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  	scope, obj := check.lookupScope(e.Value)
    26  	switch obj {
    27  	case nil:
    28  		if e.Value == "_" {
    29  			check.error(e, InvalidBlank, "cannot use _ as value or type")
    30  		} else if isValidName(e.Value) {
    31  			check.errorf(e, UndeclaredName, "undefined: %s", e.Value)
    32  		}
    33  		return
    34  	case universeComparable:
    35  		if !check.verifyVersionf(e, go1_18, "predeclared %s", e.Value) {
    36  			return // avoid follow-on errors
    37  		}
    38  	}
    39  	// Because the representation of any depends on gotypesalias, we don't check
    40  	// pointer identity here.
    41  	if obj.Name() == "any" && obj.Parent() == Universe {
    42  		if !check.verifyVersionf(e, go1_18, "predeclared %s", e.Value) {
    43  			return // avoid follow-on errors
    44  		}
    45  	}
    46  
    47  	check.recordUse(e, obj)
    48  
    49  	// If we want a type but don't have one, stop right here and avoid potential problems
    50  	// with missing underlying types. This also gives better error messages in some cases
    51  	// (see go.dev/issue/65344).
    52  	_, gotType := obj.(*TypeName)
    53  	if !gotType && wantType {
    54  		check.errorf(e, NotAType, "%s is not a type", obj.Name())
    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  			v.used = 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, def)
    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  		pkgName.used = 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  			obj.used = 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.definedType(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.definedType(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 under() 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, _ := under(typ).(*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  // definedType is like typ but also accepts a type name def.
   191  // If def != nil, e is the type specification for the type named def, declared
   192  // in a type declaration, and def.typ.underlying will be set to the type of e
   193  // before any components of e are type-checked.
   194  func (check *Checker) definedType(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  func (check *Checker) genericType(e syntax.Expr, cause *string) Type {
   209  	typ := check.typInternal(e, nil)
   210  	assert(isTyped(typ))
   211  	if isValid(typ) && !isGeneric(typ) {
   212  		if cause != nil {
   213  			*cause = check.sprintf("%s is not a generic type", typ)
   214  		}
   215  		typ = Typ[Invalid]
   216  	}
   217  	// TODO(gri) what is the correct call below?
   218  	check.recordTypeAndValue(e, typexpr, typ, nil)
   219  	return typ
   220  }
   221  
   222  // goTypeName returns the Go type name for typ and
   223  // removes any occurrences of "types2." from that name.
   224  func goTypeName(typ Type) string {
   225  	return strings.ReplaceAll(fmt.Sprintf("%T", typ), "types2.", "")
   226  }
   227  
   228  // typInternal drives type checking of types.
   229  // Must only be called by definedType or genericType.
   230  func (check *Checker) typInternal(e0 syntax.Expr, def *TypeName) (T Type) {
   231  	if check.conf.Trace {
   232  		check.trace(e0.Pos(), "-- type %s", e0)
   233  		check.indent++
   234  		defer func() {
   235  			check.indent--
   236  			var under Type
   237  			if T != nil {
   238  				// Calling under() here may lead to endless instantiations.
   239  				// Test case: type T[P any] *T[P]
   240  				under = safeUnderlying(T)
   241  			}
   242  			if T == under {
   243  				check.trace(e0.Pos(), "=> %s // %s", T, goTypeName(T))
   244  			} else {
   245  				check.trace(e0.Pos(), "=> %s (under = %s) // %s", T, under, goTypeName(T))
   246  			}
   247  		}()
   248  	}
   249  
   250  	switch e := e0.(type) {
   251  	case *syntax.BadExpr:
   252  		// ignore - error reported before
   253  
   254  	case *syntax.Name:
   255  		var x operand
   256  		check.ident(&x, e, def, true)
   257  
   258  		switch x.mode {
   259  		case typexpr:
   260  			typ := x.typ
   261  			setDefType(def, typ)
   262  			return typ
   263  		case invalid:
   264  			// ignore - error reported before
   265  		case novalue:
   266  			check.errorf(&x, NotAType, "%s used as type", &x)
   267  		default:
   268  			check.errorf(&x, NotAType, "%s is not a type", &x)
   269  		}
   270  
   271  	case *syntax.SelectorExpr:
   272  		var x operand
   273  		check.selector(&x, e, def, true)
   274  
   275  		switch x.mode {
   276  		case typexpr:
   277  			typ := x.typ
   278  			setDefType(def, typ)
   279  			return 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), def)
   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.definedType(e.X, def)
   296  
   297  	case *syntax.ArrayType:
   298  		typ := new(Array)
   299  		setDefType(def, typ)
   300  		if e.Len != nil {
   301  			typ.len = check.arrayLength(e.Len)
   302  		} else {
   303  			// [...]array
   304  			check.error(e, BadDotDotDotSyntax, "invalid use of [...] array (outside a composite literal)")
   305  			typ.len = -1
   306  		}
   307  		typ.elem = check.varType(e.Elem)
   308  		if typ.len >= 0 {
   309  			return typ
   310  		}
   311  		// report error if we encountered [...]
   312  
   313  	case *syntax.SliceType:
   314  		typ := new(Slice)
   315  		setDefType(def, typ)
   316  		typ.elem = check.varType(e.Elem)
   317  		return typ
   318  
   319  	case *syntax.DotsType:
   320  		// dots are handled explicitly where they are legal
   321  		// (array composite literals and parameter lists)
   322  		check.error(e, InvalidDotDotDot, "invalid use of '...'")
   323  		check.use(e.Elem)
   324  
   325  	case *syntax.StructType:
   326  		typ := new(Struct)
   327  		setDefType(def, typ)
   328  		check.structType(typ, e)
   329  		return typ
   330  
   331  	case *syntax.Operation:
   332  		if e.Op == syntax.Mul && e.Y == nil {
   333  			typ := new(Pointer)
   334  			typ.base = Typ[Invalid] // avoid nil base in invalid recursive type declaration
   335  			setDefType(def, typ)
   336  			typ.base = check.varType(e.X)
   337  			// If typ.base is invalid, it's unlikely that *base is particularly
   338  			// useful - even a valid dereferenciation will lead to an invalid
   339  			// type again, and in some cases we get unexpected follow-on errors
   340  			// (e.g., go.dev/issue/49005). Return an invalid type instead.
   341  			if !isValid(typ.base) {
   342  				return Typ[Invalid]
   343  			}
   344  			return typ
   345  		}
   346  
   347  		check.errorf(e0, NotAType, "%s is not a type", e0)
   348  		check.use(e0)
   349  
   350  	case *syntax.FuncType:
   351  		typ := new(Signature)
   352  		setDefType(def, typ)
   353  		check.funcType(typ, nil, nil, e)
   354  		return typ
   355  
   356  	case *syntax.InterfaceType:
   357  		typ := check.newInterface()
   358  		setDefType(def, typ)
   359  		check.interfaceType(typ, e, def)
   360  		return typ
   361  
   362  	case *syntax.MapType:
   363  		typ := new(Map)
   364  		setDefType(def, typ)
   365  
   366  		typ.key = check.varType(e.Key)
   367  		typ.elem = check.varType(e.Value)
   368  
   369  		// spec: "The comparison operators == and != must be fully defined
   370  		// for operands of the key type; thus the key type must not be a
   371  		// function, map, or slice."
   372  		//
   373  		// Delay this check because it requires fully setup types;
   374  		// it is safe to continue in any case (was go.dev/issue/6667).
   375  		check.later(func() {
   376  			if !Comparable(typ.key) {
   377  				var why string
   378  				if isTypeParam(typ.key) {
   379  					why = " (missing comparable constraint)"
   380  				}
   381  				check.errorf(e.Key, IncomparableMapKey, "invalid map key type %s%s", typ.key, why)
   382  			}
   383  		}).describef(e.Key, "check map key %s", typ.key)
   384  
   385  		return typ
   386  
   387  	case *syntax.ChanType:
   388  		typ := new(Chan)
   389  		setDefType(def, typ)
   390  
   391  		dir := SendRecv
   392  		switch e.Dir {
   393  		case 0:
   394  			// nothing to do
   395  		case syntax.SendOnly:
   396  			dir = SendOnly
   397  		case syntax.RecvOnly:
   398  			dir = RecvOnly
   399  		default:
   400  			check.errorf(e, InvalidSyntaxTree, "unknown channel direction %d", e.Dir)
   401  			// ok to continue
   402  		}
   403  
   404  		typ.dir = dir
   405  		typ.elem = check.varType(e.Elem)
   406  		return typ
   407  
   408  	default:
   409  		check.errorf(e0, NotAType, "%s is not a type", e0)
   410  		check.use(e0)
   411  	}
   412  
   413  	typ := Typ[Invalid]
   414  	setDefType(def, typ)
   415  	return typ
   416  }
   417  
   418  func setDefType(def *TypeName, typ Type) {
   419  	if def != nil {
   420  		switch t := def.typ.(type) {
   421  		case *Alias:
   422  			// t.fromRHS should always be set, either to an invalid type
   423  			// in the beginning, or to typ in certain cyclic declarations.
   424  			if t.fromRHS != Typ[Invalid] && t.fromRHS != typ {
   425  				panic(sprintf(nil, true, "t.fromRHS = %s, typ = %s\n", t.fromRHS, typ))
   426  			}
   427  			t.fromRHS = typ
   428  		case *Basic:
   429  			assert(t == Typ[Invalid])
   430  		case *Named:
   431  			t.underlying = typ
   432  		default:
   433  			panic(fmt.Sprintf("unexpected type %T", t))
   434  		}
   435  	}
   436  }
   437  
   438  func (check *Checker) instantiatedType(x syntax.Expr, xlist []syntax.Expr, def *TypeName) (res Type) {
   439  	if check.conf.Trace {
   440  		check.trace(x.Pos(), "-- instantiating type %s with %s", x, xlist)
   441  		check.indent++
   442  		defer func() {
   443  			check.indent--
   444  			// Don't format the underlying here. It will always be nil.
   445  			check.trace(x.Pos(), "=> %s", res)
   446  		}()
   447  	}
   448  
   449  	defer func() {
   450  		setDefType(def, res)
   451  	}()
   452  
   453  	var cause string
   454  	typ := check.genericType(x, &cause)
   455  	if cause != "" {
   456  		check.errorf(x, NotAGenericType, invalidOp+"%s%s (%s)", x, xlist, cause)
   457  	}
   458  	if !isValid(typ) {
   459  		return typ // error already reported
   460  	}
   461  	// typ must be a generic Alias or Named type (but not a *Signature)
   462  	if _, ok := typ.(*Signature); ok {
   463  		panic("unexpected generic signature")
   464  	}
   465  	gtyp := typ.(genericType)
   466  
   467  	// evaluate arguments
   468  	targs := check.typeList(xlist)
   469  	if targs == nil {
   470  		return Typ[Invalid]
   471  	}
   472  
   473  	// create instance
   474  	// The instance is not generic anymore as it has type arguments, but it still
   475  	// satisfies the genericType interface because it has type parameters, too.
   476  	inst := check.instance(x.Pos(), gtyp, targs, nil, check.context()).(genericType)
   477  
   478  	// For Named types, orig.tparams may not be set up, so we need to do expansion later.
   479  	check.later(func() {
   480  		// This is an instance from the source, not from recursive substitution,
   481  		// and so it must be resolved during type-checking so that we can report
   482  		// errors.
   483  		check.recordInstance(x, targs, inst)
   484  
   485  		name := inst.(interface{ Obj() *TypeName }).Obj().name
   486  		tparams := inst.TypeParams().list()
   487  		if check.validateTArgLen(x.Pos(), name, len(tparams), len(targs)) {
   488  			// check type constraints
   489  			if i, err := check.verify(x.Pos(), inst.TypeParams().list(), targs, check.context()); err != nil {
   490  				// best position for error reporting
   491  				pos := x.Pos()
   492  				if i < len(xlist) {
   493  					pos = syntax.StartPos(xlist[i])
   494  				}
   495  				check.softErrorf(pos, InvalidTypeArg, "%s", err)
   496  			} else {
   497  				check.mono.recordInstance(check.pkg, x.Pos(), tparams, targs, xlist)
   498  			}
   499  		}
   500  	}).describef(x, "verify instantiation %s", inst)
   501  
   502  	return inst
   503  }
   504  
   505  // arrayLength type-checks the array length expression e
   506  // and returns the constant length >= 0, or a value < 0
   507  // to indicate an error (and thus an unknown length).
   508  func (check *Checker) arrayLength(e syntax.Expr) int64 {
   509  	// If e is an identifier, the array declaration might be an
   510  	// attempt at a parameterized type declaration with missing
   511  	// constraint. Provide an error message that mentions array
   512  	// length.
   513  	if name, _ := e.(*syntax.Name); name != nil {
   514  		obj := check.lookup(name.Value)
   515  		if obj == nil {
   516  			check.errorf(name, InvalidArrayLen, "undefined array length %s or missing type constraint", name.Value)
   517  			return -1
   518  		}
   519  		if _, ok := obj.(*Const); !ok {
   520  			check.errorf(name, InvalidArrayLen, "invalid array length %s", name.Value)
   521  			return -1
   522  		}
   523  	}
   524  
   525  	var x operand
   526  	check.expr(nil, &x, e)
   527  	if x.mode != constant_ {
   528  		if x.mode != invalid {
   529  			check.errorf(&x, InvalidArrayLen, "array length %s must be constant", &x)
   530  		}
   531  		return -1
   532  	}
   533  
   534  	if isUntyped(x.typ) || isInteger(x.typ) {
   535  		if val := constant.ToInt(x.val); val.Kind() == constant.Int {
   536  			if representableConst(val, check, Typ[Int], nil) {
   537  				if n, ok := constant.Int64Val(val); ok && n >= 0 {
   538  					return n
   539  				}
   540  			}
   541  		}
   542  	}
   543  
   544  	var msg string
   545  	if isInteger(x.typ) {
   546  		msg = "invalid array length %s"
   547  	} else {
   548  		msg = "array length %s must be integer"
   549  	}
   550  	check.errorf(&x, InvalidArrayLen, msg, &x)
   551  	return -1
   552  }
   553  
   554  // typeList provides the list of types corresponding to the incoming expression list.
   555  // If an error occurred, the result is nil, but all list elements were type-checked.
   556  func (check *Checker) typeList(list []syntax.Expr) []Type {
   557  	res := make([]Type, len(list)) // res != nil even if len(list) == 0
   558  	for i, x := range list {
   559  		t := check.varType(x)
   560  		if !isValid(t) {
   561  			res = nil
   562  		}
   563  		if res != nil {
   564  			res[i] = t
   565  		}
   566  	}
   567  	return res
   568  }
   569
View as plain text