking
+	// the method sets.
+	if reflect.TypeOf(old.Underlying()) != reflect.TypeOf(new.Underlying()) {
+		return
+	}
+	// Interface method sets are checked in checkCompatibleInterface.
+	if _, ok := old.Underlying().(*types.Interface); ok {
+		return
+	}
+
+	// A new method set is compatible with an old if the new exported methods are a superset of the old.
+	d.checkMethodSet(otn, old, new, additionsCompatible)
+	d.checkMethodSet(otn, types.NewPointer(old), types.NewPointer(new), additionsCompatible)
+}
+
+const (
+	additionsCompatible   = true
+	additionsIncompatible = false
+)
+
+func (d *differ) checkMethodSet(otn *types.TypeName, oldt, newt types.Type, addcompat bool) {
+	// TODO: find a way to use checkCompatibleObjectSets for this.
+	oldMethodSet := exportedMethods(oldt)
+	newMethodSet := exportedMethods(newt)
+	msname := otn.Name()
+	if _, ok := oldt.(*types.Pointer); ok {
+		msname = "*" + msname
+	}
+	for name, oldMethod := range oldMethodSet {
+		newMethod := newMethodSet[name]
+		if newMethod == nil {
+			var part string
+			// Due to embedding, it's possible that the method's receiver type is not
+			// the same as the defined type whose method set we're looking at. So for
+			// a type T with removed method M that is embedded in some other type U,
+			// we will generate two "removed" messages for T.M, one for its own type
+			// T and one for the embedded type U. We want both messages to appear,
+			// but the messageSet dedup logic will allow only one message for a given
+			// object. So use the part string to distinguish them.
+			if receiverNamedType(oldMethod).Obj() != otn {
+				part = fmt.Sprintf(", method set of %s", msname)
+			}
+			d.incompatible(oldMethod, part, "removed")
+		} else {
+			obj := oldMethod
+			// If a value method is changed to a pointer method and has a signature
+			// change, then we can get two messages for the same method definition: one
+			// for the value method set that says it's removed, and another for the
+			// pointer method set that says it changed. To keep both messages (since
+			// messageSet dedups), use newMethod for the second. (Slight hack.)
+			if !hasPointerReceiver(oldMethod) && hasPointerReceiver(newMethod) {
+				obj = newMethod
+			}
+			d.checkCorrespondence(obj, "", oldMethod.Type(), newMethod.Type())
+		}
+	}
+
+	// Check for added methods.
+	for name, newMethod := range newMethodSet {
+		if oldMethodSet[name] == nil {
+			if addcompat {
+				d.compatible(newMethod, "", "added")
+			} else {
+				d.incompatible(newMethod, "", "added")
+			}
+		}
+	}
+}
+
+// exportedMethods collects all the exported methods of type's method set.
+func exportedMethods(t types.Type) map[string]types.Object {
+	m := map[string]types.Object{}
+	ms := types.NewMethodSet(t)
+	for i := 0; i < ms.Len(); i++ {
+		obj := ms.At(i).Obj()
+		if obj.Exported() {
+			m[obj.Name()] = obj
+		}
+	}
+	return m
+}
+
+func receiverType(method types.Object) types.Type {
+	return method.Type().(*types.Signature).Recv().Type()
+}
+
+func receiverNamedType(method types.Object) *types.Named {
+	switch t := receiverType(method).(type) {
+	case *types.Pointer:
+		return t.Elem().(*types.Named)
+	case *types.Named:
+		return t
+	default:
+		panic("unreachable")
+	}
+}
+
+func hasPointerReceiver(method types.Object) bool {
+	_, ok := receiverType(method).(*types.Pointer)
+	return ok
+}