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unification.go
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unification.go
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// Mgmt
// Copyright (C) 2013-2021+ James Shubin and the project contributors
// Written by James Shubin <james@shubin.ca> and the project contributors
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program. If not, see <http://www.gnu.org/licenses/>.
package interfaces
import (
"fmt"
"strings"
"github.com/purpleidea/mgmt/lang/types"
"github.com/purpleidea/mgmt/util/errwrap"
)
// Invariant represents a constraint that is described by the Expr's and Stmt's,
// and which is passed into the unification solver to describe what is known by
// the AST.
type Invariant interface {
// TODO: should we add any other methods to this type?
fmt.Stringer
// ExprList returns the list of valid expressions in this invariant.
ExprList() []Expr
// Matches returns whether an invariant matches the existing solution.
// If it is inconsistent, then it errors.
Matches(solved map[Expr]*types.Type) (bool, error)
// Possible returns an error if it is certain that it is NOT possible to
// get a solution with this invariant and the set of partials. In
// certain cases, it might not be able to determine that it's not
// possible, while simultaneously not being able to guarantee a possible
// solution either. In this situation, it should return nil, since this
// is used as a filtering mechanism, and the nil result of possible is
// preferred over eliminating a tricky, but possible one.
Possible(partials []Invariant) error
}
// EqualsInvariant is an invariant that symbolizes that the expression has a
// known type.
// TODO: is there a better name than EqualsInvariant
type EqualsInvariant struct {
Expr Expr
Type *types.Type
}
// String returns a representation of this invariant.
func (obj *EqualsInvariant) String() string {
return fmt.Sprintf("%p == %s", obj.Expr, obj.Type)
}
// ExprList returns the list of valid expressions in this invariant.
func (obj *EqualsInvariant) ExprList() []Expr {
return []Expr{obj.Expr}
}
// Matches returns whether an invariant matches the existing solution. If it is
// inconsistent, then it errors.
func (obj *EqualsInvariant) Matches(solved map[Expr]*types.Type) (bool, error) {
typ, exists := solved[obj.Expr]
if !exists {
return false, nil
}
if err := typ.Cmp(obj.Type); err != nil {
return false, err
}
return true, nil
}
// Possible returns an error if it is certain that it is NOT possible to get a
// solution with this invariant and the set of partials. In certain cases, it
// might not be able to determine that it's not possible, while simultaneously
// not being able to guarantee a possible solution either. In this situation, it
// should return nil, since this is used as a filtering mechanism, and the nil
// result of possible is preferred over eliminating a tricky, but possible one.
func (obj *EqualsInvariant) Possible(partials []Invariant) error {
// TODO: we could pass in a solver here
//set := []Invariant{}
//set = append(set, obj)
//set = append(set, partials...)
//_, err := SimpleInvariantSolver(set, ...)
//if err != nil {
// // being ambiguous doesn't guarantee that we're possible
// if err == ErrAmbiguous {
// return nil // might be possible, might not be...
// }
// return err
//}
// FIXME: This is not right because we want to know if the whole thing
// works together, and as a result, the above solver is better, however,
// the goal is to eliminate easy impossible solutions, so allow this!
// XXX: Double check this is logical.
solved := map[Expr]*types.Type{
obj.Expr: obj.Type,
}
for _, invar := range partials { // check each one
_, err := invar.Matches(solved)
if err != nil { // inconsistent, so it's not possible
return errwrap.Wrapf(err, "not possible")
}
}
return nil
}
// EqualityInvariant is an invariant that symbolizes that the two expressions
// must have equivalent types.
// TODO: is there a better name than EqualityInvariant
type EqualityInvariant struct {
Expr1 Expr
Expr2 Expr
}
// String returns a representation of this invariant.
func (obj *EqualityInvariant) String() string {
return fmt.Sprintf("%p == %p", obj.Expr1, obj.Expr2)
}
// ExprList returns the list of valid expressions in this invariant.
func (obj *EqualityInvariant) ExprList() []Expr {
return []Expr{obj.Expr1, obj.Expr2}
}
// Matches returns whether an invariant matches the existing solution. If it is
// inconsistent, then it errors.
func (obj *EqualityInvariant) Matches(solved map[Expr]*types.Type) (bool, error) {
t1, exists1 := solved[obj.Expr1]
t2, exists2 := solved[obj.Expr2]
if !exists1 || !exists2 {
return false, nil // not matched yet
}
if err := t1.Cmp(t2); err != nil {
return false, err
}
return true, nil // matched!
}
// Possible returns an error if it is certain that it is NOT possible to get a
// solution with this invariant and the set of partials. In certain cases, it
// might not be able to determine that it's not possible, while simultaneously
// not being able to guarantee a possible solution either. In this situation, it
// should return nil, since this is used as a filtering mechanism, and the nil
// result of possible is preferred over eliminating a tricky, but possible one.
func (obj *EqualityInvariant) Possible(partials []Invariant) error {
// The idea here is that we look for the expression pointers in the list
// of partial invariants. It's only impossible if we (1) find both of
// them, and (2) that they relate to each other. The second part is
// harder.
var one, two bool
exprs := []Invariant{}
for _, x := range partials {
for _, y := range x.ExprList() { // []Expr
if y == obj.Expr1 {
one = true
exprs = append(exprs, x)
}
if y == obj.Expr2 {
two = true
exprs = append(exprs, x)
}
}
}
if !one || !two {
return nil // we're unconnected to anything, this is possible!
}
// we only need to check the connections in this case...
// let's keep this simple, and less perfect for now...
var typ *types.Type
for _, x := range exprs {
eq, ok := x.(*EqualsInvariant)
if !ok {
// XXX: add support for other kinds in the future...
continue
}
if typ != nil {
if err := typ.Cmp(eq.Type); err != nil {
// we found proof it's not possible
return errwrap.Wrapf(err, "not possible")
}
}
typ = eq.Type // store for next type
}
return nil
}
// EqualityInvariantList is an invariant that symbolizes that all the
// expressions listed must have equivalent types.
type EqualityInvariantList struct {
Exprs []Expr
}
// String returns a representation of this invariant.
func (obj *EqualityInvariantList) String() string {
var a []string
for _, x := range obj.Exprs {
a = append(a, fmt.Sprintf("%p", x))
}
return fmt.Sprintf("[%s]", strings.Join(a, ", "))
}
// ExprList returns the list of valid expressions in this invariant.
func (obj *EqualityInvariantList) ExprList() []Expr {
return obj.Exprs
}
// Matches returns whether an invariant matches the existing solution. If it is
// inconsistent, then it errors.
func (obj *EqualityInvariantList) Matches(solved map[Expr]*types.Type) (bool, error) {
found := true // assume true
var typ *types.Type
for _, x := range obj.Exprs {
t, exists := solved[x]
if !exists {
found = false
continue
}
if typ == nil { // set the first time
typ = t
}
if err := typ.Cmp(t); err != nil {
return false, err
}
}
return found, nil
}
// Possible returns an error if it is certain that it is NOT possible to get a
// solution with this invariant and the set of partials. In certain cases, it
// might not be able to determine that it's not possible, while simultaneously
// not being able to guarantee a possible solution either. In this situation, it
// should return nil, since this is used as a filtering mechanism, and the nil
// result of possible is preferred over eliminating a tricky, but possible one.
func (obj *EqualityInvariantList) Possible(partials []Invariant) error {
// The idea here is that we look for the expression pointers in the list
// of partial invariants. It's only impossible if we (1) find two or
// more, and (2) that any of them relate to each other. The second part
// is harder.
inList := func(needle Expr, haystack []Expr) bool {
for _, x := range haystack {
if x == needle {
return true
}
}
return false
}
exprs := []Invariant{}
for _, x := range partials {
for _, y := range x.ExprList() { // []Expr
if inList(y, obj.Exprs) {
exprs = append(exprs, x)
}
}
}
if len(exprs) <= 1 {
return nil // we're unconnected to anything, this is possible!
}
// we only need to check the connections in this case...
// let's keep this simple, and less perfect for now...
var typ *types.Type
for _, x := range exprs {
eq, ok := x.(*EqualsInvariant)
if !ok {
// XXX: add support for other kinds in the future...
continue
}
if typ != nil {
if err := typ.Cmp(eq.Type); err != nil {
// we found proof it's not possible
return errwrap.Wrapf(err, "not possible")
}
}
typ = eq.Type // store for next type
}
return nil
}
// EqualityWrapListInvariant expresses that a list in Expr1 must have elements
// that have the same type as the expression in Expr2Val.
type EqualityWrapListInvariant struct {
Expr1 Expr
Expr2Val Expr
}
// String returns a representation of this invariant.
func (obj *EqualityWrapListInvariant) String() string {
return fmt.Sprintf("%p == [%p]", obj.Expr1, obj.Expr2Val)
}
// ExprList returns the list of valid expressions in this invariant.
func (obj *EqualityWrapListInvariant) ExprList() []Expr {
return []Expr{obj.Expr1, obj.Expr2Val}
}
// Matches returns whether an invariant matches the existing solution. If it is
// inconsistent, then it errors.
func (obj *EqualityWrapListInvariant) Matches(solved map[Expr]*types.Type) (bool, error) {
t1, exists1 := solved[obj.Expr1] // list type
t2, exists2 := solved[obj.Expr2Val]
if !exists1 || !exists2 {
return false, nil // not matched yet
}
if t1.Kind != types.KindList {
return false, fmt.Errorf("expected list kind")
}
if err := t1.Val.Cmp(t2); err != nil {
return false, err // inconsistent!
}
return true, nil // matched!
}
// Possible returns an error if it is certain that it is NOT possible to get a
// solution with this invariant and the set of partials. In certain cases, it
// might not be able to determine that it's not possible, while simultaneously
// not being able to guarantee a possible solution either. In this situation, it
// should return nil, since this is used as a filtering mechanism, and the nil
// result of possible is preferred over eliminating a tricky, but possible one.
// This particular implementation is currently not implemented!
func (obj *EqualityWrapListInvariant) Possible(partials []Invariant) error {
// XXX: not implemented
return nil // safer to return nil than error
}
// EqualityWrapMapInvariant expresses that a map in Expr1 must have keys that
// match the type of the expression in Expr2Key and values that match the type
// of the expression in Expr2Val.
type EqualityWrapMapInvariant struct {
Expr1 Expr
Expr2Key Expr
Expr2Val Expr
}
// String returns a representation of this invariant.
func (obj *EqualityWrapMapInvariant) String() string {
return fmt.Sprintf("%p == {%p: %p}", obj.Expr1, obj.Expr2Key, obj.Expr2Val)
}
// ExprList returns the list of valid expressions in this invariant.
func (obj *EqualityWrapMapInvariant) ExprList() []Expr {
return []Expr{obj.Expr1, obj.Expr2Key, obj.Expr2Val}
}
// Matches returns whether an invariant matches the existing solution. If it is
// inconsistent, then it errors.
func (obj *EqualityWrapMapInvariant) Matches(solved map[Expr]*types.Type) (bool, error) {
t1, exists1 := solved[obj.Expr1] // map type
t2, exists2 := solved[obj.Expr2Key]
t3, exists3 := solved[obj.Expr2Val]
if !exists1 || !exists2 || !exists3 {
return false, nil // not matched yet
}
if t1.Kind != types.KindMap {
return false, fmt.Errorf("expected map kind")
}
if err := t1.Key.Cmp(t2); err != nil {
return false, err // inconsistent!
}
if err := t1.Val.Cmp(t3); err != nil {
return false, err // inconsistent!
}
return true, nil // matched!
}
// Possible returns an error if it is certain that it is NOT possible to get a
// solution with this invariant and the set of partials. In certain cases, it
// might not be able to determine that it's not possible, while simultaneously
// not being able to guarantee a possible solution either. In this situation, it
// should return nil, since this is used as a filtering mechanism, and the nil
// result of possible is preferred over eliminating a tricky, but possible one.
// This particular implementation is currently not implemented!
func (obj *EqualityWrapMapInvariant) Possible(partials []Invariant) error {
// XXX: not implemented
return nil // safer to return nil than error
}
// EqualityWrapStructInvariant expresses that a struct in Expr1 must have fields
// that match the type of the expressions listed in Expr2Map.
type EqualityWrapStructInvariant struct {
Expr1 Expr
Expr2Map map[string]Expr
Expr2Ord []string
}
// String returns a representation of this invariant.
func (obj *EqualityWrapStructInvariant) String() string {
var s = make([]string, len(obj.Expr2Ord))
for i, k := range obj.Expr2Ord {
t, ok := obj.Expr2Map[k]
if !ok {
panic("malformed struct order")
}
if t == nil {
panic("malformed struct field")
}
s[i] = fmt.Sprintf("%s %p", k, t)
}
return fmt.Sprintf("%p == struct{%s}", obj.Expr1, strings.Join(s, "; "))
}
// ExprList returns the list of valid expressions in this invariant.
func (obj *EqualityWrapStructInvariant) ExprList() []Expr {
exprs := []Expr{obj.Expr1}
for _, x := range obj.Expr2Map {
exprs = append(exprs, x)
}
return exprs
}
// Matches returns whether an invariant matches the existing solution. If it is
// inconsistent, then it errors.
func (obj *EqualityWrapStructInvariant) Matches(solved map[Expr]*types.Type) (bool, error) {
t1, exists1 := solved[obj.Expr1] // struct type
if !exists1 {
return false, nil // not matched yet
}
if t1.Kind != types.KindStruct {
return false, fmt.Errorf("expected struct kind")
}
found := true // assume true
for _, key := range obj.Expr2Ord {
_, exists := t1.Map[key]
if !exists {
return false, fmt.Errorf("missing invariant struct key of: `%s`", key)
}
e, exists := obj.Expr2Map[key]
if !exists {
return false, fmt.Errorf("missing matched struct key of: `%s`", key)
}
t, exists := solved[e]
if !exists {
found = false
continue
}
if err := t1.Map[key].Cmp(t); err != nil {
return false, err // inconsistent!
}
}
return found, nil // matched!
}
// Possible returns an error if it is certain that it is NOT possible to get a
// solution with this invariant and the set of partials. In certain cases, it
// might not be able to determine that it's not possible, while simultaneously
// not being able to guarantee a possible solution either. In this situation, it
// should return nil, since this is used as a filtering mechanism, and the nil
// result of possible is preferred over eliminating a tricky, but possible one.
// This particular implementation is currently not implemented!
func (obj *EqualityWrapStructInvariant) Possible(partials []Invariant) error {
// XXX: not implemented
return nil // safer to return nil than error
}
// EqualityWrapFuncInvariant expresses that a func in Expr1 must have args that
// match the type of the expressions listed in Expr2Map and a return value that
// matches the type of the expression in Expr2Out.
// TODO: should this be named EqualityWrapCallInvariant or not?
type EqualityWrapFuncInvariant struct {
Expr1 Expr
Expr2Map map[string]Expr
Expr2Ord []string
Expr2Out Expr
}
// String returns a representation of this invariant.
func (obj *EqualityWrapFuncInvariant) String() string {
var s = make([]string, len(obj.Expr2Ord))
for i, k := range obj.Expr2Ord {
t, ok := obj.Expr2Map[k]
if !ok {
panic("malformed func order")
}
if t == nil {
panic("malformed func field")
}
s[i] = fmt.Sprintf("%s %p", k, t)
}
return fmt.Sprintf("%p == func(%s) %p", obj.Expr1, strings.Join(s, "; "), obj.Expr2Out)
}
// ExprList returns the list of valid expressions in this invariant.
func (obj *EqualityWrapFuncInvariant) ExprList() []Expr {
exprs := []Expr{obj.Expr1}
for _, x := range obj.Expr2Map {
exprs = append(exprs, x)
}
exprs = append(exprs, obj.Expr2Out)
return exprs
}
// Matches returns whether an invariant matches the existing solution. If it is
// inconsistent, then it errors.
func (obj *EqualityWrapFuncInvariant) Matches(solved map[Expr]*types.Type) (bool, error) {
t1, exists1 := solved[obj.Expr1] // func type
if !exists1 {
return false, nil // not matched yet
}
if t1.Kind != types.KindFunc {
return false, fmt.Errorf("expected func kind")
}
found := true // assume true
for _, key := range obj.Expr2Ord {
_, exists := t1.Map[key]
if !exists {
return false, fmt.Errorf("missing invariant struct key of: `%s`", key)
}
e, exists := obj.Expr2Map[key]
if !exists {
return false, fmt.Errorf("missing matched struct key of: `%s`", key)
}
t, exists := solved[e]
if !exists {
found = false
continue
}
if err := t1.Map[key].Cmp(t); err != nil {
return false, err // inconsistent!
}
}
t, exists := solved[obj.Expr2Out]
if !exists {
return false, nil
}
if err := t1.Out.Cmp(t); err != nil {
return false, err // inconsistent!
}
return found, nil // matched!
}
// Possible returns an error if it is certain that it is NOT possible to get a
// solution with this invariant and the set of partials. In certain cases, it
// might not be able to determine that it's not possible, while simultaneously
// not being able to guarantee a possible solution either. In this situation, it
// should return nil, since this is used as a filtering mechanism, and the nil
// result of possible is preferred over eliminating a tricky, but possible one.
// This particular implementation is currently not implemented!
func (obj *EqualityWrapFuncInvariant) Possible(partials []Invariant) error {
// XXX: not implemented
return nil // safer to return nil than error
}
// EqualityWrapCallInvariant expresses that a call result that happened in Expr1
// must match the type of the function result listed in Expr2. In this case,
// Expr2 will be a function expression, and the returned expression should match
// with the Expr1 expression, when comparing types.
// TODO: should this be named EqualityWrapFuncInvariant or not?
// TODO: should Expr1 and Expr2 be reversed???
type EqualityWrapCallInvariant struct {
Expr1 Expr
Expr2Func Expr
}
// String returns a representation of this invariant.
func (obj *EqualityWrapCallInvariant) String() string {
return fmt.Sprintf("%p == call(%p)", obj.Expr1, obj.Expr2Func)
}
// ExprList returns the list of valid expressions in this invariant.
func (obj *EqualityWrapCallInvariant) ExprList() []Expr {
return []Expr{obj.Expr1, obj.Expr2Func}
}
// Matches returns whether an invariant matches the existing solution. If it is
// inconsistent, then it errors.
func (obj *EqualityWrapCallInvariant) Matches(solved map[Expr]*types.Type) (bool, error) {
t1, exists1 := solved[obj.Expr1] // call type
t2, exists2 := solved[obj.Expr2Func]
if !exists1 || !exists2 {
return false, nil // not matched yet
}
//if t1.Kind != types.KindFunc {
// return false, fmt.Errorf("expected func kind")
//}
if t2.Kind != types.KindFunc {
return false, fmt.Errorf("expected func kind")
}
if err := t1.Cmp(t2.Out); err != nil {
return false, err // inconsistent!
}
return true, nil // matched!
}
// Possible returns an error if it is certain that it is NOT possible to get a
// solution with this invariant and the set of partials. In certain cases, it
// might not be able to determine that it's not possible, while simultaneously
// not being able to guarantee a possible solution either. In this situation, it
// should return nil, since this is used as a filtering mechanism, and the nil
// result of possible is preferred over eliminating a tricky, but possible one.
// This particular implementation is currently not implemented!
func (obj *EqualityWrapCallInvariant) Possible(partials []Invariant) error {
// XXX: not implemented
return nil // safer to return nil than error
}
// GeneratorInvariant is an experimental type of new invariant. The idea is that
// this is a special invariant that the solver knows how to use; the solver runs
// all the easy bits first, and then passes the current solution state into the
// function, and in response, it runs some user-defined code and builds some new
// invariants that are added to the solver! This is not without caveats... This
// should only be used sparingly, and with care. It can suffer from the
// confluence problem, if the generator code that was provided is incorrect.
// What this means is that it could generate different results (and a different
// final solution) depending on the order in which it is called. Since this is
// undesirable, you must only use it for straight-forward situations. As an
// extreme example, if it generated different invariants depending on the time
// of day, this would be very problematic, and evil. Alternatively, it could be
// a pure function, but that returns wildly different results depending on what
// invariants were passed in. Use it wisely. It was added to make the printf
// function (which can have an infinite number of signatures) possible to
// express in terms of "normal" invariants. Lastly, if you wanted to use this to
// add-in partial progress, you could have it generate a list of invariants and
// include a new generator invariant in this list. Be sure to only do this if
// you are making progress on each invocation, and make sure to avoid infinite
// looping which isn't something we can currently detect or prevent. One special
// bit about generators and returning a partial: you must always return the
// minimum set of expressions that need to be solved in the first Unify() call
// that also returns the very first generator. This is because you must not rely
// on the generator to tell the solver about new expressions that it *also*
// wants solved. This is because after the initial (pre-generator-running)
// collection of the invariants, we need to be able to build a list of all the
// expressions that need to be solved for us to consider the problem "done". If
// a new expression only appeared after we ran a generator, then this would
// require our solver be far more complicated than it needs to be and currently
// is. Besides, there's no reason (that I know of at the moment) that needs this
// sort of invariant that only appears after the solver is running.
//
// NOTE: We might *consider* an optimization where we return a different kind of
// error that represents a response of "impossible". This would mean that there
// is no way to reconcile the current world-view with what is know about things.
// However, it would be easier and better to just return your invariants and let
// the normal solver run its course, although future research might show that it
// could maybe help in some cases.
// XXX: solver question: Can our solver detect `expr1 == str` AND `expr1 == int`
// and fail the whole thing when we know of a case like this that is impossible?
type GeneratorInvariant struct {
// Func is a generator function that takes the state of the world, and
// returns new invariants that should be added to this world view. The
// state of the world includes both the currently unsolved invariants,
// as well as the known solution map that has been solved so far. If
// this returns nil, we add the invariants it returned and we remove it
// from the list. If we error, it's because we don't have any new
// information to provide at this time...
Func func(invariants []Invariant, solved map[Expr]*types.Type) ([]Invariant, error)
}
// String returns a representation of this invariant.
func (obj *GeneratorInvariant) String() string {
return fmt.Sprintf("gen(%p)", obj.Func) // TODO: improve this
}
// ExprList returns the list of valid expressions in this invariant.
func (obj *GeneratorInvariant) ExprList() []Expr {
return []Expr{}
}
// Matches returns whether an invariant matches the existing solution. If it is
// inconsistent, then it errors.
func (obj *GeneratorInvariant) Matches(solved map[Expr]*types.Type) (bool, error) {
// XXX: not implemented (don't panic though)
//return false, err // inconsistent!
//return false, nil // not matched yet
//return true, nil // matched!
return false, nil // not matched yet
// If we error, it's because we don't have any new information to
// provide at this time... If it's nil, it's because the invariants
// could have worked with this solution.
//invariants, err := obj.Func(?, solved)
//if err != nil {
//}
}
// Possible is currently not implemented!
func (obj *GeneratorInvariant) Possible(partials []Invariant) error {
// XXX: not implemented
return nil // safer to return nil than error
}
// ConjunctionInvariant represents a list of invariants which must all be true
// together. In other words, it's a grouping construct for a set of invariants.
type ConjunctionInvariant struct {
Invariants []Invariant
}
// String returns a representation of this invariant.
func (obj *ConjunctionInvariant) String() string {
var a []string
for _, x := range obj.Invariants {
s := x.String()
a = append(a, s)
}
return fmt.Sprintf("[%s]", strings.Join(a, ", "))
}
// ExprList returns the list of valid expressions in this invariant.
func (obj *ConjunctionInvariant) ExprList() []Expr {
exprs := []Expr{}
for _, x := range obj.Invariants {
exprs = append(exprs, x.ExprList()...)
}
return exprs
}
// Matches returns whether an invariant matches the existing solution. If it is
// inconsistent, then it errors.
func (obj *ConjunctionInvariant) Matches(solved map[Expr]*types.Type) (bool, error) {
found := true // assume true
for _, invar := range obj.Invariants {
match, err := invar.Matches(solved)
if err != nil {
return false, nil
}
if !match {
found = false
}
}
return found, nil
}
// Possible returns an error if it is certain that it is NOT possible to get a
// solution with this invariant and the set of partials. In certain cases, it
// might not be able to determine that it's not possible, while simultaneously
// not being able to guarantee a possible solution either. In this situation, it
// should return nil, since this is used as a filtering mechanism, and the nil
// result of possible is preferred over eliminating a tricky, but possible one.
// This particular implementation is currently not implemented!
func (obj *ConjunctionInvariant) Possible(partials []Invariant) error {
for _, invar := range obj.Invariants {
if err := invar.Possible(partials); err != nil {
// we found proof it's not possible
return errwrap.Wrapf(err, "not possible")
}
}
// XXX: unfortunately we didn't look for them all together with a solver
return nil
}
// ExclusiveInvariant represents a list of invariants where one and *only* one
// should hold true. To combine multiple invariants in one of the list elements,
// you can group multiple invariants together using a ConjunctionInvariant. Do
// note that the solver might not verify that only one of the invariants in the
// list holds true, as it might choose to be lazy and pick the first solution
// found.
type ExclusiveInvariant struct {
Invariants []Invariant
}
// String returns a representation of this invariant.
func (obj *ExclusiveInvariant) String() string {
var a []string
for _, x := range obj.Invariants {
s := x.String()
a = append(a, s)
}
return fmt.Sprintf("[%s]", strings.Join(a, ", "))
}
// ExprList returns the list of valid expressions in this invariant.
func (obj *ExclusiveInvariant) ExprList() []Expr {
// XXX: We should do this if we assume that exclusives don't have some
// sort of transient expr to satisfy that doesn't disappear depending on
// which choice in the exclusive is chosen...
//exprs := []Expr{}
//for _, x := range obj.Invariants {
// exprs = append(exprs, x.ExprList()...)
//}
//return exprs
// XXX: But if we ever specify an expr in this exclusive that isn't
// referenced anywhere else, then we'd need to use the above so that our
// type unification algorithm knows not to stop too early.
return []Expr{} // XXX: Do we want to the set instead?
}
// Matches returns whether an invariant matches the existing solution. If it is
// inconsistent, then it errors. Because this partial invariant requires only
// one to be true, it will mask children errors, since it's normal for only one
// to be consistent.
func (obj *ExclusiveInvariant) Matches(solved map[Expr]*types.Type) (bool, error) {
found := false
reterr := fmt.Errorf("all exclusives errored")
var errs error
for _, invar := range obj.Invariants {
match, err := invar.Matches(solved)
if err != nil {
errs = errwrap.Append(errs, err)
continue
}
if !match {
// at least one was false, so we're not done here yet...
// we don't want to error yet, since we can't know there
// won't be a conflict once we get more data about this!
reterr = nil // clear the error
continue
}
if found { // we already found one
return false, fmt.Errorf("more than one exclusive solution")
}
found = true
}
if found { // we got exactly one valid solution
return true, nil
}
return false, errwrap.Wrapf(reterr, errwrap.String(errs))
}
// Possible returns an error if it is certain that it is NOT possible to get a
// solution with this invariant and the set of partials. In certain cases, it
// might not be able to determine that it's not possible, while simultaneously
// not being able to guarantee a possible solution either. In this situation, it
// should return nil, since this is used as a filtering mechanism, and the nil
// result of possible is preferred over eliminating a tricky, but possible one.
// This particular implementation is currently not implemented!
func (obj *ExclusiveInvariant) Possible(partials []Invariant) error {
var errs error
for _, invar := range obj.Invariants {
err := invar.Possible(partials)
if err == nil {
// we found proof it's possible
return nil
}
errs = errwrap.Append(errs, err)
}
return errwrap.Wrapf(errs, "not possible")
}
// Simplify attempts to reduce the exclusive invariant to eliminate any
// possibilities based on the list of known partials at this time. Hopefully,
// this will weed out some of the function polymorphism possibilities so that we
// can solve the problem without recursive, combinatorial permutation, which is
// very, very slow.
func (obj *ExclusiveInvariant) Simplify(partials []Invariant) ([]Invariant, error) {
if len(obj.Invariants) == 0 { // unexpected case
return []Invariant{}, nil // we don't need anything!
}
possible := []Invariant{}
var reasons error
for _, invar := range obj.Invariants { // []Invariant
if err := invar.Possible(partials); err != nil {
reasons = errwrap.Append(reasons, err)
continue
}
possible = append(possible, invar)
}
if len(possible) == 0 { // nothing was possible
return nil, errwrap.Wrapf(reasons, "no possible simplifications")
}
if len(possible) == 1 { // we flattened out the exclusive!
return possible, nil
}
if len(possible) == len(obj.Invariants) { // nothing changed
return nil, fmt.Errorf("no possible simplifications, we're unchanged")
}
invar := &ExclusiveInvariant{
Invariants: possible, // hopefully a smaller exclusive!
}
return []Invariant{invar}, nil
}
// AnyInvariant is an invariant that symbolizes that the expression can be any
// type. It is sometimes used to ensure that an expr actually gets a solution
// type so that it is not left unreferenced, and as a result, unsolved.
// TODO: is there a better name than AnyInvariant
type AnyInvariant struct {
Expr Expr
}
// String returns a representation of this invariant.
func (obj *AnyInvariant) String() string {
return fmt.Sprintf("%p == *", obj.Expr)
}
// ExprList returns the list of valid expressions in this invariant.
func (obj *AnyInvariant) ExprList() []Expr {
return []Expr{obj.Expr}
}
// Matches returns whether an invariant matches the existing solution. If it is
// inconsistent, then it errors.
func (obj *AnyInvariant) Matches(solved map[Expr]*types.Type) (bool, error) {
_, exists := solved[obj.Expr] // we only care that it is found.
return exists, nil
}
// Possible returns an error if it is certain that it is NOT possible to get a
// solution with this invariant and the set of partials. In certain cases, it
// might not be able to determine that it's not possible, while simultaneously
// not being able to guarantee a possible solution either. In this situation, it
// should return nil, since this is used as a filtering mechanism, and the nil
// result of possible is preferred over eliminating a tricky, but possible one.
// This particular implementation always returns nil.
func (obj *AnyInvariant) Possible([]Invariant) error {
// keep it simple, even though we don't technically check the inputs...
return nil
}
// ValueInvariant is an invariant that stores the value associated with an expr
// if it happens to be known statically at unification/compile time. This must
// only be used for static/pure values. For example, in `$x = 42`, we know that
// $x is 42. It's useful here because for `printf("hello %d times", 42)` we can
// get both the format string, and the other args as these new invariants, and
// we'd store those separately into this invariant, where they can eventually be
// passed into the generator invariant, where it can parse the format string and
// we'd be able to produce a precise type for the printf function, since it's
// nearly impossible to do otherwise since the number of possibilities is
// infinite! One special note: these values are typically not consumed, by the
// solver, because they need to be around for the generator invariant to use, so
// make sure your solver implementation can still terminate with unused
// invariants!
type ValueInvariant struct {
Expr Expr
Value types.Value // pointer
}
// String returns a representation of this invariant.
func (obj *ValueInvariant) String() string {
return fmt.Sprintf("%p == %s", obj.Expr, obj.Value)
}
// ExprList returns the list of valid expressions in this invariant.
func (obj *ValueInvariant) ExprList() []Expr {
return []Expr{obj.Expr}
}
// Matches returns whether an invariant matches the existing solution. If it is
// inconsistent, then it errors.
func (obj *ValueInvariant) Matches(solved map[Expr]*types.Type) (bool, error) {
typ, exists := solved[obj.Expr]
if !exists {
return false, nil
}
if err := typ.Cmp(obj.Value.Type()); err != nil {
return false, err
}
return true, nil
}
// Possible returns an error if it is certain that it is NOT possible to get a
// solution with this invariant and the set of partials. In certain cases, it
// might not be able to determine that it's not possible, while simultaneously
// not being able to guarantee a possible solution either. In this situation, it
// should return nil, since this is used as a filtering mechanism, and the nil
// result of possible is preferred over eliminating a tricky, but possible one.
func (obj *ValueInvariant) Possible(partials []Invariant) error {
// XXX: Double check this is logical. It was modified from EqualsInvariant.
solved := map[Expr]*types.Type{
obj.Expr: obj.Value.Type(),
}
for _, invar := range partials { // check each one
_, err := invar.Matches(solved)
if err != nil { // inconsistent, so it's not possible
return errwrap.Wrapf(err, "not possible")
}
}
return nil
}
// CallFuncArgsValueInvariant expresses that a func call is associated with a
// particular func, and that it is called with a specific list of args. Expr
// must match the function call expression, Func must match the actual function
// expression, and Args matches the args used in the call to run the func.
// TODO: should this be named FuncCallArgsValueInvariant or something different
// or not?