package types2
// 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, nil)
}
-type typeInfo uint
-
// validType0 checks if the given type is valid. If typ is a type parameter
-// its value is looked up in the provided environment. The environment is
-// nil if typ is not part of (the RHS of) an instantiated type, in that case
-// any type parameter encountered must be from an enclosing function and can
-// be ignored. The path is the list of type names that lead to the current typ.
-func (check *Checker) validType0(typ Type, env *tparamEnv, path []Object) typeInfo {
- const (
- unknown typeInfo = iota
- marked
- valid
- invalid
- )
-
- switch t := typ.(type) {
+// 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.
}
case *Array:
- return check.validType0(t.elem, env, path)
+ return check.validType0(t.elem, nest, path)
case *Struct:
for _, f := range t.fields {
- if check.validType0(f.typ, env, 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, env, path) == invalid {
- return invalid
+ if !check.validType0(t.typ, nest, path) {
+ return false
}
}
case *Interface:
for _, etyp := range t.embeddeds {
- if check.validType0(etyp, env, path) == invalid {
- return invalid
+ if !check.validType0(etyp, nest, path) {
+ return false
}
}
case *Named:
+ // 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.orig.fromRHS, env.push(t), append(path, t.obj))
- case marked:
- // We have seen type t before and thus must have a cycle.
- check.infoMap[t] = invalid
- // t cannot be in an imported package otherwise that package
- // would have reported a type cycle and couldn't have been
- // imported in the first place.
- assert(t.obj.pkg == check.pkg)
- t.underlying = Typ[Invalid] // t is in the current package (no race possibilty)
- // Find the starting point of the cycle and report it.
- for i, tn := range path {
- if tn == t.obj {
- check.cycleError(path[i:])
- return 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
+ }
}
+ panic("cycle start not found")
}
- panic("cycle start not found")
}
- return check.infoMap[t]
+
+ // 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 have one.
- if env != nil {
- if targ := env.tmap[t]; targ != nil {
- // Type arguments found in targ must be looked
- // up in the enclosing environment env.link.
- return check.validType0(targ, env.link, path)
+ // 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)
+ }
}
}
}
- return valid
-}
-
-// A tparamEnv provides the environment for looking up the type arguments
-// with which type parameters for a given instance were instantiated.
-// If we don't have an instance, the corresponding tparamEnv is nil.
-type tparamEnv struct {
- tmap substMap
- link *tparamEnv
+ return true
}
-func (env *tparamEnv) push(typ *Named) *tparamEnv {
- // If typ is not an instantiated type there are no typ-specific
- // type parameters to look up and we don't need an environment.
- targs := typ.TypeArgs()
- if targs == nil {
- return nil // no instance => nil environment
+// 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
}
-
- // Populate tmap: remember the type argument for each type parameter.
- // We cannot use makeSubstMap because the number of type parameters
- // and arguments may not match due to errors in the source (too many
- // or too few type arguments). Populate tmap "manually".
- tparams := typ.TypeParams()
- n, m := targs.Len(), tparams.Len()
- if n > m {
- n = m // too many targs
- }
- tmap := make(substMap, n)
- for i := 0; i < n; i++ {
- tmap[tparams.At(i)] = targs.At(i)
- }
-
- return &tparamEnv{tmap: tmap, link: env}
+ return olist
}
-// TODO(gri) Alternative implementation:
-// We may not need to build a stack of environments to
-// look up the type arguments for type parameters. The
-// same information should be available via the path:
-// We should be able to just walk the path backwards
-// and find the type arguments in the instance objects.
+// 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.