1 // Copyright 2018 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 // This file implements type parameter inference given 6 // a list of concrete arguments and a parameter list. 7 8 package types 9 10 import ( 11 "fmt" 12 "go/token" 13 "strings" 14 ) 15 16 // infer attempts to infer the complete set of type arguments for generic function instantiation/call 17 // based on the given type parameters tparams, type arguments targs, function parameters params, and 18 // function arguments args, if any. There must be at least one type parameter, no more type arguments 19 // than type parameters, and params and args must match in number (incl. zero). 20 // If successful, infer returns the complete list of type arguments, one for each type parameter. 21 // Otherwise the result is nil and appropriate errors will be reported. 22 // 23 // Inference proceeds as follows: 24 // 25 // Starting with given type arguments 26 // 1) apply FTI (function type inference) with typed arguments, 27 // 2) apply CTI (constraint type inference), 28 // 3) apply FTI with untyped function arguments, 29 // 4) apply CTI. 30 // 31 // The process stops as soon as all type arguments are known or an error occurs. 32 func (check *Checker) infer(posn positioner, tparams []*TypeParam, targs []Type, params *Tuple, args []*operand) (result []Type) { 33 if debug { 34 defer func() { 35 assert(result == nil || len(result) == len(tparams)) 36 for _, targ := range result { 37 assert(targ != nil) 38 } 39 //check.dump("### inferred targs = %s", result) 40 }() 41 } 42 43 if traceInference { 44 check.dump("-- inferA %s%s ➞ %s", tparams, params, targs) 45 defer func() { 46 check.dump("=> inferA %s ➞ %s", tparams, result) 47 }() 48 } 49 50 // There must be at least one type parameter, and no more type arguments than type parameters. 51 n := len(tparams) 52 assert(n > 0 && len(targs) <= n) 53 54 // Function parameters and arguments must match in number. 55 assert(params.Len() == len(args)) 56 57 // If we already have all type arguments, we're done. 58 if len(targs) == n { 59 return targs 60 } 61 // len(targs) < n 62 63 const enableTparamRenaming = true 64 if enableTparamRenaming { 65 // For the purpose of type inference we must differentiate type parameters 66 // occurring in explicit type or value function arguments from the type 67 // parameters we are solving for via unification, because they may be the 68 // same in self-recursive calls. For example: 69 // 70 // func f[P *Q, Q any](p P, q Q) { 71 // f(p) 72 // } 73 // 74 // In this example, the fact that the P used in the instantation f[P] has 75 // the same pointer identity as the P we are trying to solve for via 76 // unification is coincidental: there is nothing special about recursive 77 // calls that should cause them to conflate the identity of type arguments 78 // with type parameters. To put it another way: any such self-recursive 79 // call is equivalent to a mutually recursive call, which does not run into 80 // any problems of type parameter identity. For example, the following code 81 // is equivalent to the code above. 82 // 83 // func f[P interface{*Q}, Q any](p P, q Q) { 84 // f2(p) 85 // } 86 // 87 // func f2[P interface{*Q}, Q any](p P, q Q) { 88 // f(p) 89 // } 90 // 91 // We can turn the first example into the second example by renaming type 92 // parameters in the original signature to give them a new identity. As an 93 // optimization, we do this only for self-recursive calls. 94 95 // We can detect if we are in a self-recursive call by comparing the 96 // identity of the first type parameter in the current function with the 97 // first type parameter in tparams. This works because type parameters are 98 // unique to their type parameter list. 99 selfRecursive := check.sig != nil && check.sig.tparams.Len() > 0 && tparams[0] == check.sig.tparams.At(0) 100 101 if selfRecursive { 102 // In self-recursive inference, rename the type parameters with new type 103 // parameters that are the same but for their pointer identity. 104 tparams2 := make([]*TypeParam, len(tparams)) 105 for i, tparam := range tparams { 106 tname := NewTypeName(tparam.Obj().Pos(), tparam.Obj().Pkg(), tparam.Obj().Name(), nil) 107 tparams2[i] = NewTypeParam(tname, nil) 108 tparams2[i].index = tparam.index // == i 109 } 110 111 renameMap := makeRenameMap(tparams, tparams2) 112 for i, tparam := range tparams { 113 tparams2[i].bound = check.subst(posn.Pos(), tparam.bound, renameMap, nil, check.context()) 114 } 115 116 tparams = tparams2 117 params = check.subst(posn.Pos(), params, renameMap, nil, check.context()).(*Tuple) 118 } 119 } 120 121 // If we have more than 2 arguments, we may have arguments with named and unnamed types. 122 // If that is the case, permutate params and args such that the arguments with named 123 // types are first in the list. This doesn't affect type inference if all types are taken 124 // as is. But when we have inexact unification enabled (as is the case for function type 125 // inference), when a named type is unified with an unnamed type, unification proceeds 126 // with the underlying type of the named type because otherwise unification would fail 127 // right away. This leads to an asymmetry in type inference: in cases where arguments of 128 // named and unnamed types are passed to parameters with identical type, different types 129 // (named vs underlying) may be inferred depending on the order of the arguments. 130 // By ensuring that named types are seen first, order dependence is avoided and unification 131 // succeeds where it can (issue #43056). 132 const enableArgSorting = true 133 if m := len(args); m >= 2 && enableArgSorting { 134 // Determine indices of arguments with named and unnamed types. 135 var named, unnamed []int 136 for i, arg := range args { 137 if hasName(arg.typ) { 138 named = append(named, i) 139 } else { 140 unnamed = append(unnamed, i) 141 } 142 } 143 144 // If we have named and unnamed types, move the arguments with 145 // named types first. Update the parameter list accordingly. 146 // Make copies so as not to clobber the incoming slices. 147 if len(named) != 0 && len(unnamed) != 0 { 148 params2 := make([]*Var, m) 149 args2 := make([]*operand, m) 150 i := 0 151 for _, j := range named { 152 params2[i] = params.At(j) 153 args2[i] = args[j] 154 i++ 155 } 156 for _, j := range unnamed { 157 params2[i] = params.At(j) 158 args2[i] = args[j] 159 i++ 160 } 161 params = NewTuple(params2...) 162 args = args2 163 } 164 } 165 166 // --- 1 --- 167 // Continue with the type arguments we have. Avoid matching generic 168 // parameters that already have type arguments against function arguments: 169 // It may fail because matching uses type identity while parameter passing 170 // uses assignment rules. Instantiate the parameter list with the type 171 // arguments we have, and continue with that parameter list. 172 173 // First, make sure we have a "full" list of type arguments, some of which 174 // may be nil (unknown). Make a copy so as to not clobber the incoming slice. 175 if len(targs) < n { 176 targs2 := make([]Type, n) 177 copy(targs2, targs) 178 targs = targs2 179 } 180 // len(targs) == n 181 182 // Substitute type arguments for their respective type parameters in params, 183 // if any. Note that nil targs entries are ignored by check.subst. 184 // TODO(gri) Can we avoid this (we're setting known type arguments below, 185 // but that doesn't impact the isParameterized check for now). 186 if params.Len() > 0 { 187 smap := makeSubstMap(tparams, targs) 188 params = check.subst(token.NoPos, params, smap, nil, check.context()).(*Tuple) 189 } 190 191 // Unify parameter and argument types for generic parameters with typed arguments 192 // and collect the indices of generic parameters with untyped arguments. 193 // Terminology: generic parameter = function parameter with a type-parameterized type 194 u := newUnifier(false) 195 u.x.init(tparams) 196 197 // Set the type arguments which we know already. 198 for i, targ := range targs { 199 if targ != nil { 200 u.x.set(i, targ) 201 } 202 } 203 204 errorf := func(kind string, tpar, targ Type, arg *operand) { 205 // provide a better error message if we can 206 targs, index := u.x.types() 207 if index == 0 { 208 // The first type parameter couldn't be inferred. 209 // If none of them could be inferred, don't try 210 // to provide the inferred type in the error msg. 211 allFailed := true 212 for _, targ := range targs { 213 if targ != nil { 214 allFailed = false 215 break 216 } 217 } 218 if allFailed { 219 check.errorf(arg, _CannotInferTypeArgs, "%s %s of %s does not match %s (cannot infer %s)", kind, targ, arg.expr, tpar, typeParamsString(tparams)) 220 return 221 } 222 } 223 smap := makeSubstMap(tparams, targs) 224 // TODO(rFindley): pass a positioner here, rather than arg.Pos(). 225 inferred := check.subst(arg.Pos(), tpar, smap, nil, check.context()) 226 // _CannotInferTypeArgs indicates a failure of inference, though the actual 227 // error may be better attributed to a user-provided type argument (hence 228 // _InvalidTypeArg). We can't differentiate these cases, so fall back on 229 // the more general _CannotInferTypeArgs. 230 if inferred != tpar { 231 check.errorf(arg, _CannotInferTypeArgs, "%s %s of %s does not match inferred type %s for %s", kind, targ, arg.expr, inferred, tpar) 232 } else { 233 check.errorf(arg, _CannotInferTypeArgs, "%s %s of %s does not match %s", kind, targ, arg.expr, tpar) 234 } 235 } 236 237 // indices of the generic parameters with untyped arguments - save for later 238 var indices []int 239 for i, arg := range args { 240 par := params.At(i) 241 // If we permit bidirectional unification, this conditional code needs to be 242 // executed even if par.typ is not parameterized since the argument may be a 243 // generic function (for which we want to infer its type arguments). 244 if isParameterized(tparams, par.typ) { 245 if arg.mode == invalid { 246 // An error was reported earlier. Ignore this targ 247 // and continue, we may still be able to infer all 248 // targs resulting in fewer follow-on errors. 249 continue 250 } 251 if targ := arg.typ; isTyped(targ) { 252 // If we permit bidirectional unification, and targ is 253 // a generic function, we need to initialize u.y with 254 // the respective type parameters of targ. 255 if !u.unify(par.typ, targ) { 256 errorf("type", par.typ, targ, arg) 257 return nil 258 } 259 } else if _, ok := par.typ.(*TypeParam); ok { 260 // Since default types are all basic (i.e., non-composite) types, an 261 // untyped argument will never match a composite parameter type; the 262 // only parameter type it can possibly match against is a *TypeParam. 263 // Thus, for untyped arguments we only need to look at parameter types 264 // that are single type parameters. 265 indices = append(indices, i) 266 } 267 } 268 } 269 270 // If we've got all type arguments, we're done. 271 var index int 272 targs, index = u.x.types() 273 if index < 0 { 274 return targs 275 } 276 277 // --- 2 --- 278 // See how far we get with constraint type inference. 279 // Note that even if we don't have any type arguments, constraint type inference 280 // may produce results for constraints that explicitly specify a type. 281 targs, index = check.inferB(posn, tparams, targs) 282 if targs == nil || index < 0 { 283 return targs 284 } 285 286 // --- 3 --- 287 // Use any untyped arguments to infer additional type arguments. 288 // Some generic parameters with untyped arguments may have been given 289 // a type by now, we can ignore them. 290 for _, i := range indices { 291 tpar := params.At(i).typ.(*TypeParam) // is type parameter by construction of indices 292 // Only consider untyped arguments for which the corresponding type 293 // parameter doesn't have an inferred type yet. 294 if targs[tpar.index] == nil { 295 arg := args[i] 296 targ := Default(arg.typ) 297 // The default type for an untyped nil is untyped nil. We must not 298 // infer an untyped nil type as type parameter type. Ignore untyped 299 // nil by making sure all default argument types are typed. 300 if isTyped(targ) && !u.unify(tpar, targ) { 301 errorf("default type", tpar, targ, arg) 302 return nil 303 } 304 } 305 } 306 307 // If we've got all type arguments, we're done. 308 targs, index = u.x.types() 309 if index < 0 { 310 return targs 311 } 312 313 // --- 4 --- 314 // Again, follow up with constraint type inference. 315 targs, index = check.inferB(posn, tparams, targs) 316 if targs == nil || index < 0 { 317 return targs 318 } 319 320 // At least one type argument couldn't be inferred. 321 assert(index >= 0 && targs[index] == nil) 322 tpar := tparams[index] 323 check.errorf(posn, _CannotInferTypeArgs, "cannot infer %s (%v)", tpar.obj.name, tpar.obj.pos) 324 return nil 325 } 326 327 // typeParamsString produces a string containing all the type parameter names 328 // in list suitable for human consumption. 329 func typeParamsString(list []*TypeParam) string { 330 // common cases 331 n := len(list) 332 switch n { 333 case 0: 334 return "" 335 case 1: 336 return list[0].obj.name 337 case 2: 338 return list[0].obj.name + " and " + list[1].obj.name 339 } 340 341 // general case (n > 2) 342 var b strings.Builder 343 for i, tname := range list[:n-1] { 344 if i > 0 { 345 b.WriteString(", ") 346 } 347 b.WriteString(tname.obj.name) 348 } 349 b.WriteString(", and ") 350 b.WriteString(list[n-1].obj.name) 351 return b.String() 352 } 353 354 // isParameterized reports whether typ contains any of the type parameters of tparams. 355 func isParameterized(tparams []*TypeParam, typ Type) bool { 356 w := tpWalker{ 357 seen: make(map[Type]bool), 358 tparams: tparams, 359 } 360 return w.isParameterized(typ) 361 } 362 363 type tpWalker struct { 364 seen map[Type]bool 365 tparams []*TypeParam 366 } 367 368 func (w *tpWalker) isParameterized(typ Type) (res bool) { 369 // detect cycles 370 if x, ok := w.seen[typ]; ok { 371 return x 372 } 373 w.seen[typ] = false 374 defer func() { 375 w.seen[typ] = res 376 }() 377 378 switch t := typ.(type) { 379 case nil, *Basic: // TODO(gri) should nil be handled here? 380 break 381 382 case *Array: 383 return w.isParameterized(t.elem) 384 385 case *Slice: 386 return w.isParameterized(t.elem) 387 388 case *Struct: 389 for _, fld := range t.fields { 390 if w.isParameterized(fld.typ) { 391 return true 392 } 393 } 394 395 case *Pointer: 396 return w.isParameterized(t.base) 397 398 case *Tuple: 399 n := t.Len() 400 for i := 0; i < n; i++ { 401 if w.isParameterized(t.At(i).typ) { 402 return true 403 } 404 } 405 406 case *Signature: 407 // t.tparams may not be nil if we are looking at a signature 408 // of a generic function type (or an interface method) that is 409 // part of the type we're testing. We don't care about these type 410 // parameters. 411 // Similarly, the receiver of a method may declare (rather then 412 // use) type parameters, we don't care about those either. 413 // Thus, we only need to look at the input and result parameters. 414 return w.isParameterized(t.params) || w.isParameterized(t.results) 415 416 case *Interface: 417 tset := t.typeSet() 418 for _, m := range tset.methods { 419 if w.isParameterized(m.typ) { 420 return true 421 } 422 } 423 return tset.is(func(t *term) bool { 424 return t != nil && w.isParameterized(t.typ) 425 }) 426 427 case *Map: 428 return w.isParameterized(t.key) || w.isParameterized(t.elem) 429 430 case *Chan: 431 return w.isParameterized(t.elem) 432 433 case *Named: 434 return w.isParameterizedTypeList(t.TypeArgs().list()) 435 436 case *TypeParam: 437 // t must be one of w.tparams 438 return tparamIndex(w.tparams, t) >= 0 439 440 default: 441 unreachable() 442 } 443 444 return false 445 } 446 447 func (w *tpWalker) isParameterizedTypeList(list []Type) bool { 448 for _, t := range list { 449 if w.isParameterized(t) { 450 return true 451 } 452 } 453 return false 454 } 455 456 // inferB returns the list of actual type arguments inferred from the type parameters' 457 // bounds and an initial set of type arguments. If type inference is impossible because 458 // unification fails, an error is reported if report is set to true, the resulting types 459 // list is nil, and index is 0. 460 // Otherwise, types is the list of inferred type arguments, and index is the index of the 461 // first type argument in that list that couldn't be inferred (and thus is nil). If all 462 // type arguments were inferred successfully, index is < 0. The number of type arguments 463 // provided may be less than the number of type parameters, but there must be at least one. 464 func (check *Checker) inferB(posn positioner, tparams []*TypeParam, targs []Type) (types []Type, index int) { 465 assert(len(tparams) >= len(targs) && len(targs) > 0) 466 467 if traceInference { 468 check.dump("-- inferB %s ➞ %s", tparams, targs) 469 defer func() { 470 check.dump("=> inferB %s ➞ %s", tparams, types) 471 }() 472 } 473 474 // Setup bidirectional unification between constraints 475 // and the corresponding type arguments (which may be nil!). 476 u := newUnifier(false) 477 u.x.init(tparams) 478 u.y = u.x // type parameters between LHS and RHS of unification are identical 479 480 // Set the type arguments which we know already. 481 for i, targ := range targs { 482 if targ != nil { 483 u.x.set(i, targ) 484 } 485 } 486 487 // Repeatedly apply constraint type inference as long as 488 // there are still unknown type arguments and progress is 489 // being made. 490 // 491 // This is an O(n^2) algorithm where n is the number of 492 // type parameters: if there is progress (and iteration 493 // continues), at least one type argument is inferred 494 // per iteration and we have a doubly nested loop. 495 // In practice this is not a problem because the number 496 // of type parameters tends to be very small (< 5 or so). 497 // (It should be possible for unification to efficiently 498 // signal newly inferred type arguments; then the loops 499 // here could handle the respective type parameters only, 500 // but that will come at a cost of extra complexity which 501 // may not be worth it.) 502 for n := u.x.unknowns(); n > 0; { 503 nn := n 504 505 for i, tpar := range tparams { 506 // If there is a core term (i.e., a core type with tilde information) 507 // unify the type parameter with the core type. 508 if core, single := coreTerm(tpar); core != nil { 509 // A type parameter can be unified with its core type in two cases. 510 tx := u.x.at(i) 511 switch { 512 case tx != nil: 513 // The corresponding type argument tx is known. 514 // In this case, if the core type has a tilde, the type argument's underlying 515 // type must match the core type, otherwise the type argument and the core type 516 // must match. 517 // If tx is an external type parameter, don't consider its underlying type 518 // (which is an interface). Core type unification will attempt to unify against 519 // core.typ. 520 // Note also that even with inexact unification we cannot leave away the under 521 // call here because it's possible that both tx and core.typ are named types, 522 // with under(tx) being a (named) basic type matching core.typ. Such cases do 523 // not match with inexact unification. 524 if core.tilde && !isTypeParam(tx) { 525 tx = under(tx) 526 } 527 if !u.unify(tx, core.typ) { 528 // TODO(gri) improve error message by providing the type arguments 529 // which we know already 530 // Don't use term.String() as it always qualifies types, even if they 531 // are in the current package. 532 tilde := "" 533 if core.tilde { 534 tilde = "~" 535 } 536 check.errorf(posn, _InvalidTypeArg, "%s does not match %s%s", tpar, tilde, core.typ) 537 return nil, 0 538 } 539 540 case single && !core.tilde: 541 // The corresponding type argument tx is unknown and there's a single 542 // specific type and no tilde. 543 // In this case the type argument must be that single type; set it. 544 u.x.set(i, core.typ) 545 546 default: 547 // Unification is not possible and no progress was made. 548 continue 549 } 550 551 // The number of known type arguments may have changed. 552 nn = u.x.unknowns() 553 if nn == 0 { 554 break // all type arguments are known 555 } 556 } 557 } 558 559 assert(nn <= n) 560 if nn == n { 561 break // no progress 562 } 563 n = nn 564 } 565 566 // u.x.types() now contains the incoming type arguments plus any additional type 567 // arguments which were inferred from core terms. The newly inferred non-nil 568 // entries may still contain references to other type parameters. 569 // For instance, for [A any, B interface{ []C }, C interface{ *A }], if A == int 570 // was given, unification produced the type list [int, []C, *A]. We eliminate the 571 // remaining type parameters by substituting the type parameters in this type list 572 // until nothing changes anymore. 573 types, _ = u.x.types() 574 if debug { 575 for i, targ := range targs { 576 assert(targ == nil || types[i] == targ) 577 } 578 } 579 580 // The data structure of each (provided or inferred) type represents a graph, where 581 // each node corresponds to a type and each (directed) vertice points to a component 582 // type. The substitution process described above repeatedly replaces type parameter 583 // nodes in these graphs with the graphs of the types the type parameters stand for, 584 // which creates a new (possibly bigger) graph for each type. 585 // The substitution process will not stop if the replacement graph for a type parameter 586 // also contains that type parameter. 587 // For instance, for [A interface{ *A }], without any type argument provided for A, 588 // unification produces the type list [*A]. Substituting A in *A with the value for 589 // A will lead to infinite expansion by producing [**A], [****A], [********A], etc., 590 // because the graph A -> *A has a cycle through A. 591 // Generally, cycles may occur across multiple type parameters and inferred types 592 // (for instance, consider [P interface{ *Q }, Q interface{ func(P) }]). 593 // We eliminate cycles by walking the graphs for all type parameters. If a cycle 594 // through a type parameter is detected, cycleFinder nils out the respectice type 595 // which kills the cycle; this also means that the respective type could not be 596 // inferred. 597 // 598 // TODO(gri) If useful, we could report the respective cycle as an error. We don't 599 // do this now because type inference will fail anyway, and furthermore, 600 // constraints with cycles of this kind cannot currently be satisfied by 601 // any user-suplied type. But should that change, reporting an error 602 // would be wrong. 603 w := cycleFinder{tparams, types, make(map[Type]bool)} 604 for _, t := range tparams { 605 w.typ(t) // t != nil 606 } 607 608 // dirty tracks the indices of all types that may still contain type parameters. 609 // We know that nil type entries and entries corresponding to provided (non-nil) 610 // type arguments are clean, so exclude them from the start. 611 var dirty []int 612 for i, typ := range types { 613 if typ != nil && (i >= len(targs) || targs[i] == nil) { 614 dirty = append(dirty, i) 615 } 616 } 617 618 for len(dirty) > 0 { 619 // TODO(gri) Instead of creating a new substMap for each iteration, 620 // provide an update operation for substMaps and only change when 621 // needed. Optimization. 622 smap := makeSubstMap(tparams, types) 623 n := 0 624 for _, index := range dirty { 625 t0 := types[index] 626 if t1 := check.subst(token.NoPos, t0, smap, nil, check.context()); t1 != t0 { 627 types[index] = t1 628 dirty[n] = index 629 n++ 630 } 631 } 632 dirty = dirty[:n] 633 } 634 635 // Once nothing changes anymore, we may still have type parameters left; 636 // e.g., a constraint with core type *P may match a type parameter Q but 637 // we don't have any type arguments to fill in for *P or Q (issue #45548). 638 // Don't let such inferences escape, instead nil them out. 639 for i, typ := range types { 640 if typ != nil && isParameterized(tparams, typ) { 641 types[i] = nil 642 } 643 } 644 645 // update index 646 index = -1 647 for i, typ := range types { 648 if typ == nil { 649 index = i 650 break 651 } 652 } 653 654 return 655 } 656 657 // If the type parameter has a single specific type S, coreTerm returns (S, true). 658 // Otherwise, if tpar has a core type T, it returns a term corresponding to that 659 // core type and false. In that case, if any term of tpar has a tilde, the core 660 // term has a tilde. In all other cases coreTerm returns (nil, false). 661 func coreTerm(tpar *TypeParam) (*term, bool) { 662 n := 0 663 var single *term // valid if n == 1 664 var tilde bool 665 tpar.is(func(t *term) bool { 666 if t == nil { 667 assert(n == 0) 668 return false // no terms 669 } 670 n++ 671 single = t 672 if t.tilde { 673 tilde = true 674 } 675 return true 676 }) 677 if n == 1 { 678 if debug { 679 assert(debug && under(single.typ) == coreType(tpar)) 680 } 681 return single, true 682 } 683 if typ := coreType(tpar); typ != nil { 684 // A core type is always an underlying type. 685 // If any term of tpar has a tilde, we don't 686 // have a precise core type and we must return 687 // a tilde as well. 688 return &term{tilde, typ}, false 689 } 690 return nil, false 691 } 692 693 type cycleFinder struct { 694 tparams []*TypeParam 695 types []Type 696 seen map[Type]bool 697 } 698 699 func (w *cycleFinder) typ(typ Type) { 700 if w.seen[typ] { 701 // We have seen typ before. If it is one of the type parameters 702 // in tparams, iterative substitution will lead to infinite expansion. 703 // Nil out the corresponding type which effectively kills the cycle. 704 if tpar, _ := typ.(*TypeParam); tpar != nil { 705 if i := tparamIndex(w.tparams, tpar); i >= 0 { 706 // cycle through tpar 707 w.types[i] = nil 708 } 709 } 710 // If we don't have one of our type parameters, the cycle is due 711 // to an ordinary recursive type and we can just stop walking it. 712 return 713 } 714 w.seen[typ] = true 715 defer delete(w.seen, typ) 716 717 switch t := typ.(type) { 718 case *Basic: 719 // nothing to do 720 721 case *Array: 722 w.typ(t.elem) 723 724 case *Slice: 725 w.typ(t.elem) 726 727 case *Struct: 728 w.varList(t.fields) 729 730 case *Pointer: 731 w.typ(t.base) 732 733 // case *Tuple: 734 // This case should not occur because tuples only appear 735 // in signatures where they are handled explicitly. 736 737 case *Signature: 738 if t.params != nil { 739 w.varList(t.params.vars) 740 } 741 if t.results != nil { 742 w.varList(t.results.vars) 743 } 744 745 case *Union: 746 for _, t := range t.terms { 747 w.typ(t.typ) 748 } 749 750 case *Interface: 751 for _, m := range t.methods { 752 w.typ(m.typ) 753 } 754 for _, t := range t.embeddeds { 755 w.typ(t) 756 } 757 758 case *Map: 759 w.typ(t.key) 760 w.typ(t.elem) 761 762 case *Chan: 763 w.typ(t.elem) 764 765 case *Named: 766 for _, tpar := range t.TypeArgs().list() { 767 w.typ(tpar) 768 } 769 770 case *TypeParam: 771 if i := tparamIndex(w.tparams, t); i >= 0 && w.types[i] != nil { 772 w.typ(w.types[i]) 773 } 774 775 default: 776 panic(fmt.Sprintf("unexpected %T", typ)) 777 } 778 } 779 780 func (w *cycleFinder) varList(list []*Var) { 781 for _, v := range list { 782 w.typ(v.typ) 783 } 784 } 785