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

// Copyright 2012 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 commonly used type predicates.

package types2

// isValid reports whether t is a valid type.
func isValid(t Type) bool { return _Unalias(t) != Typ[Invalid] }

// The isX predicates below report whether t is an X.
// If t is a type parameter the result is false; i.e.,
// these predicates don't look inside a type parameter.

func isBoolean(t Type) bool        { return isBasic(t, IsBoolean) }
func isInteger(t Type) bool        { return isBasic(t, IsInteger) }
func isUnsigned(t Type) bool       { return isBasic(t, IsUnsigned) }
func isFloat(t Type) bool          { return isBasic(t, IsFloat) }
func isComplex(t Type) bool        { return isBasic(t, IsComplex) }
func isNumeric(t Type) bool        { return isBasic(t, IsNumeric) }
func isString(t Type) bool         { return isBasic(t, IsString) }
func isIntegerOrFloat(t Type) bool { return isBasic(t, IsInteger|IsFloat) }
func isConstType(t Type) bool      { return isBasic(t, IsConstType) }

// isBasic reports whether under(t) is a basic type with the specified info.
// If t is a type parameter the result is false; i.e.,
// isBasic does not look inside a type parameter.
func isBasic(t Type, info BasicInfo) bool {
        u, _ := under(t).(*Basic)
        return u != nil && u.info&info != 0
}

// The allX predicates below report whether t is an X.
// If t is a type parameter the result is true if isX is true
// for all specified types of the type parameter's type set.
// allX is an optimized version of isX(coreType(t)) (which
// is the same as underIs(t, isX)).

func allBoolean(t Type) bool         { return allBasic(t, IsBoolean) }
func allInteger(t Type) bool         { return allBasic(t, IsInteger) }
func allUnsigned(t Type) bool        { return allBasic(t, IsUnsigned) }
func allNumeric(t Type) bool         { return allBasic(t, IsNumeric) }
func allString(t Type) bool          { return allBasic(t, IsString) }
func allOrdered(t Type) bool         { return allBasic(t, IsOrdered) }
func allNumericOrString(t Type) bool { return allBasic(t, IsNumeric|IsString) }

// allBasic reports whether under(t) is a basic type with the specified info.
// If t is a type parameter, the result is true if isBasic(t, info) is true
// for all specific types of the type parameter's type set.
// allBasic(t, info) is an optimized version of isBasic(coreType(t), info).
func allBasic(t Type, info BasicInfo) bool {
        if tpar, _ := _Unalias(t).(*TypeParam); tpar != nil {
                return tpar.is(func(t *term) bool { return t != nil && isBasic(t.typ, info) })
        }
        return isBasic(t, info)
}

// hasName reports whether t has a name. This includes
// predeclared types, defined types, and type parameters.
// hasName may be called with types that are not fully set up.
func hasName(t Type) bool {
        switch _Unalias(t).(type) {
        case *Basic, *Named, *TypeParam:
                return true
        }
        return false
}

// isTypeLit reports whether t is a type literal.
// This includes all non-defined types, but also basic types.
// isTypeLit may be called with types that are not fully set up.
func isTypeLit(t Type) bool {
        switch _Unalias(t).(type) {
        case *Named, *TypeParam:
                return false
        }
        return true
}

// isTyped reports whether t is typed; i.e., not an untyped
// constant or boolean. isTyped may be called with types that
// are not fully set up.
func isTyped(t Type) bool {
        // Alias or Named types cannot denote untyped types,
        // thus we don't need to call _Unalias or under
        // (which would be unsafe to do for types that are
        // not fully set up).
        b, _ := t.(*Basic)
        return b == nil || b.info&IsUntyped == 0
}

// isUntyped(t) is the same as !isTyped(t).
func isUntyped(t Type) bool {
        return !isTyped(t)
}

// IsInterface reports whether t is an interface type.
func IsInterface(t Type) bool {
        _, ok := under(t).(*Interface)
        return ok
}

// isNonTypeParamInterface reports whether t is an interface type but not a type parameter.
func isNonTypeParamInterface(t Type) bool {
        return !isTypeParam(t) && IsInterface(t)
}

// isTypeParam reports whether t is a type parameter.
func isTypeParam(t Type) bool {
        _, ok := _Unalias(t).(*TypeParam)
        return ok
}

// hasEmptyTypeset reports whether t is a type parameter with an empty type set.
// The function does not force the computation of the type set and so is safe to
// use anywhere, but it may report a false negative if the type set has not been
// computed yet.
func hasEmptyTypeset(t Type) bool {
        if tpar, _ := _Unalias(t).(*TypeParam); tpar != nil && tpar.bound != nil {
                iface, _ := safeUnderlying(tpar.bound).(*Interface)
                return iface != nil && iface.tset != nil && iface.tset.IsEmpty()
        }
        return false
}

// isGeneric reports whether a type is a generic, uninstantiated type
// (generic signatures are not included).
// TODO(gri) should we include signatures or assert that they are not present?
func isGeneric(t Type) bool {
        // A parameterized type is only generic if it doesn't have an instantiation already.
        named := asNamed(t)
        return named != nil && named.obj != nil && named.inst == nil && named.TypeParams().Len() > 0
}

// Comparable reports whether values of type T are comparable.
func Comparable(T Type) bool {
        return comparable(T, true, nil, nil)
}

// If dynamic is set, non-type parameter interfaces are always comparable.
// If reportf != nil, it may be used to report why T is not comparable.
func comparable(T Type, dynamic bool, seen map[Type]bool, reportf func(string, ...interface{})) bool {
        if seen[T] {
                return true
        }
        if seen == nil {
                seen = make(map[Type]bool)
        }
        seen[T] = true

        switch t := under(T).(type) {
        case *Basic:
                // assume invalid types to be comparable
                // to avoid follow-up errors
                return t.kind != UntypedNil
        case *Pointer, *Chan:
                return true
        case *Struct:
                for _, f := range t.fields {
                        if !comparable(f.typ, dynamic, seen, nil) {
                                if reportf != nil {
                                        reportf("struct containing %s cannot be compared", f.typ)
                                }
                                return false
                        }
                }
                return true
        case *Array:
                if !comparable(t.elem, dynamic, seen, nil) {
                        if reportf != nil {
                                reportf("%s cannot be compared", t)
                        }
                        return false
                }
                return true
        case *Interface:
                if dynamic && !isTypeParam(T) || t.typeSet().IsComparable(seen) {
                        return true
                }
                if reportf != nil {
                        if t.typeSet().IsEmpty() {
                                reportf("empty type set")
                        } else {
                                reportf("incomparable types in type set")
                        }
                }
                // fallthrough
        }
        return false
}

// hasNil reports whether type t includes the nil value.
func hasNil(t Type) bool {
        switch u := under(t).(type) {
        case *Basic:
                return u.kind == UnsafePointer
        case *Slice, *Pointer, *Signature, *Map, *Chan:
                return true
        case *Interface:
                return !isTypeParam(t) || u.typeSet().underIs(func(u Type) bool {
                        return u != nil && hasNil(u)
                })
        }
        return false
}

// An ifacePair is a node in a stack of interface type pairs compared for identity.
type ifacePair struct {
        x, y *Interface
        prev *ifacePair
}

func (p *ifacePair) identical(q *ifacePair) bool {
        return p.x == q.x && p.y == q.y || p.x == q.y && p.y == q.x
}

// A comparer is used to compare types.
type comparer struct {
        ignoreTags     bool // if set, identical ignores struct tags
        ignoreInvalids bool // if set, identical treats an invalid type as identical to any type
}

// For changes to this code the corresponding changes should be made to unifier.nify.
func (c *comparer) identical(x, y Type, p *ifacePair) bool {
        x = _Unalias(x)
        y = _Unalias(y)

        if x == y {
                return true
        }

        if c.ignoreInvalids && (!isValid(x) || !isValid(y)) {
                return true
        }

        switch x := x.(type) {
        case *Basic:
                // Basic types are singletons except for the rune and byte
                // aliases, thus we cannot solely rely on the x == y check
                // above. See also comment in TypeName.IsAlias.
                if y, ok := y.(*Basic); ok {
                        return x.kind == y.kind
                }

        case *Array:
                // Two array types are identical if they have identical element types
                // and the same array length.
                if y, ok := y.(*Array); ok {
                        // If one or both array lengths are unknown (< 0) due to some error,
                        // assume they are the same to avoid spurious follow-on errors.
                        return (x.len < 0 || y.len < 0 || x.len == y.len) && c.identical(x.elem, y.elem, p)
                }

        case *Slice:
                // Two slice types are identical if they have identical element types.
                if y, ok := y.(*Slice); ok {
                        return c.identical(x.elem, y.elem, p)
                }

        case *Struct:
                // Two struct types are identical if they have the same sequence of fields,
                // and if corresponding fields have the same names, and identical types,
                // and identical tags. Two embedded fields are considered to have the same
                // name. Lower-case field names from different packages are always different.
                if y, ok := y.(*Struct); ok {
                        if x.NumFields() == y.NumFields() {
                                for i, f := range x.fields {
                                        g := y.fields[i]
                                        if f.embedded != g.embedded ||
                                                !c.ignoreTags && x.Tag(i) != y.Tag(i) ||
                                                !f.sameId(g.pkg, g.name) ||
                                                !c.identical(f.typ, g.typ, p) {
                                                return false
                                        }
                                }
                                return true
                        }
                }

        case *Pointer:
                // Two pointer types are identical if they have identical base types.
                if y, ok := y.(*Pointer); ok {
                        return c.identical(x.base, y.base, p)
                }

        case *Tuple:
                // Two tuples types are identical if they have the same number of elements
                // and corresponding elements have identical types.
                if y, ok := y.(*Tuple); ok {
                        if x.Len() == y.Len() {
                                if x != nil {
                                        for i, v := range x.vars {
                                                w := y.vars[i]
                                                if !c.identical(v.typ, w.typ, p) {
                                                        return false
                                                }
                                        }
                                }
                                return true
                        }
                }

        case *Signature:
                y, _ := y.(*Signature)
                if y == nil {
                        return false
                }

                // Two function types are identical if they have the same number of
                // parameters and result values, corresponding parameter and result types
                // are identical, and either both functions are variadic or neither is.
                // Parameter and result names are not required to match, and type
                // parameters are considered identical modulo renaming.

                if x.TypeParams().Len() != y.TypeParams().Len() {
                        return false
                }

                // In the case of generic signatures, we will substitute in yparams and
                // yresults.
                yparams := y.params
                yresults := y.results

                if x.TypeParams().Len() > 0 {
                        // We must ignore type parameter names when comparing x and y. The
                        // easiest way to do this is to substitute x's type parameters for y's.
                        xtparams := x.TypeParams().list()
                        ytparams := y.TypeParams().list()

                        var targs []Type
                        for i := range xtparams {
                                targs = append(targs, x.TypeParams().At(i))
                        }
                        smap := makeSubstMap(ytparams, targs)

                        var check *Checker   // ok to call subst on a nil *Checker
                        ctxt := NewContext() // need a non-nil Context for the substitution below

                        // Constraints must be pair-wise identical, after substitution.
                        for i, xtparam := range xtparams {
                                ybound := check.subst(nopos, ytparams[i].bound, smap, nil, ctxt)
                                if !c.identical(xtparam.bound, ybound, p) {
                                        return false
                                }
                        }

                        yparams = check.subst(nopos, y.params, smap, nil, ctxt).(*Tuple)
                        yresults = check.subst(nopos, y.results, smap, nil, ctxt).(*Tuple)
                }

                return x.variadic == y.variadic &&
                        c.identical(x.params, yparams, p) &&
                        c.identical(x.results, yresults, p)

        case *Union:
                if y, _ := y.(*Union); y != nil {
                        // TODO(rfindley): can this be reached during type checking? If so,
                        // consider passing a type set map.
                        unionSets := make(map[*Union]*_TypeSet)
                        xset := computeUnionTypeSet(nil, unionSets, nopos, x)
                        yset := computeUnionTypeSet(nil, unionSets, nopos, y)
                        return xset.terms.equal(yset.terms)
                }

        case *Interface:
                // Two interface types are identical if they describe the same type sets.
                // With the existing implementation restriction, this simplifies to:
                //
                // Two interface types are identical if they have the same set of methods with
                // the same names and identical function types, and if any type restrictions
                // are the same. Lower-case method names from different packages are always
                // different. The order of the methods is irrelevant.
                if y, ok := y.(*Interface); ok {
                        xset := x.typeSet()
                        yset := y.typeSet()
                        if xset.comparable != yset.comparable {
                                return false
                        }
                        if !xset.terms.equal(yset.terms) {
                                return false
                        }
                        a := xset.methods
                        b := yset.methods
                        if len(a) == len(b) {
                                // Interface types are the only types where cycles can occur
                                // that are not "terminated" via named types; and such cycles
                                // can only be created via method parameter types that are
                                // anonymous interfaces (directly or indirectly) embedding
                                // the current interface. Example:
                                //
                                //    type T interface {
                                //        m() interface{T}
                                //    }
                                //
                                // If two such (differently named) interfaces are compared,
                                // endless recursion occurs if the cycle is not detected.
                                //
                                // If x and y were compared before, they must be equal
                                // (if they were not, the recursion would have stopped);
                                // search the ifacePair stack for the same pair.
                                //
                                // This is a quadratic algorithm, but in practice these stacks
                                // are extremely short (bounded by the nesting depth of interface
                                // type declarations that recur via parameter types, an extremely
                                // rare occurrence). An alternative implementation might use a
                                // "visited" map, but that is probably less efficient overall.
                                q := &ifacePair{x, y, p}
                                for p != nil {
                                        if p.identical(q) {
                                                return true // same pair was compared before
                                        }
                                        p = p.prev
                                }
                                if debug {
                                        assertSortedMethods(a)
                                        assertSortedMethods(b)
                                }
                                for i, f := range a {
                                        g := b[i]
                                        if f.Id() != g.Id() || !c.identical(f.typ, g.typ, q) {
                                                return false
                                        }
                                }
                                return true
                        }
                }

        case *Map:
                // Two map types are identical if they have identical key and value types.
                if y, ok := y.(*Map); ok {
                        return c.identical(x.key, y.key, p) && c.identical(x.elem, y.elem, p)
                }

        case *Chan:
                // Two channel types are identical if they have identical value types
                // and the same direction.
                if y, ok := y.(*Chan); ok {
                        return x.dir == y.dir && c.identical(x.elem, y.elem, p)
                }

        case *Named:
                // Two named types are identical if their type names originate
                // in the same type declaration; if they are instantiated they
                // must have identical type argument lists.
                if y := asNamed(y); y != nil {
                        // check type arguments before origins to match unifier
                        // (for correct source code we need to do all checks so
                        // order doesn't matter)
                        xargs := x.TypeArgs().list()
                        yargs := y.TypeArgs().list()
                        if len(xargs) != len(yargs) {
                                return false
                        }
                        for i, xarg := range xargs {
                                if !Identical(xarg, yargs[i]) {
                                        return false
                                }
                        }
                        return identicalOrigin(x, y)
                }

        case *TypeParam:
                // nothing to do (x and y being equal is caught in the very beginning of this function)

        case nil:
                // avoid a crash in case of nil type

        default:
                unreachable()
        }

        return false
}

// identicalOrigin reports whether x and y originated in the same declaration.
func identicalOrigin(x, y *Named) bool {
        // TODO(gri) is this correct?
        return x.Origin().obj == y.Origin().obj
}

// identicalInstance reports if two type instantiations are identical.
// Instantiations are identical if their origin and type arguments are
// identical.
func identicalInstance(xorig Type, xargs []Type, yorig Type, yargs []Type) bool {
        if len(xargs) != len(yargs) {
                return false
        }

        for i, xa := range xargs {
                if !Identical(xa, yargs[i]) {
                        return false
                }
        }

        return Identical(xorig, yorig)
}

// Default returns the default "typed" type for an "untyped" type;
// it returns the incoming type for all other types. The default type
// for untyped nil is untyped nil.
func Default(t Type) Type {
        if t, ok := _Unalias(t).(*Basic); ok {
                switch t.kind {
                case UntypedBool:
                        return Typ[Bool]
                case UntypedInt:
                        return Typ[Int]
                case UntypedRune:
                        return universeRune // use 'rune' name
                case UntypedFloat:
                        return Typ[Float64]
                case UntypedComplex:
                        return Typ[Complex128]
                case UntypedString:
                        return Typ[String]
                }
        }
        return t
}

// maxType returns the "largest" type that encompasses both x and y.
// If x and y are different untyped numeric types, the result is the type of x or y
// that appears later in this list: integer, rune, floating-point, complex.
// Otherwise, if x != y, the result is nil.
func maxType(x, y Type) Type {
        // We only care about untyped types (for now), so == is good enough.
        // TODO(gri) investigate generalizing this function to simplify code elsewhere
        if x == y {
                return x
        }
        if isUntyped(x) && isUntyped(y) && isNumeric(x) && isNumeric(y) {
                // untyped types are basic types
                if x.(*Basic).kind > y.(*Basic).kind {
                        return x
                }
                return y
        }
        return nil
}

// clone makes a "flat copy" of *p and returns a pointer to the copy.
func clone[P *T, T any](p P) P {
        c := *p
        return &c
}