signature.go

     1  // Copyright 2021 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package types2
     6  
     7  import (
     8  	"cmd/compile/internal/syntax"
     9  	"fmt"
    10  	. "internal/types/errors"
    11  	"path/filepath"
    12  	"strings"
    13  )
    14  
    15  // ----------------------------------------------------------------------------
    16  // API
    17  
    18  // A Signature represents a (non-builtin) function or method type.
    19  // The receiver is ignored when comparing signatures for identity.
    20  type Signature struct {
    21  	// We need to keep the scope in Signature (rather than passing it around
    22  	// and store it in the Func Object) because when type-checking a function
    23  	// literal we call the general type checker which returns a general Type.
    24  	// We then unpack the *Signature and use the scope for the literal body.
    25  	rparams  *TypeParamList // receiver type parameters from left to right, or nil
    26  	tparams  *TypeParamList // type parameters from left to right, or nil
    27  	scope    *Scope         // function scope for package-local and non-instantiated signatures; nil otherwise
    28  	recv     *Var           // nil if not a method
    29  	params   *Tuple         // (incoming) parameters from left to right; or nil
    30  	results  *Tuple         // (outgoing) results from left to right; or nil
    31  	variadic bool           // true if the last parameter's type is of the form ...T (or string, for append built-in only)
    32  }
    33  
    34  // NewSignatureType creates a new function type for the given receiver,
    35  // receiver type parameters, type parameters, parameters, and results.
    36  // If variadic is set, params must hold at least one parameter and the
    37  // last parameter must be an unnamed slice or a type parameter whose
    38  // type set has an unnamed slice as common underlying type.
    39  // As a special case, for variadic signatures the last parameter may
    40  // also be a string type, or a type parameter containing a mix of byte
    41  // slices and string types in its type set.
    42  // If recv is non-nil, typeParams must be empty. If recvTypeParams is
    43  // non-empty, recv must be non-nil.
    44  func NewSignatureType(recv *Var, recvTypeParams, typeParams []*TypeParam, params, results *Tuple, variadic bool) *Signature {
    45  	if variadic {
    46  		n := params.Len()
    47  		if n == 0 {
    48  			panic("variadic function must have at least one parameter")
    49  		}
    50  		last := params.At(n - 1).typ
    51  		var S *Slice
    52  		typeset(last, func(t, _ Type) bool {
    53  			if t == nil {
    54  				return false
    55  			}
    56  			var s *Slice
    57  			if isString(t) {
    58  				s = NewSlice(universeByte)
    59  			} else {
    60  				s, _ = Unalias(t).(*Slice) // don't accept a named slice type
    61  			}
    62  			if S == nil {
    63  				S = s
    64  			} else if s == nil || !Identical(S, s) {
    65  				S = nil
    66  				return false
    67  			}
    68  			return true
    69  		})
    70  		if S == nil {
    71  			panic(fmt.Sprintf("got %s, want variadic parameter of unnamed slice or string type", last))
    72  		}
    73  	}
    74  	sig := &Signature{recv: recv, params: params, results: results, variadic: variadic}
    75  	if len(recvTypeParams) != 0 {
    76  		if recv == nil {
    77  			panic("function with receiver type parameters must have a receiver")
    78  		}
    79  		sig.rparams = bindTParams(recvTypeParams)
    80  	}
    81  	if len(typeParams) != 0 {
    82  		if recv != nil {
    83  			panic("function with type parameters cannot have a receiver")
    84  		}
    85  		sig.tparams = bindTParams(typeParams)
    86  	}
    87  	return sig
    88  }
    89  
    90  // Recv returns the receiver of signature s (if a method), or nil if a
    91  // function. It is ignored when comparing signatures for identity.
    92  //
    93  // For an abstract method, Recv returns the enclosing interface either
    94  // as a *[Named] or an *[Interface]. Due to embedding, an interface may
    95  // contain methods whose receiver type is a different interface.
    96  func (s *Signature) Recv() *Var { return s.recv }
    97  
    98  // TypeParams returns the type parameters of signature s, or nil.
    99  func (s *Signature) TypeParams() *TypeParamList { return s.tparams }
   100  
   101  // RecvTypeParams returns the receiver type parameters of signature s, or nil.
   102  func (s *Signature) RecvTypeParams() *TypeParamList { return s.rparams }
   103  
   104  // Params returns the parameters of signature s, or nil.
   105  func (s *Signature) Params() *Tuple { return s.params }
   106  
   107  // Results returns the results of signature s, or nil.
   108  func (s *Signature) Results() *Tuple { return s.results }
   109  
   110  // Variadic reports whether the signature s is variadic.
   111  func (s *Signature) Variadic() bool { return s.variadic }
   112  
   113  func (s *Signature) Underlying() Type { return s }
   114  func (s *Signature) String() string   { return TypeString(s, nil) }
   115  
   116  // ----------------------------------------------------------------------------
   117  // Implementation
   118  
   119  // funcType type-checks a function or method type.
   120  func (check *Checker) funcType(sig *Signature, recvPar *syntax.Field, tparams []*syntax.Field, ftyp *syntax.FuncType) {
   121  	check.openScope(ftyp, "function")
   122  	check.scope.isFunc = true
   123  	check.recordScope(ftyp, check.scope)
   124  	sig.scope = check.scope
   125  	defer check.closeScope()
   126  
   127  	// collect method receiver, if any
   128  	var recv *Var
   129  	var rparams *TypeParamList
   130  	if recvPar != nil {
   131  		// all type parameters' scopes start after the method name
   132  		scopePos := ftyp.Pos()
   133  		recv, rparams = check.collectRecv(recvPar, scopePos)
   134  	}
   135  
   136  	// collect and declare function type parameters
   137  	if tparams != nil {
   138  		// The parser will complain about invalid type parameters for methods.
   139  		check.collectTypeParams(&sig.tparams, tparams)
   140  	}
   141  
   142  	// collect ordinary and result parameters
   143  	pnames, params, variadic := check.collectParams(ParamVar, ftyp.ParamList)
   144  	rnames, results, _ := check.collectParams(ResultVar, ftyp.ResultList)
   145  
   146  	// declare named receiver, ordinary, and result parameters
   147  	scopePos := syntax.EndPos(ftyp) // all parameter's scopes start after the signature
   148  	if recv != nil && recv.name != "" {
   149  		check.declare(check.scope, recvPar.Name, recv, scopePos)
   150  	}
   151  	check.declareParams(pnames, params, scopePos)
   152  	check.declareParams(rnames, results, scopePos)
   153  
   154  	sig.recv = recv
   155  	sig.rparams = rparams
   156  	sig.params = NewTuple(params...)
   157  	sig.results = NewTuple(results...)
   158  	sig.variadic = variadic
   159  }
   160  
   161  // collectRecv extracts the method receiver and its type parameters (if any) from rparam.
   162  // It declares the type parameters (but not the receiver) in the current scope, and
   163  // returns the receiver variable and its type parameter list (if any).
   164  func (check *Checker) collectRecv(rparam *syntax.Field, scopePos syntax.Pos) (*Var, *TypeParamList) {
   165  	// Unpack the receiver parameter which is of the form
   166  	//
   167  	//	"(" [rname] ["*"] rbase ["[" rtparams "]"] ")"
   168  	//
   169  	// The receiver name rname, the pointer indirection, and the
   170  	// receiver type parameters rtparams may not be present.
   171  	rptr, rbase, rtparams := check.unpackRecv(rparam.Type, true)
   172  
   173  	// Determine the receiver base type.
   174  	var recvType Type = Typ[Invalid]
   175  	var recvTParamsList *TypeParamList
   176  	if rtparams == nil {
   177  		// If there are no type parameters, we can simply typecheck rparam.Type.
   178  		// If that is a generic type, varType will complain.
   179  		// Further receiver constraints will be checked later, with validRecv.
   180  		// We use rparam.Type (rather than base) to correctly record pointer
   181  		// and parentheses in types2.Info (was bug, see go.dev/issue/68639).
   182  		recvType = check.varType(rparam.Type)
   183  		// Defining new methods on instantiated (alias or defined) types is not permitted.
   184  		// Follow literal pointer/alias type chain and check.
   185  		// (Correct code permits at most one pointer indirection, but for this check it
   186  		// doesn't matter if we have multiple pointers.)
   187  		a, _ := unpointer(recvType).(*Alias) // recvType is not generic per above
   188  		for a != nil {
   189  			baseType := unpointer(a.fromRHS)
   190  			if g, _ := baseType.(genericType); g != nil && g.TypeParams() != nil {
   191  				check.errorf(rbase, InvalidRecv, "cannot define new methods on instantiated type %s", g)
   192  				recvType = Typ[Invalid] // avoid follow-on errors by Checker.validRecv
   193  				break
   194  			}
   195  			a, _ = baseType.(*Alias)
   196  		}
   197  	} else {
   198  		// If there are type parameters, rbase must denote a generic base type.
   199  		// Important: rbase must be resolved before declaring any receiver type
   200  		// parameters (which may have the same name, see below).
   201  		var baseType *Named // nil if not valid
   202  		var cause string
   203  		if t := check.genericType(rbase, &cause); isValid(t) {
   204  			switch t := t.(type) {
   205  			case *Named:
   206  				baseType = t
   207  			case *Alias:
   208  				// Methods on generic aliases are not permitted.
   209  				// Only report an error if the alias type is valid.
   210  				if isValid(unalias(t)) {
   211  					check.errorf(rbase, InvalidRecv, "cannot define new methods on generic alias type %s", t)
   212  				}
   213  				// Ok to continue but do not set basetype in this case so that
   214  				// recvType remains invalid (was bug, see go.dev/issue/70417).
   215  			default:
   216  				panic("unreachable")
   217  			}
   218  		} else {
   219  			if cause != "" {
   220  				check.errorf(rbase, InvalidRecv, "%s", cause)
   221  			}
   222  			// Ok to continue but do not set baseType (see comment above).
   223  		}
   224  
   225  		// Collect the type parameters declared by the receiver (see also
   226  		// Checker.collectTypeParams). The scope of the type parameter T in
   227  		// "func (r T[T]) f() {}" starts after f, not at r, so we declare it
   228  		// after typechecking rbase (see go.dev/issue/52038).
   229  		recvTParams := make([]*TypeParam, len(rtparams))
   230  		for i, rparam := range rtparams {
   231  			tpar := check.declareTypeParam(rparam, scopePos)
   232  			recvTParams[i] = tpar
   233  			// For historic reasons, type parameters in receiver type expressions
   234  			// are considered both definitions and uses and thus must be recorded
   235  			// in the Info.Uses and Info.Types maps (see go.dev/issue/68670).
   236  			check.recordUse(rparam, tpar.obj)
   237  			check.recordTypeAndValue(rparam, typexpr, tpar, nil)
   238  		}
   239  		recvTParamsList = bindTParams(recvTParams)
   240  
   241  		// Get the type parameter bounds from the receiver base type
   242  		// and set them for the respective (local) receiver type parameters.
   243  		if baseType != nil {
   244  			baseTParams := baseType.TypeParams().list()
   245  			if len(recvTParams) == len(baseTParams) {
   246  				smap := makeRenameMap(baseTParams, recvTParams)
   247  				for i, recvTPar := range recvTParams {
   248  					baseTPar := baseTParams[i]
   249  					check.mono.recordCanon(recvTPar, baseTPar)
   250  					// baseTPar.bound is possibly parameterized by other type parameters
   251  					// defined by the generic base type. Substitute those parameters with
   252  					// the receiver type parameters declared by the current method.
   253  					recvTPar.bound = check.subst(recvTPar.obj.pos, baseTPar.bound, smap, nil, check.context())
   254  				}
   255  			} else {
   256  				got := measure(len(recvTParams), "type parameter")
   257  				check.errorf(rbase, BadRecv, "receiver declares %s, but receiver base type declares %d", got, len(baseTParams))
   258  			}
   259  
   260  			// The type parameters declared by the receiver also serve as
   261  			// type arguments for the receiver type. Instantiate the receiver.
   262  			check.verifyVersionf(rbase, go1_18, "type instantiation")
   263  			targs := make([]Type, len(recvTParams))
   264  			for i, targ := range recvTParams {
   265  				targs[i] = targ
   266  			}
   267  			recvType = check.instance(rparam.Type.Pos(), baseType, targs, nil, check.context())
   268  			check.recordInstance(rbase, targs, recvType)
   269  
   270  			// Reestablish pointerness if needed (but avoid a pointer to an invalid type).
   271  			if rptr && isValid(recvType) {
   272  				recvType = NewPointer(recvType)
   273  			}
   274  
   275  			check.recordParenthesizedRecvTypes(rparam.Type, recvType)
   276  		}
   277  	}
   278  
   279  	// Create the receiver parameter.
   280  	// recvType is invalid if baseType was never set.
   281  	var recv *Var
   282  	if rname := rparam.Name; rname != nil && rname.Value != "" {
   283  		// named receiver
   284  		recv = newVar(RecvVar, rname.Pos(), check.pkg, rname.Value, recvType)
   285  		// In this case, the receiver is declared by the caller
   286  		// because it must be declared after any type parameters
   287  		// (otherwise it might shadow one of them).
   288  	} else {
   289  		// anonymous receiver
   290  		recv = newVar(RecvVar, rparam.Pos(), check.pkg, "", recvType)
   291  		check.recordImplicit(rparam, recv)
   292  	}
   293  
   294  	// Delay validation of receiver type as it may cause premature expansion of types
   295  	// the receiver type is dependent on (see go.dev/issue/51232, go.dev/issue/51233).
   296  	check.later(func() {
   297  		check.validRecv(rbase, recv)
   298  	}).describef(recv, "validRecv(%s)", recv)
   299  
   300  	return recv, recvTParamsList
   301  }
   302  
   303  func unpointer(t Type) Type {
   304  	for {
   305  		p, _ := t.(*Pointer)
   306  		if p == nil {
   307  			return t
   308  		}
   309  		t = p.base
   310  	}
   311  }
   312  
   313  // recordParenthesizedRecvTypes records parenthesized intermediate receiver type
   314  // expressions that all map to the same type, by recursively unpacking expr and
   315  // recording the corresponding type for it. Example:
   316  //
   317  //	expression  -->  type
   318  //	----------------------
   319  //	(*(T[P]))        *T[P]
   320  //	 *(T[P])         *T[P]
   321  //	  (T[P])          T[P]
   322  //	   T[P]           T[P]
   323  func (check *Checker) recordParenthesizedRecvTypes(expr syntax.Expr, typ Type) {
   324  	for {
   325  		check.recordTypeAndValue(expr, typexpr, typ, nil)
   326  		switch e := expr.(type) {
   327  		case *syntax.ParenExpr:
   328  			expr = e.X
   329  		case *syntax.Operation:
   330  			if e.Op == syntax.Mul && e.Y == nil {
   331  				expr = e.X
   332  				// In a correct program, typ must be an unnamed
   333  				// pointer type. But be careful and don't panic.
   334  				ptr, _ := typ.(*Pointer)
   335  				if ptr == nil {
   336  					return // something is wrong
   337  				}
   338  				typ = ptr.base
   339  				break
   340  			}
   341  			return // cannot unpack any further
   342  		default:
   343  			return // cannot unpack any further
   344  		}
   345  	}
   346  }
   347  
   348  // collectParams collects (but does not declare) all parameter/result
   349  // variables of list and returns the list of names and corresponding
   350  // variables, and whether the (parameter) list is variadic.
   351  // Anonymous parameters are recorded with nil names.
   352  func (check *Checker) collectParams(kind VarKind, list []*syntax.Field) (names []*syntax.Name, params []*Var, variadic bool) {
   353  	if list == nil {
   354  		return
   355  	}
   356  
   357  	var named, anonymous bool
   358  
   359  	var typ Type
   360  	var prev syntax.Expr
   361  	for i, field := range list {
   362  		ftype := field.Type
   363  		// type-check type of grouped fields only once
   364  		if ftype != prev {
   365  			prev = ftype
   366  			if t, _ := ftype.(*syntax.DotsType); t != nil {
   367  				ftype = t.Elem
   368  				if kind == ParamVar && i == len(list)-1 {
   369  					variadic = true
   370  				} else {
   371  					check.error(t, InvalidSyntaxTree, "invalid use of ...")
   372  					// ignore ... and continue
   373  				}
   374  			}
   375  			typ = check.varType(ftype)
   376  		}
   377  		// The parser ensures that f.Tag is nil and we don't
   378  		// care if a constructed AST contains a non-nil tag.
   379  		if field.Name != nil {
   380  			// named parameter
   381  			name := field.Name.Value
   382  			if name == "" {
   383  				check.error(field.Name, InvalidSyntaxTree, "anonymous parameter")
   384  				// ok to continue
   385  			}
   386  			par := newVar(kind, field.Name.Pos(), check.pkg, name, typ)
   387  			// named parameter is declared by caller
   388  			names = append(names, field.Name)
   389  			params = append(params, par)
   390  			named = true
   391  		} else {
   392  			// anonymous parameter
   393  			par := newVar(kind, field.Pos(), check.pkg, "", typ)
   394  			check.recordImplicit(field, par)
   395  			names = append(names, nil)
   396  			params = append(params, par)
   397  			anonymous = true
   398  		}
   399  	}
   400  
   401  	if named && anonymous {
   402  		check.error(list[0], InvalidSyntaxTree, "list contains both named and anonymous parameters")
   403  		// ok to continue
   404  	}
   405  
   406  	// For a variadic function, change the last parameter's type from T to []T.
   407  	// Since we type-checked T rather than ...T, we also need to retro-actively
   408  	// record the type for ...T.
   409  	if variadic {
   410  		last := params[len(params)-1]
   411  		last.typ = &Slice{elem: last.typ}
   412  		check.recordTypeAndValue(list[len(list)-1].Type, typexpr, last.typ, nil)
   413  	}
   414  
   415  	return
   416  }
   417  
   418  // declareParams declares each named parameter in the current scope.
   419  func (check *Checker) declareParams(names []*syntax.Name, params []*Var, scopePos syntax.Pos) {
   420  	for i, name := range names {
   421  		if name != nil && name.Value != "" {
   422  			check.declare(check.scope, name, params[i], scopePos)
   423  		}
   424  	}
   425  }
   426  
   427  // validRecv verifies that the receiver satisfies its respective spec requirements
   428  // and reports an error otherwise.
   429  func (check *Checker) validRecv(pos poser, recv *Var) {
   430  	// spec: "The receiver type must be of the form T or *T where T is a type name."
   431  	rtyp, _ := deref(recv.typ)
   432  	atyp := Unalias(rtyp)
   433  	if !isValid(atyp) {
   434  		return // error was reported before
   435  	}
   436  	// spec: "The type denoted by T is called the receiver base type; it must not
   437  	// be a pointer or interface type and it must be declared in the same package
   438  	// as the method."
   439  	switch T := atyp.(type) {
   440  	case *Named:
   441  		if T.obj.pkg != check.pkg || isCGoTypeObj(T.obj) {
   442  			check.errorf(pos, InvalidRecv, "cannot define new methods on non-local type %s", rtyp)
   443  			break
   444  		}
   445  		var cause string
   446  		switch u := T.under().(type) {
   447  		case *Basic:
   448  			// unsafe.Pointer is treated like a regular pointer
   449  			if u.kind == UnsafePointer {
   450  				cause = "unsafe.Pointer"
   451  			}
   452  		case *Pointer, *Interface:
   453  			cause = "pointer or interface type"
   454  		case *TypeParam:
   455  			// The underlying type of a receiver base type cannot be a
   456  			// type parameter: "type T[P any] P" is not a valid declaration.
   457  			panic("unreachable")
   458  		}
   459  		if cause != "" {
   460  			check.errorf(pos, InvalidRecv, "invalid receiver type %s (%s)", rtyp, cause)
   461  		}
   462  	case *Basic:
   463  		check.errorf(pos, InvalidRecv, "cannot define new methods on non-local type %s", rtyp)
   464  	default:
   465  		check.errorf(pos, InvalidRecv, "invalid receiver type %s", recv.typ)
   466  	}
   467  }
   468  
   469  // isCGoTypeObj reports whether the given type name was created by cgo.
   470  func isCGoTypeObj(obj *TypeName) bool {
   471  	return strings.HasPrefix(obj.name, "_Ctype_") ||
   472  		strings.HasPrefix(filepath.Base(obj.pos.FileBase().Filename()), "_cgo_")
   473  }
   474
View as plain text