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