Fixes #58283.
Change-Id: I4a82083cddfed1b1be7776464f926a4c69a35e10
Reviewed-on: https://go-review.googlesource.com/c/go/+/470995
Reviewed-by: Robert Griesemer <gri@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Robert Griesemer <gri@google.com>
Reviewed-by: Robert Findley <rfindley@google.com>
Run-TryBot: Robert Griesemer <gri@google.com>
import (
"cmd/compile/internal/syntax"
"fmt"
- . "internal/types/errors"
"strings"
)
-// infer1 is an implementation of infer.
-// Inference proceeds as follows. Starting with given type arguments:
-//
-// 1. apply FTI (function type inference) with typed arguments,
-// 2. apply CTI (constraint type inference),
-// 3. apply FTI with untyped function arguments,
-// 4. apply CTI.
-//
-// The process stops as soon as all type arguments are known or an error occurs.
-func (check *Checker) infer1(pos syntax.Pos, tparams []*TypeParam, targs []Type, params *Tuple, args []*operand, silent bool) (result []Type) {
- if debug {
- defer func() {
- assert(result == nil || len(result) == len(tparams))
- for _, targ := range result {
- assert(targ != nil)
- }
- //check.dump("### inferred targs = %s", result)
- }()
- }
-
- if traceInference {
- check.dump("-- inferA %s%s ➞ %s", tparams, params, targs)
- defer func() {
- check.dump("=> inferA %s ➞ %s", tparams, result)
- }()
- }
-
- // There must be at least one type parameter, and no more type arguments than type parameters.
- n := len(tparams)
- assert(n > 0 && len(targs) <= n)
-
- // Function parameters and arguments must match in number.
- assert(params.Len() == len(args))
-
- // If we already have all type arguments, we're done.
- if len(targs) == n {
- return targs
- }
- // len(targs) < n
-
- // Rename type parameters to avoid conflicts in recursive instantiation scenarios.
- tparams, params = check.renameTParams(pos, tparams, params)
-
- // --- 1 ---
- // Continue with the type arguments we have. Avoid matching generic
- // parameters that already have type arguments against function arguments:
- // It may fail because matching uses type identity while parameter passing
- // uses assignment rules. Instantiate the parameter list with the type
- // arguments we have, and continue with that parameter list.
-
- // First, make sure we have a "full" list of type arguments, some of which
- // may be nil (unknown). Make a copy so as to not clobber the incoming slice.
- if len(targs) < n {
- targs2 := make([]Type, n)
- copy(targs2, targs)
- targs = targs2
- }
- // len(targs) == n
-
- // Substitute type arguments for their respective type parameters in params,
- // if any. Note that nil targs entries are ignored by check.subst.
- // TODO(gri) Can we avoid this (we're setting known type arguments below,
- // but that doesn't impact the isParameterized check for now).
- if params.Len() > 0 {
- smap := makeSubstMap(tparams, targs)
- params = check.subst(nopos, params, smap, nil, check.context()).(*Tuple)
- }
-
- // Unify parameter and argument types for generic parameters with typed arguments
- // and collect the indices of generic parameters with untyped arguments.
- // Terminology: generic parameter = function parameter with a type-parameterized type
- u := newUnifier(tparams, targs)
-
- errorf := func(kind string, tpar, targ Type, arg *operand) {
- if silent {
- return
- }
- // provide a better error message if we can
- targs := u.inferred(tparams)
- if targs[0] == nil {
- // The first type parameter couldn't be inferred.
- // If none of them could be inferred, don't try
- // to provide the inferred type in the error msg.
- allFailed := true
- for _, targ := range targs {
- if targ != nil {
- allFailed = false
- break
- }
- }
- if allFailed {
- check.errorf(arg, CannotInferTypeArgs, "%s %s of %s does not match %s (cannot infer %s)", kind, targ, arg.expr, tpar, typeParamsString(tparams))
- return
- }
- }
- smap := makeSubstMap(tparams, targs)
- // TODO(gri): pass a poser here, rather than arg.Pos().
- inferred := check.subst(arg.Pos(), tpar, smap, nil, check.context())
- // CannotInferTypeArgs indicates a failure of inference, though the actual
- // error may be better attributed to a user-provided type argument (hence
- // InvalidTypeArg). We can't differentiate these cases, so fall back on
- // the more general CannotInferTypeArgs.
- if inferred != tpar {
- check.errorf(arg, CannotInferTypeArgs, "%s %s of %s does not match inferred type %s for %s", kind, targ, arg.expr, inferred, tpar)
- } else {
- check.errorf(arg, CannotInferTypeArgs, "%s %s of %s does not match %s", kind, targ, arg.expr, tpar)
- }
- }
-
- // indices of the generic parameters with untyped arguments - save for later
- var indices []int
- for i, arg := range args {
- par := params.At(i)
- // If we permit bidirectional unification, this conditional code needs to be
- // executed even if par.typ is not parameterized since the argument may be a
- // generic function (for which we want to infer its type arguments).
- if isParameterized(tparams, par.typ) {
- if arg.mode == invalid {
- // An error was reported earlier. Ignore this targ
- // and continue, we may still be able to infer all
- // targs resulting in fewer follow-on errors.
- continue
- }
- if targ := arg.typ; isTyped(targ) {
- // If we permit bidirectional unification, and targ is
- // a generic function, we need to initialize u.y with
- // the respective type parameters of targ.
- if !u.unify(par.typ, targ) {
- errorf("type", par.typ, targ, arg)
- return nil
- }
- } else if _, ok := par.typ.(*TypeParam); ok {
- // Since default types are all basic (i.e., non-composite) types, an
- // untyped argument will never match a composite parameter type; the
- // only parameter type it can possibly match against is a *TypeParam.
- // Thus, for untyped arguments we only need to look at parameter types
- // that are single type parameters.
- indices = append(indices, i)
- }
- }
- }
-
- // If we've got all type arguments, we're done.
- targs = u.inferred(tparams)
- if u.unknowns() == 0 {
- return targs
- }
-
- // --- 2 ---
- // See how far we get with constraint type inference.
- // Note that even if we don't have any type arguments, constraint type inference
- // may produce results for constraints that explicitly specify a type.
- targs, index := check.inferB(tparams, targs)
- if targs == nil || index < 0 {
- return targs
- }
-
- // --- 3 ---
- // Use any untyped arguments to infer additional type arguments.
- // Some generic parameters with untyped arguments may have been given
- // a type by now, we can ignore them.
- for _, i := range indices {
- tpar := params.At(i).typ.(*TypeParam) // is type parameter by construction of indices
- // Only consider untyped arguments for which the corresponding type
- // parameter doesn't have an inferred type yet.
- if targs[tpar.index] == nil {
- arg := args[i]
- targ := Default(arg.typ)
- // The default type for an untyped nil is untyped nil. We must not
- // infer an untyped nil type as type parameter type. Ignore untyped
- // nil by making sure all default argument types are typed.
- if isTyped(targ) && !u.unify(tpar, targ) {
- errorf("default type", tpar, targ, arg)
- return nil
- }
- }
- }
-
- // If we've got all type arguments, we're done.
- targs = u.inferred(tparams)
- if u.unknowns() == 0 {
- return targs
- }
-
- // --- 4 ---
- // Again, follow up with constraint type inference.
- targs, index = check.inferB(tparams, targs)
- if targs == nil || index < 0 {
- return targs
- }
-
- // At least one type argument couldn't be inferred.
- assert(targs != nil && index >= 0 && targs[index] == nil)
- tpar := tparams[index]
- if !silent {
- check.errorf(pos, CannotInferTypeArgs, "cannot infer %s (%s)", tpar.obj.name, tpar.obj.pos)
- }
- return nil
-}
-
// renameTParams renames the type parameters in a function signature described by its
// type and ordinary parameters (tparams and params) such that each type parameter is
// given a new identity. renameTParams returns the new type and ordinary parameters.
return false
}
-// inferB returns the list of actual type arguments inferred from the type parameters'
-// bounds and an initial set of type arguments. If type inference is impossible because
-// unification fails, an error is reported if report is set to true, the resulting types
-// list is nil, and index is 0.
-// Otherwise, types is the list of inferred type arguments, and index is the index of the
-// first type argument in that list that couldn't be inferred (and thus is nil). If all
-// type arguments were inferred successfully, index is < 0. The number of type arguments
-// provided may be less than the number of type parameters, but there must be at least one.
-func (check *Checker) inferB(tparams []*TypeParam, targs []Type) (types []Type, index int) {
- assert(len(tparams) >= len(targs) && len(targs) > 0)
-
- if traceInference {
- check.dump("-- inferB %s ➞ %s", tparams, targs)
- defer func() {
- check.dump("=> inferB %s ➞ %s", tparams, types)
- }()
- }
-
- // Unify type parameters with their constraints.
- u := newUnifier(tparams, targs)
-
- // Repeatedly apply constraint type inference as long as
- // there are still unknown type arguments and progress is
- // being made.
- //
- // This is an O(n^2) algorithm where n is the number of
- // type parameters: if there is progress (and iteration
- // continues), at least one type argument is inferred
- // per iteration and we have a doubly nested loop.
- // In practice this is not a problem because the number
- // of type parameters tends to be very small (< 5 or so).
- // (It should be possible for unification to efficiently
- // signal newly inferred type arguments; then the loops
- // here could handle the respective type parameters only,
- // but that will come at a cost of extra complexity which
- // may not be worth it.)
- for n := u.unknowns(); n > 0; {
- nn := n
-
- for _, tpar := range tparams {
- // If there is a core term (i.e., a core type with tilde information)
- // unify the type parameter with the core type.
- if core, single := coreTerm(tpar); core != nil {
- if traceInference {
- u.tracef("core(%s) = %s (single = %v)", tpar, core, single)
- }
- // A type parameter can be unified with its core type in two cases.
- tx := u.at(tpar)
- switch {
- case tx != nil:
- // The corresponding type argument tx is known.
- // In this case, if the core type has a tilde, the type argument's underlying
- // type must match the core type, otherwise the type argument and the core type
- // must match.
- // If tx is an external type parameter, don't consider its underlying type
- // (which is an interface). Core type unification will attempt to unify against
- // core.typ.
- // Note also that even with inexact unification we cannot leave away the under
- // call here because it's possible that both tx and core.typ are named types,
- // with under(tx) being a (named) basic type matching core.typ. Such cases do
- // not match with inexact unification.
- if core.tilde && !isTypeParam(tx) {
- tx = under(tx)
- }
- // Unification may fail because it operates with limited information (core type),
- // even if a given type argument satisfies the corresponding type constraint.
- // For instance, given [P T1|T2, ...] where the type argument for P is (named
- // type) T1, and T1 and T2 have the same built-in (named) type T0 as underlying
- // type, the core type will be the named type T0, which doesn't match T1.
- // Yet the instantiation of P with T1 is clearly valid (see go.dev/issue/53650).
- // Reporting an error if unification fails would be incorrect in this case.
- // On the other hand, it is safe to ignore failing unification during constraint
- // type inference because if the failure is true, an error will be reported when
- // checking instantiation.
- u.unify(tx, core.typ)
-
- case single && !core.tilde:
- // The corresponding type argument tx is unknown and there's a single
- // specific type and no tilde.
- // In this case the type argument must be that single type; set it.
- u.set(tpar, core.typ)
-
- default:
- // Unification is not possible and no progress was made.
- continue
- }
-
- // The number of known type arguments may have changed.
- nn = u.unknowns()
- if nn == 0 {
- break // all type arguments are known
- }
- } else {
- if traceInference {
- u.tracef("core(%s) = nil", tpar)
- }
- }
- }
-
- assert(nn <= n)
- if nn == n {
- break // no progress
- }
- n = nn
- }
-
- // u.inferred(tparams) now contains the incoming type arguments plus any additional type
- // arguments which were inferred from core terms. The newly inferred non-nil
- // entries may still contain references to other type parameters.
- // For instance, for [A any, B interface{ []C }, C interface{ *A }], if A == int
- // was given, unification produced the type list [int, []C, *A]. We eliminate the
- // remaining type parameters by substituting the type parameters in this type list
- // until nothing changes anymore.
- types = u.inferred(tparams)
- if debug {
- for i, targ := range targs {
- assert(targ == nil || types[i] == targ)
- }
- }
-
- // The data structure of each (provided or inferred) type represents a graph, where
- // each node corresponds to a type and each (directed) vertex points to a component
- // type. The substitution process described above repeatedly replaces type parameter
- // nodes in these graphs with the graphs of the types the type parameters stand for,
- // which creates a new (possibly bigger) graph for each type.
- // The substitution process will not stop if the replacement graph for a type parameter
- // also contains that type parameter.
- // For instance, for [A interface{ *A }], without any type argument provided for A,
- // unification produces the type list [*A]. Substituting A in *A with the value for
- // A will lead to infinite expansion by producing [**A], [****A], [********A], etc.,
- // because the graph A -> *A has a cycle through A.
- // Generally, cycles may occur across multiple type parameters and inferred types
- // (for instance, consider [P interface{ *Q }, Q interface{ func(P) }]).
- // We eliminate cycles by walking the graphs for all type parameters. If a cycle
- // through a type parameter is detected, cycleFinder nils out the respective type
- // which kills the cycle; this also means that the respective type could not be
- // inferred.
- //
- // TODO(gri) If useful, we could report the respective cycle as an error. We don't
- // do this now because type inference will fail anyway, and furthermore,
- // constraints with cycles of this kind cannot currently be satisfied by
- // any user-supplied type. But should that change, reporting an error
- // would be wrong.
- w := cycleFinder{tparams, types, make(map[Type]bool)}
- for _, t := range tparams {
- w.typ(t) // t != nil
- }
-
- // dirty tracks the indices of all types that may still contain type parameters.
- // We know that nil type entries and entries corresponding to provided (non-nil)
- // type arguments are clean, so exclude them from the start.
- var dirty []int
- for i, typ := range types {
- if typ != nil && (i >= len(targs) || targs[i] == nil) {
- dirty = append(dirty, i)
- }
- }
-
- for len(dirty) > 0 {
- // TODO(gri) Instead of creating a new substMap for each iteration,
- // provide an update operation for substMaps and only change when
- // needed. Optimization.
- smap := makeSubstMap(tparams, types)
- n := 0
- for _, index := range dirty {
- t0 := types[index]
- if t1 := check.subst(nopos, t0, smap, nil, check.context()); t1 != t0 {
- types[index] = t1
- dirty[n] = index
- n++
- }
- }
- dirty = dirty[:n]
- }
-
- // Once nothing changes anymore, we may still have type parameters left;
- // e.g., a constraint with core type *P may match a type parameter Q but
- // we don't have any type arguments to fill in for *P or Q (go.dev/issue/45548).
- // Don't let such inferences escape, instead nil them out.
- for i, typ := range types {
- if typ != nil && isParameterized(tparams, typ) {
- types[i] = nil
- }
- }
-
- // update index
- index = -1
- for i, typ := range types {
- if typ == nil {
- index = i
- break
- }
- }
-
- return
-}
-
// If the type parameter has a single specific type S, coreTerm returns (S, true).
// Otherwise, if tpar has a core type T, it returns a term corresponding to that
// core type and false. In that case, if any term of tpar has a tilde, the core
. "internal/types/errors"
)
-// If compareWithInfer1, infer2 results must match infer1 results.
-// Disable before releasing Go 1.21.
-const compareWithInfer1 = false
-
// infer attempts to infer the complete set of type arguments for generic function instantiation/call
// based on the given type parameters tparams, type arguments targs, function parameters params, and
// function arguments args, if any. There must be at least one type parameter, no more type arguments
// than type parameters, and params and args must match in number (incl. zero).
// If successful, infer returns the complete list of given and inferred type arguments, one for each
// type parameter. Otherwise the result is nil and appropriate errors will be reported.
-func (check *Checker) infer(pos syntax.Pos, tparams []*TypeParam, targs []Type, params *Tuple, args []*operand) []Type {
- r2 := check.infer2(pos, tparams, targs, params, args)
-
- if compareWithInfer1 {
- r1 := check.infer1(pos, tparams, targs, params, args, r2 == nil) // be silent on errors if infer2 failed
- assert(len(r2) == len(r1))
- for i, targ2 := range r2 {
- targ1 := r1[i]
- var c comparer
- c.ignoreInvalids = true
- if !c.identical(targ2, targ1, nil) {
- tpar := tparams[i]
- check.dump("%v: type argument for %s: infer1: %s, infer2: %s", tpar.Obj().Pos(), tpar, targ1, targ2)
- panic("inconsistent type inference")
- }
- }
- }
-
- return r2
-}
-
-// infer2 is an implementation of infer.
-func (check *Checker) infer2(pos syntax.Pos, tparams []*TypeParam, targs []Type, params *Tuple, args []*operand) (inferred []Type) {
+func (check *Checker) infer(pos syntax.Pos, tparams []*TypeParam, targs []Type, params *Tuple, args []*operand) (inferred []Type) {
if debug {
defer func() {
assert(inferred == nil || len(inferred) == len(tparams))
}
if traceInference {
- check.dump("-- infer2 %s%s ➞ %s", tparams, params, targs)
+ check.dump("-- infer %s%s ➞ %s", tparams, params, targs)
defer func() {
check.dump("=> %s ➞ %s\n", tparams, inferred)
}()
import (
"fmt"
"go/token"
- . "internal/types/errors"
"strings"
)
-// infer1 is an implementation of infer.
-// Inference proceeds as follows. Starting with given type arguments:
-//
-// 1. apply FTI (function type inference) with typed arguments,
-// 2. apply CTI (constraint type inference),
-// 3. apply FTI with untyped function arguments,
-// 4. apply CTI.
-//
-// The process stops as soon as all type arguments are known or an error occurs.
-func (check *Checker) infer1(posn positioner, tparams []*TypeParam, targs []Type, params *Tuple, args []*operand, silent bool) (result []Type) {
- if debug {
- defer func() {
- assert(result == nil || len(result) == len(tparams))
- for _, targ := range result {
- assert(targ != nil)
- }
- //check.dump("### inferred targs = %s", result)
- }()
- }
-
- if traceInference {
- check.dump("-- inferA %s%s ➞ %s", tparams, params, targs)
- defer func() {
- check.dump("=> inferA %s ➞ %s", tparams, result)
- }()
- }
-
- // There must be at least one type parameter, and no more type arguments than type parameters.
- n := len(tparams)
- assert(n > 0 && len(targs) <= n)
-
- // Function parameters and arguments must match in number.
- assert(params.Len() == len(args))
-
- // If we already have all type arguments, we're done.
- if len(targs) == n {
- return targs
- }
- // len(targs) < n
-
- // Rename type parameters to avoid conflicts in recursive instantiation scenarios.
- tparams, params = check.renameTParams(posn.Pos(), tparams, params)
-
- // --- 1 ---
- // Continue with the type arguments we have. Avoid matching generic
- // parameters that already have type arguments against function arguments:
- // It may fail because matching uses type identity while parameter passing
- // uses assignment rules. Instantiate the parameter list with the type
- // arguments we have, and continue with that parameter list.
-
- // First, make sure we have a "full" list of type arguments, some of which
- // may be nil (unknown). Make a copy so as to not clobber the incoming slice.
- if len(targs) < n {
- targs2 := make([]Type, n)
- copy(targs2, targs)
- targs = targs2
- }
- // len(targs) == n
-
- // Substitute type arguments for their respective type parameters in params,
- // if any. Note that nil targs entries are ignored by check.subst.
- // TODO(gri) Can we avoid this (we're setting known type arguments below,
- // but that doesn't impact the isParameterized check for now).
- if params.Len() > 0 {
- smap := makeSubstMap(tparams, targs)
- params = check.subst(nopos, params, smap, nil, check.context()).(*Tuple)
- }
-
- // Unify parameter and argument types for generic parameters with typed arguments
- // and collect the indices of generic parameters with untyped arguments.
- // Terminology: generic parameter = function parameter with a type-parameterized type
- u := newUnifier(tparams, targs)
-
- errorf := func(kind string, tpar, targ Type, arg *operand) {
- if silent {
- return
- }
- // provide a better error message if we can
- targs := u.inferred(tparams)
- if targs[0] == nil {
- // The first type parameter couldn't be inferred.
- // If none of them could be inferred, don't try
- // to provide the inferred type in the error msg.
- allFailed := true
- for _, targ := range targs {
- if targ != nil {
- allFailed = false
- break
- }
- }
- if allFailed {
- check.errorf(arg, CannotInferTypeArgs, "%s %s of %s does not match %s (cannot infer %s)", kind, targ, arg.expr, tpar, typeParamsString(tparams))
- return
- }
- }
- smap := makeSubstMap(tparams, targs)
- // TODO(gri): pass a poser here, rather than arg.Pos().
- inferred := check.subst(arg.Pos(), tpar, smap, nil, check.context())
- // CannotInferTypeArgs indicates a failure of inference, though the actual
- // error may be better attributed to a user-provided type argument (hence
- // InvalidTypeArg). We can't differentiate these cases, so fall back on
- // the more general CannotInferTypeArgs.
- if inferred != tpar {
- check.errorf(arg, CannotInferTypeArgs, "%s %s of %s does not match inferred type %s for %s", kind, targ, arg.expr, inferred, tpar)
- } else {
- check.errorf(arg, CannotInferTypeArgs, "%s %s of %s does not match %s", kind, targ, arg.expr, tpar)
- }
- }
-
- // indices of the generic parameters with untyped arguments - save for later
- var indices []int
- for i, arg := range args {
- par := params.At(i)
- // If we permit bidirectional unification, this conditional code needs to be
- // executed even if par.typ is not parameterized since the argument may be a
- // generic function (for which we want to infer its type arguments).
- if isParameterized(tparams, par.typ) {
- if arg.mode == invalid {
- // An error was reported earlier. Ignore this targ
- // and continue, we may still be able to infer all
- // targs resulting in fewer follow-on errors.
- continue
- }
- if targ := arg.typ; isTyped(targ) {
- // If we permit bidirectional unification, and targ is
- // a generic function, we need to initialize u.y with
- // the respective type parameters of targ.
- if !u.unify(par.typ, targ) {
- errorf("type", par.typ, targ, arg)
- return nil
- }
- } else if _, ok := par.typ.(*TypeParam); ok {
- // Since default types are all basic (i.e., non-composite) types, an
- // untyped argument will never match a composite parameter type; the
- // only parameter type it can possibly match against is a *TypeParam.
- // Thus, for untyped arguments we only need to look at parameter types
- // that are single type parameters.
- indices = append(indices, i)
- }
- }
- }
-
- // If we've got all type arguments, we're done.
- targs = u.inferred(tparams)
- if u.unknowns() == 0 {
- return targs
- }
-
- // --- 2 ---
- // See how far we get with constraint type inference.
- // Note that even if we don't have any type arguments, constraint type inference
- // may produce results for constraints that explicitly specify a type.
- targs, index := check.inferB(tparams, targs)
- if targs == nil || index < 0 {
- return targs
- }
-
- // --- 3 ---
- // Use any untyped arguments to infer additional type arguments.
- // Some generic parameters with untyped arguments may have been given
- // a type by now, we can ignore them.
- for _, i := range indices {
- tpar := params.At(i).typ.(*TypeParam) // is type parameter by construction of indices
- // Only consider untyped arguments for which the corresponding type
- // parameter doesn't have an inferred type yet.
- if targs[tpar.index] == nil {
- arg := args[i]
- targ := Default(arg.typ)
- // The default type for an untyped nil is untyped nil. We must not
- // infer an untyped nil type as type parameter type. Ignore untyped
- // nil by making sure all default argument types are typed.
- if isTyped(targ) && !u.unify(tpar, targ) {
- errorf("default type", tpar, targ, arg)
- return nil
- }
- }
- }
-
- // If we've got all type arguments, we're done.
- targs = u.inferred(tparams)
- if u.unknowns() == 0 {
- return targs
- }
-
- // --- 4 ---
- // Again, follow up with constraint type inference.
- targs, index = check.inferB(tparams, targs)
- if targs == nil || index < 0 {
- return targs
- }
-
- // At least one type argument couldn't be inferred.
- assert(targs != nil && index >= 0 && targs[index] == nil)
- tpar := tparams[index]
- if !silent {
- check.errorf(posn, CannotInferTypeArgs, "cannot infer %s (%s)", tpar.obj.name, tpar.obj.pos)
- }
- return nil
-}
-
// renameTParams renames the type parameters in a function signature described by its
// type and ordinary parameters (tparams and params) such that each type parameter is
// given a new identity. renameTParams returns the new type and ordinary parameters.
return false
}
-// inferB returns the list of actual type arguments inferred from the type parameters'
-// bounds and an initial set of type arguments. If type inference is impossible because
-// unification fails, an error is reported if report is set to true, the resulting types
-// list is nil, and index is 0.
-// Otherwise, types is the list of inferred type arguments, and index is the index of the
-// first type argument in that list that couldn't be inferred (and thus is nil). If all
-// type arguments were inferred successfully, index is < 0. The number of type arguments
-// provided may be less than the number of type parameters, but there must be at least one.
-func (check *Checker) inferB(tparams []*TypeParam, targs []Type) (types []Type, index int) {
- assert(len(tparams) >= len(targs) && len(targs) > 0)
-
- if traceInference {
- check.dump("-- inferB %s ➞ %s", tparams, targs)
- defer func() {
- check.dump("=> inferB %s ➞ %s", tparams, types)
- }()
- }
-
- // Unify type parameters with their constraints.
- u := newUnifier(tparams, targs)
-
- // Repeatedly apply constraint type inference as long as
- // there are still unknown type arguments and progress is
- // being made.
- //
- // This is an O(n^2) algorithm where n is the number of
- // type parameters: if there is progress (and iteration
- // continues), at least one type argument is inferred
- // per iteration and we have a doubly nested loop.
- // In practice this is not a problem because the number
- // of type parameters tends to be very small (< 5 or so).
- // (It should be possible for unification to efficiently
- // signal newly inferred type arguments; then the loops
- // here could handle the respective type parameters only,
- // but that will come at a cost of extra complexity which
- // may not be worth it.)
- for n := u.unknowns(); n > 0; {
- nn := n
-
- for _, tpar := range tparams {
- // If there is a core term (i.e., a core type with tilde information)
- // unify the type parameter with the core type.
- if core, single := coreTerm(tpar); core != nil {
- if traceInference {
- u.tracef("core(%s) = %s (single = %v)", tpar, core, single)
- }
- // A type parameter can be unified with its core type in two cases.
- tx := u.at(tpar)
- switch {
- case tx != nil:
- // The corresponding type argument tx is known.
- // In this case, if the core type has a tilde, the type argument's underlying
- // type must match the core type, otherwise the type argument and the core type
- // must match.
- // If tx is an external type parameter, don't consider its underlying type
- // (which is an interface). Core type unification will attempt to unify against
- // core.typ.
- // Note also that even with inexact unification we cannot leave away the under
- // call here because it's possible that both tx and core.typ are named types,
- // with under(tx) being a (named) basic type matching core.typ. Such cases do
- // not match with inexact unification.
- if core.tilde && !isTypeParam(tx) {
- tx = under(tx)
- }
- // Unification may fail because it operates with limited information (core type),
- // even if a given type argument satisfies the corresponding type constraint.
- // For instance, given [P T1|T2, ...] where the type argument for P is (named
- // type) T1, and T1 and T2 have the same built-in (named) type T0 as underlying
- // type, the core type will be the named type T0, which doesn't match T1.
- // Yet the instantiation of P with T1 is clearly valid (see go.dev/issue/53650).
- // Reporting an error if unification fails would be incorrect in this case.
- // On the other hand, it is safe to ignore failing unification during constraint
- // type inference because if the failure is true, an error will be reported when
- // checking instantiation.
- u.unify(tx, core.typ)
-
- case single && !core.tilde:
- // The corresponding type argument tx is unknown and there's a single
- // specific type and no tilde.
- // In this case the type argument must be that single type; set it.
- u.set(tpar, core.typ)
-
- default:
- // Unification is not possible and no progress was made.
- continue
- }
-
- // The number of known type arguments may have changed.
- nn = u.unknowns()
- if nn == 0 {
- break // all type arguments are known
- }
- } else {
- if traceInference {
- u.tracef("core(%s) = nil", tpar)
- }
- }
- }
-
- assert(nn <= n)
- if nn == n {
- break // no progress
- }
- n = nn
- }
-
- // u.inferred(tparams) now contains the incoming type arguments plus any additional type
- // arguments which were inferred from core terms. The newly inferred non-nil
- // entries may still contain references to other type parameters.
- // For instance, for [A any, B interface{ []C }, C interface{ *A }], if A == int
- // was given, unification produced the type list [int, []C, *A]. We eliminate the
- // remaining type parameters by substituting the type parameters in this type list
- // until nothing changes anymore.
- types = u.inferred(tparams)
- if debug {
- for i, targ := range targs {
- assert(targ == nil || types[i] == targ)
- }
- }
-
- // The data structure of each (provided or inferred) type represents a graph, where
- // each node corresponds to a type and each (directed) vertex points to a component
- // type. The substitution process described above repeatedly replaces type parameter
- // nodes in these graphs with the graphs of the types the type parameters stand for,
- // which creates a new (possibly bigger) graph for each type.
- // The substitution process will not stop if the replacement graph for a type parameter
- // also contains that type parameter.
- // For instance, for [A interface{ *A }], without any type argument provided for A,
- // unification produces the type list [*A]. Substituting A in *A with the value for
- // A will lead to infinite expansion by producing [**A], [****A], [********A], etc.,
- // because the graph A -> *A has a cycle through A.
- // Generally, cycles may occur across multiple type parameters and inferred types
- // (for instance, consider [P interface{ *Q }, Q interface{ func(P) }]).
- // We eliminate cycles by walking the graphs for all type parameters. If a cycle
- // through a type parameter is detected, cycleFinder nils out the respective type
- // which kills the cycle; this also means that the respective type could not be
- // inferred.
- //
- // TODO(gri) If useful, we could report the respective cycle as an error. We don't
- // do this now because type inference will fail anyway, and furthermore,
- // constraints with cycles of this kind cannot currently be satisfied by
- // any user-supplied type. But should that change, reporting an error
- // would be wrong.
- w := cycleFinder{tparams, types, make(map[Type]bool)}
- for _, t := range tparams {
- w.typ(t) // t != nil
- }
-
- // dirty tracks the indices of all types that may still contain type parameters.
- // We know that nil type entries and entries corresponding to provided (non-nil)
- // type arguments are clean, so exclude them from the start.
- var dirty []int
- for i, typ := range types {
- if typ != nil && (i >= len(targs) || targs[i] == nil) {
- dirty = append(dirty, i)
- }
- }
-
- for len(dirty) > 0 {
- // TODO(gri) Instead of creating a new substMap for each iteration,
- // provide an update operation for substMaps and only change when
- // needed. Optimization.
- smap := makeSubstMap(tparams, types)
- n := 0
- for _, index := range dirty {
- t0 := types[index]
- if t1 := check.subst(nopos, t0, smap, nil, check.context()); t1 != t0 {
- types[index] = t1
- dirty[n] = index
- n++
- }
- }
- dirty = dirty[:n]
- }
-
- // Once nothing changes anymore, we may still have type parameters left;
- // e.g., a constraint with core type *P may match a type parameter Q but
- // we don't have any type arguments to fill in for *P or Q (go.dev/issue/45548).
- // Don't let such inferences escape, instead nil them out.
- for i, typ := range types {
- if typ != nil && isParameterized(tparams, typ) {
- types[i] = nil
- }
- }
-
- // update index
- index = -1
- for i, typ := range types {
- if typ == nil {
- index = i
- break
- }
- }
-
- return
-}
-
// If the type parameter has a single specific type S, coreTerm returns (S, true).
// Otherwise, if tpar has a core type T, it returns a term corresponding to that
// core type and false. In that case, if any term of tpar has a tilde, the core
. "internal/types/errors"
)
-// If compareWithInfer1, infer2 results must match infer1 results.
-// Disable before releasing Go 1.21.
-const compareWithInfer1 = false
-
// infer attempts to infer the complete set of type arguments for generic function instantiation/call
// based on the given type parameters tparams, type arguments targs, function parameters params, and
// function arguments args, if any. There must be at least one type parameter, no more type arguments
// than type parameters, and params and args must match in number (incl. zero).
// If successful, infer returns the complete list of given and inferred type arguments, one for each
// type parameter. Otherwise the result is nil and appropriate errors will be reported.
-func (check *Checker) infer(posn positioner, tparams []*TypeParam, targs []Type, params *Tuple, args []*operand) []Type {
- r2 := check.infer2(posn, tparams, targs, params, args)
-
- if compareWithInfer1 {
- r1 := check.infer1(posn, tparams, targs, params, args, r2 == nil) // be silent on errors if infer2 failed
- assert(len(r2) == len(r1))
- for i, targ2 := range r2 {
- targ1 := r1[i]
- var c comparer
- c.ignoreInvalids = true
- if !c.identical(targ2, targ1, nil) {
- tpar := tparams[i]
- check.dump("%v: type argument for %s: infer1: %s, infer2: %s", tpar.Obj().Pos(), tpar, targ1, targ2)
- panic("inconsistent type inference")
- }
- }
- }
-
- return r2
-}
-
-// infer2 is an implementation of infer.
-func (check *Checker) infer2(posn positioner, tparams []*TypeParam, targs []Type, params *Tuple, args []*operand) (inferred []Type) {
+func (check *Checker) infer(posn positioner, tparams []*TypeParam, targs []Type, params *Tuple, args []*operand) (inferred []Type) {
if debug {
defer func() {
assert(inferred == nil || len(inferred) == len(tparams))
}
if traceInference {
- check.dump("-- infer2 %s%s ➞ %s", tparams, params, targs)
+ check.dump("-- infer %s%s ➞ %s", tparams, params, targs)
defer func() {
check.dump("=> %s ➞ %s\n", tparams, inferred)
}()