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simplepoly.go
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simplepoly.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 simplepoly
import (
"fmt"
"github.com/purpleidea/mgmt/lang/funcs"
"github.com/purpleidea/mgmt/lang/interfaces"
"github.com/purpleidea/mgmt/lang/types"
langutil "github.com/purpleidea/mgmt/lang/util"
"github.com/purpleidea/mgmt/util/errwrap"
)
const (
// DirectInterface specifies whether we should use the direct function
// API or not. If we don't use it, then these simple functions are
// wrapped with the struct below.
DirectInterface = false // XXX: fix any bugs and set to true!
// AllowSimplePolyVariantDefinitions specifies whether we're allowed to
// include the `variant` type in definitons for simple poly functions.
// Long term, it's probably better to have this be false because it adds
// complexity into this simple poly API, and the root of which is the
// argComplexCmp which is only moderately powerful, but I figured I'd
// try and allow this for now because I liked how elegant the definition
// of the len() function was.
AllowSimplePolyVariantDefinitions = true
)
// RegisteredFuncs maps a function name to the corresponding static, pure funcs.
var RegisteredFuncs = make(map[string][]*types.FuncValue) // must initialize
// Register registers a simple, static, pure, polymorphic function. It is easier
// to use than the raw function API, but also limits you to small, finite
// numbers of different polymorphic type signatures per function name. You can
// also register functions which return types containing variants, if you want
// automatic matching based on partial types as well. Some complex patterns are
// not possible with this API. Implementing a function like `printf` would not
// be possible. Implementing a function which counts the number of elements in a
// list would be.
func Register(name string, fns []*types.FuncValue) {
if _, exists := RegisteredFuncs[name]; exists {
panic(fmt.Sprintf("a simple polyfunc named %s is already registered", name))
}
if len(fns) == 0 {
panic("no functions specified for simple polyfunc")
}
// check for uniqueness in type signatures
typs := []*types.Type{}
for i, f := range fns {
if f.T == nil {
panic(fmt.Sprintf("polyfunc %s contains a nil type signature", name))
}
if f.T.Kind != types.KindFunc { // even when this includes a variant
panic(fmt.Sprintf("polyfunc %s must be of kind func", name))
}
if !AllowSimplePolyVariantDefinitions && f.T.HasVariant() {
panic(fmt.Sprintf("polyfunc %s contains a variant type signature at index: %d", name, i))
}
typs = append(typs, f.T)
}
if err := langutil.HasDuplicateTypes(typs); err != nil {
panic(fmt.Sprintf("polyfunc %s has a duplicate implementation: %+v", name, err))
}
_, err := consistentArgs(fns)
if err != nil {
panic(fmt.Sprintf("polyfunc %s has inconsistent arg names: %+v", name, err))
}
RegisteredFuncs[name] = fns // store a copy for ourselves
// register a copy in the main function database
funcs.Register(name, func() interfaces.Func { return &WrappedFunc{Fns: fns} })
}
// ModuleRegister is exactly like Register, except that it registers within a
// named module. This is a helper function.
func ModuleRegister(module, name string, fns []*types.FuncValue) {
Register(module+funcs.ModuleSep+name, fns)
}
// consistentArgs returns the list of arg names across all the functions or
// errors if one consistent list could not be found.
func consistentArgs(fns []*types.FuncValue) ([]string, error) {
if len(fns) == 0 {
return nil, fmt.Errorf("no functions specified for simple polyfunc")
}
seq := []string{}
for _, x := range fns {
typ := x.Type()
if typ.Kind != types.KindFunc {
return nil, fmt.Errorf("expected %s, got %s", types.KindFunc, typ.Kind)
}
ord := typ.Ord
// check
l := len(seq)
if m := len(ord); m < l {
l = m // min
}
for i := 0; i < l; i++ { // check shorter list
if seq[i] != ord[i] {
return nil, fmt.Errorf("arg name at index %d differs (%s != %s)", i, seq[i], ord[i])
}
}
seq = ord // keep longer version!
}
return seq, nil
}
// WrappedFunc is a scaffolding function struct which fulfills the boiler-plate
// for the function API, but that can run a very simple, static, pure,
// polymorphic function.
type WrappedFunc struct {
Fns []*types.FuncValue // list of possible functions
fn *types.FuncValue // the concrete version of our chosen function
init *interfaces.Init
last types.Value // last value received to use for diff
result types.Value // last calculated output
closeChan chan struct{}
}
// ArgGen returns the Nth arg name for this function.
func (obj *WrappedFunc) ArgGen(index int) (string, error) {
seq, err := consistentArgs(obj.Fns)
if err != nil {
return "", err
}
if l := len(seq); index >= l {
return "", fmt.Errorf("index %d exceeds arg length of %d", index, l)
}
return seq[index], nil
}
// Unify returns the list of invariants that this func produces.
func (obj *WrappedFunc) Unify(expr interfaces.Expr) ([]interfaces.Invariant, error) {
if len(obj.Fns) == 0 {
return nil, fmt.Errorf("no matching signatures for simple polyfunc")
}
var invariants []interfaces.Invariant
var invar interfaces.Invariant
// Special case to help it solve faster. We still include the generator,
// in the chance that the relationship between the args is an important
// linkage that we should be specifying somehow...
if len(obj.Fns) == 1 {
fn := obj.Fns[0]
if fn == nil {
// programming error
return nil, fmt.Errorf("simple poly function value is nil")
}
typ := fn.T
if typ == nil {
// programming error
return nil, fmt.Errorf("simple poly function type is nil")
}
invar = &interfaces.EqualsInvariant{
Expr: expr,
Type: typ,
}
invariants = append(invariants, invar)
}
dummyOut := &interfaces.ExprAny{} // corresponds to the out type
// return type is currently unknown
invar = &interfaces.AnyInvariant{
Expr: dummyOut, // make sure to include it so we know it solves
}
invariants = append(invariants, invar)
// generator function
fn := func(fnInvariants []interfaces.Invariant, solved map[interfaces.Expr]*types.Type) ([]interfaces.Invariant, error) {
for _, invariant := range fnInvariants {
// search for this special type of invariant
cfavInvar, ok := invariant.(*interfaces.CallFuncArgsValueInvariant)
if !ok {
continue
}
// did we find the mapping from us to ExprCall ?
if cfavInvar.Func != expr {
continue
}
// cfavInvar.Expr is the ExprCall! (the return pointer)
// cfavInvar.Args are the args that ExprCall uses!
// any number of args are permitted
// helper function to build our complex func invariants
buildInvar := func(typ *types.Type) ([]interfaces.Invariant, error) {
var invariants []interfaces.Invariant
var invar interfaces.Invariant
// full function
mapped := make(map[string]interfaces.Expr)
ordered := []string{}
// assume this is a types.KindFunc
for i, x := range typ.Ord {
t := typ.Map[x]
if t == nil {
// programming error
return nil, fmt.Errorf("unexpected func nil arg (%d) type", i)
}
argName, err := obj.ArgGen(i)
if err != nil {
return nil, err
}
dummyArg := &interfaces.ExprAny{}
invar = &interfaces.EqualsInvariant{
Expr: dummyArg,
Type: t,
}
invariants = append(invariants, invar)
invar = &interfaces.EqualityInvariant{
Expr1: dummyArg,
Expr2: cfavInvar.Args[i],
}
invariants = append(invariants, invar)
mapped[argName] = dummyArg
ordered = append(ordered, argName)
}
invar = &interfaces.EqualityWrapFuncInvariant{
Expr1: expr, // maps directly to us!
Expr2Map: mapped,
Expr2Ord: ordered,
Expr2Out: dummyOut,
}
invariants = append(invariants, invar)
if typ.Out == nil {
// programming error
return nil, fmt.Errorf("unexpected func nil return type")
}
// remember to add the relationship to the
// return type of the functions as well...
invar = &interfaces.EqualsInvariant{
Expr: dummyOut,
Type: typ.Out,
}
invariants = append(invariants, invar)
return invariants, nil
}
// argCmp trims down the list of possible types...
// this makes our exclusive invariants smaller, and
// easier to solve without combinatorial slow recursion
argCmp := func(typ *types.Type) bool {
if len(cfavInvar.Args) != len(typ.Ord) {
return false // arg length differs
}
for i, x := range cfavInvar.Args {
if t, err := x.Type(); err == nil {
if t.Cmp(typ.Map[typ.Ord[i]]) != nil {
return false // impossible!
}
}
// is the type already known as solved?
if t, exists := solved[x]; exists { // alternate way to lookup type
if t.Cmp(typ.Map[typ.Ord[i]]) != nil {
return false // impossible!
}
}
}
return true // possible
}
argComplexCmp := func(typ *types.Type) (*types.Type, bool) {
if !typ.HasVariant() {
return typ, argCmp(typ)
}
mapped := make(map[string]*types.Type)
ordered := []string{}
out := typ.Out
if len(cfavInvar.Args) != len(typ.Ord) {
return nil, false // arg length differs
}
for i, x := range cfavInvar.Args {
name := typ.Ord[i]
if t, err := x.Type(); err == nil {
if _, err := t.ComplexCmp(typ.Map[typ.Ord[i]]); err != nil {
return nil, false // impossible!
}
mapped[name] = t // found it
}
// is the type already known as solved?
if t, exists := solved[x]; exists { // alternate way to lookup type
if _, err := t.ComplexCmp(typ.Map[typ.Ord[i]]); err != nil {
return nil, false // impossible!
}
// check it matches the above type
if oldT, exists := mapped[name]; exists && t.Cmp(oldT) != nil {
return nil, false // impossible!
}
mapped[name] = t // found it
}
if _, exists := mapped[name]; !exists {
// impossible, but for a
// different reason: we don't
// have enough information to
// plausibly allow this type to
// pass through, because we'd
// leave a variant in, so skip
// it. We'll probably fail in
// the end with a misleading
// "only recursive solutions
// left" error, but it just
// means we can't solve this!
return nil, false
}
ordered = append(ordered, name)
}
// if we happen to know the type of the return expr
if t, exists := solved[cfavInvar.Expr]; exists {
if out != nil && t.Cmp(out) != nil {
return nil, false // inconsistent!
}
out = t // learn!
}
return &types.Type{
Kind: types.KindFunc,
Map: mapped,
Ord: ordered,
Out: out,
}, true // possible
}
var invariants []interfaces.Invariant
var invar interfaces.Invariant
// add the relationship to the returned value
invar = &interfaces.EqualityInvariant{
Expr1: cfavInvar.Expr,
Expr2: dummyOut,
}
invariants = append(invariants, invar)
ors := []interfaces.Invariant{} // solve only one from this list
for _, f := range obj.Fns { // operator func types
typ := f.T
if typ == nil {
return nil, fmt.Errorf("nil type signature found")
}
if typ.Kind != types.KindFunc {
// programming error
return nil, fmt.Errorf("type must be a kind of func")
}
// filter out impossible types, and on success,
// use the replacement type that we found here!
// this is because the input might be a variant
// and after processing this, we get a concrete
// type that can be substituted in here instead
if typ, ok = argComplexCmp(typ); !ok {
continue // not a possible match
}
if typ.HasVariant() {
// programming error
return nil, fmt.Errorf("a variant type snuck through: %+v", typ)
}
invars, err := buildInvar(typ)
if err != nil {
return nil, err
}
// all of these need to be true together
and := &interfaces.ConjunctionInvariant{
Invariants: invars,
}
ors = append(ors, and) // one solution added!
}
if len(ors) == 0 {
return nil, fmt.Errorf("no matching signatures for simple poly func could be found")
}
// TODO: To improve the filtering, it would be
// excellent if we could examine the return type in
// `solved` somehow (if it is known) and use that to
// trim our list of exclusives down even further! The
// smaller the exclusives are, the faster everything in
// the solver can run.
invar = &interfaces.ExclusiveInvariant{
Invariants: ors, // one and only one of these should be true
}
if len(ors) == 1 {
invar = ors[0] // there should only be one
}
invariants = append(invariants, invar)
// TODO: do we return this relationship with ExprCall?
invar = &interfaces.EqualityWrapCallInvariant{
// TODO: should Expr1 and Expr2 be reversed???
Expr1: cfavInvar.Expr,
//Expr2Func: cfavInvar.Func, // same as below
Expr2Func: expr,
}
invariants = append(invariants, invar)
// TODO: are there any other invariants we should build?
return invariants, nil // generator return
}
// We couldn't tell the solver anything it didn't already know!
return nil, fmt.Errorf("couldn't generate new invariants")
}
invar = &interfaces.GeneratorInvariant{
Func: fn,
}
invariants = append(invariants, invar)
return invariants, nil
}
// Polymorphisms returns the list of possible function signatures available for
// this static polymorphic function. It relies on type and value hints to limit
// the number of returned possibilities.
func (obj *WrappedFunc) Polymorphisms(partialType *types.Type, partialValues []types.Value) ([]*types.Type, error) {
if len(obj.Fns) == 0 {
return nil, fmt.Errorf("no matching signatures for simple polyfunc")
}
// filter out anything that's incompatible with the partialType
typs := []*types.Type{}
for _, f := range obj.Fns {
// TODO: if status is "both", should we skip as too difficult?
_, err := f.T.ComplexCmp(partialType)
// can an f.T with a variant compare with a partial ? (yes)
if err != nil {
continue
}
typs = append(typs, f.T)
}
return typs, nil
}
// Build is run to turn the polymorphic, undetermined function, into the
// specific statically typed version. It is usually run after Unify completes,
// and must be run before Info() and any of the other Func interface methods are
// used.
func (obj *WrappedFunc) Build(typ *types.Type) error {
// typ is the KindFunc signature we're trying to build...
index, err := langutil.FnMatch(typ, obj.Fns)
if err != nil {
return err
}
obj.buildFunction(typ, index) // found match at this index
return nil
}
// buildFunction builds our concrete static function, from the potentially
// abstract, possibly variant containing list of functions.
func (obj *WrappedFunc) buildFunction(typ *types.Type, ix int) {
obj.fn = obj.Fns[ix].Copy().(*types.FuncValue)
obj.fn.T = typ.Copy() // overwrites any contained "variant" type
}
// Validate makes sure we've built our struct properly. It is usually unused for
// normal functions that users can use directly.
func (obj *WrappedFunc) Validate() error {
if len(obj.Fns) == 0 {
return fmt.Errorf("missing list of functions")
}
// check for uniqueness in type signatures
typs := []*types.Type{}
for _, f := range obj.Fns {
if f.T == nil {
return fmt.Errorf("nil type signature found")
}
typs = append(typs, f.T)
}
if err := langutil.HasDuplicateTypes(typs); err != nil {
return errwrap.Wrapf(err, "duplicate implementation found")
}
if obj.fn == nil { // build must be run first
return fmt.Errorf("a specific function has not been specified")
}
if obj.fn.T.Kind != types.KindFunc {
return fmt.Errorf("func must be a kind of func")
}
return nil
}
// Info returns some static info about itself.
func (obj *WrappedFunc) Info() *interfaces.Info {
var typ *types.Type
if obj.fn != nil { // don't panic if called speculatively
typ = obj.fn.Type()
}
return &interfaces.Info{
Pure: true,
Memo: false, // TODO: should this be something we specify here?
Sig: typ,
Err: obj.Validate(),
}
}
// Init runs some startup code for this function.
func (obj *WrappedFunc) Init(init *interfaces.Init) error {
obj.init = init
obj.closeChan = make(chan struct{})
return nil
}
// Stream returns the changing values that this func has over time.
func (obj *WrappedFunc) Stream() error {
defer close(obj.init.Output) // the sender closes
for {
select {
case input, ok := <-obj.init.Input:
if !ok {
if len(obj.fn.Type().Ord) > 0 {
return nil // can't output any more
}
// no inputs were expected, pass through once
}
if ok {
//if err := input.Type().Cmp(obj.Info().Sig.Input); err != nil {
// return errwrap.Wrapf(err, "wrong function input")
//}
if obj.last != nil && input.Cmp(obj.last) == nil {
continue // value didn't change, skip it
}
obj.last = input // store for next
}
values := []types.Value{}
for _, name := range obj.fn.Type().Ord {
x := input.Struct()[name]
values = append(values, x)
}
if obj.init.Debug {
obj.init.Logf("Calling function with: %+v", values)
}
result, err := obj.fn.Call(values) // (Value, error)
if err != nil {
if obj.init.Debug {
obj.init.Logf("Function returned error: %+v", err)
}
return errwrap.Wrapf(err, "simple poly function errored")
}
if obj.init.Debug {
obj.init.Logf("Function returned with: %+v", values)
}
// TODO: do we want obj.result to be a pointer instead?
if obj.result == result {
continue // result didn't change
}
obj.result = result // store new result
case <-obj.closeChan:
return nil
}
select {
case obj.init.Output <- obj.result: // send
if len(obj.fn.Type().Ord) == 0 {
return nil // no more values, we're a pure func
}
case <-obj.closeChan:
return nil
}
}
}
// Close runs some shutdown code for this function and turns off the stream.
func (obj *WrappedFunc) Close() error {
close(obj.closeChan)
return nil
}