blob: 7d7029bce268c7d05db4c54940ff3f058395ecab [file] [log] [blame]
// 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.
// (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) {
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(t.elem, env, path)
case *Struct:
for _, f := range t.fields {
if check.validType0(f.typ, env, path) == invalid {
return invalid
}
}
case *Union:
for _, t := range t.terms {
if check.validType0(t.typ, env, path) == invalid {
return invalid
}
}
case *Interface:
for _, etyp := range t.embeddeds {
if check.validType0(etyp, env, path) == invalid {
return invalid
}
}
case *Named:
// 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
}
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 possibility)
// 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
}
}
panic("cycle start not found")
}
return check.infoMap[t]
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)
}
}
}
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
}
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
}
// 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}
}
// 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.