Source file src/cmd/compile/internal/types2/named.go
1 // Copyright 2011 The Go Authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style 3 // license that can be found in the LICENSE file. 4 5 package types2 6 7 import ( 8 "cmd/compile/internal/syntax" 9 "strings" 10 "sync" 11 "sync/atomic" 12 ) 13 14 // Type-checking Named types is subtle, because they may be recursively 15 // defined, and because their full details may be spread across multiple 16 // declarations (via methods). For this reason they are type-checked lazily, 17 // to avoid information being accessed before it is complete. 18 // 19 // Conceptually, it is helpful to think of named types as having two distinct 20 // sets of information: 21 // - "LHS" information, defining their identity: Obj() and TypeArgs() 22 // - "RHS" information, defining their details: TypeParams(), Underlying(), 23 // and methods. 24 // 25 // In this taxonomy, LHS information is available immediately, but RHS 26 // information is lazy. Specifically, a named type N may be constructed in any 27 // of the following ways: 28 // 1. type-checked from the source 29 // 2. loaded eagerly from export data 30 // 3. loaded lazily from export data (when using unified IR) 31 // 4. instantiated from a generic type 32 // 33 // In cases 1, 3, and 4, it is possible that the underlying type or methods of 34 // N may not be immediately available. 35 // - During type-checking, we allocate N before type-checking its underlying 36 // type or methods, so that we may resolve recursive references. 37 // - When loading from export data, we may load its methods and underlying 38 // type lazily using a provided load function. 39 // - After instantiating, we lazily expand the underlying type and methods 40 // (note that instances may be created while still in the process of 41 // type-checking the original type declaration). 42 // 43 // In cases 3 and 4 this lazy construction may also occur concurrently, due to 44 // concurrent use of the type checker API (after type checking or importing has 45 // finished). It is critical that we keep track of state, so that Named types 46 // are constructed exactly once and so that we do not access their details too 47 // soon. 48 // 49 // We achieve this by tracking state with an atomic state variable, and 50 // guarding potentially concurrent calculations with a mutex. At any point in 51 // time this state variable determines which data on N may be accessed. As 52 // state monotonically progresses, any data available at state M may be 53 // accessed without acquiring the mutex at state N, provided N >= M. 54 // 55 // GLOSSARY: Here are a few terms used in this file to describe Named types: 56 // - We say that a Named type is "instantiated" if it has been constructed by 57 // instantiating a generic named type with type arguments. 58 // - We say that a Named type is "declared" if it corresponds to a type 59 // declaration in the source. Instantiated named types correspond to a type 60 // instantiation in the source, not a declaration. But their Origin type is 61 // a declared type. 62 // - We say that a Named type is "resolved" if its RHS information has been 63 // loaded or fully type-checked. For Named types constructed from export 64 // data, this may involve invoking a loader function to extract information 65 // from export data. For instantiated named types this involves reading 66 // information from their origin. 67 // - We say that a Named type is "expanded" if it is an instantiated type and 68 // type parameters in its underlying type and methods have been substituted 69 // with the type arguments from the instantiation. A type may be partially 70 // expanded if some but not all of these details have been substituted. 71 // Similarly, we refer to these individual details (underlying type or 72 // method) as being "expanded". 73 // - When all information is known for a named type, we say it is "complete". 74 // 75 // Some invariants to keep in mind: each declared Named type has a single 76 // corresponding object, and that object's type is the (possibly generic) Named 77 // type. Declared Named types are identical if and only if their pointers are 78 // identical. On the other hand, multiple instantiated Named types may be 79 // identical even though their pointers are not identical. One has to use 80 // Identical to compare them. For instantiated named types, their obj is a 81 // synthetic placeholder that records their position of the corresponding 82 // instantiation in the source (if they were constructed during type checking). 83 // 84 // To prevent infinite expansion of named instances that are created outside of 85 // type-checking, instances share a Context with other instances created during 86 // their expansion. Via the pidgeonhole principle, this guarantees that in the 87 // presence of a cycle of named types, expansion will eventually find an 88 // existing instance in the Context and short-circuit the expansion. 89 // 90 // Once an instance is complete, we can nil out this shared Context to unpin 91 // memory, though this Context may still be held by other incomplete instances 92 // in its "lineage". 93 94 // A Named represents a named (defined) type. 95 type Named struct { 96 check *Checker // non-nil during type-checking; nil otherwise 97 obj *TypeName // corresponding declared object for declared types; see above for instantiated types 98 99 // fromRHS holds the type (on RHS of declaration) this *Named type is derived 100 // from (for cycle reporting). Only used by validType, and therefore does not 101 // require synchronization. 102 fromRHS Type 103 104 // information for instantiated types; nil otherwise 105 inst *instance 106 107 mu sync.Mutex // guards all fields below 108 state_ uint32 // the current state of this type; must only be accessed atomically 109 underlying Type // possibly a *Named during setup; never a *Named once set up completely 110 tparams *TypeParamList // type parameters, or nil 111 112 // methods declared for this type (not the method set of this type) 113 // Signatures are type-checked lazily. 114 // For non-instantiated types, this is a fully populated list of methods. For 115 // instantiated types, methods are individually expanded when they are first 116 // accessed. 117 methods []*Func 118 119 // loader may be provided to lazily load type parameters, underlying type, and methods. 120 loader func(*Named) (tparams []*TypeParam, underlying Type, methods []*Func) 121 } 122 123 // instance holds information that is only necessary for instantiated named 124 // types. 125 type instance struct { 126 orig *Named // original, uninstantiated type 127 targs *TypeList // type arguments 128 expandedMethods int // number of expanded methods; expandedMethods <= len(orig.methods) 129 ctxt *Context // local Context; set to nil after full expansion 130 } 131 132 // namedState represents the possible states that a named type may assume. 133 type namedState uint32 134 135 const ( 136 unresolved namedState = iota // tparams, underlying type and methods might be unavailable 137 resolved // resolve has run; methods might be incomplete (for instances) 138 complete // all data is known 139 ) 140 141 // NewNamed returns a new named type for the given type name, underlying type, and associated methods. 142 // If the given type name obj doesn't have a type yet, its type is set to the returned named type. 143 // The underlying type must not be a *Named. 144 func NewNamed(obj *TypeName, underlying Type, methods []*Func) *Named { 145 if asNamed(underlying) != nil { 146 panic("underlying type must not be *Named") 147 } 148 return (*Checker)(nil).newNamed(obj, underlying, methods) 149 } 150 151 // resolve resolves the type parameters, methods, and underlying type of n. 152 // This information may be loaded from a provided loader function, or computed 153 // from an origin type (in the case of instances). 154 // 155 // After resolution, the type parameters, methods, and underlying type of n are 156 // accessible; but if n is an instantiated type, its methods may still be 157 // unexpanded. 158 func (n *Named) resolve() *Named { 159 if n.state() >= resolved { // avoid locking below 160 return n 161 } 162 163 // TODO(rfindley): if n.check is non-nil we can avoid locking here, since 164 // type-checking is not concurrent. Evaluate if this is worth doing. 165 n.mu.Lock() 166 defer n.mu.Unlock() 167 168 if n.state() >= resolved { 169 return n 170 } 171 172 if n.inst != nil { 173 assert(n.underlying == nil) // n is an unresolved instance 174 assert(n.loader == nil) // instances are created by instantiation, in which case n.loader is nil 175 176 orig := n.inst.orig 177 orig.resolve() 178 underlying := n.expandUnderlying() 179 180 n.tparams = orig.tparams 181 n.underlying = underlying 182 n.fromRHS = orig.fromRHS // for cycle detection 183 184 if len(orig.methods) == 0 { 185 n.setState(complete) // nothing further to do 186 n.inst.ctxt = nil 187 } else { 188 n.setState(resolved) 189 } 190 return n 191 } 192 193 // TODO(mdempsky): Since we're passing n to the loader anyway 194 // (necessary because types2 expects the receiver type for methods 195 // on defined interface types to be the Named rather than the 196 // underlying Interface), maybe it should just handle calling 197 // SetTypeParams, SetUnderlying, and AddMethod instead? Those 198 // methods would need to support reentrant calls though. It would 199 // also make the API more future-proof towards further extensions. 200 if n.loader != nil { 201 assert(n.underlying == nil) 202 assert(n.TypeArgs().Len() == 0) // instances are created by instantiation, in which case n.loader is nil 203 204 tparams, underlying, methods := n.loader(n) 205 206 n.tparams = bindTParams(tparams) 207 n.underlying = underlying 208 n.fromRHS = underlying // for cycle detection 209 n.methods = methods 210 n.loader = nil 211 } 212 213 n.setState(complete) 214 return n 215 } 216 217 // state atomically accesses the current state of the receiver. 218 func (n *Named) state() namedState { 219 return namedState(atomic.LoadUint32(&n.state_)) 220 } 221 222 // setState atomically stores the given state for n. 223 // Must only be called while holding n.mu. 224 func (n *Named) setState(state namedState) { 225 atomic.StoreUint32(&n.state_, uint32(state)) 226 } 227 228 // newNamed is like NewNamed but with a *Checker receiver. 229 func (check *Checker) newNamed(obj *TypeName, underlying Type, methods []*Func) *Named { 230 typ := &Named{check: check, obj: obj, fromRHS: underlying, underlying: underlying, methods: methods} 231 if obj.typ == nil { 232 obj.typ = typ 233 } 234 // Ensure that typ is always sanity-checked. 235 if check != nil { 236 check.needsCleanup(typ) 237 } 238 return typ 239 } 240 241 // newNamedInstance creates a new named instance for the given origin and type 242 // arguments, recording pos as the position of its synthetic object (for error 243 // reporting). 244 // 245 // If set, expanding is the named type instance currently being expanded, that 246 // led to the creation of this instance. 247 func (check *Checker) newNamedInstance(pos syntax.Pos, orig *Named, targs []Type, expanding *Named) *Named { 248 assert(len(targs) > 0) 249 250 obj := NewTypeName(pos, orig.obj.pkg, orig.obj.name, nil) 251 inst := &instance{orig: orig, targs: newTypeList(targs)} 252 253 // Only pass the expanding context to the new instance if their packages 254 // match. Since type reference cycles are only possible within a single 255 // package, this is sufficient for the purposes of short-circuiting cycles. 256 // Avoiding passing the context in other cases prevents unnecessary coupling 257 // of types across packages. 258 if expanding != nil && expanding.Obj().pkg == obj.pkg { 259 inst.ctxt = expanding.inst.ctxt 260 } 261 typ := &Named{check: check, obj: obj, inst: inst} 262 obj.typ = typ 263 // Ensure that typ is always sanity-checked. 264 if check != nil { 265 check.needsCleanup(typ) 266 } 267 return typ 268 } 269 270 func (t *Named) cleanup() { 271 assert(t.inst == nil || t.inst.orig.inst == nil) 272 // Ensure that every defined type created in the course of type-checking has 273 // either non-*Named underlying type, or is unexpanded. 274 // 275 // This guarantees that we don't leak any types whose underlying type is 276 // *Named, because any unexpanded instances will lazily compute their 277 // underlying type by substituting in the underlying type of their origin. 278 // The origin must have either been imported or type-checked and expanded 279 // here, and in either case its underlying type will be fully expanded. 280 switch t.underlying.(type) { 281 case nil: 282 if t.TypeArgs().Len() == 0 { 283 panic("nil underlying") 284 } 285 case *Named, *Alias: 286 t.under() // t.under may add entries to check.cleaners 287 } 288 t.check = nil 289 } 290 291 // Obj returns the type name for the declaration defining the named type t. For 292 // instantiated types, this is same as the type name of the origin type. 293 func (t *Named) Obj() *TypeName { 294 if t.inst == nil { 295 return t.obj 296 } 297 return t.inst.orig.obj 298 } 299 300 // Origin returns the generic type from which the named type t is 301 // instantiated. If t is not an instantiated type, the result is t. 302 func (t *Named) Origin() *Named { 303 if t.inst == nil { 304 return t 305 } 306 return t.inst.orig 307 } 308 309 // TypeParams returns the type parameters of the named type t, or nil. 310 // The result is non-nil for an (originally) generic type even if it is instantiated. 311 func (t *Named) TypeParams() *TypeParamList { return t.resolve().tparams } 312 313 // SetTypeParams sets the type parameters of the named type t. 314 // t must not have type arguments. 315 func (t *Named) SetTypeParams(tparams []*TypeParam) { 316 assert(t.inst == nil) 317 t.resolve().tparams = bindTParams(tparams) 318 } 319 320 // TypeArgs returns the type arguments used to instantiate the named type t. 321 func (t *Named) TypeArgs() *TypeList { 322 if t.inst == nil { 323 return nil 324 } 325 return t.inst.targs 326 } 327 328 // NumMethods returns the number of explicit methods defined for t. 329 func (t *Named) NumMethods() int { 330 return len(t.Origin().resolve().methods) 331 } 332 333 // Method returns the i'th method of named type t for 0 <= i < t.NumMethods(). 334 // 335 // For an ordinary or instantiated type t, the receiver base type of this 336 // method is the named type t. For an uninstantiated generic type t, each 337 // method receiver is instantiated with its receiver type parameters. 338 // 339 // Methods are numbered deterministically: given the same list of source files 340 // presented to the type checker, or the same sequence of NewMethod and AddMethod 341 // calls, the mapping from method index to corresponding method remains the same. 342 // But the specific ordering is not specified and must not be relied on as it may 343 // change in the future. 344 func (t *Named) Method(i int) *Func { 345 t.resolve() 346 347 if t.state() >= complete { 348 return t.methods[i] 349 } 350 351 assert(t.inst != nil) // only instances should have incomplete methods 352 orig := t.inst.orig 353 354 t.mu.Lock() 355 defer t.mu.Unlock() 356 357 if len(t.methods) != len(orig.methods) { 358 assert(len(t.methods) == 0) 359 t.methods = make([]*Func, len(orig.methods)) 360 } 361 362 if t.methods[i] == nil { 363 assert(t.inst.ctxt != nil) // we should still have a context remaining from the resolution phase 364 t.methods[i] = t.expandMethod(i) 365 t.inst.expandedMethods++ 366 367 // Check if we've created all methods at this point. If we have, mark the 368 // type as fully expanded. 369 if t.inst.expandedMethods == len(orig.methods) { 370 t.setState(complete) 371 t.inst.ctxt = nil // no need for a context anymore 372 } 373 } 374 375 return t.methods[i] 376 } 377 378 // expandMethod substitutes type arguments in the i'th method for an 379 // instantiated receiver. 380 func (t *Named) expandMethod(i int) *Func { 381 // t.orig.methods is not lazy. origm is the method instantiated with its 382 // receiver type parameters (the "origin" method). 383 origm := t.inst.orig.Method(i) 384 assert(origm != nil) 385 386 check := t.check 387 // Ensure that the original method is type-checked. 388 if check != nil { 389 check.objDecl(origm, nil) 390 } 391 392 origSig := origm.typ.(*Signature) 393 rbase, _ := deref(origSig.Recv().Type()) 394 395 // If rbase is t, then origm is already the instantiated method we're looking 396 // for. In this case, we return origm to preserve the invariant that 397 // traversing Method->Receiver Type->Method should get back to the same 398 // method. 399 // 400 // This occurs if t is instantiated with the receiver type parameters, as in 401 // the use of m in func (r T[_]) m() { r.m() }. 402 if rbase == t { 403 return origm 404 } 405 406 sig := origSig 407 // We can only substitute if we have a correspondence between type arguments 408 // and type parameters. This check is necessary in the presence of invalid 409 // code. 410 if origSig.RecvTypeParams().Len() == t.inst.targs.Len() { 411 smap := makeSubstMap(origSig.RecvTypeParams().list(), t.inst.targs.list()) 412 var ctxt *Context 413 if check != nil { 414 ctxt = check.context() 415 } 416 sig = check.subst(origm.pos, origSig, smap, t, ctxt).(*Signature) 417 } 418 419 if sig == origSig { 420 // No substitution occurred, but we still need to create a new signature to 421 // hold the instantiated receiver. 422 copy := *origSig 423 sig = © 424 } 425 426 var rtyp Type 427 if origm.hasPtrRecv() { 428 rtyp = NewPointer(t) 429 } else { 430 rtyp = t 431 } 432 433 sig.recv = substVar(origSig.recv, rtyp) 434 return substFunc(origm, sig) 435 } 436 437 // SetUnderlying sets the underlying type and marks t as complete. 438 // t must not have type arguments. 439 func (t *Named) SetUnderlying(underlying Type) { 440 assert(t.inst == nil) 441 if underlying == nil { 442 panic("underlying type must not be nil") 443 } 444 if asNamed(underlying) != nil { 445 panic("underlying type must not be *Named") 446 } 447 t.resolve().underlying = underlying 448 if t.fromRHS == nil { 449 t.fromRHS = underlying // for cycle detection 450 } 451 } 452 453 // AddMethod adds method m unless it is already in the method list. 454 // The method must be in the same package as t, and t must not have 455 // type arguments. 456 func (t *Named) AddMethod(m *Func) { 457 assert(samePkg(t.obj.pkg, m.pkg)) 458 assert(t.inst == nil) 459 t.resolve() 460 if t.methodIndex(m.name, false) < 0 { 461 t.methods = append(t.methods, m) 462 } 463 } 464 465 // methodIndex returns the index of the method with the given name. 466 // If foldCase is set, capitalization in the name is ignored. 467 // The result is negative if no such method exists. 468 func (t *Named) methodIndex(name string, foldCase bool) int { 469 if name == "_" { 470 return -1 471 } 472 if foldCase { 473 for i, m := range t.methods { 474 if strings.EqualFold(m.name, name) { 475 return i 476 } 477 } 478 } else { 479 for i, m := range t.methods { 480 if m.name == name { 481 return i 482 } 483 } 484 } 485 return -1 486 } 487 488 // Underlying returns the [underlying type] of the named type t, resolving all 489 // forwarding declarations. Underlying types are never Named, TypeParam, or 490 // Alias types. 491 // 492 // [underlying type]: https://go.dev/ref/spec#Underlying_types. 493 func (t *Named) Underlying() Type { 494 // TODO(gri) Investigate if Unalias can be moved to where underlying is set. 495 return Unalias(t.resolve().underlying) 496 } 497 498 func (t *Named) String() string { return TypeString(t, nil) } 499 500 // ---------------------------------------------------------------------------- 501 // Implementation 502 // 503 // TODO(rfindley): reorganize the loading and expansion methods under this 504 // heading. 505 506 // under returns the expanded underlying type of n0; possibly by following 507 // forward chains of named types. If an underlying type is found, resolve 508 // the chain by setting the underlying type for each defined type in the 509 // chain before returning it. If no underlying type is found or a cycle 510 // is detected, the result is Typ[Invalid]. If a cycle is detected and 511 // n0.check != nil, the cycle is reported. 512 // 513 // This is necessary because the underlying type of named may be itself a 514 // named type that is incomplete: 515 // 516 // type ( 517 // A B 518 // B *C 519 // C A 520 // ) 521 // 522 // The type of C is the (named) type of A which is incomplete, 523 // and which has as its underlying type the named type B. 524 func (n0 *Named) under() Type { 525 u := n0.Underlying() 526 527 // If the underlying type of a defined type is not a defined 528 // (incl. instance) type, then that is the desired underlying 529 // type. 530 var n1 *Named 531 switch u1 := u.(type) { 532 case nil: 533 // After expansion via Underlying(), we should never encounter a nil 534 // underlying. 535 panic("nil underlying") 536 default: 537 // common case 538 return u 539 case *Named: 540 // handled below 541 n1 = u1 542 } 543 544 if n0.check == nil { 545 panic("Named.check == nil but type is incomplete") 546 } 547 548 // Invariant: after this point n0 as well as any named types in its 549 // underlying chain should be set up when this function exits. 550 check := n0.check 551 n := n0 552 553 seen := make(map[*Named]int) // types that need their underlying type resolved 554 var path []Object // objects encountered, for cycle reporting 555 556 loop: 557 for { 558 seen[n] = len(seen) 559 path = append(path, n.obj) 560 n = n1 561 if i, ok := seen[n]; ok { 562 // cycle 563 check.cycleError(path[i:], firstInSrc(path[i:])) 564 u = Typ[Invalid] 565 break 566 } 567 u = n.Underlying() 568 switch u1 := u.(type) { 569 case nil: 570 u = Typ[Invalid] 571 break loop 572 default: 573 break loop 574 case *Named: 575 // Continue collecting *Named types in the chain. 576 n1 = u1 577 } 578 } 579 580 for n := range seen { 581 // We should never have to update the underlying type of an imported type; 582 // those underlying types should have been resolved during the import. 583 // Also, doing so would lead to a race condition (was go.dev/issue/31749). 584 // Do this check always, not just in debug mode (it's cheap). 585 if n.obj.pkg != check.pkg { 586 panic("imported type with unresolved underlying type") 587 } 588 n.underlying = u 589 } 590 591 return u 592 } 593 594 func (n *Named) lookupMethod(pkg *Package, name string, foldCase bool) (int, *Func) { 595 n.resolve() 596 if samePkg(n.obj.pkg, pkg) || isExported(name) || foldCase { 597 // If n is an instance, we may not have yet instantiated all of its methods. 598 // Look up the method index in orig, and only instantiate method at the 599 // matching index (if any). 600 if i := n.Origin().methodIndex(name, foldCase); i >= 0 { 601 // For instances, m.Method(i) will be different from the orig method. 602 return i, n.Method(i) 603 } 604 } 605 return -1, nil 606 } 607 608 // context returns the type-checker context. 609 func (check *Checker) context() *Context { 610 if check.ctxt == nil { 611 check.ctxt = NewContext() 612 } 613 return check.ctxt 614 } 615 616 // expandUnderlying substitutes type arguments in the underlying type n.orig, 617 // returning the result. Returns Typ[Invalid] if there was an error. 618 func (n *Named) expandUnderlying() Type { 619 check := n.check 620 if check != nil && check.conf.Trace { 621 check.trace(n.obj.pos, "-- Named.expandUnderlying %s", n) 622 check.indent++ 623 defer func() { 624 check.indent-- 625 check.trace(n.obj.pos, "=> %s (tparams = %s, under = %s)", n, n.tparams.list(), n.underlying) 626 }() 627 } 628 629 assert(n.inst.orig.underlying != nil) 630 if n.inst.ctxt == nil { 631 n.inst.ctxt = NewContext() 632 } 633 634 orig := n.inst.orig 635 targs := n.inst.targs 636 637 if asNamed(orig.underlying) != nil { 638 // We should only get a Named underlying type here during type checking 639 // (for example, in recursive type declarations). 640 assert(check != nil) 641 } 642 643 if orig.tparams.Len() != targs.Len() { 644 // Mismatching arg and tparam length may be checked elsewhere. 645 return Typ[Invalid] 646 } 647 648 // Ensure that an instance is recorded before substituting, so that we 649 // resolve n for any recursive references. 650 h := n.inst.ctxt.instanceHash(orig, targs.list()) 651 n2 := n.inst.ctxt.update(h, orig, n.TypeArgs().list(), n) 652 assert(n == n2) 653 654 smap := makeSubstMap(orig.tparams.list(), targs.list()) 655 var ctxt *Context 656 if check != nil { 657 ctxt = check.context() 658 } 659 underlying := n.check.subst(n.obj.pos, orig.underlying, smap, n, ctxt) 660 // If the underlying type of n is an interface, we need to set the receiver of 661 // its methods accurately -- we set the receiver of interface methods on 662 // the RHS of a type declaration to the defined type. 663 if iface, _ := underlying.(*Interface); iface != nil { 664 if methods, copied := replaceRecvType(iface.methods, orig, n); copied { 665 // If the underlying type doesn't actually use type parameters, it's 666 // possible that it wasn't substituted. In this case we need to create 667 // a new *Interface before modifying receivers. 668 if iface == orig.underlying { 669 old := iface 670 iface = check.newInterface() 671 iface.embeddeds = old.embeddeds 672 assert(old.complete) // otherwise we are copying incomplete data 673 iface.complete = old.complete 674 iface.implicit = old.implicit // should be false but be conservative 675 underlying = iface 676 } 677 iface.methods = methods 678 iface.tset = nil // recompute type set with new methods 679 680 // If check != nil, check.newInterface will have saved the interface for later completion. 681 if check == nil { // golang/go#61561: all newly created interfaces must be fully evaluated 682 iface.typeSet() 683 } 684 } 685 } 686 687 return underlying 688 } 689 690 // safeUnderlying returns the underlying type of typ without expanding 691 // instances, to avoid infinite recursion. 692 // 693 // TODO(rfindley): eliminate this function or give it a better name. 694 func safeUnderlying(typ Type) Type { 695 if t := asNamed(typ); t != nil { 696 return t.underlying 697 } 698 return typ.Underlying() 699 } 700