Source file src/go/types/named.go
1 // Code generated by "go test -run=Generate -write=all"; DO NOT EDIT. 2 // Source: ../../cmd/compile/internal/types2/named.go 3 4 // Copyright 2011 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 ( 11 "go/token" 12 "strings" 13 "sync" 14 "sync/atomic" 15 ) 16 17 // Type-checking Named types is subtle, because they may be recursively 18 // defined, and because their full details may be spread across multiple 19 // declarations (via methods). For this reason they are type-checked lazily, 20 // to avoid information being accessed before it is complete. 21 // 22 // Conceptually, it is helpful to think of named types as having two distinct 23 // sets of information: 24 // - "LHS" information, defining their identity: Obj() and TypeArgs() 25 // - "RHS" information, defining their details: TypeParams(), Underlying(), 26 // and methods. 27 // 28 // In this taxonomy, LHS information is available immediately, but RHS 29 // information is lazy. Specifically, a named type N may be constructed in any 30 // of the following ways: 31 // 1. type-checked from the source 32 // 2. loaded eagerly from export data 33 // 3. loaded lazily from export data (when using unified IR) 34 // 4. instantiated from a generic type 35 // 36 // In cases 1, 3, and 4, it is possible that the underlying type or methods of 37 // N may not be immediately available. 38 // - During type-checking, we allocate N before type-checking its underlying 39 // type or methods, so that we may resolve recursive references. 40 // - When loading from export data, we may load its methods and underlying 41 // type lazily using a provided load function. 42 // - After instantiating, we lazily expand the underlying type and methods 43 // (note that instances may be created while still in the process of 44 // type-checking the original type declaration). 45 // 46 // In cases 3 and 4 this lazy construction may also occur concurrently, due to 47 // concurrent use of the type checker API (after type checking or importing has 48 // finished). It is critical that we keep track of state, so that Named types 49 // are constructed exactly once and so that we do not access their details too 50 // soon. 51 // 52 // We achieve this by tracking state with an atomic state variable, and 53 // guarding potentially concurrent calculations with a mutex. At any point in 54 // time this state variable determines which data on N may be accessed. As 55 // state monotonically progresses, any data available at state M may be 56 // accessed without acquiring the mutex at state N, provided N >= M. 57 // 58 // GLOSSARY: Here are a few terms used in this file to describe Named types: 59 // - We say that a Named type is "instantiated" if it has been constructed by 60 // instantiating a generic named type with type arguments. 61 // - We say that a Named type is "declared" if it corresponds to a type 62 // declaration in the source. Instantiated named types correspond to a type 63 // instantiation in the source, not a declaration. But their Origin type is 64 // a declared type. 65 // - We say that a Named type is "resolved" if its RHS information has been 66 // loaded or fully type-checked. For Named types constructed from export 67 // data, this may involve invoking a loader function to extract information 68 // from export data. For instantiated named types this involves reading 69 // information from their origin. 70 // - We say that a Named type is "expanded" if it is an instantiated type and 71 // type parameters in its underlying type and methods have been substituted 72 // with the type arguments from the instantiation. A type may be partially 73 // expanded if some but not all of these details have been substituted. 74 // Similarly, we refer to these individual details (underlying type or 75 // method) as being "expanded". 76 // - When all information is known for a named type, we say it is "complete". 77 // 78 // Some invariants to keep in mind: each declared Named type has a single 79 // corresponding object, and that object's type is the (possibly generic) Named 80 // type. Declared Named types are identical if and only if their pointers are 81 // identical. On the other hand, multiple instantiated Named types may be 82 // identical even though their pointers are not identical. One has to use 83 // Identical to compare them. For instantiated named types, their obj is a 84 // synthetic placeholder that records their position of the corresponding 85 // instantiation in the source (if they were constructed during type checking). 86 // 87 // To prevent infinite expansion of named instances that are created outside of 88 // type-checking, instances share a Context with other instances created during 89 // their expansion. Via the pidgeonhole principle, this guarantees that in the 90 // presence of a cycle of named types, expansion will eventually find an 91 // existing instance in the Context and short-circuit the expansion. 92 // 93 // Once an instance is complete, we can nil out this shared Context to unpin 94 // memory, though this Context may still be held by other incomplete instances 95 // in its "lineage". 96 97 // A Named represents a named (defined) type. 98 // 99 // A declaration such as: 100 // 101 // type S struct { ... } 102 // 103 // creates a defined type whose underlying type is a struct, 104 // and binds this type to the object S, a [TypeName]. 105 // Use [Named.Underlying] to access the underlying type. 106 // Use [Named.Obj] to obtain the object S. 107 // 108 // Before type aliases (Go 1.9), the spec called defined types "named types". 109 type Named struct { 110 check *Checker // non-nil during type-checking; nil otherwise 111 obj *TypeName // corresponding declared object for declared types; see above for instantiated types 112 113 // fromRHS holds the type (on RHS of declaration) this *Named type is derived 114 // from (for cycle reporting). Only used by validType, and therefore does not 115 // require synchronization. 116 fromRHS Type 117 118 // information for instantiated types; nil otherwise 119 inst *instance 120 121 mu sync.Mutex // guards all fields below 122 state_ uint32 // the current state of this type; must only be accessed atomically 123 underlying Type // possibly a *Named during setup; never a *Named once set up completely 124 tparams *TypeParamList // type parameters, or nil 125 126 // methods declared for this type (not the method set of this type) 127 // Signatures are type-checked lazily. 128 // For non-instantiated types, this is a fully populated list of methods. For 129 // instantiated types, methods are individually expanded when they are first 130 // accessed. 131 methods []*Func 132 133 // loader may be provided to lazily load type parameters, underlying type, and methods. 134 loader func(*Named) (tparams []*TypeParam, underlying Type, methods []*Func) 135 } 136 137 // instance holds information that is only necessary for instantiated named 138 // types. 139 type instance struct { 140 orig *Named // original, uninstantiated type 141 targs *TypeList // type arguments 142 expandedMethods int // number of expanded methods; expandedMethods <= len(orig.methods) 143 ctxt *Context // local Context; set to nil after full expansion 144 } 145 146 // namedState represents the possible states that a named type may assume. 147 type namedState uint32 148 149 const ( 150 unresolved namedState = iota // tparams, underlying type and methods might be unavailable 151 resolved // resolve has run; methods might be incomplete (for instances) 152 complete // all data is known 153 ) 154 155 // NewNamed returns a new named type for the given type name, underlying type, and associated methods. 156 // If the given type name obj doesn't have a type yet, its type is set to the returned named type. 157 // The underlying type must not be a *Named. 158 func NewNamed(obj *TypeName, underlying Type, methods []*Func) *Named { 159 if asNamed(underlying) != nil { 160 panic("underlying type must not be *Named") 161 } 162 return (*Checker)(nil).newNamed(obj, underlying, methods) 163 } 164 165 // resolve resolves the type parameters, methods, and underlying type of n. 166 // This information may be loaded from a provided loader function, or computed 167 // from an origin type (in the case of instances). 168 // 169 // After resolution, the type parameters, methods, and underlying type of n are 170 // accessible; but if n is an instantiated type, its methods may still be 171 // unexpanded. 172 func (n *Named) resolve() *Named { 173 if n.state() >= resolved { // avoid locking below 174 return n 175 } 176 177 // TODO(rfindley): if n.check is non-nil we can avoid locking here, since 178 // type-checking is not concurrent. Evaluate if this is worth doing. 179 n.mu.Lock() 180 defer n.mu.Unlock() 181 182 if n.state() >= resolved { 183 return n 184 } 185 186 if n.inst != nil { 187 assert(n.underlying == nil) // n is an unresolved instance 188 assert(n.loader == nil) // instances are created by instantiation, in which case n.loader is nil 189 190 orig := n.inst.orig 191 orig.resolve() 192 underlying := n.expandUnderlying() 193 194 n.tparams = orig.tparams 195 n.underlying = underlying 196 n.fromRHS = orig.fromRHS // for cycle detection 197 198 if len(orig.methods) == 0 { 199 n.setState(complete) // nothing further to do 200 n.inst.ctxt = nil 201 } else { 202 n.setState(resolved) 203 } 204 return n 205 } 206 207 // TODO(mdempsky): Since we're passing n to the loader anyway 208 // (necessary because types2 expects the receiver type for methods 209 // on defined interface types to be the Named rather than the 210 // underlying Interface), maybe it should just handle calling 211 // SetTypeParams, SetUnderlying, and AddMethod instead? Those 212 // methods would need to support reentrant calls though. It would 213 // also make the API more future-proof towards further extensions. 214 if n.loader != nil { 215 assert(n.underlying == nil) 216 assert(n.TypeArgs().Len() == 0) // instances are created by instantiation, in which case n.loader is nil 217 218 tparams, underlying, methods := n.loader(n) 219 220 n.tparams = bindTParams(tparams) 221 n.underlying = underlying 222 n.fromRHS = underlying // for cycle detection 223 n.methods = methods 224 n.loader = nil 225 } 226 227 n.setState(complete) 228 return n 229 } 230 231 // state atomically accesses the current state of the receiver. 232 func (n *Named) state() namedState { 233 return namedState(atomic.LoadUint32(&n.state_)) 234 } 235 236 // setState atomically stores the given state for n. 237 // Must only be called while holding n.mu. 238 func (n *Named) setState(state namedState) { 239 atomic.StoreUint32(&n.state_, uint32(state)) 240 } 241 242 // newNamed is like NewNamed but with a *Checker receiver. 243 func (check *Checker) newNamed(obj *TypeName, underlying Type, methods []*Func) *Named { 244 typ := &Named{check: check, obj: obj, fromRHS: underlying, underlying: underlying, methods: methods} 245 if obj.typ == nil { 246 obj.typ = typ 247 } 248 // Ensure that typ is always sanity-checked. 249 if check != nil { 250 check.needsCleanup(typ) 251 } 252 return typ 253 } 254 255 // newNamedInstance creates a new named instance for the given origin and type 256 // arguments, recording pos as the position of its synthetic object (for error 257 // reporting). 258 // 259 // If set, expanding is the named type instance currently being expanded, that 260 // led to the creation of this instance. 261 func (check *Checker) newNamedInstance(pos token.Pos, orig *Named, targs []Type, expanding *Named) *Named { 262 assert(len(targs) > 0) 263 264 obj := NewTypeName(pos, orig.obj.pkg, orig.obj.name, nil) 265 inst := &instance{orig: orig, targs: newTypeList(targs)} 266 267 // Only pass the expanding context to the new instance if their packages 268 // match. Since type reference cycles are only possible within a single 269 // package, this is sufficient for the purposes of short-circuiting cycles. 270 // Avoiding passing the context in other cases prevents unnecessary coupling 271 // of types across packages. 272 if expanding != nil && expanding.Obj().pkg == obj.pkg { 273 inst.ctxt = expanding.inst.ctxt 274 } 275 typ := &Named{check: check, obj: obj, inst: inst} 276 obj.typ = typ 277 // Ensure that typ is always sanity-checked. 278 if check != nil { 279 check.needsCleanup(typ) 280 } 281 return typ 282 } 283 284 func (t *Named) cleanup() { 285 assert(t.inst == nil || t.inst.orig.inst == nil) 286 // Ensure that every defined type created in the course of type-checking has 287 // either non-*Named underlying type, or is unexpanded. 288 // 289 // This guarantees that we don't leak any types whose underlying type is 290 // *Named, because any unexpanded instances will lazily compute their 291 // underlying type by substituting in the underlying type of their origin. 292 // The origin must have either been imported or type-checked and expanded 293 // here, and in either case its underlying type will be fully expanded. 294 switch t.underlying.(type) { 295 case nil: 296 if t.TypeArgs().Len() == 0 { 297 panic("nil underlying") 298 } 299 case *Named, *Alias: 300 t.under() // t.under may add entries to check.cleaners 301 } 302 t.check = nil 303 } 304 305 // Obj returns the type name for the declaration defining the named type t. For 306 // instantiated types, this is same as the type name of the origin type. 307 func (t *Named) Obj() *TypeName { 308 if t.inst == nil { 309 return t.obj 310 } 311 return t.inst.orig.obj 312 } 313 314 // Origin returns the generic type from which the named type t is 315 // instantiated. If t is not an instantiated type, the result is t. 316 func (t *Named) Origin() *Named { 317 if t.inst == nil { 318 return t 319 } 320 return t.inst.orig 321 } 322 323 // TypeParams returns the type parameters of the named type t, or nil. 324 // The result is non-nil for an (originally) generic type even if it is instantiated. 325 func (t *Named) TypeParams() *TypeParamList { return t.resolve().tparams } 326 327 // SetTypeParams sets the type parameters of the named type t. 328 // t must not have type arguments. 329 func (t *Named) SetTypeParams(tparams []*TypeParam) { 330 assert(t.inst == nil) 331 t.resolve().tparams = bindTParams(tparams) 332 } 333 334 // TypeArgs returns the type arguments used to instantiate the named type t. 335 func (t *Named) TypeArgs() *TypeList { 336 if t.inst == nil { 337 return nil 338 } 339 return t.inst.targs 340 } 341 342 // NumMethods returns the number of explicit methods defined for t. 343 func (t *Named) NumMethods() int { 344 return len(t.Origin().resolve().methods) 345 } 346 347 // Method returns the i'th method of named type t for 0 <= i < t.NumMethods(). 348 // 349 // For an ordinary or instantiated type t, the receiver base type of this 350 // method is the named type t. For an uninstantiated generic type t, each 351 // method receiver is instantiated with its receiver type parameters. 352 // 353 // Methods are numbered deterministically: given the same list of source files 354 // presented to the type checker, or the same sequence of NewMethod and AddMethod 355 // calls, the mapping from method index to corresponding method remains the same. 356 // But the specific ordering is not specified and must not be relied on as it may 357 // change in the future. 358 func (t *Named) Method(i int) *Func { 359 t.resolve() 360 361 if t.state() >= complete { 362 return t.methods[i] 363 } 364 365 assert(t.inst != nil) // only instances should have incomplete methods 366 orig := t.inst.orig 367 368 t.mu.Lock() 369 defer t.mu.Unlock() 370 371 if len(t.methods) != len(orig.methods) { 372 assert(len(t.methods) == 0) 373 t.methods = make([]*Func, len(orig.methods)) 374 } 375 376 if t.methods[i] == nil { 377 assert(t.inst.ctxt != nil) // we should still have a context remaining from the resolution phase 378 t.methods[i] = t.expandMethod(i) 379 t.inst.expandedMethods++ 380 381 // Check if we've created all methods at this point. If we have, mark the 382 // type as fully expanded. 383 if t.inst.expandedMethods == len(orig.methods) { 384 t.setState(complete) 385 t.inst.ctxt = nil // no need for a context anymore 386 } 387 } 388 389 return t.methods[i] 390 } 391 392 // expandMethod substitutes type arguments in the i'th method for an 393 // instantiated receiver. 394 func (t *Named) expandMethod(i int) *Func { 395 // t.orig.methods is not lazy. origm is the method instantiated with its 396 // receiver type parameters (the "origin" method). 397 origm := t.inst.orig.Method(i) 398 assert(origm != nil) 399 400 check := t.check 401 // Ensure that the original method is type-checked. 402 if check != nil { 403 check.objDecl(origm, nil) 404 } 405 406 origSig := origm.typ.(*Signature) 407 rbase, _ := deref(origSig.Recv().Type()) 408 409 // If rbase is t, then origm is already the instantiated method we're looking 410 // for. In this case, we return origm to preserve the invariant that 411 // traversing Method->Receiver Type->Method should get back to the same 412 // method. 413 // 414 // This occurs if t is instantiated with the receiver type parameters, as in 415 // the use of m in func (r T[_]) m() { r.m() }. 416 if rbase == t { 417 return origm 418 } 419 420 sig := origSig 421 // We can only substitute if we have a correspondence between type arguments 422 // and type parameters. This check is necessary in the presence of invalid 423 // code. 424 if origSig.RecvTypeParams().Len() == t.inst.targs.Len() { 425 smap := makeSubstMap(origSig.RecvTypeParams().list(), t.inst.targs.list()) 426 var ctxt *Context 427 if check != nil { 428 ctxt = check.context() 429 } 430 sig = check.subst(origm.pos, origSig, smap, t, ctxt).(*Signature) 431 } 432 433 if sig == origSig { 434 // No substitution occurred, but we still need to create a new signature to 435 // hold the instantiated receiver. 436 copy := *origSig 437 sig = © 438 } 439 440 var rtyp Type 441 if origm.hasPtrRecv() { 442 rtyp = NewPointer(t) 443 } else { 444 rtyp = t 445 } 446 447 sig.recv = cloneVar(origSig.recv, rtyp) 448 return cloneFunc(origm, sig) 449 } 450 451 // SetUnderlying sets the underlying type and marks t as complete. 452 // t must not have type arguments. 453 func (t *Named) SetUnderlying(underlying Type) { 454 assert(t.inst == nil) 455 if underlying == nil { 456 panic("underlying type must not be nil") 457 } 458 if asNamed(underlying) != nil { 459 panic("underlying type must not be *Named") 460 } 461 t.resolve().underlying = underlying 462 if t.fromRHS == nil { 463 t.fromRHS = underlying // for cycle detection 464 } 465 } 466 467 // AddMethod adds method m unless it is already in the method list. 468 // The method must be in the same package as t, and t must not have 469 // type arguments. 470 func (t *Named) AddMethod(m *Func) { 471 assert(samePkg(t.obj.pkg, m.pkg)) 472 assert(t.inst == nil) 473 t.resolve() 474 if t.methodIndex(m.name, false) < 0 { 475 t.methods = append(t.methods, m) 476 } 477 } 478 479 // methodIndex returns the index of the method with the given name. 480 // If foldCase is set, capitalization in the name is ignored. 481 // The result is negative if no such method exists. 482 func (t *Named) methodIndex(name string, foldCase bool) int { 483 if name == "_" { 484 return -1 485 } 486 if foldCase { 487 for i, m := range t.methods { 488 if strings.EqualFold(m.name, name) { 489 return i 490 } 491 } 492 } else { 493 for i, m := range t.methods { 494 if m.name == name { 495 return i 496 } 497 } 498 } 499 return -1 500 } 501 502 // Underlying returns the [underlying type] of the named type t, resolving all 503 // forwarding declarations. Underlying types are never Named, TypeParam, or 504 // Alias types. 505 // 506 // [underlying type]: https://go.dev/ref/spec#Underlying_types. 507 func (t *Named) Underlying() Type { 508 // TODO(gri) Investigate if Unalias can be moved to where underlying is set. 509 return Unalias(t.resolve().underlying) 510 } 511 512 func (t *Named) String() string { return TypeString(t, nil) } 513 514 // ---------------------------------------------------------------------------- 515 // Implementation 516 // 517 // TODO(rfindley): reorganize the loading and expansion methods under this 518 // heading. 519 520 // under returns the expanded underlying type of n0; possibly by following 521 // forward chains of named types. If an underlying type is found, resolve 522 // the chain by setting the underlying type for each defined type in the 523 // chain before returning it. If no underlying type is found or a cycle 524 // is detected, the result is Typ[Invalid]. If a cycle is detected and 525 // n0.check != nil, the cycle is reported. 526 // 527 // This is necessary because the underlying type of named may be itself a 528 // named type that is incomplete: 529 // 530 // type ( 531 // A B 532 // B *C 533 // C A 534 // ) 535 // 536 // The type of C is the (named) type of A which is incomplete, 537 // and which has as its underlying type the named type B. 538 func (n0 *Named) under() Type { 539 u := n0.Underlying() 540 541 // If the underlying type of a defined type is not a defined 542 // (incl. instance) type, then that is the desired underlying 543 // type. 544 var n1 *Named 545 switch u1 := u.(type) { 546 case nil: 547 // After expansion via Underlying(), we should never encounter a nil 548 // underlying. 549 panic("nil underlying") 550 default: 551 // common case 552 return u 553 case *Named: 554 // handled below 555 n1 = u1 556 } 557 558 if n0.check == nil { 559 panic("Named.check == nil but type is incomplete") 560 } 561 562 // Invariant: after this point n0 as well as any named types in its 563 // underlying chain should be set up when this function exits. 564 check := n0.check 565 n := n0 566 567 seen := make(map[*Named]int) // types that need their underlying type resolved 568 var path []Object // objects encountered, for cycle reporting 569 570 loop: 571 for { 572 seen[n] = len(seen) 573 path = append(path, n.obj) 574 n = n1 575 if i, ok := seen[n]; ok { 576 // cycle 577 check.cycleError(path[i:], firstInSrc(path[i:])) 578 u = Typ[Invalid] 579 break 580 } 581 u = n.Underlying() 582 switch u1 := u.(type) { 583 case nil: 584 u = Typ[Invalid] 585 break loop 586 default: 587 break loop 588 case *Named: 589 // Continue collecting *Named types in the chain. 590 n1 = u1 591 } 592 } 593 594 for n := range seen { 595 // We should never have to update the underlying type of an imported type; 596 // those underlying types should have been resolved during the import. 597 // Also, doing so would lead to a race condition (was go.dev/issue/31749). 598 // Do this check always, not just in debug mode (it's cheap). 599 if n.obj.pkg != check.pkg { 600 panic("imported type with unresolved underlying type") 601 } 602 n.underlying = u 603 } 604 605 return u 606 } 607 608 func (n *Named) lookupMethod(pkg *Package, name string, foldCase bool) (int, *Func) { 609 n.resolve() 610 if samePkg(n.obj.pkg, pkg) || isExported(name) || foldCase { 611 // If n is an instance, we may not have yet instantiated all of its methods. 612 // Look up the method index in orig, and only instantiate method at the 613 // matching index (if any). 614 if i := n.Origin().methodIndex(name, foldCase); i >= 0 { 615 // For instances, m.Method(i) will be different from the orig method. 616 return i, n.Method(i) 617 } 618 } 619 return -1, nil 620 } 621 622 // context returns the type-checker context. 623 func (check *Checker) context() *Context { 624 if check.ctxt == nil { 625 check.ctxt = NewContext() 626 } 627 return check.ctxt 628 } 629 630 // expandUnderlying substitutes type arguments in the underlying type n.orig, 631 // returning the result. Returns Typ[Invalid] if there was an error. 632 func (n *Named) expandUnderlying() Type { 633 check := n.check 634 if check != nil && check.conf._Trace { 635 check.trace(n.obj.pos, "-- Named.expandUnderlying %s", n) 636 check.indent++ 637 defer func() { 638 check.indent-- 639 check.trace(n.obj.pos, "=> %s (tparams = %s, under = %s)", n, n.tparams.list(), n.underlying) 640 }() 641 } 642 643 assert(n.inst.orig.underlying != nil) 644 if n.inst.ctxt == nil { 645 n.inst.ctxt = NewContext() 646 } 647 648 orig := n.inst.orig 649 targs := n.inst.targs 650 651 if asNamed(orig.underlying) != nil { 652 // We should only get a Named underlying type here during type checking 653 // (for example, in recursive type declarations). 654 assert(check != nil) 655 } 656 657 if orig.tparams.Len() != targs.Len() { 658 // Mismatching arg and tparam length may be checked elsewhere. 659 return Typ[Invalid] 660 } 661 662 // Ensure that an instance is recorded before substituting, so that we 663 // resolve n for any recursive references. 664 h := n.inst.ctxt.instanceHash(orig, targs.list()) 665 n2 := n.inst.ctxt.update(h, orig, n.TypeArgs().list(), n) 666 assert(n == n2) 667 668 smap := makeSubstMap(orig.tparams.list(), targs.list()) 669 var ctxt *Context 670 if check != nil { 671 ctxt = check.context() 672 } 673 underlying := n.check.subst(n.obj.pos, orig.underlying, smap, n, ctxt) 674 // If the underlying type of n is an interface, we need to set the receiver of 675 // its methods accurately -- we set the receiver of interface methods on 676 // the RHS of a type declaration to the defined type. 677 if iface, _ := underlying.(*Interface); iface != nil { 678 if methods, copied := replaceRecvType(iface.methods, orig, n); copied { 679 // If the underlying type doesn't actually use type parameters, it's 680 // possible that it wasn't substituted. In this case we need to create 681 // a new *Interface before modifying receivers. 682 if iface == orig.underlying { 683 old := iface 684 iface = check.newInterface() 685 iface.embeddeds = old.embeddeds 686 assert(old.complete) // otherwise we are copying incomplete data 687 iface.complete = old.complete 688 iface.implicit = old.implicit // should be false but be conservative 689 underlying = iface 690 } 691 iface.methods = methods 692 iface.tset = nil // recompute type set with new methods 693 694 // If check != nil, check.newInterface will have saved the interface for later completion. 695 if check == nil { // golang/go#61561: all newly created interfaces must be fully evaluated 696 iface.typeSet() 697 } 698 } 699 } 700 701 return underlying 702 } 703 704 // safeUnderlying returns the underlying type of typ without expanding 705 // instances, to avoid infinite recursion. 706 // 707 // TODO(rfindley): eliminate this function or give it a better name. 708 func safeUnderlying(typ Type) Type { 709 if t := asNamed(typ); t != nil { 710 return t.underlying 711 } 712 return typ.Underlying() 713 } 714