1 // Code generated by "go test -run=Generate -write=all"; DO NOT EDIT.
2 // Source: ../../cmd/compile/internal/types2/validtype.go
3 4 // Copyright 2022 The Go Authors. All rights reserved.
5 // Use of this source code is governed by a BSD-style
6 // license that can be found in the LICENSE file.
7 8 package types
9 10 import "go/token"
11 12 // validType verifies that the given type does not "expand" indefinitely
13 // producing a cycle in the type graph.
14 // (Cycles involving alias types, as in "type A = [10]A" are detected
15 // earlier, via the objDecl cycle detection mechanism.)
16 func (check *Checker) validType(typ *Named) {
17 check.validType0(nopos, typ, nil, nil)
18 }
19 20 // validType0 checks if the given type is valid. If typ is a type parameter
21 // its value is looked up in the type argument list of the instantiated
22 // (enclosing) type, if it exists. Otherwise the type parameter must be from
23 // an enclosing function and can be ignored.
24 // The nest list describes the stack (the "nest in memory") of types which
25 // contain (or embed in the case of interfaces) other types. For instance, a
26 // struct named S which contains a field of named type F contains (the memory
27 // of) F in S, leading to the nest S->F. If a type appears in its own nest
28 // (say S->F->S) we have an invalid recursive type. The path list is the full
29 // path of named types in a cycle, it is only needed for error reporting.
30 func (check *Checker) validType0(pos token.Pos, typ Type, nest, path []*Named) bool {
31 typ = Unalias(typ)
32 33 if check.conf._Trace {
34 if t, _ := typ.(*Named); t != nil && t.obj != nil /* obj should always exist but be conservative */ {
35 pos = t.obj.pos
36 }
37 check.indent++
38 check.trace(pos, "validType(%s) nest %v, path %v", typ, pathString(makeObjList(nest)), pathString(makeObjList(path)))
39 defer func() {
40 check.indent--
41 }()
42 }
43 44 switch t := typ.(type) {
45 case nil:
46 // We should never see a nil type but be conservative and panic
47 // only in debug mode.
48 if debug {
49 panic("validType0(nil)")
50 }
51 52 case *Array:
53 return check.validType0(pos, t.elem, nest, path)
54 55 case *Struct:
56 for _, f := range t.fields {
57 if !check.validType0(pos, f.typ, nest, path) {
58 return false
59 }
60 }
61 62 case *Union:
63 for _, t := range t.terms {
64 if !check.validType0(pos, t.typ, nest, path) {
65 return false
66 }
67 }
68 69 case *Interface:
70 for _, etyp := range t.embeddeds {
71 if !check.validType0(pos, etyp, nest, path) {
72 return false
73 }
74 }
75 76 case *Named:
77 // TODO(gri) The optimization below is incorrect (see go.dev/issue/65711):
78 // in that issue `type A[P any] [1]P` is a valid type on its own
79 // and the (uninstantiated) A is recorded in check.valids. As a
80 // consequence, when checking the remaining declarations, which
81 // are not valid, the validity check ends prematurely because A
82 // is considered valid, even though its validity depends on the
83 // type argument provided to it.
84 //
85 // A correct optimization is important for pathological cases.
86 // Keep code around for reference until we found an optimization.
87 //
88 // // Exit early if we already know t is valid.
89 // // This is purely an optimization but it prevents excessive computation
90 // // times in pathological cases such as testdata/fixedbugs/issue6977.go.
91 // // (Note: The valids map could also be allocated locally, once for each
92 // // validType call.)
93 // if check.valids.lookup(t) != nil {
94 // break
95 // }
96 97 // Don't report a 2nd error if we already know the type is invalid
98 // (e.g., if a cycle was detected earlier, via under).
99 // Note: ensure that t.orig is fully resolved by calling Underlying().
100 if !isValid(t.Underlying()) {
101 return false
102 }
103 104 // If the current type t is also found in nest, (the memory of) t is
105 // embedded in itself, indicating an invalid recursive type.
106 for _, e := range nest {
107 if Identical(e, t) {
108 // We have a cycle. If t != t.Origin() then t is an instance of
109 // the generic type t.Origin(). Because t is in the nest, t must
110 // occur within the definition (RHS) of the generic type t.Origin(),
111 // directly or indirectly, after expansion of the RHS.
112 // Therefore t.Origin() must be invalid, no matter how it is
113 // instantiated since the instantiation t of t.Origin() happens
114 // inside t.Origin()'s RHS and thus is always the same and always
115 // present.
116 // Therefore we can mark the underlying of both t and t.Origin()
117 // as invalid. If t is not an instance of a generic type, t and
118 // t.Origin() are the same.
119 // Furthermore, because we check all types in a package for validity
120 // before type checking is complete, any exported type that is invalid
121 // will have an invalid underlying type and we can't reach here with
122 // such a type (invalid types are excluded above).
123 // Thus, if we reach here with a type t, both t and t.Origin() (if
124 // different in the first place) must be from the current package;
125 // they cannot have been imported.
126 // Therefore it is safe to change their underlying types; there is
127 // no chance for a race condition (the types of the current package
128 // are not yet available to other goroutines).
129 assert(t.obj.pkg == check.pkg)
130 assert(t.Origin().obj.pkg == check.pkg)
131 t.underlying = Typ[Invalid]
132 t.Origin().underlying = Typ[Invalid]
133 134 // Find the starting point of the cycle and report it.
135 // Because each type in nest must also appear in path (see invariant below),
136 // type t must be in path since it was found in nest. But not every type in path
137 // is in nest. Specifically t may appear in path with an earlier index than the
138 // index of t in nest. Search again.
139 for start, p := range path {
140 if Identical(p, t) {
141 check.cycleError(makeObjList(path[start:]), 0)
142 return false
143 }
144 }
145 panic("cycle start not found")
146 }
147 }
148 149 // No cycle was found. Check the RHS of t.
150 // Every type added to nest is also added to path; thus every type that is in nest
151 // must also be in path (invariant). But not every type in path is in nest, since
152 // nest may be pruned (see below, *TypeParam case).
153 if !check.validType0(pos, t.Origin().fromRHS, append(nest, t), append(path, t)) {
154 return false
155 }
156 157 // see TODO above
158 // check.valids.add(t) // t is valid
159 160 case *TypeParam:
161 // A type parameter stands for the type (argument) it was instantiated with.
162 // Check the corresponding type argument for validity if we are in an
163 // instantiated type.
164 if d := len(nest) - 1; d >= 0 {
165 inst := nest[d] // the type instance
166 // Find the corresponding type argument for the type parameter
167 // and proceed with checking that type argument.
168 for i, tparam := range inst.TypeParams().list() {
169 // The type parameter and type argument lists should
170 // match in length but be careful in case of errors.
171 if t == tparam && i < inst.TypeArgs().Len() {
172 targ := inst.TypeArgs().At(i)
173 // The type argument must be valid in the enclosing
174 // type (where inst was instantiated), hence we must
175 // check targ's validity in the type nest excluding
176 // the current (instantiated) type (see the example
177 // at the end of this file).
178 // For error reporting we keep the full path.
179 res := check.validType0(pos, targ, nest[:d], path)
180 // The check.validType0 call with nest[:d] may have
181 // overwritten the entry at the current depth d.
182 // Restore the entry (was issue go.dev/issue/66323).
183 nest[d] = inst
184 return res
185 }
186 }
187 }
188 }
189 190 return true
191 }
192 193 // makeObjList returns the list of type name objects for the given
194 // list of named types.
195 func makeObjList(tlist []*Named) []Object {
196 olist := make([]Object, len(tlist))
197 for i, t := range tlist {
198 olist[i] = t.obj
199 }
200 return olist
201 }
202 203 // Here is an example illustrating why we need to exclude the
204 // instantiated type from nest when evaluating the validity of
205 // a type parameter. Given the declarations
206 //
207 // var _ A[A[string]]
208 //
209 // type A[P any] struct { _ B[P] }
210 // type B[P any] struct { _ P }
211 //
212 // we want to determine if the type A[A[string]] is valid.
213 // We start evaluating A[A[string]] outside any type nest:
214 //
215 // A[A[string]]
216 // nest =
217 // path =
218 //
219 // The RHS of A is now evaluated in the A[A[string]] nest:
220 //
221 // struct{_ B[P₁]}
222 // nest = A[A[string]]
223 // path = A[A[string]]
224 //
225 // The struct has a single field of type B[P₁] with which
226 // we continue:
227 //
228 // B[P₁]
229 // nest = A[A[string]]
230 // path = A[A[string]]
231 //
232 // struct{_ P₂}
233 // nest = A[A[string]]->B[P]
234 // path = A[A[string]]->B[P]
235 //
236 // Eventually we reach the type parameter P of type B (P₂):
237 //
238 // P₂
239 // nest = A[A[string]]->B[P]
240 // path = A[A[string]]->B[P]
241 //
242 // The type argument for P of B is the type parameter P of A (P₁).
243 // It must be evaluated in the type nest that existed when B was
244 // instantiated:
245 //
246 // P₁
247 // nest = A[A[string]] <== type nest at B's instantiation time
248 // path = A[A[string]]->B[P]
249 //
250 // If we'd use the current nest it would correspond to the path
251 // which will be wrong as we will see shortly. P's type argument
252 // is A[string], which again must be evaluated in the type nest
253 // that existed when A was instantiated with A[string]. That type
254 // nest is empty:
255 //
256 // A[string]
257 // nest = <== type nest at A's instantiation time
258 // path = A[A[string]]->B[P]
259 //
260 // Evaluation then proceeds as before for A[string]:
261 //
262 // struct{_ B[P₁]}
263 // nest = A[string]
264 // path = A[A[string]]->B[P]->A[string]
265 //
266 // Now we reach B[P] again. If we had not adjusted nest, it would
267 // correspond to path, and we would find B[P] in nest, indicating
268 // a cycle, which would clearly be wrong since there's no cycle in
269 // A[string]:
270 //
271 // B[P₁]
272 // nest = A[string]
273 // path = A[A[string]]->B[P]->A[string] <== path contains B[P]!
274 //
275 // But because we use the correct type nest, evaluation proceeds without
276 // errors and we get the evaluation sequence:
277 //
278 // struct{_ P₂}
279 // nest = A[string]->B[P]
280 // path = A[A[string]]->B[P]->A[string]->B[P]
281 // P₂
282 // nest = A[string]->B[P]
283 // path = A[A[string]]->B[P]->A[string]->B[P]
284 // P₁
285 // nest = A[string]
286 // path = A[A[string]]->B[P]->A[string]->B[P]
287 // string
288 // nest =
289 // path = A[A[string]]->B[P]->A[string]->B[P]
290 //
291 // At this point we're done and A[A[string]] and is valid.
292