typexpr.go

     1  // Copyright 2013 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  // This file implements type-checking of identifiers and type expressions.
     6  
     7  package types2
     8  
     9  import (
    10  	"cmd/compile/internal/syntax"
    11  	"fmt"
    12  	"go/constant"
    13  	. "internal/types/errors"
    14  	"strings"
    15  )
    16  
    17  // ident type-checks identifier e and initializes x with the value or type of e.
    18  // If an error occurred, x.mode is set to invalid.
    19  // For the meaning of def, see Checker.definedType, below.
    20  // If wantType is set, the identifier e is expected to denote a type.
    21  func (check *Checker) ident(x *operand, e *syntax.Name, def *TypeName, wantType bool) {
    22  	x.mode = invalid
    23  	x.expr = e
    24  
    25  	// Note that we cannot use check.lookup here because the returned scope
    26  	// may be different from obj.Parent(). See also Scope.LookupParent doc.
    27  	scope, obj := check.scope.LookupParent(e.Value, check.pos)
    28  	switch obj {
    29  	case nil:
    30  		if e.Value == "_" {
    31  			// Blank identifiers are never declared, but the current identifier may
    32  			// be a placeholder for a receiver type parameter. In this case we can
    33  			// resolve its type and object from Checker.recvTParamMap.
    34  			if tpar := check.recvTParamMap[e]; tpar != nil {
    35  				x.mode = typexpr
    36  				x.typ = tpar
    37  			} else {
    38  				check.error(e, InvalidBlank, "cannot use _ as value or type")
    39  			}
    40  		} else {
    41  			check.errorf(e, UndeclaredName, "undefined: %s", e.Value)
    42  		}
    43  		return
    44  	case universeComparable:
    45  		if !check.verifyVersionf(e, go1_18, "predeclared %s", e.Value) {
    46  			return // avoid follow-on errors
    47  		}
    48  	}
    49  	// Because the representation of any depends on gotypesalias, we don't check
    50  	// pointer identity here.
    51  	if obj.Name() == "any" && obj.Parent() == Universe {
    52  		if !check.verifyVersionf(e, go1_18, "predeclared %s", e.Value) {
    53  			return // avoid follow-on errors
    54  		}
    55  	}
    56  
    57  	check.recordUse(e, obj)
    58  
    59  	// If we want a type but don't have one, stop right here and avoid potential problems
    60  	// with missing underlying types. This also gives better error messages in some cases
    61  	// (see go.dev/issue/65344).
    62  	_, gotType := obj.(*TypeName)
    63  	if !gotType && wantType {
    64  		check.errorf(e, NotAType, "%s is not a type", obj.Name())
    65  		// avoid "declared but not used" errors
    66  		// (don't use Checker.use - we don't want to evaluate too much)
    67  		if v, _ := obj.(*Var); v != nil && v.pkg == check.pkg /* see Checker.use1 */ {
    68  			v.used = true
    69  		}
    70  		return
    71  	}
    72  
    73  	// Type-check the object.
    74  	// Only call Checker.objDecl if the object doesn't have a type yet
    75  	// (in which case we must actually determine it) or the object is a
    76  	// TypeName and we also want a type (in which case we might detect
    77  	// a cycle which needs to be reported). Otherwise we can skip the
    78  	// call and avoid a possible cycle error in favor of the more
    79  	// informative "not a type/value" error that this function's caller
    80  	// will issue (see go.dev/issue/25790).
    81  	typ := obj.Type()
    82  	if typ == nil || gotType && wantType {
    83  		check.objDecl(obj, def)
    84  		typ = obj.Type() // type must have been assigned by Checker.objDecl
    85  	}
    86  	assert(typ != nil)
    87  
    88  	// The object may have been dot-imported.
    89  	// If so, mark the respective package as used.
    90  	// (This code is only needed for dot-imports. Without them,
    91  	// we only have to mark variables, see *Var case below).
    92  	if pkgName := check.dotImportMap[dotImportKey{scope, obj.Name()}]; pkgName != nil {
    93  		pkgName.used = true
    94  	}
    95  
    96  	switch obj := obj.(type) {
    97  	case *PkgName:
    98  		check.errorf(e, InvalidPkgUse, "use of package %s not in selector", obj.name)
    99  		return
   100  
   101  	case *Const:
   102  		check.addDeclDep(obj)
   103  		if !isValid(typ) {
   104  			return
   105  		}
   106  		if obj == universeIota {
   107  			if check.iota == nil {
   108  				check.error(e, InvalidIota, "cannot use iota outside constant declaration")
   109  				return
   110  			}
   111  			x.val = check.iota
   112  		} else {
   113  			x.val = obj.val
   114  		}
   115  		assert(x.val != nil)
   116  		x.mode = constant_
   117  
   118  	case *TypeName:
   119  		if !check.conf.EnableAlias && check.isBrokenAlias(obj) {
   120  			check.errorf(e, InvalidDeclCycle, "invalid use of type alias %s in recursive type (see go.dev/issue/50729)", obj.name)
   121  			return
   122  		}
   123  		x.mode = typexpr
   124  
   125  	case *Var:
   126  		// It's ok to mark non-local variables, but ignore variables
   127  		// from other packages to avoid potential race conditions with
   128  		// dot-imported variables.
   129  		if obj.pkg == check.pkg {
   130  			obj.used = true
   131  		}
   132  		check.addDeclDep(obj)
   133  		if !isValid(typ) {
   134  			return
   135  		}
   136  		x.mode = variable
   137  
   138  	case *Func:
   139  		check.addDeclDep(obj)
   140  		x.mode = value
   141  
   142  	case *Builtin:
   143  		x.id = obj.id
   144  		x.mode = builtin
   145  
   146  	case *Nil:
   147  		x.mode = nilvalue
   148  
   149  	default:
   150  		panic("unreachable")
   151  	}
   152  
   153  	x.typ = typ
   154  }
   155  
   156  // typ type-checks the type expression e and returns its type, or Typ[Invalid].
   157  // The type must not be an (uninstantiated) generic type.
   158  func (check *Checker) typ(e syntax.Expr) Type {
   159  	return check.definedType(e, nil)
   160  }
   161  
   162  // varType type-checks the type expression e and returns its type, or Typ[Invalid].
   163  // The type must not be an (uninstantiated) generic type and it must not be a
   164  // constraint interface.
   165  func (check *Checker) varType(e syntax.Expr) Type {
   166  	typ := check.definedType(e, nil)
   167  	check.validVarType(e, typ)
   168  	return typ
   169  }
   170  
   171  // validVarType reports an error if typ is a constraint interface.
   172  // The expression e is used for error reporting, if any.
   173  func (check *Checker) validVarType(e syntax.Expr, typ Type) {
   174  	// If we have a type parameter there's nothing to do.
   175  	if isTypeParam(typ) {
   176  		return
   177  	}
   178  
   179  	// We don't want to call under() or complete interfaces while we are in
   180  	// the middle of type-checking parameter declarations that might belong
   181  	// to interface methods. Delay this check to the end of type-checking.
   182  	check.later(func() {
   183  		if t, _ := under(typ).(*Interface); t != nil {
   184  			pos := syntax.StartPos(e)
   185  			tset := computeInterfaceTypeSet(check, pos, t) // TODO(gri) is this the correct position?
   186  			if !tset.IsMethodSet() {
   187  				if tset.comparable {
   188  					check.softErrorf(pos, MisplacedConstraintIface, "cannot use type %s outside a type constraint: interface is (or embeds) comparable", typ)
   189  				} else {
   190  					check.softErrorf(pos, MisplacedConstraintIface, "cannot use type %s outside a type constraint: interface contains type constraints", typ)
   191  				}
   192  			}
   193  		}
   194  	}).describef(e, "check var type %s", typ)
   195  }
   196  
   197  // definedType is like typ but also accepts a type name def.
   198  // If def != nil, e is the type specification for the type named def, declared
   199  // in a type declaration, and def.typ.underlying will be set to the type of e
   200  // before any components of e are type-checked.
   201  func (check *Checker) definedType(e syntax.Expr, def *TypeName) Type {
   202  	typ := check.typInternal(e, def)
   203  	assert(isTyped(typ))
   204  	if isGeneric(typ) {
   205  		check.errorf(e, WrongTypeArgCount, "cannot use generic type %s without instantiation", typ)
   206  		typ = Typ[Invalid]
   207  	}
   208  	check.recordTypeAndValue(e, typexpr, typ, nil)
   209  	return typ
   210  }
   211  
   212  // genericType is like typ but the type must be an (uninstantiated) generic
   213  // type. If cause is non-nil and the type expression was a valid type but not
   214  // generic, cause will be populated with a message describing the error.
   215  func (check *Checker) genericType(e syntax.Expr, cause *string) Type {
   216  	typ := check.typInternal(e, nil)
   217  	assert(isTyped(typ))
   218  	if isValid(typ) && !isGeneric(typ) {
   219  		if cause != nil {
   220  			*cause = check.sprintf("%s is not a generic type", typ)
   221  		}
   222  		typ = Typ[Invalid]
   223  	}
   224  	// TODO(gri) what is the correct call below?
   225  	check.recordTypeAndValue(e, typexpr, typ, nil)
   226  	return typ
   227  }
   228  
   229  // goTypeName returns the Go type name for typ and
   230  // removes any occurrences of "types2." from that name.
   231  func goTypeName(typ Type) string {
   232  	return strings.ReplaceAll(fmt.Sprintf("%T", typ), "types2.", "")
   233  }
   234  
   235  // typInternal drives type checking of types.
   236  // Must only be called by definedType or genericType.
   237  func (check *Checker) typInternal(e0 syntax.Expr, def *TypeName) (T Type) {
   238  	if check.conf.Trace {
   239  		check.trace(e0.Pos(), "-- type %s", e0)
   240  		check.indent++
   241  		defer func() {
   242  			check.indent--
   243  			var under Type
   244  			if T != nil {
   245  				// Calling under() here may lead to endless instantiations.
   246  				// Test case: type T[P any] *T[P]
   247  				under = safeUnderlying(T)
   248  			}
   249  			if T == under {
   250  				check.trace(e0.Pos(), "=> %s // %s", T, goTypeName(T))
   251  			} else {
   252  				check.trace(e0.Pos(), "=> %s (under = %s) // %s", T, under, goTypeName(T))
   253  			}
   254  		}()
   255  	}
   256  
   257  	switch e := e0.(type) {
   258  	case *syntax.BadExpr:
   259  		// ignore - error reported before
   260  
   261  	case *syntax.Name:
   262  		var x operand
   263  		check.ident(&x, e, def, true)
   264  
   265  		switch x.mode {
   266  		case typexpr:
   267  			typ := x.typ
   268  			setDefType(def, typ)
   269  			return typ
   270  		case invalid:
   271  			// ignore - error reported before
   272  		case novalue:
   273  			check.errorf(&x, NotAType, "%s used as type", &x)
   274  		default:
   275  			check.errorf(&x, NotAType, "%s is not a type", &x)
   276  		}
   277  
   278  	case *syntax.SelectorExpr:
   279  		var x operand
   280  		check.selector(&x, e, def, true)
   281  
   282  		switch x.mode {
   283  		case typexpr:
   284  			typ := x.typ
   285  			setDefType(def, typ)
   286  			return typ
   287  		case invalid:
   288  			// ignore - error reported before
   289  		case novalue:
   290  			check.errorf(&x, NotAType, "%s used as type", &x)
   291  		default:
   292  			check.errorf(&x, NotAType, "%s is not a type", &x)
   293  		}
   294  
   295  	case *syntax.IndexExpr:
   296  		check.verifyVersionf(e, go1_18, "type instantiation")
   297  		return check.instantiatedType(e.X, syntax.UnpackListExpr(e.Index), def)
   298  
   299  	case *syntax.ParenExpr:
   300  		// Generic types must be instantiated before they can be used in any form.
   301  		// Consequently, generic types cannot be parenthesized.
   302  		return check.definedType(e.X, def)
   303  
   304  	case *syntax.ArrayType:
   305  		typ := new(Array)
   306  		setDefType(def, typ)
   307  		if e.Len != nil {
   308  			typ.len = check.arrayLength(e.Len)
   309  		} else {
   310  			// [...]array
   311  			check.error(e, BadDotDotDotSyntax, "invalid use of [...] array (outside a composite literal)")
   312  			typ.len = -1
   313  		}
   314  		typ.elem = check.varType(e.Elem)
   315  		if typ.len >= 0 {
   316  			return typ
   317  		}
   318  		// report error if we encountered [...]
   319  
   320  	case *syntax.SliceType:
   321  		typ := new(Slice)
   322  		setDefType(def, typ)
   323  		typ.elem = check.varType(e.Elem)
   324  		return typ
   325  
   326  	case *syntax.DotsType:
   327  		// dots are handled explicitly where they are legal
   328  		// (array composite literals and parameter lists)
   329  		check.error(e, InvalidDotDotDot, "invalid use of '...'")
   330  		check.use(e.Elem)
   331  
   332  	case *syntax.StructType:
   333  		typ := new(Struct)
   334  		setDefType(def, typ)
   335  		check.structType(typ, e)
   336  		return typ
   337  
   338  	case *syntax.Operation:
   339  		if e.Op == syntax.Mul && e.Y == nil {
   340  			typ := new(Pointer)
   341  			typ.base = Typ[Invalid] // avoid nil base in invalid recursive type declaration
   342  			setDefType(def, typ)
   343  			typ.base = check.varType(e.X)
   344  			// If typ.base is invalid, it's unlikely that *base is particularly
   345  			// useful - even a valid dereferenciation will lead to an invalid
   346  			// type again, and in some cases we get unexpected follow-on errors
   347  			// (e.g., go.dev/issue/49005). Return an invalid type instead.
   348  			if !isValid(typ.base) {
   349  				return Typ[Invalid]
   350  			}
   351  			return typ
   352  		}
   353  
   354  		check.errorf(e0, NotAType, "%s is not a type", e0)
   355  		check.use(e0)
   356  
   357  	case *syntax.FuncType:
   358  		typ := new(Signature)
   359  		setDefType(def, typ)
   360  		check.funcType(typ, nil, nil, e)
   361  		return typ
   362  
   363  	case *syntax.InterfaceType:
   364  		typ := check.newInterface()
   365  		setDefType(def, typ)
   366  		check.interfaceType(typ, e, def)
   367  		return typ
   368  
   369  	case *syntax.MapType:
   370  		typ := new(Map)
   371  		setDefType(def, typ)
   372  
   373  		typ.key = check.varType(e.Key)
   374  		typ.elem = check.varType(e.Value)
   375  
   376  		// spec: "The comparison operators == and != must be fully defined
   377  		// for operands of the key type; thus the key type must not be a
   378  		// function, map, or slice."
   379  		//
   380  		// Delay this check because it requires fully setup types;
   381  		// it is safe to continue in any case (was go.dev/issue/6667).
   382  		check.later(func() {
   383  			if !Comparable(typ.key) {
   384  				var why string
   385  				if isTypeParam(typ.key) {
   386  					why = " (missing comparable constraint)"
   387  				}
   388  				check.errorf(e.Key, IncomparableMapKey, "invalid map key type %s%s", typ.key, why)
   389  			}
   390  		}).describef(e.Key, "check map key %s", typ.key)
   391  
   392  		return typ
   393  
   394  	case *syntax.ChanType:
   395  		typ := new(Chan)
   396  		setDefType(def, typ)
   397  
   398  		dir := SendRecv
   399  		switch e.Dir {
   400  		case 0:
   401  			// nothing to do
   402  		case syntax.SendOnly:
   403  			dir = SendOnly
   404  		case syntax.RecvOnly:
   405  			dir = RecvOnly
   406  		default:
   407  			check.errorf(e, InvalidSyntaxTree, "unknown channel direction %d", e.Dir)
   408  			// ok to continue
   409  		}
   410  
   411  		typ.dir = dir
   412  		typ.elem = check.varType(e.Elem)
   413  		return typ
   414  
   415  	default:
   416  		check.errorf(e0, NotAType, "%s is not a type", e0)
   417  		check.use(e0)
   418  	}
   419  
   420  	typ := Typ[Invalid]
   421  	setDefType(def, typ)
   422  	return typ
   423  }
   424  
   425  func setDefType(def *TypeName, typ Type) {
   426  	if def != nil {
   427  		switch t := def.typ.(type) {
   428  		case *Alias:
   429  			// t.fromRHS should always be set, either to an invalid type
   430  			// in the beginning, or to typ in certain cyclic declarations.
   431  			if t.fromRHS != Typ[Invalid] && t.fromRHS != typ {
   432  				panic(sprintf(nil, true, "t.fromRHS = %s, typ = %s\n", t.fromRHS, typ))
   433  			}
   434  			t.fromRHS = typ
   435  		case *Basic:
   436  			assert(t == Typ[Invalid])
   437  		case *Named:
   438  			t.underlying = typ
   439  		default:
   440  			panic(fmt.Sprintf("unexpected type %T", t))
   441  		}
   442  	}
   443  }
   444  
   445  func (check *Checker) instantiatedType(x syntax.Expr, xlist []syntax.Expr, def *TypeName) (res Type) {
   446  	if check.conf.Trace {
   447  		check.trace(x.Pos(), "-- instantiating type %s with %s", x, xlist)
   448  		check.indent++
   449  		defer func() {
   450  			check.indent--
   451  			// Don't format the underlying here. It will always be nil.
   452  			check.trace(x.Pos(), "=> %s", res)
   453  		}()
   454  	}
   455  
   456  	defer func() {
   457  		setDefType(def, res)
   458  	}()
   459  
   460  	var cause string
   461  	gtyp := check.genericType(x, &cause)
   462  	if cause != "" {
   463  		check.errorf(x, NotAGenericType, invalidOp+"%s%s (%s)", x, xlist, cause)
   464  	}
   465  	if !isValid(gtyp) {
   466  		return gtyp // error already reported
   467  	}
   468  
   469  	// evaluate arguments
   470  	targs := check.typeList(xlist)
   471  	if targs == nil {
   472  		return Typ[Invalid]
   473  	}
   474  
   475  	if orig, _ := gtyp.(*Alias); orig != nil {
   476  		return check.instance(x.Pos(), orig, targs, nil, check.context())
   477  	}
   478  
   479  	orig := asNamed(gtyp)
   480  	if orig == nil {
   481  		panic(fmt.Sprintf("%v: cannot instantiate %v", x.Pos(), gtyp))
   482  	}
   483  
   484  	// create the instance
   485  	inst := asNamed(check.instance(x.Pos(), orig, targs, nil, check.context()))
   486  
   487  	// orig.tparams may not be set up, so we need to do expansion later.
   488  	check.later(func() {
   489  		// This is an instance from the source, not from recursive substitution,
   490  		// and so it must be resolved during type-checking so that we can report
   491  		// errors.
   492  		check.recordInstance(x, inst.TypeArgs().list(), inst)
   493  
   494  		if check.validateTArgLen(x.Pos(), inst.obj.name, inst.TypeParams().Len(), inst.TypeArgs().Len()) {
   495  			if i, err := check.verify(x.Pos(), inst.TypeParams().list(), inst.TypeArgs().list(), check.context()); err != nil {
   496  				// best position for error reporting
   497  				pos := x.Pos()
   498  				if i < len(xlist) {
   499  					pos = syntax.StartPos(xlist[i])
   500  				}
   501  				check.softErrorf(pos, InvalidTypeArg, "%s", err)
   502  			} else {
   503  				check.mono.recordInstance(check.pkg, x.Pos(), inst.TypeParams().list(), inst.TypeArgs().list(), xlist)
   504  			}
   505  		}
   506  
   507  		// TODO(rfindley): remove this call: we don't need to call validType here,
   508  		// as cycles can only occur for types used inside a Named type declaration,
   509  		// and so it suffices to call validType from declared types.
   510  		check.validType(inst)
   511  	}).describef(x, "resolve instance %s", inst)
   512  
   513  	return inst
   514  }
   515  
   516  // arrayLength type-checks the array length expression e
   517  // and returns the constant length >= 0, or a value < 0
   518  // to indicate an error (and thus an unknown length).
   519  func (check *Checker) arrayLength(e syntax.Expr) int64 {
   520  	// If e is an identifier, the array declaration might be an
   521  	// attempt at a parameterized type declaration with missing
   522  	// constraint. Provide an error message that mentions array
   523  	// length.
   524  	if name, _ := e.(*syntax.Name); name != nil {
   525  		obj := check.lookup(name.Value)
   526  		if obj == nil {
   527  			check.errorf(name, InvalidArrayLen, "undefined array length %s or missing type constraint", name.Value)
   528  			return -1
   529  		}
   530  		if _, ok := obj.(*Const); !ok {
   531  			check.errorf(name, InvalidArrayLen, "invalid array length %s", name.Value)
   532  			return -1
   533  		}
   534  	}
   535  
   536  	var x operand
   537  	check.expr(nil, &x, e)
   538  	if x.mode != constant_ {
   539  		if x.mode != invalid {
   540  			check.errorf(&x, InvalidArrayLen, "array length %s must be constant", &x)
   541  		}
   542  		return -1
   543  	}
   544  
   545  	if isUntyped(x.typ) || isInteger(x.typ) {
   546  		if val := constant.ToInt(x.val); val.Kind() == constant.Int {
   547  			if representableConst(val, check, Typ[Int], nil) {
   548  				if n, ok := constant.Int64Val(val); ok && n >= 0 {
   549  					return n
   550  				}
   551  			}
   552  		}
   553  	}
   554  
   555  	var msg string
   556  	if isInteger(x.typ) {
   557  		msg = "invalid array length %s"
   558  	} else {
   559  		msg = "array length %s must be integer"
   560  	}
   561  	check.errorf(&x, InvalidArrayLen, msg, &x)
   562  	return -1
   563  }
   564  
   565  // typeList provides the list of types corresponding to the incoming expression list.
   566  // If an error occurred, the result is nil, but all list elements were type-checked.
   567  func (check *Checker) typeList(list []syntax.Expr) []Type {
   568  	res := make([]Type, len(list)) // res != nil even if len(list) == 0
   569  	for i, x := range list {
   570  		t := check.varType(x)
   571  		if !isValid(t) {
   572  			res = nil
   573  		}
   574  		if res != nil {
   575  			res[i] = t
   576  		}
   577  	}
   578  	return res
   579  }
   580
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