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 can create 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. See [stateMask] 54 // for details. 55 // 56 // GLOSSARY: Here are a few terms used in this file to describe Named types: 57 // - We say that a Named type is "instantiated" if it has been constructed by 58 // instantiating a generic named type with type arguments. 59 // - We say that a Named type is "declared" if it corresponds to a type 60 // declaration in the source. Instantiated named types correspond to a type 61 // instantiation in the source, not a declaration. But their Origin type is 62 // a declared type. 63 // - We say that a Named type is "unpacked" if its RHS information has been 64 // populated, normalizing its representation for use in type-checking 65 // operations and abstracting away how it was created: 66 // - For a Named type constructed from unified IR, this involves invoking 67 // a lazy loader function to extract details from UIR as needed. 68 // - For an instantiated Named type, this involves extracting information 69 // from its origin and substituting type arguments into a "synthetic" 70 // RHS; this process is called "expanding" the RHS (see below). 71 // - We say that a Named type is "expanded" if it is an instantiated type and 72 // type parameters in its RHS and methods have been substituted with the type 73 // arguments from the instantiation. A type may be partially expanded if some 74 // but not all of these details have been substituted. Similarly, we refer to 75 // these individual details (RHS or method) as being "expanded". 76 // 77 // Some invariants to keep in mind: each declared Named type has a single 78 // corresponding object, and that object's type is the (possibly generic) Named 79 // type. Declared Named types are identical if and only if their pointers are 80 // identical. On the other hand, multiple instantiated Named types may be 81 // identical even though their pointers are not identical. One has to use 82 // Identical to compare them. For instantiated named types, their obj is a 83 // synthetic placeholder that records their position of the corresponding 84 // instantiation in the source (if they were constructed during type checking). 85 // 86 // To prevent infinite expansion of named instances that are created outside of 87 // type-checking, instances share a Context with other instances created during 88 // their expansion. Via the pidgeonhole principle, this guarantees that in the 89 // presence of a cycle of named types, expansion will eventually find an 90 // existing instance in the Context and short-circuit the expansion. 91 // 92 // Once an instance is fully expanded, we can nil out this shared Context to unpin 93 // memory, though the Context may still be held by other incomplete instances 94 // in its "lineage". 95 96 // A Named represents a named (defined) type. 97 // 98 // A declaration such as: 99 // 100 // type S struct { ... } 101 // 102 // creates a defined type whose underlying type is a struct, 103 // and binds this type to the object S, a [TypeName]. 104 // Use [Named.Underlying] to access the underlying type. 105 // Use [Named.Obj] to obtain the object S. 106 // 107 // Before type aliases (Go 1.9), the spec called defined types "named types". 108 type Named struct { 109 check *Checker // non-nil during type-checking; nil otherwise 110 obj *TypeName // corresponding declared object for declared types; see above for instantiated types 111 112 // flags indicating temporary violations of the invariants for fromRHS and underlying 113 allowNilRHS bool // same as below, as well as briefly during checking of a type declaration 114 allowNilUnderlying bool // may be true from creation via [NewNamed] until [Named.SetUnderlying] 115 116 inst *instance // information for instantiated types; nil otherwise 117 118 mu sync.Mutex // guards all fields below 119 state_ uint32 // the current state of this type; must only be accessed atomically or when mu is held 120 fromRHS Type // the declaration RHS this type is derived from 121 tparams *TypeParamList // type parameters, or nil 122 underlying Type // underlying type, or nil 123 finite bool // whether the type has finite size 124 125 // methods declared for this type (not the method set of this type) 126 // Signatures are type-checked lazily. 127 // For non-instantiated types, this is a fully populated list of methods. For 128 // instantiated types, methods are individually expanded when they are first 129 // accessed. 130 methods []*Func 131 132 // loader may be provided to lazily load type parameters, underlying type, methods, and delayed functions 133 loader func(*Named) ([]*TypeParam, Type, []*Func, []func()) 134 } 135 136 // instance holds information that is only necessary for instantiated named 137 // types. 138 type instance struct { 139 orig *Named // original, uninstantiated type 140 targs *TypeList // type arguments 141 expandedMethods int // number of expanded methods; expandedMethods <= len(orig.methods) 142 ctxt *Context // local Context; set to nil after full expansion 143 } 144 145 // stateMask represents each state in the lifecycle of a named type. 146 // 147 // Each named type begins in the initial state. A named type may transition to a new state 148 // according to the below diagram: 149 // 150 // initial 151 // lazyLoaded 152 // unpacked 153 // └── hasMethods 154 // └── hasUnder 155 // └── hasFinite 156 // 157 // That is, descent down the tree is mostly linear (initial through unpacked), except upon 158 // reaching the leaves (hasMethods, hasUnder, and hasFinite). A type may occupy any 159 // combination of the leaf states at once (they are independent states). 160 // 161 // To represent this independence, the set of active states is represented with a bit set. State 162 // transitions are monotonic. Once a state bit is set, it remains set. 163 // 164 // The above constraints significantly narrow the possible bit sets for a named type. With bits 165 // set left-to-right, they are: 166 // 167 // 00000 | initial 168 // 10000 | lazyLoaded 169 // 11000 | unpacked, which implies lazyLoaded 170 // 11100 | hasMethods, which implies unpacked (which in turn implies lazyLoaded) 171 // 11010 | hasUnder, which implies unpacked ... 172 // 11001 | hasFinite, which implies unpacked ... 173 // 11110 | both hasMethods and hasUnder which implies unpacked ... 174 // ... | (other combinations of leaf states) 175 // 176 // To read the state of a named type, use [Named.stateHas]; to write, use [Named.setState]. 177 type stateMask uint32 178 179 const ( 180 // initially, type parameters, RHS, underlying, and methods might be unavailable 181 lazyLoaded stateMask = 1 << iota // methods are available, but constraints might be unexpanded (for generic types) 182 unpacked // methods might be unexpanded (for instances) 183 hasMethods // methods are all expanded (for instances) 184 hasUnder // underlying type is available 185 hasFinite // size finiteness is available 186 ) 187 188 // NewNamed returns a new named type for the given type name, underlying type, and associated methods. 189 // If the given type name obj doesn't have a type yet, its type is set to the returned named type. 190 // The underlying type must not be a *Named. 191 func NewNamed(obj *TypeName, underlying Type, methods []*Func) *Named { 192 if asNamed(underlying) != nil { 193 panic("underlying type must not be *Named") 194 } 195 n := (*Checker)(nil).newNamed(obj, underlying, methods) 196 if underlying == nil { 197 n.allowNilRHS = true 198 n.allowNilUnderlying = true 199 } else { 200 n.SetUnderlying(underlying) 201 } 202 return n 203 204 } 205 206 // unpack populates the type parameters, methods, and RHS of n. 207 // 208 // For the purposes of unpacking, there are three categories of named types: 209 // 1. Lazy loaded types 210 // 2. Instantiated types 211 // 3. All others 212 // 213 // Note that the above form a partition. 214 // 215 // Lazy loaded types: 216 // Type parameters, methods, and RHS of n become accessible and are fully 217 // expanded. 218 // 219 // Instantiated types: 220 // Type parameters, methods, and RHS of n become accessible, though methods 221 // are lazily populated as needed. 222 // 223 // All others: 224 // Effectively, nothing happens. 225 func (n *Named) unpack() *Named { 226 if n.stateHas(lazyLoaded | unpacked) { // avoid locking below 227 return n 228 } 229 230 // TODO(rfindley): if n.check is non-nil we can avoid locking here, since 231 // type-checking is not concurrent. Evaluate if this is worth doing. 232 n.mu.Lock() 233 defer n.mu.Unlock() 234 235 // only atomic for consistency; we are holding the mutex 236 if n.stateHas(lazyLoaded | unpacked) { 237 return n 238 } 239 240 // underlying comes after unpacking, do not set it 241 defer (func() { assert(!n.stateHas(hasUnder)) })() 242 243 if n.inst != nil { 244 assert(n.fromRHS == nil) // instantiated types are not declared types 245 assert(n.loader == nil) // cannot import an instantiation 246 247 orig := n.inst.orig 248 orig.unpack() 249 250 n.fromRHS = n.expandRHS() 251 n.tparams = orig.tparams 252 253 if len(orig.methods) == 0 { 254 n.setState(lazyLoaded | unpacked | hasMethods) // nothing further to do 255 n.inst.ctxt = nil 256 } else { 257 n.setState(lazyLoaded | unpacked) 258 } 259 return n 260 } 261 262 // TODO(mdempsky): Since we're passing n to the loader anyway 263 // (necessary because types2 expects the receiver type for methods 264 // on defined interface types to be the Named rather than the 265 // underlying Interface), maybe it should just handle calling 266 // SetTypeParams, SetUnderlying, and AddMethod instead? Those 267 // methods would need to support reentrant calls though. It would 268 // also make the API more future-proof towards further extensions. 269 if n.loader != nil { 270 assert(n.fromRHS == nil) // not loaded yet 271 assert(n.inst == nil) // cannot import an instantiation 272 273 tparams, underlying, methods, delayed := n.loader(n) 274 n.loader = nil 275 276 n.tparams = bindTParams(tparams) 277 n.fromRHS = underlying // for cycle detection 278 n.methods = methods 279 280 n.setState(lazyLoaded) // avoid deadlock calling delayed functions 281 for _, f := range delayed { 282 f() 283 } 284 } 285 286 n.setState(lazyLoaded | unpacked | hasMethods) 287 return n 288 } 289 290 // stateHas atomically determines whether the current state includes any active bit in sm. 291 func (n *Named) stateHas(m stateMask) bool { 292 return stateMask(atomic.LoadUint32(&n.state_))&m != 0 293 } 294 295 // setState atomically sets the current state to include each active bit in sm. 296 // Must only be called while holding n.mu. 297 func (n *Named) setState(m stateMask) { 298 atomic.OrUint32(&n.state_, uint32(m)) 299 // verify state transitions 300 if debug { 301 m := stateMask(atomic.LoadUint32(&n.state_)) 302 u := m&unpacked != 0 303 // unpacked => lazyLoaded 304 if u { 305 assert(m&lazyLoaded != 0) 306 } 307 // hasMethods => unpacked 308 if m&hasMethods != 0 { 309 assert(u) 310 } 311 // hasUnder => unpacked 312 if m&hasUnder != 0 { 313 assert(u) 314 } 315 // hasFinite => unpacked 316 if m&hasFinite != 0 { 317 assert(u) 318 } 319 } 320 } 321 322 // newNamed is like NewNamed but with a *Checker receiver. 323 func (check *Checker) newNamed(obj *TypeName, fromRHS Type, methods []*Func) *Named { 324 typ := &Named{check: check, obj: obj, fromRHS: fromRHS, methods: methods} 325 if obj.typ == nil { 326 obj.typ = typ 327 } 328 // Ensure that typ is always sanity-checked. 329 if check != nil { 330 check.needsCleanup(typ) 331 } 332 return typ 333 } 334 335 // newNamedInstance creates a new named instance for the given origin and type 336 // arguments, recording pos as the position of its synthetic object (for error 337 // reporting). 338 // 339 // If set, expanding is the named type instance currently being expanded, that 340 // led to the creation of this instance. 341 func (check *Checker) newNamedInstance(pos token.Pos, orig *Named, targs []Type, expanding *Named) *Named { 342 assert(len(targs) > 0) 343 344 obj := NewTypeName(pos, orig.obj.pkg, orig.obj.name, nil) 345 inst := &instance{orig: orig, targs: newTypeList(targs)} 346 347 // Only pass the expanding context to the new instance if their packages 348 // match. Since type reference cycles are only possible within a single 349 // package, this is sufficient for the purposes of short-circuiting cycles. 350 // Avoiding passing the context in other cases prevents unnecessary coupling 351 // of types across packages. 352 if expanding != nil && expanding.Obj().pkg == obj.pkg { 353 inst.ctxt = expanding.inst.ctxt 354 } 355 typ := &Named{check: check, obj: obj, inst: inst} 356 obj.typ = typ 357 // Ensure that typ is always sanity-checked. 358 if check != nil { 359 check.needsCleanup(typ) 360 } 361 return typ 362 } 363 364 func (n *Named) cleanup() { 365 // Instances can have a nil underlying at the end of type checking — they 366 // will lazily expand it as needed. All other types must have one. 367 if n.inst == nil { 368 n.Underlying() 369 } 370 n.check = nil 371 } 372 373 // Obj returns the type name for the declaration defining the named type t. For 374 // instantiated types, this is same as the type name of the origin type. 375 func (t *Named) Obj() *TypeName { 376 if t.inst == nil { 377 return t.obj 378 } 379 return t.inst.orig.obj 380 } 381 382 // Origin returns the generic type from which the named type t is 383 // instantiated. If t is not an instantiated type, the result is t. 384 func (t *Named) Origin() *Named { 385 if t.inst == nil { 386 return t 387 } 388 return t.inst.orig 389 } 390 391 // TypeParams returns the type parameters of the named type t, or nil. 392 // The result is non-nil for an (originally) generic type even if it is instantiated. 393 func (t *Named) TypeParams() *TypeParamList { return t.unpack().tparams } 394 395 // SetTypeParams sets the type parameters of the named type t. 396 // t must not have type arguments. 397 func (t *Named) SetTypeParams(tparams []*TypeParam) { 398 assert(t.inst == nil) 399 t.unpack().tparams = bindTParams(tparams) 400 } 401 402 // TypeArgs returns the type arguments used to instantiate the named type t. 403 func (t *Named) TypeArgs() *TypeList { 404 if t.inst == nil { 405 return nil 406 } 407 return t.inst.targs 408 } 409 410 // NumMethods returns the number of explicit methods defined for t. 411 func (t *Named) NumMethods() int { 412 return len(t.Origin().unpack().methods) 413 } 414 415 // Method returns the i'th method of named type t for 0 <= i < t.NumMethods(). 416 // 417 // For an ordinary or instantiated type t, the receiver base type of this 418 // method is the named type t. For an uninstantiated generic type t, each 419 // method receiver is instantiated with its receiver type parameters. 420 // 421 // Methods are numbered deterministically: given the same list of source files 422 // presented to the type checker, or the same sequence of NewMethod and AddMethod 423 // calls, the mapping from method index to corresponding method remains the same. 424 // But the specific ordering is not specified and must not be relied on as it may 425 // change in the future. 426 func (t *Named) Method(i int) *Func { 427 t.unpack() 428 429 if t.stateHas(hasMethods) { 430 return t.methods[i] 431 } 432 433 assert(t.inst != nil) // only instances should have unexpanded methods 434 orig := t.inst.orig 435 436 t.mu.Lock() 437 defer t.mu.Unlock() 438 439 if len(t.methods) != len(orig.methods) { 440 assert(len(t.methods) == 0) 441 t.methods = make([]*Func, len(orig.methods)) 442 } 443 444 if t.methods[i] == nil { 445 assert(t.inst.ctxt != nil) // we should still have a context remaining from the resolution phase 446 t.methods[i] = t.expandMethod(i) 447 t.inst.expandedMethods++ 448 449 // Check if we've created all methods at this point. If we have, mark the 450 // type as having all of its methods. 451 if t.inst.expandedMethods == len(orig.methods) { 452 t.setState(hasMethods) 453 t.inst.ctxt = nil // no need for a context anymore 454 } 455 } 456 457 return t.methods[i] 458 } 459 460 // expandMethod substitutes type arguments in the i'th method for an 461 // instantiated receiver. 462 func (t *Named) expandMethod(i int) *Func { 463 // t.orig.methods is not lazy. origm is the method instantiated with its 464 // receiver type parameters (the "origin" method). 465 origm := t.inst.orig.Method(i) 466 assert(origm != nil) 467 468 check := t.check 469 // Ensure that the original method is type-checked. 470 if check != nil { 471 check.objDecl(origm) 472 } 473 474 origSig := origm.typ.(*Signature) 475 rbase, _ := deref(origSig.Recv().Type()) 476 477 // If rbase is t, then origm is already the instantiated method we're looking 478 // for. In this case, we return origm to preserve the invariant that 479 // traversing Method->Receiver Type->Method should get back to the same 480 // method. 481 // 482 // This occurs if t is instantiated with the receiver type parameters, as in 483 // the use of m in func (r T[_]) m() { r.m() }. 484 if rbase == t { 485 return origm 486 } 487 488 sig := origSig 489 // We can only substitute if we have a correspondence between type arguments 490 // and type parameters. This check is necessary in the presence of invalid 491 // code. 492 if origSig.RecvTypeParams().Len() == t.inst.targs.Len() { 493 smap := makeSubstMap(origSig.RecvTypeParams().list(), t.inst.targs.list()) 494 var ctxt *Context 495 if check != nil { 496 ctxt = check.context() 497 } 498 sig = check.subst(origm.pos, origSig, smap, t, ctxt).(*Signature) 499 } 500 501 if sig == origSig { 502 // No substitution occurred, but we still need to create a new signature to 503 // hold the instantiated receiver. 504 copy := *origSig 505 sig = © 506 } 507 508 var rtyp Type 509 if origm.hasPtrRecv() { 510 rtyp = NewPointer(t) 511 } else { 512 rtyp = t 513 } 514 515 sig.recv = cloneVar(origSig.recv, rtyp) 516 return cloneFunc(origm, sig) 517 } 518 519 // SetUnderlying sets the underlying type and marks t as complete. 520 // t must not have type arguments. 521 func (t *Named) SetUnderlying(u Type) { 522 assert(t.inst == nil) 523 if u == nil { 524 panic("underlying type must not be nil") 525 } 526 if asNamed(u) != nil { 527 panic("underlying type must not be *Named") 528 } 529 // be careful to uphold the state invariants 530 t.mu.Lock() 531 defer t.mu.Unlock() 532 533 t.fromRHS = u 534 t.allowNilRHS = false 535 t.setState(lazyLoaded | unpacked | hasMethods) // TODO(markfreeman): Why hasMethods? 536 537 t.underlying = u 538 t.allowNilUnderlying = false 539 t.setState(hasUnder) 540 } 541 542 // AddMethod adds method m unless it is already in the method list. 543 // The method must be in the same package as t, and t must not have 544 // type arguments. 545 func (t *Named) AddMethod(m *Func) { 546 assert(samePkg(t.obj.pkg, m.pkg)) 547 assert(t.inst == nil) 548 t.unpack() 549 if t.methodIndex(m.name, false) < 0 { 550 t.methods = append(t.methods, m) 551 } 552 } 553 554 // methodIndex returns the index of the method with the given name. 555 // If foldCase is set, capitalization in the name is ignored. 556 // The result is negative if no such method exists. 557 func (t *Named) methodIndex(name string, foldCase bool) int { 558 if name == "_" { 559 return -1 560 } 561 if foldCase { 562 for i, m := range t.methods { 563 if strings.EqualFold(m.name, name) { 564 return i 565 } 566 } 567 } else { 568 for i, m := range t.methods { 569 if m.name == name { 570 return i 571 } 572 } 573 } 574 return -1 575 } 576 577 // rhs returns [Named.fromRHS]. 578 // 579 // In debug mode, it also asserts that n is in an appropriate state. 580 func (n *Named) rhs() Type { 581 if debug { 582 assert(n.stateHas(lazyLoaded | unpacked)) 583 } 584 return n.fromRHS 585 } 586 587 // Underlying returns the [underlying type] of the named type t, resolving all 588 // forwarding declarations. Underlying types are never Named, TypeParam, or 589 // Alias types. 590 // 591 // [underlying type]: https://go.dev/ref/spec#Underlying_types. 592 func (n *Named) Underlying() Type { 593 n.unpack() 594 595 // The gccimporter depends on writing a nil underlying via NewNamed and 596 // immediately reading it back. Rather than putting that in Named.under 597 // and complicating things there, we just check for that special case here. 598 if n.rhs() == nil { 599 assert(n.allowNilRHS) 600 if n.allowNilUnderlying { 601 return nil 602 } 603 } 604 605 if !n.stateHas(hasUnder) { // minor performance optimization 606 n.resolveUnderlying() 607 } 608 609 return n.underlying 610 } 611 612 func (t *Named) String() string { return TypeString(t, nil) } 613 614 // ---------------------------------------------------------------------------- 615 // Implementation 616 // 617 // TODO(rfindley): reorganize the loading and expansion methods under this 618 // heading. 619 620 // resolveUnderlying computes the underlying type of n. If n already has an 621 // underlying type, nothing happens. 622 // 623 // It does so by following RHS type chains for alias and named types. If any 624 // other type T is found, each named type in the chain has its underlying 625 // type set to T. Aliases are skipped because their underlying type is 626 // not memoized. 627 // 628 // resolveUnderlying assumes that there are no direct cycles; if there were 629 // any, they were broken (by setting the respective types to invalid) during 630 // the directCycles check phase. 631 func (n *Named) resolveUnderlying() { 632 assert(n.stateHas(unpacked)) 633 634 var seen map[*Named]bool // for debugging only 635 if debug { 636 seen = make(map[*Named]bool) 637 } 638 639 var path []*Named 640 var u Type 641 for rhs := Type(n); u == nil; { 642 switch t := rhs.(type) { 643 case nil: 644 u = Typ[Invalid] 645 646 case *Alias: 647 rhs = unalias(t) 648 649 case *Named: 650 if debug { 651 assert(!seen[t]) 652 seen[t] = true 653 } 654 655 // don't recalculate the underlying 656 if t.stateHas(hasUnder) { 657 u = t.underlying 658 break 659 } 660 661 if debug { 662 seen[t] = true 663 } 664 path = append(path, t) 665 666 t.unpack() 667 assert(t.rhs() != nil || t.allowNilRHS) 668 rhs = t.rhs() 669 670 default: 671 u = rhs // any type literal or predeclared type works 672 } 673 } 674 675 for _, t := range path { 676 func() { 677 t.mu.Lock() 678 defer t.mu.Unlock() 679 // Careful, t.underlying has lock-free readers. Since we might be racing 680 // another call to resolveUnderlying, we have to avoid overwriting 681 // t.underlying. Otherwise, the race detector will be tripped. 682 if !t.stateHas(hasUnder) { 683 t.underlying = u 684 t.setState(hasUnder) 685 } 686 }() 687 } 688 } 689 690 func (n *Named) lookupMethod(pkg *Package, name string, foldCase bool) (int, *Func) { 691 n.unpack() 692 if samePkg(n.obj.pkg, pkg) || isExported(name) || foldCase { 693 // If n is an instance, we may not have yet instantiated all of its methods. 694 // Look up the method index in orig, and only instantiate method at the 695 // matching index (if any). 696 if i := n.Origin().methodIndex(name, foldCase); i >= 0 { 697 // For instances, m.Method(i) will be different from the orig method. 698 return i, n.Method(i) 699 } 700 } 701 return -1, nil 702 } 703 704 // context returns the type-checker context. 705 func (check *Checker) context() *Context { 706 if check.ctxt == nil { 707 check.ctxt = NewContext() 708 } 709 return check.ctxt 710 } 711 712 // expandRHS crafts a synthetic RHS for an instantiated type using the RHS of 713 // its origin type (which must be a generic type). 714 // 715 // Suppose that we had: 716 // 717 // type T[P any] struct { 718 // f P 719 // } 720 // 721 // type U T[int] 722 // 723 // When we go to U, we observe T[int]. Since T[int] is an instantiation, it has no 724 // declaration. Here, we craft a synthetic RHS for T[int] as if it were declared, 725 // somewhat similar to: 726 // 727 // type T[int] struct { 728 // f int 729 // } 730 // 731 // And note that the synthetic RHS here is the same as the underlying for U. Now, 732 // consider: 733 // 734 // type T[_ any] U 735 // type U int 736 // type V T[U] 737 // 738 // The synthetic RHS for T[U] becomes: 739 // 740 // type T[U] U 741 // 742 // Whereas the underlying of V is int, not U. 743 func (n *Named) expandRHS() (rhs Type) { 744 check := n.check 745 if check != nil && check.conf._Trace { 746 check.trace(n.obj.pos, "-- Named.expandRHS %s", n) 747 check.indent++ 748 defer func() { 749 check.indent-- 750 check.trace(n.obj.pos, "=> %s (rhs = %s)", n, rhs) 751 }() 752 } 753 754 assert(!n.stateHas(unpacked)) 755 assert(n.inst.orig.stateHas(lazyLoaded | unpacked)) 756 757 if n.inst.ctxt == nil { 758 n.inst.ctxt = NewContext() 759 } 760 761 ctxt := n.inst.ctxt 762 orig := n.inst.orig 763 764 targs := n.inst.targs 765 tpars := orig.tparams 766 767 if targs.Len() != tpars.Len() { 768 return Typ[Invalid] 769 } 770 771 h := ctxt.instanceHash(orig, targs.list()) 772 u := ctxt.update(h, orig, targs.list(), n) // block fixed point infinite instantiation 773 assert(n == u) 774 775 m := makeSubstMap(tpars.list(), targs.list()) 776 if check != nil { 777 ctxt = check.context() 778 } 779 780 rhs = check.subst(n.obj.pos, orig.rhs(), m, n, ctxt) 781 782 // TODO(markfreeman): Can we handle this in substitution? 783 // If the RHS is an interface, we must set the receiver of interface methods 784 // to the named type. 785 if iface, _ := rhs.(*Interface); iface != nil { 786 if methods, copied := replaceRecvType(iface.methods, orig, n); copied { 787 // If the RHS doesn't use type parameters, it may not have been 788 // substituted; we need to craft a new interface first. 789 if iface == orig.rhs() { 790 assert(iface.complete) // otherwise we are copying incomplete data 791 792 crafted := check.newInterface() 793 crafted.complete = true 794 crafted.implicit = false 795 crafted.embeddeds = iface.embeddeds 796 797 iface = crafted 798 } 799 iface.methods = methods 800 iface.tset = nil // recompute type set with new methods 801 802 // go.dev/issue/61561: We have to complete the interface even without a checker. 803 if check == nil { 804 iface.typeSet() 805 } 806 807 return iface 808 } 809 } 810 811 return rhs 812 } 813 814 // safeUnderlying returns the underlying type of typ without expanding 815 // instances, to avoid infinite recursion. 816 // 817 // TODO(rfindley): eliminate this function or give it a better name. 818 func safeUnderlying(typ Type) Type { 819 if t := asNamed(typ); t != nil { 820 return t.underlying 821 } 822 return typ.Underlying() 823 } 824