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// 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 types
import (
"go/ast"
"go/token"
)
// ----------------------------------------------------------------------------
// API
// A Signature represents a (non-builtin) function or method type.
// The receiver is ignored when comparing signatures for identity.
type Signature struct {
// We need to keep the scope in Signature (rather than passing it around
// and store it in the Func Object) because when type-checking a function
// literal we call the general type checker which returns a general Type.
// We then unpack the *Signature and use the scope for the literal body.
rparams *TypeParamList // receiver type parameters from left to right, or nil
tparams *TypeParamList // type parameters from left to right, or nil
scope *Scope // function scope for package-local and non-instantiated signatures; nil otherwise
recv *Var // nil if not a method
params *Tuple // (incoming) parameters from left to right; or nil
results *Tuple // (outgoing) results from left to right; or nil
variadic bool // true if the last parameter's type is of the form ...T (or string, for append built-in only)
}
// NewSignature returns a new function type for the given receiver, parameters,
// and results, either of which may be nil. If variadic is set, the function
// is variadic, it must have at least one parameter, and the last parameter
// must be of unnamed slice type.
//
// Deprecated: Use NewSignatureType instead which allows for type parameters.
func NewSignature(recv *Var, params, results *Tuple, variadic bool) *Signature {
return NewSignatureType(recv, nil, nil, params, results, variadic)
}
// NewSignatureType creates a new function type for the given receiver,
// receiver type parameters, type parameters, parameters, and results. If
// variadic is set, params must hold at least one parameter and the last
// parameter must be of unnamed slice type. If recv is non-nil, typeParams must
// be empty. If recvTypeParams is non-empty, recv must be non-nil.
func NewSignatureType(recv *Var, recvTypeParams, typeParams []*TypeParam, params, results *Tuple, variadic bool) *Signature {
if variadic {
n := params.Len()
if n == 0 {
panic("variadic function must have at least one parameter")
}
if _, ok := params.At(n - 1).typ.(*Slice); !ok {
panic("variadic parameter must be of unnamed slice type")
}
}
sig := &Signature{recv: recv, params: params, results: results, variadic: variadic}
if len(recvTypeParams) != 0 {
if recv == nil {
panic("function with receiver type parameters must have a receiver")
}
sig.rparams = bindTParams(recvTypeParams)
}
if len(typeParams) != 0 {
if recv != nil {
panic("function with type parameters cannot have a receiver")
}
sig.tparams = bindTParams(typeParams)
}
return sig
}
// Recv returns the receiver of signature s (if a method), or nil if a
// function. It is ignored when comparing signatures for identity.
//
// For an abstract method, Recv returns the enclosing interface either
// as a *Named or an *Interface. Due to embedding, an interface may
// contain methods whose receiver type is a different interface.
func (s *Signature) Recv() *Var { return s.recv }
// TypeParams returns the type parameters of signature s, or nil.
func (s *Signature) TypeParams() *TypeParamList { return s.tparams }
// RecvTypeParams returns the receiver type parameters of signature s, or nil.
func (s *Signature) RecvTypeParams() *TypeParamList { return s.rparams }
// Params returns the parameters of signature s, or nil.
func (s *Signature) Params() *Tuple { return s.params }
// Results returns the results of signature s, or nil.
func (s *Signature) Results() *Tuple { return s.results }
// Variadic reports whether the signature s is variadic.
func (s *Signature) Variadic() bool { return s.variadic }
func (t *Signature) Underlying() Type { return t }
func (t *Signature) String() string { return TypeString(t, nil) }
// ----------------------------------------------------------------------------
// Implementation
// funcType type-checks a function or method type.
func (check *Checker) funcType(sig *Signature, recvPar *ast.FieldList, ftyp *ast.FuncType) {
check.openScope(ftyp, "function")
check.scope.isFunc = true
check.recordScope(ftyp, check.scope)
sig.scope = check.scope
defer check.closeScope()
if recvPar != nil && len(recvPar.List) > 0 {
// collect generic receiver type parameters, if any
// - a receiver type parameter is like any other type parameter, except that it is declared implicitly
// - the receiver specification acts as local declaration for its type parameters, which may be blank
_, rname, rparams := check.unpackRecv(recvPar.List[0].Type, true)
if len(rparams) > 0 {
tparams := check.declareTypeParams(nil, rparams)
sig.rparams = bindTParams(tparams)
// Blank identifiers don't get declared, so naive type-checking of the
// receiver type expression would fail in Checker.collectParams below,
// when Checker.ident cannot resolve the _ to a type.
//
// Checker.recvTParamMap maps these blank identifiers to their type parameter
// types, so that they may be resolved in Checker.ident when they fail
// lookup in the scope.
for i, p := range rparams {
if p.Name == "_" {
if check.recvTParamMap == nil {
check.recvTParamMap = make(map[*ast.Ident]*TypeParam)
}
check.recvTParamMap[p] = tparams[i]
}
}
// determine receiver type to get its type parameters
// and the respective type parameter bounds
var recvTParams []*TypeParam
if rname != nil {
// recv should be a Named type (otherwise an error is reported elsewhere)
// Also: Don't report an error via genericType since it will be reported
// again when we type-check the signature.
// TODO(gri) maybe the receiver should be marked as invalid instead?
if recv, _ := check.genericType(rname, nil).(*Named); recv != nil {
recvTParams = recv.TypeParams().list()
}
}
// provide type parameter bounds
if len(tparams) == len(recvTParams) {
smap := makeRenameMap(recvTParams, tparams)
for i, tpar := range tparams {
recvTPar := recvTParams[i]
check.mono.recordCanon(tpar, recvTPar)
// recvTPar.bound is (possibly) parameterized in the context of the
// receiver type declaration. Substitute parameters for the current
// context.
tpar.bound = check.subst(tpar.obj.pos, recvTPar.bound, smap, nil)
}
} else if len(tparams) < len(recvTParams) {
// Reporting an error here is a stop-gap measure to avoid crashes in the
// compiler when a type parameter/argument cannot be inferred later. It
// may lead to follow-on errors (see issues #51339, #51343).
// TODO(gri) find a better solution
got := measure(len(tparams), "type parameter")
check.errorf(recvPar, _BadRecv, "got %s, but receiver base type declares %d", got, len(recvTParams))
}
}
}
if ftyp.TypeParams != nil {
check.collectTypeParams(&sig.tparams, ftyp.TypeParams)
// Always type-check method type parameters but complain that they are not allowed.
// (A separate check is needed when type-checking interface method signatures because
// they don't have a receiver specification.)
if recvPar != nil {
check.errorf(ftyp.TypeParams, _InvalidMethodTypeParams, "methods cannot have type parameters")
}
}
// Value (non-type) parameters' scope starts in the function body. Use a temporary scope for their
// declarations and then squash that scope into the parent scope (and report any redeclarations at
// that time).
scope := NewScope(check.scope, token.NoPos, token.NoPos, "function body (temp. scope)")
recvList, _ := check.collectParams(scope, recvPar, false)
params, variadic := check.collectParams(scope, ftyp.Params, true)
results, _ := check.collectParams(scope, ftyp.Results, false)
scope.squash(func(obj, alt Object) {
check.errorf(obj, _DuplicateDecl, "%s redeclared in this block", obj.Name())
check.reportAltDecl(alt)
})
if recvPar != nil {
// recv parameter list present (may be empty)
// spec: "The receiver is specified via an extra parameter section preceding the
// method name. That parameter section must declare a single parameter, the receiver."
var recv *Var
switch len(recvList) {
case 0:
// error reported by resolver
recv = NewParam(token.NoPos, nil, "", Typ[Invalid]) // ignore recv below
default:
// more than one receiver
check.error(recvList[len(recvList)-1], _InvalidRecv, "method must have exactly one receiver")
fallthrough // continue with first receiver
case 1:
recv = recvList[0]
}
sig.recv = recv
// Delay validation of receiver type as it may cause premature expansion
// of types the receiver type is dependent on (see issues #51232, #51233).
check.later(func() {
rtyp, _ := deref(recv.typ)
// spec: "The receiver type must be of the form T or *T where T is a type name."
// (ignore invalid types - error was reported before)
if rtyp != Typ[Invalid] {
var err string
switch T := rtyp.(type) {
case *Named:
T.resolve(check.bestContext(nil))
// The receiver type may be an instantiated type referred to
// by an alias (which cannot have receiver parameters for now).
if T.TypeArgs() != nil && sig.RecvTypeParams() == nil {
check.errorf(recv, _InvalidRecv, "cannot define methods on instantiated type %s", recv.typ)
break
}
// spec: "The type denoted by T is called the receiver base type; it must not
// be a pointer or interface type and it must be declared in the same package
// as the method."
if T.obj.pkg != check.pkg {
err = "type not defined in this package"
if compilerErrorMessages {
check.errorf(recv, _InvalidRecv, "cannot define new methods on non-local type %s", recv.typ)
err = ""
}
} else {
// The underlying type of a receiver base type can be a type parameter;
// e.g. for methods with a generic receiver T[P] with type T[P any] P.
// TODO(gri) Such declarations are currently disallowed.
// Revisit the need for underIs.
underIs(T, func(u Type) bool {
switch u := u.(type) {
case *Basic:
// unsafe.Pointer is treated like a regular pointer
if u.kind == UnsafePointer {
err = "unsafe.Pointer"
return false
}
case *Pointer, *Interface:
err = "pointer or interface type"
return false
}
return true
})
}
case *Basic:
err = "basic or unnamed type"
if compilerErrorMessages {
check.errorf(recv, _InvalidRecv, "cannot define new methods on non-local type %s", recv.typ)
err = ""
}
default:
check.errorf(recv, _InvalidRecv, "invalid receiver type %s", recv.typ)
}
if err != "" {
check.errorf(recv, _InvalidRecv, "invalid receiver type %s (%s)", recv.typ, err)
}
}
}).describef(recv, "validate receiver %s", recv)
}
sig.params = NewTuple(params...)
sig.results = NewTuple(results...)
sig.variadic = variadic
}
// collectParams declares the parameters of list in scope and returns the corresponding
// variable list.
func (check *Checker) collectParams(scope *Scope, list *ast.FieldList, variadicOk bool) (params []*Var, variadic bool) {
if list == nil {
return
}
var named, anonymous bool
for i, field := range list.List {
ftype := field.Type
if t, _ := ftype.(*ast.Ellipsis); t != nil {
ftype = t.Elt
if variadicOk && i == len(list.List)-1 && len(field.Names) <= 1 {
variadic = true
} else {
check.softErrorf(t, _MisplacedDotDotDot, "can only use ... with final parameter in list")
// ignore ... and continue
}
}
typ := check.varType(ftype)
// The parser ensures that f.Tag is nil and we don't
// care if a constructed AST contains a non-nil tag.
if len(field.Names) > 0 {
// named parameter
for _, name := range field.Names {
if name.Name == "" {
check.invalidAST(name, "anonymous parameter")
// ok to continue
}
par := NewParam(name.Pos(), check.pkg, name.Name, typ)
check.declare(scope, name, par, scope.pos)
params = append(params, par)
}
named = true
} else {
// anonymous parameter
par := NewParam(ftype.Pos(), check.pkg, "", typ)
check.recordImplicit(field, par)
params = append(params, par)
anonymous = true
}
}
if named && anonymous {
check.invalidAST(list, "list contains both named and anonymous parameters")
// ok to continue
}
// For a variadic function, change the last parameter's type from T to []T.
// Since we type-checked T rather than ...T, we also need to retro-actively
// record the type for ...T.
if variadic {
last := params[len(params)-1]
last.typ = &Slice{elem: last.typ}
check.recordTypeAndValue(list.List[len(list.List)-1].Type, typexpr, last.typ, nil)
}
return
}