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  // If wantType is set, the identifier e is expected to denote a type.
    20  func (check *Checker) ident(x *operand, e *syntax.Name, wantType bool) {
    21  	x.mode = invalid
    22  	x.expr = e
    23  
    24  	scope, obj := check.lookupScope(e.Value)
    25  	switch obj {
    26  	case nil:
    27  		if e.Value == "_" {
    28  			check.error(e, InvalidBlank, "cannot use _ as value or type")
    29  		} else if isValidName(e.Value) {
    30  			check.errorf(e, UndeclaredName, "undefined: %s", e.Value)
    31  		}
    32  		return
    33  	case universeComparable:
    34  		if !check.verifyVersionf(e, go1_18, "predeclared %s", e.Value) {
    35  			return // avoid follow-on errors
    36  		}
    37  	}
    38  	// Because the representation of any depends on gotypesalias, we don't check
    39  	// pointer identity here.
    40  	if obj.Name() == "any" && obj.Parent() == Universe {
    41  		if !check.verifyVersionf(e, go1_18, "predeclared %s", e.Value) {
    42  			return // avoid follow-on errors
    43  		}
    44  	}
    45  
    46  	check.recordUse(e, obj)
    47  
    48  	// If we want a type but don't have one, stop right here and avoid potential problems
    49  	// with missing underlying types. This also gives better error messages in some cases
    50  	// (see go.dev/issue/65344).
    51  	_, gotType := obj.(*TypeName)
    52  	if !gotType && wantType {
    53  		check.errorf(e, NotAType, "%s (%s) is not a type", obj.Name(), objectKind(obj))
    54  
    55  		// avoid "declared but not used" errors
    56  		// (don't use Checker.use - we don't want to evaluate too much)
    57  		if v, _ := obj.(*Var); v != nil && v.pkg == check.pkg /* see Checker.use1 */ {
    58  			check.usedVars[v] = true
    59  		}
    60  		return
    61  	}
    62  
    63  	// Type-check the object.
    64  	// Only call Checker.objDecl if the object doesn't have a type yet
    65  	// (in which case we must actually determine it) or the object is a
    66  	// TypeName from the current package and we also want a type (in which case
    67  	// we might detect a cycle which needs to be reported). Otherwise we can skip
    68  	// the call and avoid a possible cycle error in favor of the more informative
    69  	// "not a type/value" error that this function's caller will issue (see
    70  	// go.dev/issue/25790).
    71  	//
    72  	// Note that it is important to avoid calling objDecl on objects from other
    73  	// packages, to avoid races: see issue #69912.
    74  	typ := obj.Type()
    75  	if typ == nil || (gotType && wantType && obj.Pkg() == check.pkg) {
    76  		check.objDecl(obj)
    77  		typ = obj.Type() // type must have been assigned by Checker.objDecl
    78  	}
    79  	assert(typ != nil)
    80  
    81  	// The object may have been dot-imported.
    82  	// If so, mark the respective package as used.
    83  	// (This code is only needed for dot-imports. Without them,
    84  	// we only have to mark variables, see *Var case below).
    85  	if pkgName := check.dotImportMap[dotImportKey{scope, obj.Name()}]; pkgName != nil {
    86  		check.usedPkgNames[pkgName] = true
    87  	}
    88  
    89  	switch obj := obj.(type) {
    90  	case *PkgName:
    91  		check.errorf(e, InvalidPkgUse, "use of package %s not in selector", obj.name)
    92  		return
    93  
    94  	case *Const:
    95  		check.addDeclDep(obj)
    96  		if !isValid(typ) {
    97  			return
    98  		}
    99  		if obj == universeIota {
   100  			if check.iota == nil {
   101  				check.error(e, InvalidIota, "cannot use iota outside constant declaration")
   102  				return
   103  			}
   104  			x.val = check.iota
   105  		} else {
   106  			x.val = obj.val
   107  		}
   108  		assert(x.val != nil)
   109  		x.mode = constant_
   110  
   111  	case *TypeName:
   112  		if !check.conf.EnableAlias && check.isBrokenAlias(obj) {
   113  			check.errorf(e, InvalidDeclCycle, "invalid use of type alias %s in recursive type (see go.dev/issue/50729)", obj.name)
   114  			return
   115  		}
   116  		x.mode = typexpr
   117  
   118  	case *Var:
   119  		// It's ok to mark non-local variables, but ignore variables
   120  		// from other packages to avoid potential race conditions with
   121  		// dot-imported variables.
   122  		if obj.pkg == check.pkg {
   123  			check.usedVars[obj] = true
   124  		}
   125  		check.addDeclDep(obj)
   126  		if !isValid(typ) {
   127  			return
   128  		}
   129  		x.mode = variable
   130  
   131  	case *Func:
   132  		check.addDeclDep(obj)
   133  		x.mode = value
   134  
   135  	case *Builtin:
   136  		x.id = obj.id
   137  		x.mode = builtin
   138  
   139  	case *Nil:
   140  		x.mode = nilvalue
   141  
   142  	default:
   143  		panic("unreachable")
   144  	}
   145  
   146  	x.typ = typ
   147  }
   148  
   149  // typ type-checks the type expression e and returns its type, or Typ[Invalid].
   150  // The type must not be an (uninstantiated) generic type.
   151  func (check *Checker) typ(e syntax.Expr) Type {
   152  	return check.declaredType(e, nil)
   153  }
   154  
   155  // varType type-checks the type expression e and returns its type, or Typ[Invalid].
   156  // The type must not be an (uninstantiated) generic type and it must not be a
   157  // constraint interface.
   158  func (check *Checker) varType(e syntax.Expr) Type {
   159  	typ := check.declaredType(e, nil)
   160  	check.validVarType(e, typ)
   161  	return typ
   162  }
   163  
   164  // validVarType reports an error if typ is a constraint interface.
   165  // The expression e is used for error reporting, if any.
   166  func (check *Checker) validVarType(e syntax.Expr, typ Type) {
   167  	// If we have a type parameter there's nothing to do.
   168  	if isTypeParam(typ) {
   169  		return
   170  	}
   171  
   172  	// We don't want to call typ.Underlying() or complete interfaces while we are in
   173  	// the middle of type-checking parameter declarations that might belong
   174  	// to interface methods. Delay this check to the end of type-checking.
   175  	check.later(func() {
   176  		if t, _ := typ.Underlying().(*Interface); t != nil {
   177  			pos := syntax.StartPos(e)
   178  			tset := computeInterfaceTypeSet(check, pos, t) // TODO(gri) is this the correct position?
   179  			if !tset.IsMethodSet() {
   180  				if tset.comparable {
   181  					check.softErrorf(pos, MisplacedConstraintIface, "cannot use type %s outside a type constraint: interface is (or embeds) comparable", typ)
   182  				} else {
   183  					check.softErrorf(pos, MisplacedConstraintIface, "cannot use type %s outside a type constraint: interface contains type constraints", typ)
   184  				}
   185  			}
   186  		}
   187  	}).describef(e, "check var type %s", typ)
   188  }
   189  
   190  // declaredType is like typ but also accepts a type name def.
   191  // If def != nil, e is the type specification for the [Alias] or [Named] type
   192  // named def, and def.typ.fromRHS will be set to the [Type] of e immediately
   193  // after its creation.
   194  func (check *Checker) declaredType(e syntax.Expr, def *TypeName) Type {
   195  	typ := check.typInternal(e, def)
   196  	assert(isTyped(typ))
   197  	if isGeneric(typ) {
   198  		check.errorf(e, WrongTypeArgCount, "cannot use generic type %s without instantiation", typ)
   199  		typ = Typ[Invalid]
   200  	}
   201  	check.recordTypeAndValue(e, typexpr, typ, nil)
   202  	return typ
   203  }
   204  
   205  // genericType is like typ but the type must be an (uninstantiated) generic
   206  // type. If cause is non-nil and the type expression was a valid type but not
   207  // generic, cause will be populated with a message describing the error.
   208  //
   209  // Note: If the type expression was invalid and an error was reported before,
   210  // cause will not be populated; thus cause alone cannot be used to determine
   211  // if an error occurred.
   212  func (check *Checker) genericType(e syntax.Expr, cause *string) Type {
   213  	typ := check.typInternal(e, nil)
   214  	assert(isTyped(typ))
   215  	if isValid(typ) && !isGeneric(typ) {
   216  		if cause != nil {
   217  			*cause = check.sprintf("%s is not a generic type", typ)
   218  		}
   219  		typ = Typ[Invalid]
   220  	}
   221  	// TODO(gri) what is the correct call below?
   222  	check.recordTypeAndValue(e, typexpr, typ, nil)
   223  	return typ
   224  }
   225  
   226  // goTypeName returns the Go type name for typ and
   227  // removes any occurrences of "types2." from that name.
   228  func goTypeName(typ Type) string {
   229  	return strings.ReplaceAll(fmt.Sprintf("%T", typ), "types2.", "")
   230  }
   231  
   232  // typInternal drives type checking of types.
   233  // Must only be called by declaredType or genericType.
   234  func (check *Checker) typInternal(e0 syntax.Expr, def *TypeName) (T Type) {
   235  	if check.conf.Trace {
   236  		check.trace(e0.Pos(), "-- type %s", e0)
   237  		check.indent++
   238  		defer func() {
   239  			check.indent--
   240  			var under Type
   241  			if T != nil {
   242  				// Calling T.Underlying() here may lead to endless instantiations.
   243  				// Test case: type T[P any] *T[P]
   244  				under = safeUnderlying(T)
   245  			}
   246  			if T == under {
   247  				check.trace(e0.Pos(), "=> %s // %s", T, goTypeName(T))
   248  			} else {
   249  				check.trace(e0.Pos(), "=> %s (under = %s) // %s", T, under, goTypeName(T))
   250  			}
   251  		}()
   252  	}
   253  
   254  	switch e := e0.(type) {
   255  	case *syntax.BadExpr:
   256  		// ignore - error reported before
   257  
   258  	case *syntax.Name:
   259  		var x operand
   260  		check.ident(&x, e, true)
   261  
   262  		switch x.mode {
   263  		case typexpr:
   264  			return x.typ
   265  		case invalid:
   266  			// ignore - error reported before
   267  		case novalue:
   268  			check.errorf(&x, NotAType, "%s used as type", &x)
   269  		default:
   270  			check.errorf(&x, NotAType, "%s is not a type", &x)
   271  		}
   272  
   273  	case *syntax.SelectorExpr:
   274  		var x operand
   275  		check.selector(&x, e, true)
   276  
   277  		switch x.mode {
   278  		case typexpr:
   279  			return x.typ
   280  		case invalid:
   281  			// ignore - error reported before
   282  		case novalue:
   283  			check.errorf(&x, NotAType, "%s used as type", &x)
   284  		default:
   285  			check.errorf(&x, NotAType, "%s is not a type", &x)
   286  		}
   287  
   288  	case *syntax.IndexExpr:
   289  		check.verifyVersionf(e, go1_18, "type instantiation")
   290  		return check.instantiatedType(e.X, syntax.UnpackListExpr(e.Index))
   291  
   292  	case *syntax.ParenExpr:
   293  		// Generic types must be instantiated before they can be used in any form.
   294  		// Consequently, generic types cannot be parenthesized.
   295  		return check.declaredType(e.X, def)
   296  
   297  	case *syntax.ArrayType:
   298  		typ := new(Array)
   299  		if e.Len != nil {
   300  			typ.len = check.arrayLength(e.Len)
   301  		} else {
   302  			// [...]array
   303  			check.error(e, BadDotDotDotSyntax, "invalid use of [...] array (outside a composite literal)")
   304  			typ.len = -1
   305  		}
   306  		typ.elem = check.varType(e.Elem)
   307  		if typ.len >= 0 {
   308  			return typ
   309  		}
   310  		// report error if we encountered [...]
   311  
   312  	case *syntax.SliceType:
   313  		typ := new(Slice)
   314  		typ.elem = check.varType(e.Elem)
   315  		return typ
   316  
   317  	case *syntax.DotsType:
   318  		// dots are handled explicitly where they are valid
   319  		check.error(e, InvalidSyntaxTree, "invalid use of ...")
   320  
   321  	case *syntax.StructType:
   322  		typ := new(Struct)
   323  		check.structType(typ, e)
   324  		return typ
   325  
   326  	case *syntax.Operation:
   327  		if e.Op == syntax.Mul && e.Y == nil {
   328  			typ := new(Pointer)
   329  			typ.base = Typ[Invalid] // avoid nil base in invalid recursive type declaration
   330  			typ.base = check.varType(e.X)
   331  			// If typ.base is invalid, it's unlikely that *base is particularly
   332  			// useful - even a valid dereferenciation will lead to an invalid
   333  			// type again, and in some cases we get unexpected follow-on errors
   334  			// (e.g., go.dev/issue/49005). Return an invalid type instead.
   335  			if !isValid(typ.base) {
   336  				return Typ[Invalid]
   337  			}
   338  			return typ
   339  		}
   340  
   341  		check.errorf(e0, NotAType, "%s is not a type", e0)
   342  		check.use(e0)
   343  
   344  	case *syntax.FuncType:
   345  		typ := new(Signature)
   346  		check.funcType(typ, nil, nil, e)
   347  		return typ
   348  
   349  	case *syntax.InterfaceType:
   350  		typ := check.newInterface()
   351  		check.interfaceType(typ, e, def)
   352  		return typ
   353  
   354  	case *syntax.MapType:
   355  		typ := new(Map)
   356  		typ.key = check.varType(e.Key)
   357  		typ.elem = check.varType(e.Value)
   358  
   359  		// spec: "The comparison operators == and != must be fully defined
   360  		// for operands of the key type; thus the key type must not be a
   361  		// function, map, or slice."
   362  		//
   363  		// Delay this check because it requires fully setup types;
   364  		// it is safe to continue in any case (was go.dev/issue/6667).
   365  		check.later(func() {
   366  			if !Comparable(typ.key) {
   367  				var why string
   368  				if isTypeParam(typ.key) {
   369  					why = " (missing comparable constraint)"
   370  				}
   371  				check.errorf(e.Key, IncomparableMapKey, "invalid map key type %s%s", typ.key, why)
   372  			}
   373  		}).describef(e.Key, "check map key %s", typ.key)
   374  
   375  		return typ
   376  
   377  	case *syntax.ChanType:
   378  		typ := new(Chan)
   379  
   380  		dir := SendRecv
   381  		switch e.Dir {
   382  		case 0:
   383  			// nothing to do
   384  		case syntax.SendOnly:
   385  			dir = SendOnly
   386  		case syntax.RecvOnly:
   387  			dir = RecvOnly
   388  		default:
   389  			check.errorf(e, InvalidSyntaxTree, "unknown channel direction %d", e.Dir)
   390  			// ok to continue
   391  		}
   392  
   393  		typ.dir = dir
   394  		typ.elem = check.varType(e.Elem)
   395  		return typ
   396  
   397  	default:
   398  		check.errorf(e0, NotAType, "%s is not a type", e0)
   399  		check.use(e0)
   400  	}
   401  
   402  	typ := Typ[Invalid]
   403  	return typ
   404  }
   405  
   406  func (check *Checker) instantiatedType(x syntax.Expr, xlist []syntax.Expr) (res Type) {
   407  	if check.conf.Trace {
   408  		check.trace(x.Pos(), "-- instantiating type %s with %s", x, xlist)
   409  		check.indent++
   410  		defer func() {
   411  			check.indent--
   412  			// Don't format the underlying here. It will always be nil.
   413  			check.trace(x.Pos(), "=> %s", res)
   414  		}()
   415  	}
   416  
   417  	var cause string
   418  	typ := check.genericType(x, &cause)
   419  	if cause != "" {
   420  		check.errorf(x, NotAGenericType, invalidOp+"%s%s (%s)", x, xlist, cause)
   421  	}
   422  	if !isValid(typ) {
   423  		return typ // error already reported
   424  	}
   425  	// typ must be a generic Alias or Named type (but not a *Signature)
   426  	if _, ok := typ.(*Signature); ok {
   427  		panic("unexpected generic signature")
   428  	}
   429  	gtyp := typ.(genericType)
   430  
   431  	// evaluate arguments
   432  	targs := check.typeList(xlist)
   433  	if targs == nil {
   434  		return Typ[Invalid]
   435  	}
   436  
   437  	// create instance
   438  	// The instance is not generic anymore as it has type arguments, but unless
   439  	// instantiation failed, it still satisfies the genericType interface because
   440  	// it has type parameters, too.
   441  	ityp := check.instance(x.Pos(), gtyp, targs, nil, check.context())
   442  	inst, _ := ityp.(genericType)
   443  	if inst == nil {
   444  		return Typ[Invalid]
   445  	}
   446  
   447  	// For Named types, orig.tparams may not be set up, so we need to do expansion later.
   448  	check.later(func() {
   449  		// This is an instance from the source, not from recursive substitution,
   450  		// and so it must be resolved during type-checking so that we can report
   451  		// errors.
   452  		check.recordInstance(x, targs, inst)
   453  
   454  		name := inst.(interface{ Obj() *TypeName }).Obj().name
   455  		tparams := inst.TypeParams().list()
   456  		if check.validateTArgLen(x.Pos(), name, len(tparams), len(targs)) {
   457  			// check type constraints
   458  			if i, err := check.verify(x.Pos(), inst.TypeParams().list(), targs, check.context()); err != nil {
   459  				// best position for error reporting
   460  				pos := x.Pos()
   461  				if i < len(xlist) {
   462  					pos = syntax.StartPos(xlist[i])
   463  				}
   464  				check.softErrorf(pos, InvalidTypeArg, "%s", err)
   465  			} else {
   466  				check.mono.recordInstance(check.pkg, x.Pos(), tparams, targs, xlist)
   467  			}
   468  		}
   469  	}).describef(x, "verify instantiation %s", inst)
   470  
   471  	return inst
   472  }
   473  
   474  // arrayLength type-checks the array length expression e
   475  // and returns the constant length >= 0, or a value < 0
   476  // to indicate an error (and thus an unknown length).
   477  func (check *Checker) arrayLength(e syntax.Expr) int64 {
   478  	// If e is an identifier, the array declaration might be an
   479  	// attempt at a parameterized type declaration with missing
   480  	// constraint. Provide an error message that mentions array
   481  	// length.
   482  	if name, _ := e.(*syntax.Name); name != nil {
   483  		obj := check.lookup(name.Value)
   484  		if obj == nil {
   485  			check.errorf(name, InvalidArrayLen, "undefined array length %s or missing type constraint", name.Value)
   486  			return -1
   487  		}
   488  		if _, ok := obj.(*Const); !ok {
   489  			check.errorf(name, InvalidArrayLen, "invalid array length %s", name.Value)
   490  			return -1
   491  		}
   492  	}
   493  
   494  	var x operand
   495  	check.expr(nil, &x, e)
   496  	if x.mode != constant_ {
   497  		if x.mode != invalid {
   498  			check.errorf(&x, InvalidArrayLen, "array length %s must be constant", &x)
   499  		}
   500  		return -1
   501  	}
   502  
   503  	if isUntyped(x.typ) || isInteger(x.typ) {
   504  		if val := constant.ToInt(x.val); val.Kind() == constant.Int {
   505  			if representableConst(val, check, Typ[Int], nil) {
   506  				if n, ok := constant.Int64Val(val); ok && n >= 0 {
   507  					return n
   508  				}
   509  			}
   510  		}
   511  	}
   512  
   513  	var msg string
   514  	if isInteger(x.typ) {
   515  		msg = "invalid array length %s"
   516  	} else {
   517  		msg = "array length %s must be integer"
   518  	}
   519  	check.errorf(&x, InvalidArrayLen, msg, &x)
   520  	return -1
   521  }
   522  
   523  // typeList provides the list of types corresponding to the incoming expression list.
   524  // If an error occurred, the result is nil, but all list elements were type-checked.
   525  func (check *Checker) typeList(list []syntax.Expr) []Type {
   526  	res := make([]Type, len(list)) // res != nil even if len(list) == 0
   527  	for i, x := range list {
   528  		t := check.varType(x)
   529  		if !isValid(t) {
   530  			res = nil
   531  		}
   532  		if res != nil {
   533  			res[i] = t
   534  		}
   535  	}
   536  	return res
   537  }
   538
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