[gostls13.git] / src / cmd / compile / internal / types2 / typexpr.go

// Copyright 2013 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// This file implements type-checking of identifiers and type expressions.

package types2

import (
        "cmd/compile/internal/syntax"
        "fmt"
        "go/constant"
        . "internal/types/errors"
        "strings"
)

// ident type-checks identifier e and initializes x with the value or type of e.
// If an error occurred, x.mode is set to invalid.
// For the meaning of def, see Checker.definedType, below.
// If wantType is set, the identifier e is expected to denote a type.
func (check *Checker) ident(x *operand, e *syntax.Name, def *TypeName, wantType bool) {
        x.mode = invalid
        x.expr = e

        // Note that we cannot use check.lookup here because the returned scope
        // may be different from obj.Parent(). See also Scope.LookupParent doc.
        scope, obj := check.scope.LookupParent(e.Value, check.pos)
        switch obj {
        case nil:
                if e.Value == "_" {
                        // Blank identifiers are never declared, but the current identifier may
                        // be a placeholder for a receiver type parameter. In this case we can
                        // resolve its type and object from Checker.recvTParamMap.
                        if tpar := check.recvTParamMap[e]; tpar != nil {
                                x.mode = typexpr
                                x.typ = tpar
                        } else {
                                check.error(e, InvalidBlank, "cannot use _ as value or type")
                        }
                } else {
                        check.errorf(e, UndeclaredName, "undefined: %s", e.Value)
                }
                return
        case universeAny, universeComparable:
                if !check.verifyVersionf(e, go1_18, "predeclared %s", e.Value) {
                        return // avoid follow-on errors
                }
        }
        check.recordUse(e, obj)

        // Type-check the object.
        // Only call Checker.objDecl if the object doesn't have a type yet
        // (in which case we must actually determine it) or the object is a
        // TypeName and we also want a type (in which case we might detect
        // a cycle which needs to be reported). Otherwise we can skip the
        // call and avoid a possible cycle error in favor of the more
        // informative "not a type/value" error that this function's caller
        // will issue (see go.dev/issue/25790).
        typ := obj.Type()
        if _, gotType := obj.(*TypeName); typ == nil || gotType && wantType {
                check.objDecl(obj, def)
                typ = obj.Type() // type must have been assigned by Checker.objDecl
        }
        assert(typ != nil)

        // The object may have been dot-imported.
        // If so, mark the respective package as used.
        // (This code is only needed for dot-imports. Without them,
        // we only have to mark variables, see *Var case below).
        if pkgName := check.dotImportMap[dotImportKey{scope, obj.Name()}]; pkgName != nil {
                pkgName.used = true
        }

        switch obj := obj.(type) {
        case *PkgName:
                check.errorf(e, InvalidPkgUse, "use of package %s not in selector", obj.name)
                return

        case *Const:
                check.addDeclDep(obj)
                if !isValid(typ) {
                        return
                }
                if obj == universeIota {
                        if check.iota == nil {
                                check.error(e, InvalidIota, "cannot use iota outside constant declaration")
                                return
                        }
                        x.val = check.iota
                } else {
                        x.val = obj.val
                }
                assert(x.val != nil)
                x.mode = constant_

        case *TypeName:
                if !check.conf._EnableAlias && check.isBrokenAlias(obj) {
                        check.errorf(e, InvalidDeclCycle, "invalid use of type alias %s in recursive type (see go.dev/issue/50729)", obj.name)
                        return
                }
                x.mode = typexpr

        case *Var:
                // It's ok to mark non-local variables, but ignore variables
                // from other packages to avoid potential race conditions with
                // dot-imported variables.
                if obj.pkg == check.pkg {
                        obj.used = true
                }
                check.addDeclDep(obj)
                if !isValid(typ) {
                        return
                }
                x.mode = variable

        case *Func:
                check.addDeclDep(obj)
                x.mode = value

        case *Builtin:
                x.id = obj.id
                x.mode = builtin

        case *Nil:
                x.mode = nilvalue

        default:
                unreachable()
        }

        x.typ = typ
}

// typ type-checks the type expression e and returns its type, or Typ[Invalid].
// The type must not be an (uninstantiated) generic type.
func (check *Checker) typ(e syntax.Expr) Type {
        return check.definedType(e, nil)
}

// varType type-checks the type expression e and returns its type, or Typ[Invalid].
// The type must not be an (uninstantiated) generic type and it must not be a
// constraint interface.
func (check *Checker) varType(e syntax.Expr) Type {
        typ := check.definedType(e, nil)
        check.validVarType(e, typ)
        return typ
}

// validVarType reports an error if typ is a constraint interface.
// The expression e is used for error reporting, if any.
func (check *Checker) validVarType(e syntax.Expr, typ Type) {
        // If we have a type parameter there's nothing to do.
        if isTypeParam(typ) {
                return
        }

        // We don't want to call under() or complete interfaces while we are in
        // the middle of type-checking parameter declarations that might belong
        // to interface methods. Delay this check to the end of type-checking.
        check.later(func() {
                if t, _ := under(typ).(*Interface); t != nil {
                        pos := syntax.StartPos(e)
                        tset := computeInterfaceTypeSet(check, pos, t) // TODO(gri) is this the correct position?
                        if !tset.IsMethodSet() {
                                if tset.comparable {
                                        check.softErrorf(pos, MisplacedConstraintIface, "cannot use type %s outside a type constraint: interface is (or embeds) comparable", typ)
                                } else {
                                        check.softErrorf(pos, MisplacedConstraintIface, "cannot use type %s outside a type constraint: interface contains type constraints", typ)
                                }
                        }
                }
        }).describef(e, "check var type %s", typ)
}

// definedType is like typ but also accepts a type name def.
// If def != nil, e is the type specification for the type named def, declared
// in a type declaration, and def.typ.underlying will be set to the type of e
// before any components of e are type-checked.
func (check *Checker) definedType(e syntax.Expr, def *TypeName) Type {
        typ := check.typInternal(e, def)
        assert(isTyped(typ))
        if isGeneric(typ) {
                check.errorf(e, WrongTypeArgCount, "cannot use generic type %s without instantiation", typ)
                typ = Typ[Invalid]
        }
        check.recordTypeAndValue(e, typexpr, typ, nil)
        return typ
}

// genericType is like typ but the type must be an (uninstantiated) generic
// type. If cause is non-nil and the type expression was a valid type but not
// generic, cause will be populated with a message describing the error.
func (check *Checker) genericType(e syntax.Expr, cause *string) Type {
        typ := check.typInternal(e, nil)
        assert(isTyped(typ))
        if isValid(typ) && !isGeneric(typ) {
                if cause != nil {
                        *cause = check.sprintf("%s is not a generic type", typ)
                }
                typ = Typ[Invalid]
        }
        // TODO(gri) what is the correct call below?
        check.recordTypeAndValue(e, typexpr, typ, nil)
        return typ
}

// goTypeName returns the Go type name for typ and
// removes any occurrences of "types2." from that name.
func goTypeName(typ Type) string {
        return strings.ReplaceAll(fmt.Sprintf("%T", typ), "types2.", "")
}

// typInternal drives type checking of types.
// Must only be called by definedType or genericType.
func (check *Checker) typInternal(e0 syntax.Expr, def *TypeName) (T Type) {
        if check.conf.Trace {
                check.trace(e0.Pos(), "-- type %s", e0)
                check.indent++
                defer func() {
                        check.indent--
                        var under Type
                        if T != nil {
                                // Calling under() here may lead to endless instantiations.
                                // Test case: type T[P any] *T[P]
                                under = safeUnderlying(T)
                        }
                        if T == under {
                                check.trace(e0.Pos(), "=> %s // %s", T, goTypeName(T))
                        } else {
                                check.trace(e0.Pos(), "=> %s (under = %s) // %s", T, under, goTypeName(T))
                        }
                }()
        }

        switch e := e0.(type) {
        case *syntax.BadExpr:
                // ignore - error reported before

        case *syntax.Name:
                var x operand
                check.ident(&x, e, def, true)

                switch x.mode {
                case typexpr:
                        typ := x.typ
                        setDefType(def, typ)
                        return typ
                case invalid:
                        // ignore - error reported before
                case novalue:
                        check.errorf(&x, NotAType, "%s used as type", &x)
                default:
                        check.errorf(&x, NotAType, "%s is not a type", &x)
                }

        case *syntax.SelectorExpr:
                var x operand
                check.selector(&x, e, def, true)

                switch x.mode {
                case typexpr:
                        typ := x.typ
                        setDefType(def, typ)
                        return typ
                case invalid:
                        // ignore - error reported before
                case novalue:
                        check.errorf(&x, NotAType, "%s used as type", &x)
                default:
                        check.errorf(&x, NotAType, "%s is not a type", &x)
                }

        case *syntax.IndexExpr:
                check.verifyVersionf(e, go1_18, "type instantiation")
                return check.instantiatedType(e.X, syntax.UnpackListExpr(e.Index), def)

        case *syntax.ParenExpr:
                // Generic types must be instantiated before they can be used in any form.
                // Consequently, generic types cannot be parenthesized.
                return check.definedType(e.X, def)

        case *syntax.ArrayType:
                typ := new(Array)
                setDefType(def, typ)
                if e.Len != nil {
                        typ.len = check.arrayLength(e.Len)
                } else {
                        // [...]array
                        check.error(e, BadDotDotDotSyntax, "invalid use of [...] array (outside a composite literal)")
                        typ.len = -1
                }
                typ.elem = check.varType(e.Elem)
                if typ.len >= 0 {
                        return typ
                }
                // report error if we encountered [...]

        case *syntax.SliceType:
                typ := new(Slice)
                setDefType(def, typ)
                typ.elem = check.varType(e.Elem)
                return typ

        case *syntax.DotsType:
                // dots are handled explicitly where they are legal
                // (array composite literals and parameter lists)
                check.error(e, InvalidDotDotDot, "invalid use of '...'")
                check.use(e.Elem)

        case *syntax.StructType:
                typ := new(Struct)
                setDefType(def, typ)
                check.structType(typ, e)
                return typ

        case *syntax.Operation:
                if e.Op == syntax.Mul && e.Y == nil {
                        typ := new(Pointer)
                        typ.base = Typ[Invalid] // avoid nil base in invalid recursive type declaration
                        setDefType(def, typ)
                        typ.base = check.varType(e.X)
                        // If typ.base is invalid, it's unlikely that *base is particularly
                        // useful - even a valid dereferenciation will lead to an invalid
                        // type again, and in some cases we get unexpected follow-on errors
                        // (e.g., go.dev/issue/49005). Return an invalid type instead.
                        if !isValid(typ.base) {
                                return Typ[Invalid]
                        }
                        return typ
                }

                check.errorf(e0, NotAType, "%s is not a type", e0)
                check.use(e0)

        case *syntax.FuncType:
                typ := new(Signature)
                setDefType(def, typ)
                check.funcType(typ, nil, nil, e)
                return typ

        case *syntax.InterfaceType:
                typ := check.newInterface()
                setDefType(def, typ)
                check.interfaceType(typ, e, def)
                return typ

        case *syntax.MapType:
                typ := new(Map)
                setDefType(def, typ)

                typ.key = check.varType(e.Key)
                typ.elem = check.varType(e.Value)

                // spec: "The comparison operators == and != must be fully defined
                // for operands of the key type; thus the key type must not be a
                // function, map, or slice."
                //
                // Delay this check because it requires fully setup types;
                // it is safe to continue in any case (was go.dev/issue/6667).
                check.later(func() {
                        if !Comparable(typ.key) {
                                var why string
                                if isTypeParam(typ.key) {
                                        why = " (missing comparable constraint)"
                                }
                                check.errorf(e.Key, IncomparableMapKey, "invalid map key type %s%s", typ.key, why)
                        }
                }).describef(e.Key, "check map key %s", typ.key)

                return typ

        case *syntax.ChanType:
                typ := new(Chan)
                setDefType(def, typ)

                dir := SendRecv
                switch e.Dir {
                case 0:
                        // nothing to do
                case syntax.SendOnly:
                        dir = SendOnly
                case syntax.RecvOnly:
                        dir = RecvOnly
                default:
                        check.errorf(e, InvalidSyntaxTree, "unknown channel direction %d", e.Dir)
                        // ok to continue
                }

                typ.dir = dir
                typ.elem = check.varType(e.Elem)
                return typ

        default:
                check.errorf(e0, NotAType, "%s is not a type", e0)
                check.use(e0)
        }

        typ := Typ[Invalid]
        setDefType(def, typ)
        return typ
}

func setDefType(def *TypeName, typ Type) {
        if def != nil {
                switch t := def.typ.(type) {
                case *_Alias:
                        // t.fromRHS should always be set, either to an invalid type
                        // in the beginning, or to typ in certain cyclic declarations.
                        if t.fromRHS != Typ[Invalid] && t.fromRHS != typ {
                                panic(sprintf(nil, true, "t.fromRHS = %s, typ = %s\n", t.fromRHS, typ))
                        }
                        t.fromRHS = typ
                case *Basic:
                        assert(t == Typ[Invalid])
                case *Named:
                        t.underlying = typ
                default:
                        panic(fmt.Sprintf("unexpected type %T", t))
                }
        }
}

func (check *Checker) instantiatedType(x syntax.Expr, xlist []syntax.Expr, def *TypeName) (res Type) {
        if check.conf.Trace {
                check.trace(x.Pos(), "-- instantiating type %s with %s", x, xlist)
                check.indent++
                defer func() {
                        check.indent--
                        // Don't format the underlying here. It will always be nil.
                        check.trace(x.Pos(), "=> %s", res)
                }()
        }

        var cause string
        gtyp := check.genericType(x, &cause)
        if cause != "" {
                check.errorf(x, NotAGenericType, invalidOp+"%s%s (%s)", x, xlist, cause)
        }
        if !isValid(gtyp) {
                return gtyp // error already reported
        }

        orig := asNamed(gtyp)
        if orig == nil {
                panic(fmt.Sprintf("%v: cannot instantiate %v", x.Pos(), gtyp))
        }

        // evaluate arguments
        targs := check.typeList(xlist)
        if targs == nil {
                setDefType(def, Typ[Invalid]) // avoid errors later due to lazy instantiation
                return Typ[Invalid]
        }

        // create the instance
        inst := asNamed(check.instance(x.Pos(), orig, targs, nil, check.context()))
        setDefType(def, inst)

        // orig.tparams may not be set up, so we need to do expansion later.
        check.later(func() {
                // This is an instance from the source, not from recursive substitution,
                // and so it must be resolved during type-checking so that we can report
                // errors.
                check.recordInstance(x, inst.TypeArgs().list(), inst)

                if check.validateTArgLen(x.Pos(), inst.TypeParams().Len(), inst.TypeArgs().Len()) {
                        if i, err := check.verify(x.Pos(), inst.TypeParams().list(), inst.TypeArgs().list(), check.context()); err != nil {
                                // best position for error reporting
                                pos := x.Pos()
                                if i < len(xlist) {
                                        pos = syntax.StartPos(xlist[i])
                                }
                                check.softErrorf(pos, InvalidTypeArg, "%s", err)
                        } else {
                                check.mono.recordInstance(check.pkg, x.Pos(), inst.TypeParams().list(), inst.TypeArgs().list(), xlist)
                        }
                }

                // TODO(rfindley): remove this call: we don't need to call validType here,
                // as cycles can only occur for types used inside a Named type declaration,
                // and so it suffices to call validType from declared types.
                check.validType(inst)
        }).describef(x, "resolve instance %s", inst)

        return inst
}

// arrayLength type-checks the array length expression e
// and returns the constant length >= 0, or a value < 0
// to indicate an error (and thus an unknown length).
func (check *Checker) arrayLength(e syntax.Expr) int64 {
        // If e is an identifier, the array declaration might be an
        // attempt at a parameterized type declaration with missing
        // constraint. Provide an error message that mentions array
        // length.
        if name, _ := e.(*syntax.Name); name != nil {
                obj := check.lookup(name.Value)
                if obj == nil {
                        check.errorf(name, InvalidArrayLen, "undefined array length %s or missing type constraint", name.Value)
                        return -1
                }
                if _, ok := obj.(*Const); !ok {
                        check.errorf(name, InvalidArrayLen, "invalid array length %s", name.Value)
                        return -1
                }
        }

        var x operand
        check.expr(nil, &x, e)
        if x.mode != constant_ {
                if x.mode != invalid {
                        check.errorf(&x, InvalidArrayLen, "array length %s must be constant", &x)
                }
                return -1
        }

        if isUntyped(x.typ) || isInteger(x.typ) {
                if val := constant.ToInt(x.val); val.Kind() == constant.Int {
                        if representableConst(val, check, Typ[Int], nil) {
                                if n, ok := constant.Int64Val(val); ok && n >= 0 {
                                        return n
                                }
                        }
                }
        }

        var msg string
        if isInteger(x.typ) {
                msg = "invalid array length %s"
        } else {
                msg = "array length %s must be integer"
        }
        check.errorf(&x, InvalidArrayLen, msg, &x)
        return -1
}

// typeList provides the list of types corresponding to the incoming expression list.
// If an error occurred, the result is nil, but all list elements were type-checked.
func (check *Checker) typeList(list []syntax.Expr) []Type {
        res := make([]Type, len(list)) // res != nil even if len(list) == 0
        for i, x := range list {
                t := check.varType(x)
                if !isValid(t) {
                        res = nil
                }
                if res != nil {
                        res[i] = t
                }
        }
        return res
}