// Code generated by "go test -run=Generate -write=all"; DO NOT EDIT.
// Source: ../../cmd/compile/internal/types2/validtype.go
// 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
import "go/token"
// validType verifies that the given type does not "expand" indefinitely
// 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(nopos, typ, nil, nil)
}
// 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(pos token.Pos, typ Type, nest, path []*Named) bool {
typ = Unalias(typ)
if check.conf._Trace {
if t, _ := typ.(*Named); t != nil && t.obj != nil /* obj should always exist but be conservative */ {
pos = t.obj.pos
}
check.indent++
check.trace(pos, "validType(%s) nest %v, path %v", typ, pathString(makeObjList(nest)), pathString(makeObjList(path)))
defer func() {
check.indent--
}()
}
switch t := 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)")
}
case *Array:
return check.validType0(pos, t.elem, nest, path)
case *Struct:
for _, f := range t.fields {
if !check.validType0(pos, f.typ, nest, path) {
return false
}
}
case *Union:
for _, t := range t.terms {
if !check.validType0(pos, t.typ, nest, path) {
return false
}
}
case *Interface:
for _, etyp := range t.embeddeds {
if !check.validType0(pos, etyp, nest, path) {
return false
}
}
case *Named:
// TODO(gri) The optimization below is incorrect (see go.dev/issue/65711):
// in that issue `type A[P any] [1]P` is a valid type on its own
// and the (uninstantiated) A is recorded in check.valids. As a
// consequence, when checking the remaining declarations, which
// are not valid, the validity check ends prematurely because A
// is considered valid, even though its validity depends on the
// type argument provided to it.
//
// A correct optimization is important for pathological cases.
// Keep code around for reference until we found an optimization.
//
// // 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).
// Note: ensure that t.orig is fully resolved by calling Underlying().
if !isValid(t.Underlying()) {
return false
}
// 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:]), 0)
return false
}
}
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(pos, t.Origin().fromRHS, append(nest, t), append(path, t)) {
return false
}
// see TODO above
// 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 d := len(nest) - 1; d >= 0 {
inst := nest[d] // 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.
res := check.validType0(pos, targ, nest[:d], path)
// The check.validType0 call with nest[:d] may have
// overwritten the entry at the current depth d.
// Restore the entry (was issue go.dev/issue/66323).
nest[d] = inst
return res
}
}
}
}
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.
