+// Code generated by "go test -run=Generate -write=all"; DO NOT EDIT.
+
// Copyright 2022 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 types
// validType verifies that the given type does not "expand" indefinitely
-// producing a cycle in the type graph. Cycles are detected by marking
-// defined types.
+// producing a cycle in the type graph.
// (Cycles involving alias types, as in "type A = [10]A" are detected
// earlier, via the objDecl cycle detection mechanism.)
func (check *Checker) validType(typ *Named) {
- check.validType0(typ, nil)
+ check.validType0(typ, nil, nil)
}
-type typeInfo uint
-
-func (check *Checker) validType0(typ Type, path []Object) typeInfo {
- const (
- unknown typeInfo = iota
- marked
- valid
- invalid
- )
+// validType0 checks if the given type is valid. If typ is a type parameter
+// its value is looked up in the type argument list of the instantiated
+// (enclosing) type, if it exists. Otherwise the type parameter must be from
+// an enclosing function and can be ignored.
+// The nest list describes the stack (the "nest in memory") of types which
+// contain (or embed in the case of interfaces) other types. For instance, a
+// struct named S which contains a field of named type F contains (the memory
+// of) F in S, leading to the nest S->F. If a type appears in its own nest
+// (say S->F->S) we have an invalid recursive type. The path list is the full
+// path of named types in a cycle, it is only needed for error reporting.
+func (check *Checker) validType0(typ Type, nest, path []*Named) bool {
+ switch t := Unalias(typ).(type) {
+ case nil:
+ // We should never see a nil type but be conservative and panic
+ // only in debug mode.
+ if debug {
+ panic("validType0(nil)")
+ }
- switch t := typ.(type) {
case *Array:
- return check.validType0(t.elem, path)
+ return check.validType0(t.elem, nest, path)
case *Struct:
for _, f := range t.fields {
- if check.validType0(f.typ, path) == invalid {
- return invalid
+ if !check.validType0(f.typ, nest, path) {
+ return false
}
}
case *Union:
for _, t := range t.terms {
- if check.validType0(t.typ, path) == invalid {
- return invalid
+ if !check.validType0(t.typ, nest, path) {
+ return false
}
}
case *Interface:
for _, etyp := range t.embeddeds {
- if check.validType0(etyp, path) == invalid {
- return invalid
+ if !check.validType0(etyp, nest, path) {
+ return false
}
}
case *Named:
- // If t is parameterized, we should be considering the instantiated (expanded)
- // form of t, but in general we can't with this algorithm: if t is an invalid
- // type it may be so because it infinitely expands through a type parameter.
- // Instantiating such a type would lead to an infinite sequence of instantiations.
- // In general, we need "type flow analysis" to recognize those cases.
- // Example: type A[T any] struct{ x A[*T] } (issue #48951)
- // In this algorithm we always only consider the original, uninstantiated type.
- // This won't recognize some invalid cases with parameterized types, but it
- // will terminate.
- t = t.orig
-
- // don't report a 2nd error if we already know the type is invalid
+ // Exit early if we already know t is valid.
+ // This is purely an optimization but it prevents excessive computation
+ // times in pathological cases such as testdata/fixedbugs/issue6977.go.
+ // (Note: The valids map could also be allocated locally, once for each
+ // validType call.)
+ if check.valids.lookup(t) != nil {
+ break
+ }
+
+ // Don't report a 2nd error if we already know the type is invalid
// (e.g., if a cycle was detected earlier, via under).
- if t.underlying == Typ[Invalid] {
- check.infoMap[t] = invalid
- return invalid
+ // Note: ensure that t.orig is fully resolved by calling Underlying().
+ if !isValid(t.Underlying()) {
+ return false
}
- switch check.infoMap[t] {
- case unknown:
- check.infoMap[t] = marked
- check.infoMap[t] = check.validType0(t.fromRHS, append(path, t.obj))
- case marked:
- // cycle detected
- for i, tn := range path {
- // Even though validType now can hande cycles through external
- // types, we can't have cycles through external types because
- // no such types are detected yet.
- // TODO(gri) Remove this check once we can detect such cycles,
- // and adjust cycleError accordingly.
- if t.obj.pkg != check.pkg {
- panic("type cycle via package-external type")
- }
- if tn == t.obj {
- check.cycleError(path[i:])
- check.infoMap[t] = invalid
- // don't modify imported types (leads to race condition, see #35049)
- if t.obj.pkg == check.pkg {
- t.underlying = Typ[Invalid]
+ // If the current type t is also found in nest, (the memory of) t is
+ // embedded in itself, indicating an invalid recursive type.
+ for _, e := range nest {
+ if Identical(e, t) {
+ // We have a cycle. If t != t.Origin() then t is an instance of
+ // the generic type t.Origin(). Because t is in the nest, t must
+ // occur within the definition (RHS) of the generic type t.Origin(),
+ // directly or indirectly, after expansion of the RHS.
+ // Therefore t.Origin() must be invalid, no matter how it is
+ // instantiated since the instantiation t of t.Origin() happens
+ // inside t.Origin()'s RHS and thus is always the same and always
+ // present.
+ // Therefore we can mark the underlying of both t and t.Origin()
+ // as invalid. If t is not an instance of a generic type, t and
+ // t.Origin() are the same.
+ // Furthermore, because we check all types in a package for validity
+ // before type checking is complete, any exported type that is invalid
+ // will have an invalid underlying type and we can't reach here with
+ // such a type (invalid types are excluded above).
+ // Thus, if we reach here with a type t, both t and t.Origin() (if
+ // different in the first place) must be from the current package;
+ // they cannot have been imported.
+ // Therefore it is safe to change their underlying types; there is
+ // no chance for a race condition (the types of the current package
+ // are not yet available to other goroutines).
+ assert(t.obj.pkg == check.pkg)
+ assert(t.Origin().obj.pkg == check.pkg)
+ t.underlying = Typ[Invalid]
+ t.Origin().underlying = Typ[Invalid]
+
+ // Find the starting point of the cycle and report it.
+ // Because each type in nest must also appear in path (see invariant below),
+ // type t must be in path since it was found in nest. But not every type in path
+ // is in nest. Specifically t may appear in path with an earlier index than the
+ // index of t in nest. Search again.
+ for start, p := range path {
+ if Identical(p, t) {
+ check.cycleError(makeObjList(path[start:]))
+ return false
}
- return invalid
+ }
+ panic("cycle start not found")
+ }
+ }
+
+ // No cycle was found. Check the RHS of t.
+ // Every type added to nest is also added to path; thus every type that is in nest
+ // must also be in path (invariant). But not every type in path is in nest, since
+ // nest may be pruned (see below, *TypeParam case).
+ if !check.validType0(t.Origin().fromRHS, append(nest, t), append(path, t)) {
+ return false
+ }
+
+ check.valids.add(t) // t is valid
+
+ case *TypeParam:
+ // A type parameter stands for the type (argument) it was instantiated with.
+ // Check the corresponding type argument for validity if we are in an
+ // instantiated type.
+ if len(nest) > 0 {
+ inst := nest[len(nest)-1] // the type instance
+ // Find the corresponding type argument for the type parameter
+ // and proceed with checking that type argument.
+ for i, tparam := range inst.TypeParams().list() {
+ // The type parameter and type argument lists should
+ // match in length but be careful in case of errors.
+ if t == tparam && i < inst.TypeArgs().Len() {
+ targ := inst.TypeArgs().At(i)
+ // The type argument must be valid in the enclosing
+ // type (where inst was instantiated), hence we must
+ // check targ's validity in the type nest excluding
+ // the current (instantiated) type (see the example
+ // at the end of this file).
+ // For error reporting we keep the full path.
+ return check.validType0(targ, nest[:len(nest)-1], path)
}
}
- panic("cycle start not found")
}
- return check.infoMap[t]
}
- return valid
+ return true
}
+
+// makeObjList returns the list of type name objects for the given
+// list of named types.
+func makeObjList(tlist []*Named) []Object {
+ olist := make([]Object, len(tlist))
+ for i, t := range tlist {
+ olist[i] = t.obj
+ }
+ return olist
+}
+
+// Here is an example illustrating why we need to exclude the
+// instantiated type from nest when evaluating the validity of
+// a type parameter. Given the declarations
+//
+// var _ A[A[string]]
+//
+// type A[P any] struct { _ B[P] }
+// type B[P any] struct { _ P }
+//
+// we want to determine if the type A[A[string]] is valid.
+// We start evaluating A[A[string]] outside any type nest:
+//
+// A[A[string]]
+// nest =
+// path =
+//
+// The RHS of A is now evaluated in the A[A[string]] nest:
+//
+// struct{_ B[P₁]}
+// nest = A[A[string]]
+// path = A[A[string]]
+//
+// The struct has a single field of type B[P₁] with which
+// we continue:
+//
+// B[P₁]
+// nest = A[A[string]]
+// path = A[A[string]]
+//
+// struct{_ P₂}
+// nest = A[A[string]]->B[P]
+// path = A[A[string]]->B[P]
+//
+// Eventually we reach the type parameter P of type B (P₂):
+//
+// P₂
+// nest = A[A[string]]->B[P]
+// path = A[A[string]]->B[P]
+//
+// The type argument for P of B is the type parameter P of A (P₁).
+// It must be evaluated in the type nest that existed when B was
+// instantiated:
+//
+// P₁
+// nest = A[A[string]] <== type nest at B's instantiation time
+// path = A[A[string]]->B[P]
+//
+// If we'd use the current nest it would correspond to the path
+// which will be wrong as we will see shortly. P's type argument
+// is A[string], which again must be evaluated in the type nest
+// that existed when A was instantiated with A[string]. That type
+// nest is empty:
+//
+// A[string]
+// nest = <== type nest at A's instantiation time
+// path = A[A[string]]->B[P]
+//
+// Evaluation then proceeds as before for A[string]:
+//
+// struct{_ B[P₁]}
+// nest = A[string]
+// path = A[A[string]]->B[P]->A[string]
+//
+// Now we reach B[P] again. If we had not adjusted nest, it would
+// correspond to path, and we would find B[P] in nest, indicating
+// a cycle, which would clearly be wrong since there's no cycle in
+// A[string]:
+//
+// B[P₁]
+// nest = A[string]
+// path = A[A[string]]->B[P]->A[string] <== path contains B[P]!
+//
+// But because we use the correct type nest, evaluation proceeds without
+// errors and we get the evaluation sequence:
+//
+// struct{_ P₂}
+// nest = A[string]->B[P]
+// path = A[A[string]]->B[P]->A[string]->B[P]
+// P₂
+// nest = A[string]->B[P]
+// path = A[A[string]]->B[P]->A[string]->B[P]
+// P₁
+// nest = A[string]
+// path = A[A[string]]->B[P]->A[string]->B[P]
+// string
+// nest =
+// path = A[A[string]]->B[P]->A[string]->B[P]
+//
+// At this point we're done and A[A[string]] and is valid.