| // 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. |
| |
| package types |
| |
| import ( |
| "bytes" |
| "fmt" |
| "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 = true |
| |
| // If enableCoreTypeUnification is set, unification will consider |
| // the core types, if any, of non-local (unbound) type parameters. |
| enableCoreTypeUnification = 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 { |
| // tparams is the initial list of type parameters provided. |
| // Only used to print/return types in reproducible order. |
| tparams []*TypeParam |
| // 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{tparams, 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 { |
| var buf bytes.Buffer |
| w := newTypeWriter(&buf, nil) |
| w.byte('[') |
| for i, x := range u.tparams { |
| if i > 0 { |
| w.string(", ") |
| } |
| w.typ(x) |
| w.string(": ") |
| w.typ(u.at(x)) |
| } |
| w.byte(']') |
| return buf.String() |
| } |
| |
| // 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 and it must not have been set before. |
| func (u *unifier) set(x *TypeParam, t Type) { |
| assert(t != nil) |
| if traceInference { |
| u.tracef("%s ➞ %s", x, t) |
| } |
| h := u.handles[x] |
| assert(*h == nil) |
| *h = 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 (via unification) for the type parameters |
| // recorded with u, and an index. If all types were inferred, the returned index is < 0. |
| // Otherwise, it is the index of the first type parameter which couldn't be inferred; |
| // i.e., for which list[index] is nil. |
| func (u *unifier) inferred() (list []Type, index int) { |
| list = make([]Type, len(u.tparams)) |
| index = -1 |
| for i, x := range u.tparams { |
| t := u.at(x) |
| list[i] = t |
| if index < 0 && t == nil { |
| index = i |
| } |
| } |
| return |
| } |
| |
| func (u *unifier) nifyEq(x, y Type, p *ifacePair) bool { |
| return x == y || u.nify(x, y, p) |
| } |
| |
| // 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) { |
| if traceInference { |
| u.tracef("%s ≡ %s", x, y) |
| } |
| |
| // 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 |
| } |
| u.depth++ |
| defer func() { |
| u.depth-- |
| if traceInference && !result { |
| u.tracef("%s ≢ %s", x, y) |
| } |
| }() |
| |
| // If exact unification is known to fail because we attempt to |
| // match a type name against an unnamed type literal, consider |
| // the underlying type of the named type. |
| // (We use !hasName to exclude any type with a name, including |
| // basic types and type parameters; the rest are unamed types.) |
| if nx, _ := x.(*Named); nx != nil && !hasName(y) { |
| if traceInference { |
| u.tracef("under %s ≡ %s", nx, y) |
| } |
| x = nx.under() |
| // Per the spec, a defined type cannot have an underlying type |
| // that is a type parameter. |
| assert(!isTypeParam(x)) |
| } else if ny, _ := y.(*Named); ny != nil && !hasName(x) { |
| if traceInference { |
| u.tracef("%s ≡ under %s", x, ny) |
| } |
| y = ny.under() |
| assert(!isTypeParam(y)) |
| } |
| |
| // Cases where at least one of x or y is a type parameter recorded with u. |
| 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.nifyEq(u.at(px), u.at(py), p) |
| |
| case px != nil: |
| // x is a type parameter, y is not |
| if tx := u.at(px); tx != nil { |
| return u.nifyEq(tx, y, p) |
| } |
| // otherwise, infer type from y |
| u.set(px, y) |
| return true |
| |
| case py != nil: |
| // y is a type parameter, x is not |
| if ty := u.at(py); ty != nil { |
| return u.nifyEq(x, ty, p) |
| } |
| // otherwise, infer type from x |
| u.set(py, x) |
| return true |
| } |
| |
| // If we get here and x or y is a type parameter, they are type parameters |
| // from outside our declaration list. Try to unify their core types, if any |
| // (see go.dev/issue/50755 for a test case). |
| if enableCoreTypeUnification { |
| if isTypeParam(x) && !hasName(y) { |
| // When considering the type parameter for unification |
| // we look at the adjusted core term (adjusted core type |
| // with tilde information). |
| // If the adjusted core type is a named type N; the |
| // corresponding core type is under(N). |
| // Since y doesn't have a name, unification will end up |
| // comparing under(N) to y, so we can just use the core |
| // type instead. And we can ignore the tilde because we |
| // already look at the underlying types on both sides |
| // and we have known types on both sides. |
| // Optimization. |
| if cx := coreType(x); cx != nil { |
| if traceInference { |
| u.tracef("core %s ≡ %s", x, y) |
| } |
| return u.nify(cx, y, p) |
| } |
| } else if isTypeParam(y) && !hasName(x) { |
| // see comment above |
| if cy := coreType(y); cy != nil { |
| if traceInference { |
| u.tracef("%s ≡ core %s", x, y) |
| } |
| return u.nify(x, cy, p) |
| } |
| } |
| } |
| |
| // For type unification, do not shortcut (x == y) for identical |
| // types. Instead keep comparing them element-wise to unify the |
| // matching (and equal type parameter types). A simple test case |
| // where this matters is: func f[P any](a P) { f(a) } . |
| |
| 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 are identical if they have identical element types |
| // and the same array length. |
| 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 are identical if they have identical element types. |
| if y, ok := y.(*Slice); ok { |
| return u.nify(x.elem, y.elem, p) |
| } |
| |
| case *Struct: |
| // Two struct types are identical if they have the same sequence of fields, |
| // and if corresponding fields have the same names, and identical types, |
| // and 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 are identical if they have identical base types. |
| if y, ok := y.(*Pointer); ok { |
| return u.nify(x.base, y.base, p) |
| } |
| |
| case *Tuple: |
| // Two tuples types are identical if they have the same number of elements |
| // and corresponding elements have identical types. |
| 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 are identical if they have the same number of parameters |
| // and result values, corresponding parameter and result types are identical, |
| // 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: |
| // Two interface types are identical if they have the same set of methods with |
| // the same names and identical function types. 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 are identical if they have identical key and value types. |
| 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 are identical if they have identical value types. |
| if y, ok := y.(*Chan); ok { |
| return u.nify(x.elem, y.elem, p) |
| } |
| |
| case *Named: |
| // TODO(gri) This code differs now from the parallel code in Checker.identical. Investigate. |
| if y, ok := y.(*Named); ok { |
| xargs := x.TypeArgs().list() |
| yargs := y.TypeArgs().list() |
| |
| if len(xargs) != len(yargs) { |
| return false |
| } |
| |
| // TODO(gri) This is not always correct: two types may have the same names |
| // in the same package if one of them is nested in a function. |
| // Extremely unlikely but we need an always correct solution. |
| if x.obj.pkg == y.obj.pkg && x.obj.name == y.obj.name { |
| for i, x := range xargs { |
| if !u.nify(x, yargs[i], p) { |
| return false |
| } |
| } |
| return true |
| } |
| } |
| |
| case *TypeParam: |
| // Two type parameters (which are not part of the type parameters of the |
| // enclosing type as those are handled in the beginning of this function) |
| // are identical if they originate in the same declaration. |
| return x == y |
| |
| case nil: |
| // avoid a crash in case of nil type |
| |
| default: |
| panic(sprintf(nil, nil, true, "u.nify(%s, %s), u.tparams = %s", x, y, u.tparams)) |
| } |
| |
| return false |
| } |