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 "cmd/compile/internal/syntax"
     8  
     9  // ----------------------------------------------------------------------------
    10  // API
    11  
    12  // A Signature represents a (non-builtin) function or method type.
    13  // The receiver is ignored when comparing signatures for identity.
    14  type Signature struct {
    15  	// We need to keep the scope in Signature (rather than passing it around
    16  	// and store it in the Func Object) because when type-checking a function
    17  	// literal we call the general type checker which returns a general Type.
    18  	// We then unpack the *Signature and use the scope for the literal body.
    19  	rparams  *TypeParamList // receiver type parameters from left to right, or nil
    20  	tparams  *TypeParamList // type parameters from left to right, or nil
    21  	scope    *Scope         // function scope for package-local and non-instantiated signatures; nil otherwise
    22  	recv     *Var           // nil if not a method
    23  	params   *Tuple         // (incoming) parameters from left to right; or nil
    24  	results  *Tuple         // (outgoing) results from left to right; or nil
    25  	variadic bool           // true if the last parameter's type is of the form ...T (or string, for append built-in only)
    26  }
    27  
    28  // NewSignatureType creates a new function type for the given receiver,
    29  // receiver type parameters, type parameters, parameters, and results. If
    30  // variadic is set, params must hold at least one parameter and the last
    31  // parameter must be of unnamed slice type. If recv is non-nil, typeParams must
    32  // be empty. If recvTypeParams is non-empty, recv must be non-nil.
    33  func NewSignatureType(recv *Var, recvTypeParams, typeParams []*TypeParam, params, results *Tuple, variadic bool) *Signature {
    34  	if variadic {
    35  		n := params.Len()
    36  		if n == 0 {
    37  			panic("variadic function must have at least one parameter")
    38  		}
    39  		if _, ok := params.At(n - 1).typ.(*Slice); !ok {
    40  			panic("variadic parameter must be of unnamed slice type")
    41  		}
    42  	}
    43  	sig := &Signature{recv: recv, params: params, results: results, variadic: variadic}
    44  	if len(recvTypeParams) != 0 {
    45  		if recv == nil {
    46  			panic("function with receiver type parameters must have a receiver")
    47  		}
    48  		sig.rparams = bindTParams(recvTypeParams)
    49  	}
    50  	if len(typeParams) != 0 {
    51  		if recv != nil {
    52  			panic("function with type parameters cannot have a receiver")
    53  		}
    54  		sig.tparams = bindTParams(typeParams)
    55  	}
    56  	return sig
    57  }
    58  
    59  // Recv returns the receiver of signature s (if a method), or nil if a
    60  // function. It is ignored when comparing signatures for identity.
    61  //
    62  // For an abstract method, Recv returns the enclosing interface either
    63  // as a *Named or an *Interface. Due to embedding, an interface may
    64  // contain methods whose receiver type is a different interface.
    65  func (s *Signature) Recv() *Var { return s.recv }
    66  
    67  // TypeParams returns the type parameters of signature s, or nil.
    68  func (s *Signature) TypeParams() *TypeParamList { return s.tparams }
    69  
    70  // SetTypeParams sets the type parameters of signature s.
    71  func (s *Signature) SetTypeParams(tparams []*TypeParam) { s.tparams = bindTParams(tparams) }
    72  
    73  // RecvTypeParams returns the receiver type parameters of signature s, or nil.
    74  func (s *Signature) RecvTypeParams() *TypeParamList { return s.rparams }
    75  
    76  // Params returns the parameters of signature s, or nil.
    77  func (s *Signature) Params() *Tuple { return s.params }
    78  
    79  // Results returns the results of signature s, or nil.
    80  func (s *Signature) Results() *Tuple { return s.results }
    81  
    82  // Variadic reports whether the signature s is variadic.
    83  func (s *Signature) Variadic() bool { return s.variadic }
    84  
    85  func (s *Signature) Underlying() Type { return s }
    86  func (s *Signature) String() string   { return TypeString(s, nil) }
    87  
    88  // ----------------------------------------------------------------------------
    89  // Implementation
    90  
    91  // funcType type-checks a function or method type.
    92  func (check *Checker) funcType(sig *Signature, recvPar *syntax.Field, tparams []*syntax.Field, ftyp *syntax.FuncType) {
    93  	check.openScope(ftyp, "function")
    94  	check.scope.isFunc = true
    95  	check.recordScope(ftyp, check.scope)
    96  	sig.scope = check.scope
    97  	defer check.closeScope()
    98  
    99  	if recvPar != nil {
   100  		// collect generic receiver type parameters, if any
   101  		// - a receiver type parameter is like any other type parameter, except that it is declared implicitly
   102  		// - the receiver specification acts as local declaration for its type parameters, which may be blank
   103  		_, rname, rparams := check.unpackRecv(recvPar.Type, true)
   104  		if len(rparams) > 0 {
   105  			tparams := make([]*TypeParam, len(rparams))
   106  			for i, rparam := range rparams {
   107  				tparams[i] = check.declareTypeParam(rparam)
   108  			}
   109  			sig.rparams = bindTParams(tparams)
   110  			// Blank identifiers don't get declared, so naive type-checking of the
   111  			// receiver type expression would fail in Checker.collectParams below,
   112  			// when Checker.ident cannot resolve the _ to a type.
   113  			//
   114  			// Checker.recvTParamMap maps these blank identifiers to their type parameter
   115  			// types, so that they may be resolved in Checker.ident when they fail
   116  			// lookup in the scope.
   117  			for i, p := range rparams {
   118  				if p.Value == "_" {
   119  					if check.recvTParamMap == nil {
   120  						check.recvTParamMap = make(map[*syntax.Name]*TypeParam)
   121  					}
   122  					check.recvTParamMap[p] = tparams[i]
   123  				}
   124  			}
   125  			// determine receiver type to get its type parameters
   126  			// and the respective type parameter bounds
   127  			var recvTParams []*TypeParam
   128  			if rname != nil {
   129  				// recv should be a Named type (otherwise an error is reported elsewhere)
   130  				// Also: Don't report an error via genericType since it will be reported
   131  				//       again when we type-check the signature.
   132  				// TODO(gri) maybe the receiver should be marked as invalid instead?
   133  				if recv, _ := check.genericType(rname, false).(*Named); recv != nil {
   134  					recvTParams = recv.TypeParams().list()
   135  				}
   136  			}
   137  			// provide type parameter bounds
   138  			if len(tparams) == len(recvTParams) {
   139  				smap := makeRenameMap(recvTParams, tparams)
   140  				for i, tpar := range tparams {
   141  					recvTPar := recvTParams[i]
   142  					check.mono.recordCanon(tpar, recvTPar)
   143  					// recvTPar.bound is (possibly) parameterized in the context of the
   144  					// receiver type declaration. Substitute parameters for the current
   145  					// context.
   146  					tpar.bound = check.subst(tpar.obj.pos, recvTPar.bound, smap, nil)
   147  				}
   148  			} else if len(tparams) < len(recvTParams) {
   149  				// Reporting an error here is a stop-gap measure to avoid crashes in the
   150  				// compiler when a type parameter/argument cannot be inferred later. It
   151  				// may lead to follow-on errors (see issues #51339, #51343).
   152  				// TODO(gri) find a better solution
   153  				got := measure(len(tparams), "type parameter")
   154  				check.errorf(recvPar, "got %s, but receiver base type declares %d", got, len(recvTParams))
   155  			}
   156  		}
   157  	}
   158  
   159  	if tparams != nil {
   160  		// The parser will complain about invalid type parameters for methods.
   161  		check.collectTypeParams(&sig.tparams, tparams)
   162  	}
   163  
   164  	// Value (non-type) parameters' scope starts in the function body. Use a temporary scope for their
   165  	// declarations and then squash that scope into the parent scope (and report any redeclarations at
   166  	// that time).
   167  	scope := NewScope(check.scope, nopos, nopos, "function body (temp. scope)")
   168  	var recvList []*Var // TODO(gri) remove the need for making a list here
   169  	if recvPar != nil {
   170  		recvList, _ = check.collectParams(scope, []*syntax.Field{recvPar}, false) // use rewritten receiver type, if any
   171  	}
   172  	params, variadic := check.collectParams(scope, ftyp.ParamList, true)
   173  	results, _ := check.collectParams(scope, ftyp.ResultList, false)
   174  	scope.Squash(func(obj, alt Object) {
   175  		var err error_
   176  		err.errorf(obj, "%s redeclared in this block", obj.Name())
   177  		err.recordAltDecl(alt)
   178  		check.report(&err)
   179  	})
   180  
   181  	if recvPar != nil {
   182  		// recv parameter list present (may be empty)
   183  		// spec: "The receiver is specified via an extra parameter section preceding the
   184  		// method name. That parameter section must declare a single parameter, the receiver."
   185  		var recv *Var
   186  		switch len(recvList) {
   187  		case 0:
   188  			// error reported by resolver
   189  			recv = NewParam(nopos, nil, "", Typ[Invalid]) // ignore recv below
   190  		default:
   191  			// more than one receiver
   192  			check.error(recvList[len(recvList)-1].Pos(), "method must have exactly one receiver")
   193  			fallthrough // continue with first receiver
   194  		case 1:
   195  			recv = recvList[0]
   196  		}
   197  		sig.recv = recv
   198  
   199  		// Delay validation of receiver type as it may cause premature expansion
   200  		// of types the receiver type is dependent on (see issues #51232, #51233).
   201  		check.later(func() {
   202  			rtyp, _ := deref(recv.typ)
   203  
   204  			// spec: "The receiver type must be of the form T or *T where T is a type name."
   205  			// (ignore invalid types - error was reported before)
   206  			if rtyp != Typ[Invalid] {
   207  				var err string
   208  				switch T := rtyp.(type) {
   209  				case *Named:
   210  					T.resolve(check.bestContext(nil))
   211  					// The receiver type may be an instantiated type referred to
   212  					// by an alias (which cannot have receiver parameters for now).
   213  					if T.TypeArgs() != nil && sig.RecvTypeParams() == nil {
   214  						check.errorf(recv.pos, "cannot define methods on instantiated type %s", recv.typ)
   215  						break
   216  					}
   217  					// spec: "The type denoted by T is called the receiver base type; it must not
   218  					// be a pointer or interface type and it must be declared in the same package
   219  					// as the method."
   220  					if T.obj.pkg != check.pkg {
   221  						err = "type not defined in this package"
   222  						if check.conf.CompilerErrorMessages {
   223  							check.errorf(recv.pos, "cannot define new methods on non-local type %s", recv.typ)
   224  							err = ""
   225  						}
   226  					} else {
   227  						// The underlying type of a receiver base type can be a type parameter;
   228  						// e.g. for methods with a generic receiver T[P] with type T[P any] P.
   229  						// TODO(gri) Such declarations are currently disallowed.
   230  						//           Revisit the need for underIs.
   231  						underIs(T, func(u Type) bool {
   232  							switch u := u.(type) {
   233  							case *Basic:
   234  								// unsafe.Pointer is treated like a regular pointer
   235  								if u.kind == UnsafePointer {
   236  									err = "unsafe.Pointer"
   237  									return false
   238  								}
   239  							case *Pointer, *Interface:
   240  								err = "pointer or interface type"
   241  								return false
   242  							}
   243  							return true
   244  						})
   245  					}
   246  				case *Basic:
   247  					err = "basic or unnamed type"
   248  					if check.conf.CompilerErrorMessages {
   249  						check.errorf(recv.pos, "cannot define new methods on non-local type %s", recv.typ)
   250  						err = ""
   251  					}
   252  				default:
   253  					check.errorf(recv.pos, "invalid receiver type %s", recv.typ)
   254  				}
   255  				if err != "" {
   256  					check.errorf(recv.pos, "invalid receiver type %s (%s)", recv.typ, err)
   257  				}
   258  			}
   259  		}).describef(recv, "validate receiver %s", recv)
   260  	}
   261  
   262  	sig.params = NewTuple(params...)
   263  	sig.results = NewTuple(results...)
   264  	sig.variadic = variadic
   265  }
   266  
   267  // collectParams declares the parameters of list in scope and returns the corresponding
   268  // variable list.
   269  func (check *Checker) collectParams(scope *Scope, list []*syntax.Field, variadicOk bool) (params []*Var, variadic bool) {
   270  	if list == nil {
   271  		return
   272  	}
   273  
   274  	var named, anonymous bool
   275  
   276  	var typ Type
   277  	var prev syntax.Expr
   278  	for i, field := range list {
   279  		ftype := field.Type
   280  		// type-check type of grouped fields only once
   281  		if ftype != prev {
   282  			prev = ftype
   283  			if t, _ := ftype.(*syntax.DotsType); t != nil {
   284  				ftype = t.Elem
   285  				if variadicOk && i == len(list)-1 {
   286  					variadic = true
   287  				} else {
   288  					check.softErrorf(t, "can only use ... with final parameter in list")
   289  					// ignore ... and continue
   290  				}
   291  			}
   292  			typ = check.varType(ftype)
   293  		}
   294  		// The parser ensures that f.Tag is nil and we don't
   295  		// care if a constructed AST contains a non-nil tag.
   296  		if field.Name != nil {
   297  			// named parameter
   298  			name := field.Name.Value
   299  			if name == "" {
   300  				check.error(field.Name, invalidAST+"anonymous parameter")
   301  				// ok to continue
   302  			}
   303  			par := NewParam(field.Name.Pos(), check.pkg, name, typ)
   304  			check.declare(scope, field.Name, par, scope.pos)
   305  			params = append(params, par)
   306  			named = true
   307  		} else {
   308  			// anonymous parameter
   309  			par := NewParam(field.Pos(), check.pkg, "", typ)
   310  			check.recordImplicit(field, par)
   311  			params = append(params, par)
   312  			anonymous = true
   313  		}
   314  	}
   315  
   316  	if named && anonymous {
   317  		check.error(list[0], invalidAST+"list contains both named and anonymous parameters")
   318  		// ok to continue
   319  	}
   320  
   321  	// For a variadic function, change the last parameter's type from T to []T.
   322  	// Since we type-checked T rather than ...T, we also need to retro-actively
   323  	// record the type for ...T.
   324  	if variadic {
   325  		last := params[len(params)-1]
   326  		last.typ = &Slice{elem: last.typ}
   327  		check.recordTypeAndValue(list[len(list)-1].Type, typexpr, last.typ, nil)
   328  	}
   329  
   330  	return
   331  }
   332
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