1 // Code generated by "go test -run=Generate -write=all"; DO NOT EDIT. 2 3 // Copyright 2020 The Go Authors. All rights reserved. 4 // Use of this source code is governed by a BSD-style 5 // license that can be found in the LICENSE file. 6 7 // This file implements type unification. 8 // 9 // Type unification attempts to make two types x and y structurally 10 // equivalent by determining the types for a given list of (bound) 11 // type parameters which may occur within x and y. If x and y are 12 // structurally different (say []T vs chan T), or conflicting 13 // types are determined for type parameters, unification fails. 14 // If unification succeeds, as a side-effect, the types of the 15 // bound type parameters may be determined. 16 // 17 // Unification typically requires multiple calls u.unify(x, y) to 18 // a given unifier u, with various combinations of types x and y. 19 // In each call, additional type parameter types may be determined 20 // as a side effect and recorded in u. 21 // If a call fails (returns false), unification fails. 22 // 23 // In the unification context, structural equivalence of two types 24 // ignores the difference between a defined type and its underlying 25 // type if one type is a defined type and the other one is not. 26 // It also ignores the difference between an (external, unbound) 27 // type parameter and its core type. 28 // If two types are not structurally equivalent, they cannot be Go 29 // identical types. On the other hand, if they are structurally 30 // equivalent, they may be Go identical or at least assignable, or 31 // they may be in the type set of a constraint. 32 // Whether they indeed are identical or assignable is determined 33 // upon instantiation and function argument passing. 34 35 package types 36 37 import ( 38 "bytes" 39 "fmt" 40 "sort" 41 "strings" 42 ) 43 44 const ( 45 // Upper limit for recursion depth. Used to catch infinite recursions 46 // due to implementation issues (e.g., see issues go.dev/issue/48619, go.dev/issue/48656). 47 unificationDepthLimit = 50 48 49 // Whether to panic when unificationDepthLimit is reached. 50 // If disabled, a recursion depth overflow results in a (quiet) 51 // unification failure. 52 panicAtUnificationDepthLimit = true 53 54 // If enableCoreTypeUnification is set, unification will consider 55 // the core types, if any, of non-local (unbound) type parameters. 56 enableCoreTypeUnification = true 57 58 // If traceInference is set, unification will print a trace of its operation. 59 // Interpretation of trace: 60 // x ≡ y attempt to unify types x and y 61 // p ➞ y type parameter p is set to type y (p is inferred to be y) 62 // p ⇄ q type parameters p and q match (p is inferred to be q and vice versa) 63 // x ≢ y types x and y cannot be unified 64 // [p, q, ...] ➞ [x, y, ...] mapping from type parameters to types 65 traceInference = false 66 ) 67 68 // A unifier maintains a list of type parameters and 69 // corresponding types inferred for each type parameter. 70 // A unifier is created by calling newUnifier. 71 type unifier struct { 72 // handles maps each type parameter to its inferred type through 73 // an indirection *Type called (inferred type) "handle". 74 // Initially, each type parameter has its own, separate handle, 75 // with a nil (i.e., not yet inferred) type. 76 // After a type parameter P is unified with a type parameter Q, 77 // P and Q share the same handle (and thus type). This ensures 78 // that inferring the type for a given type parameter P will 79 // automatically infer the same type for all other parameters 80 // unified (joined) with P. 81 handles map[*TypeParam]*Type 82 depth int // recursion depth during unification 83 enableInterfaceInference bool // use shared methods for better inference 84 } 85 86 // newUnifier returns a new unifier initialized with the given type parameter 87 // and corresponding type argument lists. The type argument list may be shorter 88 // than the type parameter list, and it may contain nil types. Matching type 89 // parameters and arguments must have the same index. 90 func newUnifier(tparams []*TypeParam, targs []Type, enableInterfaceInference bool) *unifier { 91 assert(len(tparams) >= len(targs)) 92 handles := make(map[*TypeParam]*Type, len(tparams)) 93 // Allocate all handles up-front: in a correct program, all type parameters 94 // must be resolved and thus eventually will get a handle. 95 // Also, sharing of handles caused by unified type parameters is rare and 96 // so it's ok to not optimize for that case (and delay handle allocation). 97 for i, x := range tparams { 98 var t Type 99 if i < len(targs) { 100 t = targs[i] 101 } 102 handles[x] = &t 103 } 104 return &unifier{handles, 0, enableInterfaceInference} 105 } 106 107 // unifyMode controls the behavior of the unifier. 108 type unifyMode uint 109 110 const ( 111 // If assign is set, we are unifying types involved in an assignment: 112 // they may match inexactly at the top, but element types must match 113 // exactly. 114 assign unifyMode = 1 << iota 115 116 // If exact is set, types unify if they are identical (or can be 117 // made identical with suitable arguments for type parameters). 118 // Otherwise, a named type and a type literal unify if their 119 // underlying types unify, channel directions are ignored, and 120 // if there is an interface, the other type must implement the 121 // interface. 122 exact 123 ) 124 125 func (m unifyMode) String() string { 126 switch m { 127 case 0: 128 return "inexact" 129 case assign: 130 return "assign" 131 case exact: 132 return "exact" 133 case assign | exact: 134 return "assign, exact" 135 } 136 return fmt.Sprintf("mode %d", m) 137 } 138 139 // unify attempts to unify x and y and reports whether it succeeded. 140 // As a side-effect, types may be inferred for type parameters. 141 // The mode parameter controls how types are compared. 142 func (u *unifier) unify(x, y Type, mode unifyMode) bool { 143 return u.nify(x, y, mode, nil) 144 } 145 146 func (u *unifier) tracef(format string, args ...interface{}) { 147 fmt.Println(strings.Repeat(". ", u.depth) + sprintf(nil, nil, true, format, args...)) 148 } 149 150 // String returns a string representation of the current mapping 151 // from type parameters to types. 152 func (u *unifier) String() string { 153 // sort type parameters for reproducible strings 154 tparams := make(typeParamsById, len(u.handles)) 155 i := 0 156 for tpar := range u.handles { 157 tparams[i] = tpar 158 i++ 159 } 160 sort.Sort(tparams) 161 162 var buf bytes.Buffer 163 w := newTypeWriter(&buf, nil) 164 w.byte('[') 165 for i, x := range tparams { 166 if i > 0 { 167 w.string(", ") 168 } 169 w.typ(x) 170 w.string(": ") 171 w.typ(u.at(x)) 172 } 173 w.byte(']') 174 return buf.String() 175 } 176 177 type typeParamsById []*TypeParam 178 179 func (s typeParamsById) Len() int { return len(s) } 180 func (s typeParamsById) Less(i, j int) bool { return s[i].id < s[j].id } 181 func (s typeParamsById) Swap(i, j int) { s[i], s[j] = s[j], s[i] } 182 183 // join unifies the given type parameters x and y. 184 // If both type parameters already have a type associated with them 185 // and they are not joined, join fails and returns false. 186 func (u *unifier) join(x, y *TypeParam) bool { 187 if traceInference { 188 u.tracef("%s ⇄ %s", x, y) 189 } 190 switch hx, hy := u.handles[x], u.handles[y]; { 191 case hx == hy: 192 // Both type parameters already share the same handle. Nothing to do. 193 case *hx != nil && *hy != nil: 194 // Both type parameters have (possibly different) inferred types. Cannot join. 195 return false 196 case *hx != nil: 197 // Only type parameter x has an inferred type. Use handle of x. 198 u.setHandle(y, hx) 199 // This case is treated like the default case. 200 // case *hy != nil: 201 // // Only type parameter y has an inferred type. Use handle of y. 202 // u.setHandle(x, hy) 203 default: 204 // Neither type parameter has an inferred type. Use handle of y. 205 u.setHandle(x, hy) 206 } 207 return true 208 } 209 210 // asTypeParam returns x.(*TypeParam) if x is a type parameter recorded with u. 211 // Otherwise, the result is nil. 212 func (u *unifier) asTypeParam(x Type) *TypeParam { 213 if x, _ := x.(*TypeParam); x != nil { 214 if _, found := u.handles[x]; found { 215 return x 216 } 217 } 218 return nil 219 } 220 221 // setHandle sets the handle for type parameter x 222 // (and all its joined type parameters) to h. 223 func (u *unifier) setHandle(x *TypeParam, h *Type) { 224 hx := u.handles[x] 225 assert(hx != nil) 226 for y, hy := range u.handles { 227 if hy == hx { 228 u.handles[y] = h 229 } 230 } 231 } 232 233 // at returns the (possibly nil) type for type parameter x. 234 func (u *unifier) at(x *TypeParam) Type { 235 return *u.handles[x] 236 } 237 238 // set sets the type t for type parameter x; 239 // t must not be nil. 240 func (u *unifier) set(x *TypeParam, t Type) { 241 assert(t != nil) 242 if traceInference { 243 u.tracef("%s ➞ %s", x, t) 244 } 245 *u.handles[x] = t 246 } 247 248 // unknowns returns the number of type parameters for which no type has been set yet. 249 func (u *unifier) unknowns() int { 250 n := 0 251 for _, h := range u.handles { 252 if *h == nil { 253 n++ 254 } 255 } 256 return n 257 } 258 259 // inferred returns the list of inferred types for the given type parameter list. 260 // The result is never nil and has the same length as tparams; result types that 261 // could not be inferred are nil. Corresponding type parameters and result types 262 // have identical indices. 263 func (u *unifier) inferred(tparams []*TypeParam) []Type { 264 list := make([]Type, len(tparams)) 265 for i, x := range tparams { 266 list[i] = u.at(x) 267 } 268 return list 269 } 270 271 // asInterface returns the underlying type of x as an interface if 272 // it is a non-type parameter interface. Otherwise it returns nil. 273 func asInterface(x Type) (i *Interface) { 274 if _, ok := x.(*TypeParam); !ok { 275 i, _ = under(x).(*Interface) 276 } 277 return i 278 } 279 280 // nify implements the core unification algorithm which is an 281 // adapted version of Checker.identical. For changes to that 282 // code the corresponding changes should be made here. 283 // Must not be called directly from outside the unifier. 284 func (u *unifier) nify(x, y Type, mode unifyMode, p *ifacePair) (result bool) { 285 u.depth++ 286 if traceInference { 287 u.tracef("%s ≡ %s\t// %s", x, y, mode) 288 } 289 defer func() { 290 if traceInference && !result { 291 u.tracef("%s ≢ %s", x, y) 292 } 293 u.depth-- 294 }() 295 296 x = Unalias(x) 297 y = Unalias(y) 298 299 // nothing to do if x == y 300 if x == y { 301 return true 302 } 303 304 // Stop gap for cases where unification fails. 305 if u.depth > unificationDepthLimit { 306 if traceInference { 307 u.tracef("depth %d >= %d", u.depth, unificationDepthLimit) 308 } 309 if panicAtUnificationDepthLimit { 310 panic("unification reached recursion depth limit") 311 } 312 return false 313 } 314 315 // Unification is symmetric, so we can swap the operands. 316 // Ensure that if we have at least one 317 // - defined type, make sure one is in y 318 // - type parameter recorded with u, make sure one is in x 319 if asNamed(x) != nil || u.asTypeParam(y) != nil { 320 if traceInference { 321 u.tracef("%s ≡ %s\t// swap", y, x) 322 } 323 x, y = y, x 324 } 325 326 // Unification will fail if we match a defined type against a type literal. 327 // If we are matching types in an assignment, at the top-level, types with 328 // the same type structure are permitted as long as at least one of them 329 // is not a defined type. To accommodate for that possibility, we continue 330 // unification with the underlying type of a defined type if the other type 331 // is a type literal. This is controlled by the exact unification mode. 332 // We also continue if the other type is a basic type because basic types 333 // are valid underlying types and may appear as core types of type constraints. 334 // If we exclude them, inferred defined types for type parameters may not 335 // match against the core types of their constraints (even though they might 336 // correctly match against some of the types in the constraint's type set). 337 // Finally, if unification (incorrectly) succeeds by matching the underlying 338 // type of a defined type against a basic type (because we include basic types 339 // as type literals here), and if that leads to an incorrectly inferred type, 340 // we will fail at function instantiation or argument assignment time. 341 // 342 // If we have at least one defined type, there is one in y. 343 if ny := asNamed(y); mode&exact == 0 && ny != nil && isTypeLit(x) && !(u.enableInterfaceInference && IsInterface(x)) { 344 if traceInference { 345 u.tracef("%s ≡ under %s", x, ny) 346 } 347 y = ny.under() 348 // Per the spec, a defined type cannot have an underlying type 349 // that is a type parameter. 350 assert(!isTypeParam(y)) 351 // x and y may be identical now 352 if x == y { 353 return true 354 } 355 } 356 357 // Cases where at least one of x or y is a type parameter recorded with u. 358 // If we have at least one type parameter, there is one in x. 359 // If we have exactly one type parameter, because it is in x, 360 // isTypeLit(x) is false and y was not changed above. In other 361 // words, if y was a defined type, it is still a defined type 362 // (relevant for the logic below). 363 switch px, py := u.asTypeParam(x), u.asTypeParam(y); { 364 case px != nil && py != nil: 365 // both x and y are type parameters 366 if u.join(px, py) { 367 return true 368 } 369 // both x and y have an inferred type - they must match 370 return u.nify(u.at(px), u.at(py), mode, p) 371 372 case px != nil: 373 // x is a type parameter, y is not 374 if x := u.at(px); x != nil { 375 // x has an inferred type which must match y 376 if u.nify(x, y, mode, p) { 377 // We have a match, possibly through underlying types. 378 xi := asInterface(x) 379 yi := asInterface(y) 380 xn := asNamed(x) != nil 381 yn := asNamed(y) != nil 382 // If we have two interfaces, what to do depends on 383 // whether they are named and their method sets. 384 if xi != nil && yi != nil { 385 // Both types are interfaces. 386 // If both types are defined types, they must be identical 387 // because unification doesn't know which type has the "right" name. 388 if xn && yn { 389 return Identical(x, y) 390 } 391 // In all other cases, the method sets must match. 392 // The types unified so we know that corresponding methods 393 // match and we can simply compare the number of methods. 394 // TODO(gri) We may be able to relax this rule and select 395 // the more general interface. But if one of them is a defined 396 // type, it's not clear how to choose and whether we introduce 397 // an order dependency or not. Requiring the same method set 398 // is conservative. 399 if len(xi.typeSet().methods) != len(yi.typeSet().methods) { 400 return false 401 } 402 } else if xi != nil || yi != nil { 403 // One but not both of them are interfaces. 404 // In this case, either x or y could be viable matches for the corresponding 405 // type parameter, which means choosing either introduces an order dependence. 406 // Therefore, we must fail unification (go.dev/issue/60933). 407 return false 408 } 409 // If we have inexact unification and one of x or y is a defined type, select the 410 // defined type. This ensures that in a series of types, all matching against the 411 // same type parameter, we infer a defined type if there is one, independent of 412 // order. Type inference or assignment may fail, which is ok. 413 // Selecting a defined type, if any, ensures that we don't lose the type name; 414 // and since we have inexact unification, a value of equally named or matching 415 // undefined type remains assignable (go.dev/issue/43056). 416 // 417 // Similarly, if we have inexact unification and there are no defined types but 418 // channel types, select a directed channel, if any. This ensures that in a series 419 // of unnamed types, all matching against the same type parameter, we infer the 420 // directed channel if there is one, independent of order. 421 // Selecting a directional channel, if any, ensures that a value of another 422 // inexactly unifying channel type remains assignable (go.dev/issue/62157). 423 // 424 // If we have multiple defined channel types, they are either identical or we 425 // have assignment conflicts, so we can ignore directionality in this case. 426 // 427 // If we have defined and literal channel types, a defined type wins to avoid 428 // order dependencies. 429 if mode&exact == 0 { 430 switch { 431 case xn: 432 // x is a defined type: nothing to do. 433 case yn: 434 // x is not a defined type and y is a defined type: select y. 435 u.set(px, y) 436 default: 437 // Neither x nor y are defined types. 438 if yc, _ := under(y).(*Chan); yc != nil && yc.dir != SendRecv { 439 // y is a directed channel type: select y. 440 u.set(px, y) 441 } 442 } 443 } 444 return true 445 } 446 return false 447 } 448 // otherwise, infer type from y 449 u.set(px, y) 450 return true 451 } 452 453 // x != y if we get here 454 assert(x != y) 455 456 // If u.EnableInterfaceInference is set and we don't require exact unification, 457 // if both types are interfaces, one interface must have a subset of the 458 // methods of the other and corresponding method signatures must unify. 459 // If only one type is an interface, all its methods must be present in the 460 // other type and corresponding method signatures must unify. 461 if u.enableInterfaceInference && mode&exact == 0 { 462 // One or both interfaces may be defined types. 463 // Look under the name, but not under type parameters (go.dev/issue/60564). 464 xi := asInterface(x) 465 yi := asInterface(y) 466 // If we have two interfaces, check the type terms for equivalence, 467 // and unify common methods if possible. 468 if xi != nil && yi != nil { 469 xset := xi.typeSet() 470 yset := yi.typeSet() 471 if xset.comparable != yset.comparable { 472 return false 473 } 474 // For now we require terms to be equal. 475 // We should be able to relax this as well, eventually. 476 if !xset.terms.equal(yset.terms) { 477 return false 478 } 479 // Interface types are the only types where cycles can occur 480 // that are not "terminated" via named types; and such cycles 481 // can only be created via method parameter types that are 482 // anonymous interfaces (directly or indirectly) embedding 483 // the current interface. Example: 484 // 485 // type T interface { 486 // m() interface{T} 487 // } 488 // 489 // If two such (differently named) interfaces are compared, 490 // endless recursion occurs if the cycle is not detected. 491 // 492 // If x and y were compared before, they must be equal 493 // (if they were not, the recursion would have stopped); 494 // search the ifacePair stack for the same pair. 495 // 496 // This is a quadratic algorithm, but in practice these stacks 497 // are extremely short (bounded by the nesting depth of interface 498 // type declarations that recur via parameter types, an extremely 499 // rare occurrence). An alternative implementation might use a 500 // "visited" map, but that is probably less efficient overall. 501 q := &ifacePair{xi, yi, p} 502 for p != nil { 503 if p.identical(q) { 504 return true // same pair was compared before 505 } 506 p = p.prev 507 } 508 // The method set of x must be a subset of the method set 509 // of y or vice versa, and the common methods must unify. 510 xmethods := xset.methods 511 ymethods := yset.methods 512 // The smaller method set must be the subset, if it exists. 513 if len(xmethods) > len(ymethods) { 514 xmethods, ymethods = ymethods, xmethods 515 } 516 // len(xmethods) <= len(ymethods) 517 // Collect the ymethods in a map for quick lookup. 518 ymap := make(map[string]*Func, len(ymethods)) 519 for _, ym := range ymethods { 520 ymap[ym.Id()] = ym 521 } 522 // All xmethods must exist in ymethods and corresponding signatures must unify. 523 for _, xm := range xmethods { 524 if ym := ymap[xm.Id()]; ym == nil || !u.nify(xm.typ, ym.typ, exact, p) { 525 return false 526 } 527 } 528 return true 529 } 530 531 // We don't have two interfaces. If we have one, make sure it's in xi. 532 if yi != nil { 533 xi = yi 534 y = x 535 } 536 537 // If we have one interface, at a minimum each of the interface methods 538 // must be implemented and thus unify with a corresponding method from 539 // the non-interface type, otherwise unification fails. 540 if xi != nil { 541 // All xi methods must exist in y and corresponding signatures must unify. 542 xmethods := xi.typeSet().methods 543 for _, xm := range xmethods { 544 obj, _, _ := LookupFieldOrMethod(y, false, xm.pkg, xm.name) 545 if ym, _ := obj.(*Func); ym == nil || !u.nify(xm.typ, ym.typ, exact, p) { 546 return false 547 } 548 } 549 return true 550 } 551 } 552 553 // Unless we have exact unification, neither x nor y are interfaces now. 554 // Except for unbound type parameters (see below), x and y must be structurally 555 // equivalent to unify. 556 557 // If we get here and x or y is a type parameter, they are unbound 558 // (not recorded with the unifier). 559 // Ensure that if we have at least one type parameter, it is in x 560 // (the earlier swap checks for _recorded_ type parameters only). 561 // This ensures that the switch switches on the type parameter. 562 // 563 // TODO(gri) Factor out type parameter handling from the switch. 564 if isTypeParam(y) { 565 if traceInference { 566 u.tracef("%s ≡ %s\t// swap", y, x) 567 } 568 x, y = y, x 569 } 570 571 // Type elements (array, slice, etc. elements) use emode for unification. 572 // Element types must match exactly if the types are used in an assignment. 573 emode := mode 574 if mode&assign != 0 { 575 emode |= exact 576 } 577 578 switch x := x.(type) { 579 case *Basic: 580 // Basic types are singletons except for the rune and byte 581 // aliases, thus we cannot solely rely on the x == y check 582 // above. See also comment in TypeName.IsAlias. 583 if y, ok := y.(*Basic); ok { 584 return x.kind == y.kind 585 } 586 587 case *Array: 588 // Two array types unify if they have the same array length 589 // and their element types unify. 590 if y, ok := y.(*Array); ok { 591 // If one or both array lengths are unknown (< 0) due to some error, 592 // assume they are the same to avoid spurious follow-on errors. 593 return (x.len < 0 || y.len < 0 || x.len == y.len) && u.nify(x.elem, y.elem, emode, p) 594 } 595 596 case *Slice: 597 // Two slice types unify if their element types unify. 598 if y, ok := y.(*Slice); ok { 599 return u.nify(x.elem, y.elem, emode, p) 600 } 601 602 case *Struct: 603 // Two struct types unify if they have the same sequence of fields, 604 // and if corresponding fields have the same names, their (field) types unify, 605 // and they have identical tags. Two embedded fields are considered to have the same 606 // name. Lower-case field names from different packages are always different. 607 if y, ok := y.(*Struct); ok { 608 if x.NumFields() == y.NumFields() { 609 for i, f := range x.fields { 610 g := y.fields[i] 611 if f.embedded != g.embedded || 612 x.Tag(i) != y.Tag(i) || 613 !f.sameId(g.pkg, g.name) || 614 !u.nify(f.typ, g.typ, emode, p) { 615 return false 616 } 617 } 618 return true 619 } 620 } 621 622 case *Pointer: 623 // Two pointer types unify if their base types unify. 624 if y, ok := y.(*Pointer); ok { 625 return u.nify(x.base, y.base, emode, p) 626 } 627 628 case *Tuple: 629 // Two tuples types unify if they have the same number of elements 630 // and the types of corresponding elements unify. 631 if y, ok := y.(*Tuple); ok { 632 if x.Len() == y.Len() { 633 if x != nil { 634 for i, v := range x.vars { 635 w := y.vars[i] 636 if !u.nify(v.typ, w.typ, mode, p) { 637 return false 638 } 639 } 640 } 641 return true 642 } 643 } 644 645 case *Signature: 646 // Two function types unify if they have the same number of parameters 647 // and result values, corresponding parameter and result types unify, 648 // and either both functions are variadic or neither is. 649 // Parameter and result names are not required to match. 650 // TODO(gri) handle type parameters or document why we can ignore them. 651 if y, ok := y.(*Signature); ok { 652 return x.variadic == y.variadic && 653 u.nify(x.params, y.params, emode, p) && 654 u.nify(x.results, y.results, emode, p) 655 } 656 657 case *Interface: 658 assert(!u.enableInterfaceInference || mode&exact != 0) // handled before this switch 659 660 // Two interface types unify if they have the same set of methods with 661 // the same names, and corresponding function types unify. 662 // Lower-case method names from different packages are always different. 663 // The order of the methods is irrelevant. 664 if y, ok := y.(*Interface); ok { 665 xset := x.typeSet() 666 yset := y.typeSet() 667 if xset.comparable != yset.comparable { 668 return false 669 } 670 if !xset.terms.equal(yset.terms) { 671 return false 672 } 673 a := xset.methods 674 b := yset.methods 675 if len(a) == len(b) { 676 // Interface types are the only types where cycles can occur 677 // that are not "terminated" via named types; and such cycles 678 // can only be created via method parameter types that are 679 // anonymous interfaces (directly or indirectly) embedding 680 // the current interface. Example: 681 // 682 // type T interface { 683 // m() interface{T} 684 // } 685 // 686 // If two such (differently named) interfaces are compared, 687 // endless recursion occurs if the cycle is not detected. 688 // 689 // If x and y were compared before, they must be equal 690 // (if they were not, the recursion would have stopped); 691 // search the ifacePair stack for the same pair. 692 // 693 // This is a quadratic algorithm, but in practice these stacks 694 // are extremely short (bounded by the nesting depth of interface 695 // type declarations that recur via parameter types, an extremely 696 // rare occurrence). An alternative implementation might use a 697 // "visited" map, but that is probably less efficient overall. 698 q := &ifacePair{x, y, p} 699 for p != nil { 700 if p.identical(q) { 701 return true // same pair was compared before 702 } 703 p = p.prev 704 } 705 if debug { 706 assertSortedMethods(a) 707 assertSortedMethods(b) 708 } 709 for i, f := range a { 710 g := b[i] 711 if f.Id() != g.Id() || !u.nify(f.typ, g.typ, exact, q) { 712 return false 713 } 714 } 715 return true 716 } 717 } 718 719 case *Map: 720 // Two map types unify if their key and value types unify. 721 if y, ok := y.(*Map); ok { 722 return u.nify(x.key, y.key, emode, p) && u.nify(x.elem, y.elem, emode, p) 723 } 724 725 case *Chan: 726 // Two channel types unify if their value types unify 727 // and if they have the same direction. 728 // The channel direction is ignored for inexact unification. 729 if y, ok := y.(*Chan); ok { 730 return (mode&exact == 0 || x.dir == y.dir) && u.nify(x.elem, y.elem, emode, p) 731 } 732 733 case *Named: 734 // Two named types unify if their type names originate in the same type declaration. 735 // If they are instantiated, their type argument lists must unify. 736 if y := asNamed(y); y != nil { 737 // Check type arguments before origins so they unify 738 // even if the origins don't match; for better error 739 // messages (see go.dev/issue/53692). 740 xargs := x.TypeArgs().list() 741 yargs := y.TypeArgs().list() 742 if len(xargs) != len(yargs) { 743 return false 744 } 745 for i, xarg := range xargs { 746 if !u.nify(xarg, yargs[i], mode, p) { 747 return false 748 } 749 } 750 return identicalOrigin(x, y) 751 } 752 753 case *TypeParam: 754 // x must be an unbound type parameter (see comment above). 755 if debug { 756 assert(u.asTypeParam(x) == nil) 757 } 758 // By definition, a valid type argument must be in the type set of 759 // the respective type constraint. Therefore, the type argument's 760 // underlying type must be in the set of underlying types of that 761 // constraint. If there is a single such underlying type, it's the 762 // constraint's core type. It must match the type argument's under- 763 // lying type, irrespective of whether the actual type argument, 764 // which may be a defined type, is actually in the type set (that 765 // will be determined at instantiation time). 766 // Thus, if we have the core type of an unbound type parameter, 767 // we know the structure of the possible types satisfying such 768 // parameters. Use that core type for further unification 769 // (see go.dev/issue/50755 for a test case). 770 if enableCoreTypeUnification { 771 // Because the core type is always an underlying type, 772 // unification will take care of matching against a 773 // defined or literal type automatically. 774 // If y is also an unbound type parameter, we will end 775 // up here again with x and y swapped, so we don't 776 // need to take care of that case separately. 777 if cx := coreType(x); cx != nil { 778 if traceInference { 779 u.tracef("core %s ≡ %s", x, y) 780 } 781 // If y is a defined type, it may not match against cx which 782 // is an underlying type (incl. int, string, etc.). Use assign 783 // mode here so that the unifier automatically takes under(y) 784 // if necessary. 785 return u.nify(cx, y, assign, p) 786 } 787 } 788 // x != y and there's nothing to do 789 790 case nil: 791 // avoid a crash in case of nil type 792 793 default: 794 panic(sprintf(nil, nil, true, "u.nify(%s, %s, %d)", x, y, mode)) 795 } 796 797 return false 798 } 799