instantiate.go

     1  // Code generated by "go test -run=Generate -write=all"; DO NOT EDIT.
     2  // Source: ../../cmd/compile/internal/types2/instantiate.go
     3  
     4  // Copyright 2021 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  // This file implements instantiation of generic types
     9  // through substitution of type parameters by type arguments.
    10  
    11  package types
    12  
    13  import (
    14  	"errors"
    15  	"fmt"
    16  	"go/token"
    17  	"internal/buildcfg"
    18  	. "internal/types/errors"
    19  )
    20  
    21  // A genericType implements access to its type parameters.
    22  type genericType interface {
    23  	Type
    24  	TypeParams() *TypeParamList
    25  }
    26  
    27  // Instantiate instantiates the type orig with the given type arguments targs.
    28  // orig must be an *Alias, *Named, or *Signature type. If there is no error,
    29  // the resulting Type is an instantiated type of the same kind (*Alias, *Named
    30  // or *Signature, respectively).
    31  //
    32  // Methods attached to a *Named type are also instantiated, and associated with
    33  // a new *Func that has the same position as the original method, but nil function
    34  // scope.
    35  //
    36  // If ctxt is non-nil, it may be used to de-duplicate the instance against
    37  // previous instances with the same identity. As a special case, generic
    38  // *Signature origin types are only considered identical if they are pointer
    39  // equivalent, so that instantiating distinct (but possibly identical)
    40  // signatures will yield different instances. The use of a shared context does
    41  // not guarantee that identical instances are deduplicated in all cases.
    42  //
    43  // If validate is set, Instantiate verifies that the number of type arguments
    44  // and parameters match, and that the type arguments satisfy their respective
    45  // type constraints. If verification fails, the resulting error may wrap an
    46  // *ArgumentError indicating which type argument did not satisfy its type parameter
    47  // constraint, and why.
    48  //
    49  // If validate is not set, Instantiate does not verify the type argument count
    50  // or whether the type arguments satisfy their constraints. Instantiate is
    51  // guaranteed to not return an error, but may panic. Specifically, for
    52  // *Signature types, Instantiate will panic immediately if the type argument
    53  // count is incorrect; for *Named types, a panic may occur later inside the
    54  // *Named API.
    55  func Instantiate(ctxt *Context, orig Type, targs []Type, validate bool) (Type, error) {
    56  	assert(len(targs) > 0)
    57  	if ctxt == nil {
    58  		ctxt = NewContext()
    59  	}
    60  	orig_ := orig.(genericType) // signature of Instantiate must not change for backward-compatibility
    61  
    62  	if validate {
    63  		tparams := orig_.TypeParams().list()
    64  		assert(len(tparams) > 0)
    65  		if len(targs) != len(tparams) {
    66  			return nil, fmt.Errorf("got %d type arguments but %s has %d type parameters", len(targs), orig, len(tparams))
    67  		}
    68  		if i, err := (*Checker)(nil).verify(nopos, tparams, targs, ctxt); err != nil {
    69  			return nil, &ArgumentError{i, err}
    70  		}
    71  	}
    72  
    73  	inst := (*Checker)(nil).instance(nopos, orig_, targs, nil, ctxt)
    74  	return inst, nil
    75  }
    76  
    77  // instance instantiates the given original (generic) function or type with the
    78  // provided type arguments and returns the resulting instance. If an identical
    79  // instance exists already in the given contexts, it returns that instance,
    80  // otherwise it creates a new one. If there is an error (such as wrong number
    81  // of type arguments), the result is Typ[Invalid].
    82  //
    83  // If expanding is non-nil, it is the Named instance type currently being
    84  // expanded. If ctxt is non-nil, it is the context associated with the current
    85  // type-checking pass or call to Instantiate. At least one of expanding or ctxt
    86  // must be non-nil.
    87  //
    88  // For Named types the resulting instance may be unexpanded.
    89  //
    90  // check may be nil (when not type-checking syntax); pos is used only only if check is non-nil.
    91  func (check *Checker) instance(pos token.Pos, orig genericType, targs []Type, expanding *Named, ctxt *Context) (res Type) {
    92  	// The order of the contexts below matters: we always prefer instances in the
    93  	// expanding instance context in order to preserve reference cycles.
    94  	//
    95  	// Invariant: if expanding != nil, the returned instance will be the instance
    96  	// recorded in expanding.inst.ctxt.
    97  	var ctxts []*Context
    98  	if expanding != nil {
    99  		ctxts = append(ctxts, expanding.inst.ctxt)
   100  	}
   101  	if ctxt != nil {
   102  		ctxts = append(ctxts, ctxt)
   103  	}
   104  	assert(len(ctxts) > 0)
   105  
   106  	// Compute all hashes; hashes may differ across contexts due to different
   107  	// unique IDs for Named types within the hasher.
   108  	hashes := make([]string, len(ctxts))
   109  	for i, ctxt := range ctxts {
   110  		hashes[i] = ctxt.instanceHash(orig, targs)
   111  	}
   112  
   113  	// Record the result in all contexts.
   114  	// Prefer to re-use existing types from expanding context, if it exists, to reduce
   115  	// the memory pinned by the Named type.
   116  	updateContexts := func(res Type) Type {
   117  		for i := len(ctxts) - 1; i >= 0; i-- {
   118  			res = ctxts[i].update(hashes[i], orig, targs, res)
   119  		}
   120  		return res
   121  	}
   122  
   123  	// typ may already have been instantiated with identical type arguments. In
   124  	// that case, re-use the existing instance.
   125  	for i, ctxt := range ctxts {
   126  		if inst := ctxt.lookup(hashes[i], orig, targs); inst != nil {
   127  			return updateContexts(inst)
   128  		}
   129  	}
   130  
   131  	switch orig := orig.(type) {
   132  	case *Named:
   133  		res = check.newNamedInstance(pos, orig, targs, expanding) // substituted lazily
   134  
   135  	case *Alias:
   136  		if !buildcfg.Experiment.AliasTypeParams {
   137  			assert(expanding == nil) // Alias instances cannot be reached from Named types
   138  		}
   139  
   140  		// verify type parameter count (see go.dev/issue/71198 for a test case)
   141  		tparams := orig.TypeParams()
   142  		if !check.validateTArgLen(pos, orig.obj.Name(), tparams.Len(), len(targs)) {
   143  			// TODO(gri) Consider returning a valid alias instance with invalid
   144  			//           underlying (aliased) type to match behavior of *Named
   145  			//           types. Then this function will never return an invalid
   146  			//           result.
   147  			return Typ[Invalid]
   148  		}
   149  		if tparams.Len() == 0 {
   150  			return orig // nothing to do (minor optimization)
   151  		}
   152  
   153  		res = check.newAliasInstance(pos, orig, targs, expanding, ctxt)
   154  
   155  	case *Signature:
   156  		assert(expanding == nil) // function instances cannot be reached from Named types
   157  
   158  		tparams := orig.TypeParams()
   159  		// TODO(gri) investigate if this is needed (type argument and parameter count seem to be correct here)
   160  		if !check.validateTArgLen(pos, orig.String(), tparams.Len(), len(targs)) {
   161  			return Typ[Invalid]
   162  		}
   163  		if tparams.Len() == 0 {
   164  			return orig // nothing to do (minor optimization)
   165  		}
   166  		sig := check.subst(pos, orig, makeSubstMap(tparams.list(), targs), nil, ctxt).(*Signature)
   167  		// If the signature doesn't use its type parameters, subst
   168  		// will not make a copy. In that case, make a copy now (so
   169  		// we can set tparams to nil w/o causing side-effects).
   170  		if sig == orig {
   171  			copy := *sig
   172  			sig = &copy
   173  		}
   174  		// After instantiating a generic signature, it is not generic
   175  		// anymore; we need to set tparams to nil.
   176  		sig.tparams = nil
   177  		res = sig
   178  
   179  	default:
   180  		// only types and functions can be generic
   181  		panic(fmt.Sprintf("%v: cannot instantiate %v", pos, orig))
   182  	}
   183  
   184  	// Update all contexts; it's possible that we've lost a race.
   185  	return updateContexts(res)
   186  }
   187  
   188  // validateTArgLen checks that the number of type arguments (got) matches the
   189  // number of type parameters (want); if they don't match an error is reported.
   190  // If validation fails and check is nil, validateTArgLen panics.
   191  func (check *Checker) validateTArgLen(pos token.Pos, name string, want, got int) bool {
   192  	var qual string
   193  	switch {
   194  	case got < want:
   195  		qual = "not enough"
   196  	case got > want:
   197  		qual = "too many"
   198  	default:
   199  		return true
   200  	}
   201  
   202  	msg := check.sprintf("%s type arguments for type %s: have %d, want %d", qual, name, got, want)
   203  	if check != nil {
   204  		check.error(atPos(pos), WrongTypeArgCount, msg)
   205  		return false
   206  	}
   207  
   208  	panic(fmt.Sprintf("%v: %s", pos, msg))
   209  }
   210  
   211  // check may be nil; pos is used only if check is non-nil.
   212  func (check *Checker) verify(pos token.Pos, tparams []*TypeParam, targs []Type, ctxt *Context) (int, error) {
   213  	smap := makeSubstMap(tparams, targs)
   214  	for i, tpar := range tparams {
   215  		// Ensure that we have a (possibly implicit) interface as type bound (go.dev/issue/51048).
   216  		tpar.iface()
   217  		// The type parameter bound is parameterized with the same type parameters
   218  		// as the instantiated type; before we can use it for bounds checking we
   219  		// need to instantiate it with the type arguments with which we instantiated
   220  		// the parameterized type.
   221  		bound := check.subst(pos, tpar.bound, smap, nil, ctxt)
   222  		var cause string
   223  		if !check.implements(targs[i], bound, true, &cause) {
   224  			return i, errors.New(cause)
   225  		}
   226  	}
   227  	return -1, nil
   228  }
   229  
   230  // implements checks if V implements T. The receiver may be nil if implements
   231  // is called through an exported API call such as AssignableTo. If constraint
   232  // is set, T is a type constraint.
   233  //
   234  // If the provided cause is non-nil, it may be set to an error string
   235  // explaining why V does not implement (or satisfy, for constraints) T.
   236  func (check *Checker) implements(V, T Type, constraint bool, cause *string) bool {
   237  	Vu := under(V)
   238  	Tu := under(T)
   239  	if !isValid(Vu) || !isValid(Tu) {
   240  		return true // avoid follow-on errors
   241  	}
   242  	if p, _ := Vu.(*Pointer); p != nil && !isValid(under(p.base)) {
   243  		return true // avoid follow-on errors (see go.dev/issue/49541 for an example)
   244  	}
   245  
   246  	verb := "implement"
   247  	if constraint {
   248  		verb = "satisfy"
   249  	}
   250  
   251  	Ti, _ := Tu.(*Interface)
   252  	if Ti == nil {
   253  		if cause != nil {
   254  			var detail string
   255  			if isInterfacePtr(Tu) {
   256  				detail = check.sprintf("type %s is pointer to interface, not interface", T)
   257  			} else {
   258  				detail = check.sprintf("%s is not an interface", T)
   259  			}
   260  			*cause = check.sprintf("%s does not %s %s (%s)", V, verb, T, detail)
   261  		}
   262  		return false
   263  	}
   264  
   265  	// Every type satisfies the empty interface.
   266  	if Ti.Empty() {
   267  		return true
   268  	}
   269  	// T is not the empty interface (i.e., the type set of T is restricted)
   270  
   271  	// An interface V with an empty type set satisfies any interface.
   272  	// (The empty set is a subset of any set.)
   273  	Vi, _ := Vu.(*Interface)
   274  	if Vi != nil && Vi.typeSet().IsEmpty() {
   275  		return true
   276  	}
   277  	// type set of V is not empty
   278  
   279  	// No type with non-empty type set satisfies the empty type set.
   280  	if Ti.typeSet().IsEmpty() {
   281  		if cause != nil {
   282  			*cause = check.sprintf("cannot %s %s (empty type set)", verb, T)
   283  		}
   284  		return false
   285  	}
   286  
   287  	// V must implement T's methods, if any.
   288  	if !check.hasAllMethods(V, T, true, Identical, cause) /* !Implements(V, T) */ {
   289  		if cause != nil {
   290  			*cause = check.sprintf("%s does not %s %s %s", V, verb, T, *cause)
   291  		}
   292  		return false
   293  	}
   294  
   295  	// Only check comparability if we don't have a more specific error.
   296  	checkComparability := func() bool {
   297  		if !Ti.IsComparable() {
   298  			return true
   299  		}
   300  		// If T is comparable, V must be comparable.
   301  		// If V is strictly comparable, we're done.
   302  		if comparableType(V, false /* strict comparability */, nil, nil) {
   303  			return true
   304  		}
   305  		// For constraint satisfaction, use dynamic (spec) comparability
   306  		// so that ordinary, non-type parameter interfaces implement comparable.
   307  		if constraint && comparableType(V, true /* spec comparability */, nil, nil) {
   308  			// V is comparable if we are at Go 1.20 or higher.
   309  			if check == nil || check.allowVersion(go1_20) {
   310  				return true
   311  			}
   312  			if cause != nil {
   313  				*cause = check.sprintf("%s to %s comparable requires go1.20 or later", V, verb)
   314  			}
   315  			return false
   316  		}
   317  		if cause != nil {
   318  			*cause = check.sprintf("%s does not %s comparable", V, verb)
   319  		}
   320  		return false
   321  	}
   322  
   323  	// V must also be in the set of types of T, if any.
   324  	// Constraints with empty type sets were already excluded above.
   325  	if !Ti.typeSet().hasTerms() {
   326  		return checkComparability() // nothing to do
   327  	}
   328  
   329  	// If V is itself an interface, each of its possible types must be in the set
   330  	// of T types (i.e., the V type set must be a subset of the T type set).
   331  	// Interfaces V with empty type sets were already excluded above.
   332  	if Vi != nil {
   333  		if !Vi.typeSet().subsetOf(Ti.typeSet()) {
   334  			// TODO(gri) report which type is missing
   335  			if cause != nil {
   336  				*cause = check.sprintf("%s does not %s %s", V, verb, T)
   337  			}
   338  			return false
   339  		}
   340  		return checkComparability()
   341  	}
   342  
   343  	// Otherwise, V's type must be included in the iface type set.
   344  	var alt Type
   345  	if Ti.typeSet().is(func(t *term) bool {
   346  		if !t.includes(V) {
   347  			// If V ∉ t.typ but V ∈ ~t.typ then remember this type
   348  			// so we can suggest it as an alternative in the error
   349  			// message.
   350  			if alt == nil && !t.tilde && Identical(t.typ, under(t.typ)) {
   351  				tt := *t
   352  				tt.tilde = true
   353  				if tt.includes(V) {
   354  					alt = t.typ
   355  				}
   356  			}
   357  			return true
   358  		}
   359  		return false
   360  	}) {
   361  		if cause != nil {
   362  			var detail string
   363  			switch {
   364  			case alt != nil:
   365  				detail = check.sprintf("possibly missing ~ for %s in %s", alt, T)
   366  			case mentions(Ti, V):
   367  				detail = check.sprintf("%s mentions %s, but %s is not in the type set of %s", T, V, V, T)
   368  			default:
   369  				detail = check.sprintf("%s missing in %s", V, Ti.typeSet().terms)
   370  			}
   371  			*cause = check.sprintf("%s does not %s %s (%s)", V, verb, T, detail)
   372  		}
   373  		return false
   374  	}
   375  
   376  	return checkComparability()
   377  }
   378  
   379  // mentions reports whether type T "mentions" typ in an (embedded) element or term
   380  // of T (whether typ is in the type set of T or not). For better error messages.
   381  func mentions(T, typ Type) bool {
   382  	switch T := T.(type) {
   383  	case *Interface:
   384  		for _, e := range T.embeddeds {
   385  			if mentions(e, typ) {
   386  				return true
   387  			}
   388  		}
   389  	case *Union:
   390  		for _, t := range T.terms {
   391  			if mentions(t.typ, typ) {
   392  				return true
   393  			}
   394  		}
   395  	default:
   396  		if Identical(T, typ) {
   397  			return true
   398  		}
   399  	}
   400  	return false
   401  }
   402
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