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Diffstat (limited to 'vendor/golang.org/x/tools/go/ssa/subst.go')
| -rw-r--r-- | vendor/golang.org/x/tools/go/ssa/subst.go | 642 |
1 files changed, 642 insertions, 0 deletions
diff --git a/vendor/golang.org/x/tools/go/ssa/subst.go b/vendor/golang.org/x/tools/go/ssa/subst.go new file mode 100644 index 0000000..4dcb871 --- /dev/null +++ b/vendor/golang.org/x/tools/go/ssa/subst.go @@ -0,0 +1,642 @@ +// Copyright 2022 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. + +package ssa + +import ( + "go/types" + + "golang.org/x/tools/go/types/typeutil" + "golang.org/x/tools/internal/aliases" +) + +// subster defines a type substitution operation of a set of type parameters +// to type parameter free replacement types. Substitution is done within +// the context of a package-level function instantiation. *Named types +// declared in the function are unique to the instantiation. +// +// For example, given a parameterized function F +// +// func F[S, T any]() any { +// type X struct{ s S; next *X } +// var p *X +// return p +// } +// +// calling the instantiation F[string, int]() returns an interface +// value (*X[string,int], nil) where the underlying value of +// X[string,int] is a struct{s string; next *X[string,int]}. +// +// A nil *subster is a valid, empty substitution map. It always acts as +// the identity function. This allows for treating parameterized and +// non-parameterized functions identically while compiling to ssa. +// +// Not concurrency-safe. +// +// Note: Some may find it helpful to think through some of the most +// complex substitution cases using lambda calculus inspired notation. +// subst.typ() solves evaluating a type expression E +// within the body of a function Fn[m] with the type parameters m +// once we have applied the type arguments N. +// We can succinctly write this as a function application: +// +// ((λm. E) N) +// +// go/types does not provide this interface directly. +// So what subster provides is a type substitution operation +// +// E[m:=N] +type subster struct { + replacements map[*types.TypeParam]types.Type // values should contain no type params + cache map[types.Type]types.Type // cache of subst results + origin *types.Func // types.Objects declared within this origin function are unique within this context + ctxt *types.Context // speeds up repeated instantiations + uniqueness typeutil.Map // determines the uniqueness of the instantiations within the function + // TODO(taking): consider adding Pos +} + +// Returns a subster that replaces tparams[i] with targs[i]. Uses ctxt as a cache. +// targs should not contain any types in tparams. +// fn is the generic function for which we are substituting. +func makeSubster(ctxt *types.Context, fn *types.Func, tparams *types.TypeParamList, targs []types.Type, debug bool) *subster { + assert(tparams.Len() == len(targs), "makeSubster argument count must match") + + subst := &subster{ + replacements: make(map[*types.TypeParam]types.Type, tparams.Len()), + cache: make(map[types.Type]types.Type), + origin: fn.Origin(), + ctxt: ctxt, + } + for i := 0; i < tparams.Len(); i++ { + subst.replacements[tparams.At(i)] = targs[i] + } + return subst +} + +// typ returns the type of t with the type parameter tparams[i] substituted +// for the type targs[i] where subst was created using tparams and targs. +func (subst *subster) typ(t types.Type) (res types.Type) { + if subst == nil { + return t // A nil subst is type preserving. + } + if r, ok := subst.cache[t]; ok { + return r + } + defer func() { + subst.cache[t] = res + }() + + switch t := t.(type) { + case *types.TypeParam: + if r := subst.replacements[t]; r != nil { + return r + } + return t + + case *types.Basic: + return t + + case *types.Array: + if r := subst.typ(t.Elem()); r != t.Elem() { + return types.NewArray(r, t.Len()) + } + return t + + case *types.Slice: + if r := subst.typ(t.Elem()); r != t.Elem() { + return types.NewSlice(r) + } + return t + + case *types.Pointer: + if r := subst.typ(t.Elem()); r != t.Elem() { + return types.NewPointer(r) + } + return t + + case *types.Tuple: + return subst.tuple(t) + + case *types.Struct: + return subst.struct_(t) + + case *types.Map: + key := subst.typ(t.Key()) + elem := subst.typ(t.Elem()) + if key != t.Key() || elem != t.Elem() { + return types.NewMap(key, elem) + } + return t + + case *types.Chan: + if elem := subst.typ(t.Elem()); elem != t.Elem() { + return types.NewChan(t.Dir(), elem) + } + return t + + case *types.Signature: + return subst.signature(t) + + case *types.Union: + return subst.union(t) + + case *types.Interface: + return subst.interface_(t) + + case *aliases.Alias: + return subst.alias(t) + + case *types.Named: + return subst.named(t) + + case *opaqueType: + return t // opaque types are never substituted + + default: + panic("unreachable") + } +} + +// types returns the result of {subst.typ(ts[i])}. +func (subst *subster) types(ts []types.Type) []types.Type { + res := make([]types.Type, len(ts)) + for i := range ts { + res[i] = subst.typ(ts[i]) + } + return res +} + +func (subst *subster) tuple(t *types.Tuple) *types.Tuple { + if t != nil { + if vars := subst.varlist(t); vars != nil { + return types.NewTuple(vars...) + } + } + return t +} + +type varlist interface { + At(i int) *types.Var + Len() int +} + +// fieldlist is an adapter for structs for the varlist interface. +type fieldlist struct { + str *types.Struct +} + +func (fl fieldlist) At(i int) *types.Var { return fl.str.Field(i) } +func (fl fieldlist) Len() int { return fl.str.NumFields() } + +func (subst *subster) struct_(t *types.Struct) *types.Struct { + if t != nil { + if fields := subst.varlist(fieldlist{t}); fields != nil { + tags := make([]string, t.NumFields()) + for i, n := 0, t.NumFields(); i < n; i++ { + tags[i] = t.Tag(i) + } + return types.NewStruct(fields, tags) + } + } + return t +} + +// varlist returns subst(in[i]) or return nils if subst(v[i]) == v[i] for all i. +func (subst *subster) varlist(in varlist) []*types.Var { + var out []*types.Var // nil => no updates + for i, n := 0, in.Len(); i < n; i++ { + v := in.At(i) + w := subst.var_(v) + if v != w && out == nil { + out = make([]*types.Var, n) + for j := 0; j < i; j++ { + out[j] = in.At(j) + } + } + if out != nil { + out[i] = w + } + } + return out +} + +func (subst *subster) var_(v *types.Var) *types.Var { + if v != nil { + if typ := subst.typ(v.Type()); typ != v.Type() { + if v.IsField() { + return types.NewField(v.Pos(), v.Pkg(), v.Name(), typ, v.Embedded()) + } + return types.NewVar(v.Pos(), v.Pkg(), v.Name(), typ) + } + } + return v +} + +func (subst *subster) union(u *types.Union) *types.Union { + var out []*types.Term // nil => no updates + + for i, n := 0, u.Len(); i < n; i++ { + t := u.Term(i) + r := subst.typ(t.Type()) + if r != t.Type() && out == nil { + out = make([]*types.Term, n) + for j := 0; j < i; j++ { + out[j] = u.Term(j) + } + } + if out != nil { + out[i] = types.NewTerm(t.Tilde(), r) + } + } + + if out != nil { + return types.NewUnion(out) + } + return u +} + +func (subst *subster) interface_(iface *types.Interface) *types.Interface { + if iface == nil { + return nil + } + + // methods for the interface. Initially nil if there is no known change needed. + // Signatures for the method where recv is nil. NewInterfaceType fills in the receivers. + var methods []*types.Func + initMethods := func(n int) { // copy first n explicit methods + methods = make([]*types.Func, iface.NumExplicitMethods()) + for i := 0; i < n; i++ { + f := iface.ExplicitMethod(i) + norecv := changeRecv(f.Type().(*types.Signature), nil) + methods[i] = types.NewFunc(f.Pos(), f.Pkg(), f.Name(), norecv) + } + } + for i := 0; i < iface.NumExplicitMethods(); i++ { + f := iface.ExplicitMethod(i) + // On interfaces, we need to cycle break on anonymous interface types + // being in a cycle with their signatures being in cycles with their receivers + // that do not go through a Named. + norecv := changeRecv(f.Type().(*types.Signature), nil) + sig := subst.typ(norecv) + if sig != norecv && methods == nil { + initMethods(i) + } + if methods != nil { + methods[i] = types.NewFunc(f.Pos(), f.Pkg(), f.Name(), sig.(*types.Signature)) + } + } + + var embeds []types.Type + initEmbeds := func(n int) { // copy first n embedded types + embeds = make([]types.Type, iface.NumEmbeddeds()) + for i := 0; i < n; i++ { + embeds[i] = iface.EmbeddedType(i) + } + } + for i := 0; i < iface.NumEmbeddeds(); i++ { + e := iface.EmbeddedType(i) + r := subst.typ(e) + if e != r && embeds == nil { + initEmbeds(i) + } + if embeds != nil { + embeds[i] = r + } + } + + if methods == nil && embeds == nil { + return iface + } + if methods == nil { + initMethods(iface.NumExplicitMethods()) + } + if embeds == nil { + initEmbeds(iface.NumEmbeddeds()) + } + return types.NewInterfaceType(methods, embeds).Complete() +} + +func (subst *subster) alias(t *aliases.Alias) types.Type { + // See subster.named. This follows the same strategy. + tparams := aliases.TypeParams(t) + targs := aliases.TypeArgs(t) + tname := t.Obj() + torigin := aliases.Origin(t) + + if !declaredWithin(tname, subst.origin) { + // t is declared outside of the function origin. So t is a package level type alias. + if targs.Len() == 0 { + // No type arguments so no instantiation needed. + return t + } + + // Instantiate with the substituted type arguments. + newTArgs := subst.typelist(targs) + return subst.instantiate(torigin, newTArgs) + } + + if targs.Len() == 0 { + // t is declared within the function origin and has no type arguments. + // + // Example: This corresponds to A or B in F, but not A[int]: + // + // func F[T any]() { + // type A[S any] = struct{t T, s S} + // type B = T + // var x A[int] + // ... + // } + // + // This is somewhat different than *Named as *Alias cannot be created recursively. + + // Copy and substitute type params. + var newTParams []*types.TypeParam + for i := 0; i < tparams.Len(); i++ { + cur := tparams.At(i) + cobj := cur.Obj() + cname := types.NewTypeName(cobj.Pos(), cobj.Pkg(), cobj.Name(), nil) + ntp := types.NewTypeParam(cname, nil) + subst.cache[cur] = ntp // See the comment "Note: Subtle" in subster.named. + newTParams = append(newTParams, ntp) + } + + // Substitute rhs. + rhs := subst.typ(aliases.Rhs(t)) + + // Create the fresh alias. + obj := aliases.NewAlias(true, tname.Pos(), tname.Pkg(), tname.Name(), rhs) + fresh := obj.Type() + if fresh, ok := fresh.(*aliases.Alias); ok { + // TODO: assume ok when aliases are always materialized (go1.27). + aliases.SetTypeParams(fresh, newTParams) + } + + // Substitute into all of the constraints after they are created. + for i, ntp := range newTParams { + bound := tparams.At(i).Constraint() + ntp.SetConstraint(subst.typ(bound)) + } + return fresh + } + + // t is declared within the function origin and has type arguments. + // + // Example: This corresponds to A[int] in F. Cases A and B are handled above. + // func F[T any]() { + // type A[S any] = struct{t T, s S} + // type B = T + // var x A[int] + // ... + // } + subOrigin := subst.typ(torigin) + subTArgs := subst.typelist(targs) + return subst.instantiate(subOrigin, subTArgs) +} + +func (subst *subster) named(t *types.Named) types.Type { + // A Named type is a user defined type. + // Ignoring generics, Named types are canonical: they are identical if + // and only if they have the same defining symbol. + // Generics complicate things, both if the type definition itself is + // parameterized, and if the type is defined within the scope of a + // parameterized function. In this case, two named types are identical if + // and only if their identifying symbols are identical, and all type + // arguments bindings in scope of the named type definition (including the + // type parameters of the definition itself) are equivalent. + // + // Notably: + // 1. For type definition type T[P1 any] struct{}, T[A] and T[B] are identical + // only if A and B are identical. + // 2. Inside the generic func Fn[m any]() any { type T struct{}; return T{} }, + // the result of Fn[A] and Fn[B] have identical type if and only if A and + // B are identical. + // 3. Both 1 and 2 could apply, such as in + // func F[m any]() any { type T[x any] struct{}; return T{} } + // + // A subster replaces type parameters within a function scope, and therefore must + // also replace free type parameters in the definitions of local types. + // + // Note: There are some detailed notes sprinkled throughout that borrow from + // lambda calculus notation. These contain some over simplifying math. + // + // LC: One way to think about subster is that it is a way of evaluating + // ((λm. E) N) as E[m:=N]. + // Each Named type t has an object *TypeName within a scope S that binds an + // underlying type expression U. U can refer to symbols within S (+ S's ancestors). + // Let x = t.TypeParams() and A = t.TypeArgs(). + // Each Named type t is then either: + // U where len(x) == 0 && len(A) == 0 + // λx. U where len(x) != 0 && len(A) == 0 + // ((λx. U) A) where len(x) == len(A) + // In each case, we will evaluate t[m:=N]. + tparams := t.TypeParams() // x + targs := t.TypeArgs() // A + + if !declaredWithin(t.Obj(), subst.origin) { + // t is declared outside of Fn[m]. + // + // In this case, we can skip substituting t.Underlying(). + // The underlying type cannot refer to the type parameters. + // + // LC: Let free(E) be the set of free type parameters in an expression E. + // Then whenever m ∉ free(E), then E = E[m:=N]. + // t ∉ Scope(fn) so therefore m ∉ free(U) and m ∩ x = ∅. + if targs.Len() == 0 { + // t has no type arguments. So it does not need to be instantiated. + // + // This is the normal case in real Go code, where t is not parameterized, + // declared at some package scope, and m is a TypeParam from a parameterized + // function F[m] or method. + // + // LC: m ∉ free(A) lets us conclude m ∉ free(t). So t=t[m:=N]. + return t + } + + // t is declared outside of Fn[m] and has type arguments. + // The type arguments may contain type parameters m so + // substitute the type arguments, and instantiate the substituted + // type arguments. + // + // LC: Evaluate this as ((λx. U) A') where A' = A[m := N]. + newTArgs := subst.typelist(targs) + return subst.instantiate(t.Origin(), newTArgs) + } + + // t is declared within Fn[m]. + + if targs.Len() == 0 { // no type arguments? + assert(t == t.Origin(), "local parameterized type abstraction must be an origin type") + + // t has no type arguments. + // The underlying type of t may contain the function's type parameters, + // replace these, and create a new type. + // + // Subtle: We short circuit substitution and use a newly created type in + // subst, i.e. cache[t]=fresh, to preemptively replace t with fresh + // in recursive types during traversal. This both breaks infinite cycles + // and allows for constructing types with the replacement applied in + // subst.typ(U). + // + // A new copy of the Named and Typename (and constraints) per function + // instantiation matches the semantics of Go, which treats all function + // instantiations F[N] as having distinct local types. + // + // LC: x.Len()=0 can be thought of as a special case of λx. U. + // LC: Evaluate (λx. U)[m:=N] as (λx'. U') where U'=U[x:=x',m:=N]. + tname := t.Obj() + obj := types.NewTypeName(tname.Pos(), tname.Pkg(), tname.Name(), nil) + fresh := types.NewNamed(obj, nil, nil) + var newTParams []*types.TypeParam + for i := 0; i < tparams.Len(); i++ { + cur := tparams.At(i) + cobj := cur.Obj() + cname := types.NewTypeName(cobj.Pos(), cobj.Pkg(), cobj.Name(), nil) + ntp := types.NewTypeParam(cname, nil) + subst.cache[cur] = ntp + newTParams = append(newTParams, ntp) + } + fresh.SetTypeParams(newTParams) + subst.cache[t] = fresh + subst.cache[fresh] = fresh + fresh.SetUnderlying(subst.typ(t.Underlying())) + // Substitute into all of the constraints after they are created. + for i, ntp := range newTParams { + bound := tparams.At(i).Constraint() + ntp.SetConstraint(subst.typ(bound)) + } + return fresh + } + + // t is defined within Fn[m] and t has type arguments (an instantiation). + // We reduce this to the two cases above: + // (1) substitute the function's type parameters into t.Origin(). + // (2) substitute t's type arguments A and instantiate the updated t.Origin() with these. + // + // LC: Evaluate ((λx. U) A)[m:=N] as (t' A') where t' = (λx. U)[m:=N] and A'=A [m:=N] + subOrigin := subst.typ(t.Origin()) + subTArgs := subst.typelist(targs) + return subst.instantiate(subOrigin, subTArgs) +} + +func (subst *subster) instantiate(orig types.Type, targs []types.Type) types.Type { + i, err := types.Instantiate(subst.ctxt, orig, targs, false) + assert(err == nil, "failed to Instantiate named (Named or Alias) type") + if c, _ := subst.uniqueness.At(i).(types.Type); c != nil { + return c.(types.Type) + } + subst.uniqueness.Set(i, i) + return i +} + +func (subst *subster) typelist(l *types.TypeList) []types.Type { + res := make([]types.Type, l.Len()) + for i := 0; i < l.Len(); i++ { + res[i] = subst.typ(l.At(i)) + } + return res +} + +func (subst *subster) signature(t *types.Signature) types.Type { + tparams := t.TypeParams() + + // We are choosing not to support tparams.Len() > 0 until a need has been observed in practice. + // + // There are some known usages for types.Types coming from types.{Eval,CheckExpr}. + // To support tparams.Len() > 0, we just need to do the following [psuedocode]: + // targs := {subst.replacements[tparams[i]]]}; Instantiate(ctxt, t, targs, false) + + assert(tparams.Len() == 0, "Substituting types.Signatures with generic functions are currently unsupported.") + + // Either: + // (1)non-generic function. + // no type params to substitute + // (2)generic method and recv needs to be substituted. + + // Receivers can be either: + // named + // pointer to named + // interface + // nil + // interface is the problematic case. We need to cycle break there! + recv := subst.var_(t.Recv()) + params := subst.tuple(t.Params()) + results := subst.tuple(t.Results()) + if recv != t.Recv() || params != t.Params() || results != t.Results() { + return types.NewSignatureType(recv, nil, nil, params, results, t.Variadic()) + } + return t +} + +// reaches returns true if a type t reaches any type t' s.t. c[t'] == true. +// It updates c to cache results. +// +// reaches is currently only part of the wellFormed debug logic, and +// in practice c is initially only type parameters. It is not currently +// relied on in production. +func reaches(t types.Type, c map[types.Type]bool) (res bool) { + if c, ok := c[t]; ok { + return c + } + + // c is populated with temporary false entries as types are visited. + // This avoids repeat visits and break cycles. + c[t] = false + defer func() { + c[t] = res + }() + + switch t := t.(type) { + case *types.TypeParam, *types.Basic: + return false + case *types.Array: + return reaches(t.Elem(), c) + case *types.Slice: + return reaches(t.Elem(), c) + case *types.Pointer: + return reaches(t.Elem(), c) + case *types.Tuple: + for i := 0; i < t.Len(); i++ { + if reaches(t.At(i).Type(), c) { + return true + } + } + case *types.Struct: + for i := 0; i < t.NumFields(); i++ { + if reaches(t.Field(i).Type(), c) { + return true + } + } + case *types.Map: + return reaches(t.Key(), c) || reaches(t.Elem(), c) + case *types.Chan: + return reaches(t.Elem(), c) + case *types.Signature: + if t.Recv() != nil && reaches(t.Recv().Type(), c) { + return true + } + return reaches(t.Params(), c) || reaches(t.Results(), c) + case *types.Union: + for i := 0; i < t.Len(); i++ { + if reaches(t.Term(i).Type(), c) { + return true + } + } + case *types.Interface: + for i := 0; i < t.NumEmbeddeds(); i++ { + if reaches(t.Embedded(i), c) { + return true + } + } + for i := 0; i < t.NumExplicitMethods(); i++ { + if reaches(t.ExplicitMethod(i).Type(), c) { + return true + } + } + case *types.Named, *aliases.Alias: + return reaches(t.Underlying(), c) + default: + panic("unreachable") + } + return false +} |