| // Code generated by "go test -run=Generate -write=all"; DO NOT EDIT. |
| |
| // Copyright 2020 The Go Authors. All rights reserved. |
| // Use of this source code is governed by a BSD-style |
| // license that can be found in the LICENSE file. |
| |
| // This file implements type unification. |
| // |
| // Type unification attempts to make two types x and y structurally |
| // equivalent by determining the types for a given list of (bound) |
| // type parameters which may occur within x and y. If x and y are |
| // structurally different (say []T vs chan T), or conflicting |
| // types are determined for type parameters, unification fails. |
| // If unification succeeds, as a side-effect, the types of the |
| // bound type parameters may be determined. |
| // |
| // Unification typically requires multiple calls u.unify(x, y) to |
| // a given unifier u, with various combinations of types x and y. |
| // In each call, additional type parameter types may be determined |
| // as a side effect and recorded in u. |
| // If a call fails (returns false), unification fails. |
| // |
| // In the unification context, structural equivalence of two types |
| // ignores the difference between a defined type and its underlying |
| // type if one type is a defined type and the other one is not. |
| // It also ignores the difference between an (external, unbound) |
| // type parameter and its core type. |
| // If two types are not structurally equivalent, they cannot be Go |
| // identical types. On the other hand, if they are structurally |
| // equivalent, they may be Go identical or at least assignable, or |
| // they may be in the type set of a constraint. |
| // Whether they indeed are identical or assignable is determined |
| // upon instantiation and function argument passing. |
| |
| package types |
| |
| import ( |
| "bytes" |
| "fmt" |
| "sort" |
| "strings" |
| ) |
| |
| const ( |
| // Upper limit for recursion depth. Used to catch infinite recursions |
| // due to implementation issues (e.g., see issues go.dev/issue/48619, go.dev/issue/48656). |
| unificationDepthLimit = 50 |
| |
| // Whether to panic when unificationDepthLimit is reached. |
| // If disabled, a recursion depth overflow results in a (quiet) |
| // unification failure. |
| panicAtUnificationDepthLimit = false // go.dev/issue/59740 |
| |
| // If enableCoreTypeUnification is set, unification will consider |
| // the core types, if any, of non-local (unbound) type parameters. |
| enableCoreTypeUnification = true |
| |
| // If enableInterfaceInference is set, type inference uses |
| // shared methods for improved type inference involving |
| // interfaces. |
| enableInterfaceInference = true |
| |
| // If traceInference is set, unification will print a trace of its operation. |
| // Interpretation of trace: |
| // x ≡ y attempt to unify types x and y |
| // p ➞ y type parameter p is set to type y (p is inferred to be y) |
| // p ⇄ q type parameters p and q match (p is inferred to be q and vice versa) |
| // x ≢ y types x and y cannot be unified |
| // [p, q, ...] ➞ [x, y, ...] mapping from type parameters to types |
| traceInference = false |
| ) |
| |
| // A unifier maintains a list of type parameters and |
| // corresponding types inferred for each type parameter. |
| // A unifier is created by calling newUnifier. |
| type unifier struct { |
| // handles maps each type parameter to its inferred type through |
| // an indirection *Type called (inferred type) "handle". |
| // Initially, each type parameter has its own, separate handle, |
| // with a nil (i.e., not yet inferred) type. |
| // After a type parameter P is unified with a type parameter Q, |
| // P and Q share the same handle (and thus type). This ensures |
| // that inferring the type for a given type parameter P will |
| // automatically infer the same type for all other parameters |
| // unified (joined) with P. |
| handles map[*TypeParam]*Type |
| depth int // recursion depth during unification |
| } |
| |
| // newUnifier returns a new unifier initialized with the given type parameter |
| // and corresponding type argument lists. The type argument list may be shorter |
| // than the type parameter list, and it may contain nil types. Matching type |
| // parameters and arguments must have the same index. |
| func newUnifier(tparams []*TypeParam, targs []Type) *unifier { |
| assert(len(tparams) >= len(targs)) |
| handles := make(map[*TypeParam]*Type, len(tparams)) |
| // Allocate all handles up-front: in a correct program, all type parameters |
| // must be resolved and thus eventually will get a handle. |
| // Also, sharing of handles caused by unified type parameters is rare and |
| // so it's ok to not optimize for that case (and delay handle allocation). |
| for i, x := range tparams { |
| var t Type |
| if i < len(targs) { |
| t = targs[i] |
| } |
| handles[x] = &t |
| } |
| return &unifier{handles, 0} |
| } |
| |
| // unify attempts to unify x and y and reports whether it succeeded. |
| // As a side-effect, types may be inferred for type parameters. |
| func (u *unifier) unify(x, y Type) bool { |
| return u.nify(x, y, nil) |
| } |
| |
| func (u *unifier) tracef(format string, args ...interface{}) { |
| fmt.Println(strings.Repeat(". ", u.depth) + sprintf(nil, nil, true, format, args...)) |
| } |
| |
| // String returns a string representation of the current mapping |
| // from type parameters to types. |
| func (u *unifier) String() string { |
| // sort type parameters for reproducible strings |
| tparams := make(typeParamsById, len(u.handles)) |
| i := 0 |
| for tpar := range u.handles { |
| tparams[i] = tpar |
| i++ |
| } |
| sort.Sort(tparams) |
| |
| var buf bytes.Buffer |
| w := newTypeWriter(&buf, nil) |
| w.byte('[') |
| for i, x := range tparams { |
| if i > 0 { |
| w.string(", ") |
| } |
| w.typ(x) |
| w.string(": ") |
| w.typ(u.at(x)) |
| } |
| w.byte(']') |
| return buf.String() |
| } |
| |
| type typeParamsById []*TypeParam |
| |
| func (s typeParamsById) Len() int { return len(s) } |
| func (s typeParamsById) Less(i, j int) bool { return s[i].id < s[j].id } |
| func (s typeParamsById) Swap(i, j int) { s[i], s[j] = s[j], s[i] } |
| |
| // join unifies the given type parameters x and y. |
| // If both type parameters already have a type associated with them |
| // and they are not joined, join fails and returns false. |
| func (u *unifier) join(x, y *TypeParam) bool { |
| if traceInference { |
| u.tracef("%s ⇄ %s", x, y) |
| } |
| switch hx, hy := u.handles[x], u.handles[y]; { |
| case hx == hy: |
| // Both type parameters already share the same handle. Nothing to do. |
| case *hx != nil && *hy != nil: |
| // Both type parameters have (possibly different) inferred types. Cannot join. |
| return false |
| case *hx != nil: |
| // Only type parameter x has an inferred type. Use handle of x. |
| u.setHandle(y, hx) |
| // This case is treated like the default case. |
| // case *hy != nil: |
| // // Only type parameter y has an inferred type. Use handle of y. |
| // u.setHandle(x, hy) |
| default: |
| // Neither type parameter has an inferred type. Use handle of y. |
| u.setHandle(x, hy) |
| } |
| return true |
| } |
| |
| // asTypeParam returns x.(*TypeParam) if x is a type parameter recorded with u. |
| // Otherwise, the result is nil. |
| func (u *unifier) asTypeParam(x Type) *TypeParam { |
| if x, _ := x.(*TypeParam); x != nil { |
| if _, found := u.handles[x]; found { |
| return x |
| } |
| } |
| return nil |
| } |
| |
| // setHandle sets the handle for type parameter x |
| // (and all its joined type parameters) to h. |
| func (u *unifier) setHandle(x *TypeParam, h *Type) { |
| hx := u.handles[x] |
| assert(hx != nil) |
| for y, hy := range u.handles { |
| if hy == hx { |
| u.handles[y] = h |
| } |
| } |
| } |
| |
| // at returns the (possibly nil) type for type parameter x. |
| func (u *unifier) at(x *TypeParam) Type { |
| return *u.handles[x] |
| } |
| |
| // set sets the type t for type parameter x; |
| // t must not be nil. |
| func (u *unifier) set(x *TypeParam, t Type) { |
| assert(t != nil) |
| if traceInference { |
| u.tracef("%s ➞ %s", x, t) |
| } |
| *u.handles[x] = t |
| } |
| |
| // unknowns returns the number of type parameters for which no type has been set yet. |
| func (u *unifier) unknowns() int { |
| n := 0 |
| for _, h := range u.handles { |
| if *h == nil { |
| n++ |
| } |
| } |
| return n |
| } |
| |
| // inferred returns the list of inferred types for the given type parameter list. |
| // The result is never nil and has the same length as tparams; result types that |
| // could not be inferred are nil. Corresponding type parameters and result types |
| // have identical indices. |
| func (u *unifier) inferred(tparams []*TypeParam) []Type { |
| list := make([]Type, len(tparams)) |
| for i, x := range tparams { |
| list[i] = u.at(x) |
| } |
| return list |
| } |
| |
| // nify implements the core unification algorithm which is an |
| // adapted version of Checker.identical. For changes to that |
| // code the corresponding changes should be made here. |
| // Must not be called directly from outside the unifier. |
| func (u *unifier) nify(x, y Type, p *ifacePair) (result bool) { |
| u.depth++ |
| if traceInference { |
| u.tracef("%s ≡ %s", x, y) |
| } |
| defer func() { |
| if traceInference && !result { |
| u.tracef("%s ≢ %s", x, y) |
| } |
| u.depth-- |
| }() |
| |
| // nothing to do if x == y |
| if x == y { |
| return true |
| } |
| |
| // Stop gap for cases where unification fails. |
| if u.depth > unificationDepthLimit { |
| if traceInference { |
| u.tracef("depth %d >= %d", u.depth, unificationDepthLimit) |
| } |
| if panicAtUnificationDepthLimit { |
| panic("unification reached recursion depth limit") |
| } |
| return false |
| } |
| |
| // Unification is symmetric, so we can swap the operands. |
| // Ensure that if we have at least one |
| // - defined type, make sure one is in y |
| // - type parameter recorded with u, make sure one is in x |
| if _, ok := x.(*Named); ok || u.asTypeParam(y) != nil { |
| if traceInference { |
| u.tracef("%s ≡ %s (swap)", y, x) |
| } |
| x, y = y, x |
| } |
| |
| // Unification will fail if we match a defined type against a type literal. |
| // Per the (spec) assignment rules, assignments of values to variables with |
| // the same type structure are permitted as long as at least one of them |
| // is not a defined type. To accommodate for that possibility, we continue |
| // unification with the underlying type of a defined type if the other type |
| // is a type literal. |
| // We also continue if the other type is a basic type because basic types |
| // are valid underlying types and may appear as core types of type constraints. |
| // If we exclude them, inferred defined types for type parameters may not |
| // match against the core types of their constraints (even though they might |
| // correctly match against some of the types in the constraint's type set). |
| // Finally, if unification (incorrectly) succeeds by matching the underlying |
| // type of a defined type against a basic type (because we include basic types |
| // as type literals here), and if that leads to an incorrectly inferred type, |
| // we will fail at function instantiation or argument assignment time. |
| // |
| // If we have at least one defined type, there is one in y. |
| if ny, _ := y.(*Named); ny != nil && isTypeLit(x) && !(enableInterfaceInference && IsInterface(x)) { |
| if traceInference { |
| u.tracef("%s ≡ under %s", x, ny) |
| } |
| y = ny.under() |
| // Per the spec, a defined type cannot have an underlying type |
| // that is a type parameter. |
| assert(!isTypeParam(y)) |
| // x and y may be identical now |
| if x == y { |
| return true |
| } |
| } |
| |
| // Cases where at least one of x or y is a type parameter recorded with u. |
| // If we have at least one type parameter, there is one in x. |
| // If we have exactly one type parameter, because it is in x, |
| // isTypeLit(x) is false and y was not changed above. In other |
| // words, if y was a defined type, it is still a defined type |
| // (relevant for the logic below). |
| switch px, py := u.asTypeParam(x), u.asTypeParam(y); { |
| case px != nil && py != nil: |
| // both x and y are type parameters |
| if u.join(px, py) { |
| return true |
| } |
| // both x and y have an inferred type - they must match |
| return u.nify(u.at(px), u.at(py), p) |
| |
| case px != nil: |
| // x is a type parameter, y is not |
| if x := u.at(px); x != nil { |
| // x has an inferred type which must match y |
| if u.nify(x, y, p) { |
| // If we have a match, possibly through underlying types, |
| // and y is a defined type, make sure we record that type |
| // for type parameter x, which may have until now only |
| // recorded an underlying type (go.dev/issue/43056). |
| if _, ok := y.(*Named); ok { |
| u.set(px, y) |
| } |
| return true |
| } |
| return false |
| } |
| // otherwise, infer type from y |
| u.set(px, y) |
| return true |
| } |
| |
| // x != y if we get here |
| assert(x != y) |
| |
| // If we get here and x or y is a type parameter, they are unbound |
| // (not recorded with the unifier). |
| // Ensure that if we have at least one type parameter, it is in x |
| // (the earlier swap checks for _recorded_ type parameters only). |
| if isTypeParam(y) { |
| if traceInference { |
| u.tracef("%s ≡ %s (swap)", y, x) |
| } |
| x, y = y, x |
| } |
| |
| // If EnableInterfaceInference is set and both types are interfaces, one |
| // interface must have a subset of the methods of the other and corresponding |
| // method signatures must unify. |
| // If only one type is an interface, all its methods must be present in the |
| // other type and corresponding method signatures must unify. |
| if enableInterfaceInference { |
| xi, _ := x.(*Interface) |
| yi, _ := y.(*Interface) |
| // If we have two interfaces, check the type terms for equivalence, |
| // and unify common methods if possible. |
| if xi != nil && yi != nil { |
| xset := xi.typeSet() |
| yset := yi.typeSet() |
| if xset.comparable != yset.comparable { |
| return false |
| } |
| // For now we require terms to be equal. |
| // We should be able to relax this as well, eventually. |
| if !xset.terms.equal(yset.terms) { |
| return false |
| } |
| // Interface types are the only types where cycles can occur |
| // that are not "terminated" via named types; and such cycles |
| // can only be created via method parameter types that are |
| // anonymous interfaces (directly or indirectly) embedding |
| // the current interface. Example: |
| // |
| // type T interface { |
| // m() interface{T} |
| // } |
| // |
| // If two such (differently named) interfaces are compared, |
| // endless recursion occurs if the cycle is not detected. |
| // |
| // If x and y were compared before, they must be equal |
| // (if they were not, the recursion would have stopped); |
| // search the ifacePair stack for the same pair. |
| // |
| // This is a quadratic algorithm, but in practice these stacks |
| // are extremely short (bounded by the nesting depth of interface |
| // type declarations that recur via parameter types, an extremely |
| // rare occurrence). An alternative implementation might use a |
| // "visited" map, but that is probably less efficient overall. |
| q := &ifacePair{xi, yi, p} |
| for p != nil { |
| if p.identical(q) { |
| return true // same pair was compared before |
| } |
| p = p.prev |
| } |
| // The method set of x must be a subset of the method set |
| // of y or vice versa, and the common methods must unify. |
| xmethods := xset.methods |
| ymethods := yset.methods |
| // The smaller method set must be the subset, if it exists. |
| if len(xmethods) > len(ymethods) { |
| xmethods, ymethods = ymethods, xmethods |
| } |
| // len(xmethods) <= len(ymethods) |
| // Collect the ymethods in a map for quick lookup. |
| ymap := make(map[string]*Func, len(ymethods)) |
| for _, ym := range ymethods { |
| ymap[ym.Id()] = ym |
| } |
| // All xmethods must exist in ymethods and corresponding signatures must unify. |
| for _, xm := range xmethods { |
| if ym := ymap[xm.Id()]; ym == nil || !u.nify(xm.typ, ym.typ, p) { |
| return false |
| } |
| } |
| return true |
| } |
| |
| // We don't have two interfaces. If we have one, make sure it's in xi. |
| if yi != nil { |
| xi = yi |
| y = x |
| } |
| |
| // If we have one interface, at a minimum each of the interface methods |
| // must be implemented and thus unify with a corresponding method from |
| // the non-interface type, otherwise unification fails. |
| if xi != nil { |
| // All xi methods must exist in y and corresponding signatures must unify. |
| xmethods := xi.typeSet().methods |
| for _, xm := range xmethods { |
| obj, _, _ := LookupFieldOrMethod(y, false, xm.pkg, xm.name) |
| if ym, _ := obj.(*Func); ym == nil || !u.nify(xm.typ, ym.typ, p) { |
| return false |
| } |
| } |
| return true |
| } |
| |
| // Neither x nor y are interface types. |
| // They must be structurally equivalent to unify. |
| } |
| |
| switch x := x.(type) { |
| case *Basic: |
| // Basic types are singletons except for the rune and byte |
| // aliases, thus we cannot solely rely on the x == y check |
| // above. See also comment in TypeName.IsAlias. |
| if y, ok := y.(*Basic); ok { |
| return x.kind == y.kind |
| } |
| |
| case *Array: |
| // Two array types unify if they have the same array length |
| // and their element types unify. |
| if y, ok := y.(*Array); ok { |
| // If one or both array lengths are unknown (< 0) due to some error, |
| // assume they are the same to avoid spurious follow-on errors. |
| return (x.len < 0 || y.len < 0 || x.len == y.len) && u.nify(x.elem, y.elem, p) |
| } |
| |
| case *Slice: |
| // Two slice types unify if their element types unify. |
| if y, ok := y.(*Slice); ok { |
| return u.nify(x.elem, y.elem, p) |
| } |
| |
| case *Struct: |
| // Two struct types unify if they have the same sequence of fields, |
| // and if corresponding fields have the same names, their (field) types unify, |
| // and they have identical tags. Two embedded fields are considered to have the same |
| // name. Lower-case field names from different packages are always different. |
| if y, ok := y.(*Struct); ok { |
| if x.NumFields() == y.NumFields() { |
| for i, f := range x.fields { |
| g := y.fields[i] |
| if f.embedded != g.embedded || |
| x.Tag(i) != y.Tag(i) || |
| !f.sameId(g.pkg, g.name) || |
| !u.nify(f.typ, g.typ, p) { |
| return false |
| } |
| } |
| return true |
| } |
| } |
| |
| case *Pointer: |
| // Two pointer types unify if their base types unify. |
| if y, ok := y.(*Pointer); ok { |
| return u.nify(x.base, y.base, p) |
| } |
| |
| case *Tuple: |
| // Two tuples types unify if they have the same number of elements |
| // and the types of corresponding elements unify. |
| if y, ok := y.(*Tuple); ok { |
| if x.Len() == y.Len() { |
| if x != nil { |
| for i, v := range x.vars { |
| w := y.vars[i] |
| if !u.nify(v.typ, w.typ, p) { |
| return false |
| } |
| } |
| } |
| return true |
| } |
| } |
| |
| case *Signature: |
| // Two function types unify if they have the same number of parameters |
| // and result values, corresponding parameter and result types unify, |
| // and either both functions are variadic or neither is. |
| // Parameter and result names are not required to match. |
| // TODO(gri) handle type parameters or document why we can ignore them. |
| if y, ok := y.(*Signature); ok { |
| return x.variadic == y.variadic && |
| u.nify(x.params, y.params, p) && |
| u.nify(x.results, y.results, p) |
| } |
| |
| case *Interface: |
| assert(!enableInterfaceInference) // handled before this switch |
| |
| // Two interface types unify if they have the same set of methods with |
| // the same names, and corresponding function types unify. |
| // Lower-case method names from different packages are always different. |
| // The order of the methods is irrelevant. |
| if y, ok := y.(*Interface); ok { |
| xset := x.typeSet() |
| yset := y.typeSet() |
| if xset.comparable != yset.comparable { |
| return false |
| } |
| if !xset.terms.equal(yset.terms) { |
| return false |
| } |
| a := xset.methods |
| b := yset.methods |
| if len(a) == len(b) { |
| // Interface types are the only types where cycles can occur |
| // that are not "terminated" via named types; and such cycles |
| // can only be created via method parameter types that are |
| // anonymous interfaces (directly or indirectly) embedding |
| // the current interface. Example: |
| // |
| // type T interface { |
| // m() interface{T} |
| // } |
| // |
| // If two such (differently named) interfaces are compared, |
| // endless recursion occurs if the cycle is not detected. |
| // |
| // If x and y were compared before, they must be equal |
| // (if they were not, the recursion would have stopped); |
| // search the ifacePair stack for the same pair. |
| // |
| // This is a quadratic algorithm, but in practice these stacks |
| // are extremely short (bounded by the nesting depth of interface |
| // type declarations that recur via parameter types, an extremely |
| // rare occurrence). An alternative implementation might use a |
| // "visited" map, but that is probably less efficient overall. |
| q := &ifacePair{x, y, p} |
| for p != nil { |
| if p.identical(q) { |
| return true // same pair was compared before |
| } |
| p = p.prev |
| } |
| if debug { |
| assertSortedMethods(a) |
| assertSortedMethods(b) |
| } |
| for i, f := range a { |
| g := b[i] |
| if f.Id() != g.Id() || !u.nify(f.typ, g.typ, q) { |
| return false |
| } |
| } |
| return true |
| } |
| } |
| |
| case *Map: |
| // Two map types unify if their key and value types unify. |
| if y, ok := y.(*Map); ok { |
| return u.nify(x.key, y.key, p) && u.nify(x.elem, y.elem, p) |
| } |
| |
| case *Chan: |
| // Two channel types unify if their value types unify. |
| if y, ok := y.(*Chan); ok { |
| return u.nify(x.elem, y.elem, p) |
| } |
| |
| case *Named: |
| // Two named non-interface types unify if their type names originate |
| // in the same type declaration. If they are instantiated, their type |
| // argument lists must unify. |
| // If one or both named types are interfaces, the types unify if the |
| // respective methods unify (per the rules for interface unification). |
| if y, ok := y.(*Named); ok { |
| if enableInterfaceInference { |
| xi, _ := x.under().(*Interface) |
| yi, _ := y.under().(*Interface) |
| // If one or both of x and y are interfaces, use interface unification. |
| switch { |
| case xi != nil && yi != nil: |
| return u.nify(xi, yi, p) |
| case xi != nil: |
| return u.nify(xi, y, p) |
| case yi != nil: |
| return u.nify(x, yi, p) |
| } |
| // In all other cases, the type arguments and origins must match. |
| } |
| |
| // Check type arguments before origins so they unify |
| // even if the origins don't match; for better error |
| // messages (see go.dev/issue/53692). |
| xargs := x.TypeArgs().list() |
| yargs := y.TypeArgs().list() |
| if len(xargs) != len(yargs) { |
| return false |
| } |
| for i, xarg := range xargs { |
| if !u.nify(xarg, yargs[i], p) { |
| return false |
| } |
| } |
| return indenticalOrigin(x, y) |
| } |
| |
| case *TypeParam: |
| // x must be an unbound type parameter (see comment above). |
| if debug { |
| assert(u.asTypeParam(x) == nil) |
| } |
| // By definition, a valid type argument must be in the type set of |
| // the respective type constraint. Therefore, the type argument's |
| // underlying type must be in the set of underlying types of that |
| // constraint. If there is a single such underlying type, it's the |
| // constraint's core type. It must match the type argument's under- |
| // lying type, irrespective of whether the actual type argument, |
| // which may be a defined type, is actually in the type set (that |
| // will be determined at instantiation time). |
| // Thus, if we have the core type of an unbound type parameter, |
| // we know the structure of the possible types satisfying such |
| // parameters. Use that core type for further unification |
| // (see go.dev/issue/50755 for a test case). |
| if enableCoreTypeUnification { |
| // Because the core type is always an underlying type, |
| // unification will take care of matching against a |
| // defined or literal type automatically. |
| // If y is also an unbound type parameter, we will end |
| // up here again with x and y swapped, so we don't |
| // need to take care of that case separately. |
| if cx := coreType(x); cx != nil { |
| if traceInference { |
| u.tracef("core %s ≡ %s", x, y) |
| } |
| return u.nify(cx, y, p) |
| } |
| } |
| // x != y and there's nothing to do |
| |
| case nil: |
| // avoid a crash in case of nil type |
| |
| default: |
| panic(sprintf(nil, nil, true, "u.nify(%s, %s)", x, y)) |
| } |
| |
| return false |
| } |