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Diffstat (limited to 'vendor/golang.org/x/tools/internal/typeparams/common.go')
-rw-r--r-- | vendor/golang.org/x/tools/internal/typeparams/common.go | 180 |
1 files changed, 180 insertions, 0 deletions
diff --git a/vendor/golang.org/x/tools/internal/typeparams/common.go b/vendor/golang.org/x/tools/internal/typeparams/common.go new file mode 100644 index 000000000..ab6b30b83 --- /dev/null +++ b/vendor/golang.org/x/tools/internal/typeparams/common.go @@ -0,0 +1,180 @@ +// Copyright 2021 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 typeparams contains common utilities for writing tools that interact +// with generic Go code, as introduced with Go 1.18. +// +// Many of the types and functions in this package are proxies for the new APIs +// introduced in the standard library with Go 1.18. For example, the +// typeparams.Union type is an alias for go/types.Union, and the ForTypeSpec +// function returns the value of the go/ast.TypeSpec.TypeParams field. At Go +// versions older than 1.18 these helpers are implemented as stubs, allowing +// users of this package to write code that handles generic constructs inline, +// even if the Go version being used to compile does not support generics. +// +// Additionally, this package contains common utilities for working with the +// new generic constructs, to supplement the standard library APIs. Notably, +// the StructuralTerms API computes a minimal representation of the structural +// restrictions on a type parameter. In the future, this API may be available +// from go/types. +// +// See the example/README.md for a more detailed guide on how to update tools +// to support generics. +package typeparams + +import ( + "go/ast" + "go/token" + "go/types" +) + +// UnpackIndexExpr extracts data from AST nodes that represent index +// expressions. +// +// For an ast.IndexExpr, the resulting indices slice will contain exactly one +// index expression. For an ast.IndexListExpr (go1.18+), it may have a variable +// number of index expressions. +// +// For nodes that don't represent index expressions, the first return value of +// UnpackIndexExpr will be nil. +func UnpackIndexExpr(n ast.Node) (x ast.Expr, lbrack token.Pos, indices []ast.Expr, rbrack token.Pos) { + switch e := n.(type) { + case *ast.IndexExpr: + return e.X, e.Lbrack, []ast.Expr{e.Index}, e.Rbrack + case *IndexListExpr: + return e.X, e.Lbrack, e.Indices, e.Rbrack + } + return nil, token.NoPos, nil, token.NoPos +} + +// PackIndexExpr returns an *ast.IndexExpr or *ast.IndexListExpr, depending on +// the cardinality of indices. Calling PackIndexExpr with len(indices) == 0 +// will panic. +func PackIndexExpr(x ast.Expr, lbrack token.Pos, indices []ast.Expr, rbrack token.Pos) ast.Expr { + switch len(indices) { + case 0: + panic("empty indices") + case 1: + return &ast.IndexExpr{ + X: x, + Lbrack: lbrack, + Index: indices[0], + Rbrack: rbrack, + } + default: + return &IndexListExpr{ + X: x, + Lbrack: lbrack, + Indices: indices, + Rbrack: rbrack, + } + } +} + +// IsTypeParam reports whether t is a type parameter. +func IsTypeParam(t types.Type) bool { + _, ok := t.(*TypeParam) + return ok +} + +// OriginMethod returns the origin method associated with the method fn. +// For methods on a non-generic receiver base type, this is just +// fn. However, for methods with a generic receiver, OriginMethod returns the +// corresponding method in the method set of the origin type. +// +// As a special case, if fn is not a method (has no receiver), OriginMethod +// returns fn. +func OriginMethod(fn *types.Func) *types.Func { + recv := fn.Type().(*types.Signature).Recv() + if recv == nil { + + return fn + } + base := recv.Type() + p, isPtr := base.(*types.Pointer) + if isPtr { + base = p.Elem() + } + named, isNamed := base.(*types.Named) + if !isNamed { + // Receiver is a *types.Interface. + return fn + } + if ForNamed(named).Len() == 0 { + // Receiver base has no type parameters, so we can avoid the lookup below. + return fn + } + orig := NamedTypeOrigin(named) + gfn, _, _ := types.LookupFieldOrMethod(orig, true, fn.Pkg(), fn.Name()) + return gfn.(*types.Func) +} + +// GenericAssignableTo is a generalization of types.AssignableTo that +// implements the following rule for uninstantiated generic types: +// +// If V and T are generic named types, then V is considered assignable to T if, +// for every possible instantation of V[A_1, ..., A_N], the instantiation +// T[A_1, ..., A_N] is valid and V[A_1, ..., A_N] implements T[A_1, ..., A_N]. +// +// If T has structural constraints, they must be satisfied by V. +// +// For example, consider the following type declarations: +// +// type Interface[T any] interface { +// Accept(T) +// } +// +// type Container[T any] struct { +// Element T +// } +// +// func (c Container[T]) Accept(t T) { c.Element = t } +// +// In this case, GenericAssignableTo reports that instantiations of Container +// are assignable to the corresponding instantiation of Interface. +func GenericAssignableTo(ctxt *Context, V, T types.Type) bool { + // If V and T are not both named, or do not have matching non-empty type + // parameter lists, fall back on types.AssignableTo. + + VN, Vnamed := V.(*types.Named) + TN, Tnamed := T.(*types.Named) + if !Vnamed || !Tnamed { + return types.AssignableTo(V, T) + } + + vtparams := ForNamed(VN) + ttparams := ForNamed(TN) + if vtparams.Len() == 0 || vtparams.Len() != ttparams.Len() || NamedTypeArgs(VN).Len() != 0 || NamedTypeArgs(TN).Len() != 0 { + return types.AssignableTo(V, T) + } + + // V and T have the same (non-zero) number of type params. Instantiate both + // with the type parameters of V. This must always succeed for V, and will + // succeed for T if and only if the type set of each type parameter of V is a + // subset of the type set of the corresponding type parameter of T, meaning + // that every instantiation of V corresponds to a valid instantiation of T. + + // Minor optimization: ensure we share a context across the two + // instantiations below. + if ctxt == nil { + ctxt = NewContext() + } + + var targs []types.Type + for i := 0; i < vtparams.Len(); i++ { + targs = append(targs, vtparams.At(i)) + } + + vinst, err := Instantiate(ctxt, V, targs, true) + if err != nil { + panic("type parameters should satisfy their own constraints") + } + + tinst, err := Instantiate(ctxt, T, targs, true) + if err != nil { + return false + } + + return types.AssignableTo(vinst, tinst) +} |