lang: funcs: Add struct lookup with an optional field
This adds an interesting version of the struct lookup function. In the situation where we can't type-check the field name, it will use the optional value passed in. This makes it easy to write a function that will pull in the desired value, even as the input struct changes type between compilations, without having to re-write your code. It's structurally different from the other default lookup functions, which is why it is named differently.
This commit is contained in:
James Shubin
547
lang/funcs/struct_lookup_optional_func.go
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547
lang/funcs/struct_lookup_optional_func.go
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@@ -0,0 +1,547 @@
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// Mgmt
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// Copyright (C) 2013-2023+ James Shubin and the project contributors
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// Written by James Shubin <james@shubin.ca> and the project contributors
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//
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// This program is free software: you can redistribute it and/or modify
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// it under the terms of the GNU General Public License as published by
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// the Free Software Foundation, either version 3 of the License, or
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// (at your option) any later version.
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//
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// This program is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU General Public License for more details.
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//
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// You should have received a copy of the GNU General Public License
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// along with this program. If not, see <http://www.gnu.org/licenses/>.
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package funcs
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import (
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"context"
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"fmt"
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"github.com/purpleidea/mgmt/lang/interfaces"
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"github.com/purpleidea/mgmt/lang/types"
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"github.com/purpleidea/mgmt/util/errwrap"
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)
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const (
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// StructLookupOptionalFuncName is the name this function is registered
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// as. This starts with an underscore so that it cannot be used from the
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// lexer.
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StructLookupOptionalFuncName = "_struct_lookup_optional"
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// arg names...
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structLookupOptionalArgNameStruct = "struct"
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structLookupOptionalArgNameField = "field"
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structLookupOptionalArgNameOptional = "optional"
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)
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func init() {
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Register(StructLookupOptionalFuncName, func() interfaces.Func { return &StructLookupOptionalFunc{} }) // must register the func and name
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}
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var _ interfaces.PolyFunc = &StructLookupOptionalFunc{} // ensure it meets this expectation
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// StructLookupOptionalFunc is a struct field lookup function. It does a special
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// trick in that it will unify on a struct that doesn't have the specified field
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// in it, but in that case, it will always return the optional value. This is a
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// bit different from the "default" mechanism that is used by list and map
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// lookup functions.
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type StructLookupOptionalFunc struct {
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Type *types.Type // Kind == Struct, that is used as the struct we lookup
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Out *types.Type // type of field we're extracting (also the type of optional)
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init *interfaces.Init
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last types.Value // last value received to use for diff
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field string
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result types.Value // last calculated output
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}
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// String returns a simple name for this function. This is needed so this struct
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// can satisfy the pgraph.Vertex interface.
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func (obj *StructLookupOptionalFunc) String() string {
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return StructLookupOptionalFuncName
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}
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// ArgGen returns the Nth arg name for this function.
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func (obj *StructLookupOptionalFunc) ArgGen(index int) (string, error) {
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seq := []string{structLookupOptionalArgNameStruct, structLookupOptionalArgNameField, structLookupOptionalArgNameOptional}
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if l := len(seq); index >= l {
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return "", fmt.Errorf("index %d exceeds arg length of %d", index, l)
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}
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return seq[index], nil
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}
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// Unify returns the list of invariants that this func produces.
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func (obj *StructLookupOptionalFunc) Unify(expr interfaces.Expr) ([]interfaces.Invariant, error) {
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var invariants []interfaces.Invariant
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var invar interfaces.Invariant
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// func(struct T1, field str, optional T2) T2
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structName, err := obj.ArgGen(0)
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if err != nil {
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return nil, err
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}
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fieldName, err := obj.ArgGen(1)
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if err != nil {
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return nil, err
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}
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optionalName, err := obj.ArgGen(2)
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if err != nil {
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return nil, err
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}
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dummyStruct := &interfaces.ExprAny{} // corresponds to the struct type
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dummyField := &interfaces.ExprAny{} // corresponds to the field type
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dummyOptional := &interfaces.ExprAny{} // corresponds to the optional type
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dummyOut := &interfaces.ExprAny{} // corresponds to the out string
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// field arg type of string
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invar = &interfaces.EqualsInvariant{
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Expr: dummyField,
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Type: types.TypeStr,
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}
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invariants = append(invariants, invar)
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// XXX: we could use this relationship *if* our solver could understand
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// different fields, and partial struct matches. I guess we'll leave it
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// for another day!
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//mapped := make(map[string]interfaces.Expr)
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//ordered := []string{???}
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//mapped[???] = dummyField
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//invar = &interfaces.EqualityWrapStructInvariant{
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// Expr1: dummyStruct,
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// Expr2Map: mapped,
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// Expr2Ord: ordered,
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//}
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//invariants = append(invariants, invar)
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// These two types should be identical. This is the safest approach. In
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// the case where the struct field is missing, then this should be true,
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// and when it is present, we'll never use the optional value, but we
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// can still enforce it's the same type.
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invar = &interfaces.EqualityInvariant{
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Expr1: dummyOptional,
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Expr2: dummyOut,
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}
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invariants = append(invariants, invar)
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// full function
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mapped := make(map[string]interfaces.Expr)
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ordered := []string{structName, fieldName, optionalName}
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mapped[structName] = dummyStruct
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mapped[fieldName] = dummyField
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mapped[optionalName] = dummyOptional
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invar = &interfaces.EqualityWrapFuncInvariant{
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Expr1: expr, // maps directly to us!
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Expr2Map: mapped,
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Expr2Ord: ordered,
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Expr2Out: dummyOut,
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}
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invariants = append(invariants, invar)
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// generator function
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fn := func(fnInvariants []interfaces.Invariant, solved map[interfaces.Expr]*types.Type) ([]interfaces.Invariant, error) {
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for _, invariant := range fnInvariants {
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// search for this special type of invariant
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cfavInvar, ok := invariant.(*interfaces.CallFuncArgsValueInvariant)
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if !ok {
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continue
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}
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// did we find the mapping from us to ExprCall ?
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if cfavInvar.Func != expr {
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continue
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}
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// cfavInvar.Expr is the ExprCall! (the return pointer)
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// cfavInvar.Args are the args that ExprCall uses!
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if l := len(cfavInvar.Args); l != 3 {
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return nil, fmt.Errorf("unable to build function with %d args", l)
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}
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var invariants []interfaces.Invariant
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var invar interfaces.Invariant
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// add the relationship to the returned value
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invar = &interfaces.EqualityInvariant{
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Expr1: cfavInvar.Expr,
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Expr2: dummyOut,
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}
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invariants = append(invariants, invar)
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// add the relationships to the called args
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invar = &interfaces.EqualityInvariant{
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Expr1: cfavInvar.Args[0],
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Expr2: dummyStruct,
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}
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invariants = append(invariants, invar)
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invar = &interfaces.EqualityInvariant{
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Expr1: cfavInvar.Args[1],
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Expr2: dummyField,
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}
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invariants = append(invariants, invar)
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invar = &interfaces.EqualityInvariant{
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Expr1: cfavInvar.Args[2],
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Expr2: dummyOptional,
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}
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invariants = append(invariants, invar)
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// second arg must be a string
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invar = &interfaces.EqualsInvariant{
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Expr: cfavInvar.Args[1],
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Type: types.TypeStr,
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}
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invariants = append(invariants, invar)
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// Not necessary for the field to be known or be static!
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var field string
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value, err := cfavInvar.Args[1].Value() // is it known?
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if err == nil {
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if k := value.Type().Kind; k != types.KindStr {
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return nil, fmt.Errorf("unable to build function with 1st arg of kind: %s", k)
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}
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field = value.Str() // must not panic
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}
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// If we figure out both of these types, we'll know the
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var t1 *types.Type // struct type
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var t2 *types.Type // optional / return type
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// validateArg0 checks: struct T1
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validateArg0 := func(typ *types.Type) error {
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if typ == nil { // unknown so far
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return nil
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}
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// we happen to have a struct!
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if k := typ.Kind; k != types.KindStruct {
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return fmt.Errorf("unable to build function with 0th arg of kind: %s", k)
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}
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// check both Ord and Map for safety
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found := false
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for _, s := range typ.Ord {
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if s == field {
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found = true
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break
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}
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}
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t, exists := typ.Map[field] // type found is T2
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if field != "" {
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if !exists || !found {
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//fmt.Printf("might be using optional arg, struct is missing field: %s\n", field)
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} else if err := t.Cmp(t2); t2 != nil && err != nil {
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return errwrap.Wrapf(err, "input type was inconsistent")
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}
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// learn!
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t2 = t
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}
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if err := typ.Cmp(t1); t1 != nil && err != nil {
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return errwrap.Wrapf(err, "input type was inconsistent")
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}
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// learn!
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t1 = typ
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return nil
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}
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validateArg2OrOut := func(typ *types.Type) error {
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if typ == nil { // unknown so far
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return nil
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}
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if err := typ.Cmp(t2); t2 != nil && err != nil {
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return errwrap.Wrapf(err, "input type was inconsistent")
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}
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// learn!
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t2 = typ
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return nil
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}
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if typ, err := cfavInvar.Args[0].Type(); err == nil { // is it known?
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// this sets t1 (and sometimes t2) on success if it learned
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if err := validateArg0(typ); err != nil {
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return nil, errwrap.Wrapf(err, "first struct arg type is inconsistent")
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}
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}
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if typ, exists := solved[cfavInvar.Args[0]]; exists { // alternate way to lookup type
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// this sets t1 (and sometimes t2) on success if it learned
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if err := validateArg0(typ); err != nil {
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return nil, errwrap.Wrapf(err, "first struct arg type is inconsistent")
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}
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}
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if typ, err := cfavInvar.Args[2].Type(); err == nil { // is it known?
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// this sets t2 on success if it learned
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if err := validateArg2OrOut(typ); err != nil {
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return nil, errwrap.Wrapf(err, "third struct arg type is inconsistent")
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}
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}
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if typ, exists := solved[cfavInvar.Args[2]]; exists { // alternate way to lookup type
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// this sets t2 on success if it learned
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if err := validateArg2OrOut(typ); err != nil {
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return nil, errwrap.Wrapf(err, "third struct arg type is inconsistent")
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}
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}
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// look at the return type too (if known)
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if typ, err := cfavInvar.Expr.Type(); err == nil { // is it known?
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// this sets t2 on success if it learned
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if err := validateArg2OrOut(typ); err != nil {
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return nil, errwrap.Wrapf(err, "third struct arg type is inconsistent")
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}
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}
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if typ, exists := solved[cfavInvar.Expr]; exists { // alternate way to lookup type
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// this sets t2 on success if it learned
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if err := validateArg2OrOut(typ); err != nil {
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return nil, errwrap.Wrapf(err, "third struct arg type is inconsistent")
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}
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}
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// XXX: if the struct type/value isn't know statically?
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if t1 != nil {
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invar = &interfaces.EqualsInvariant{
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Expr: dummyStruct,
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Type: t1,
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}
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invariants = append(invariants, invar)
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// We know *some* information about the struct!
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// Let's hope the unusedField expr won't trip
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// up the solver...
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mapped := make(map[string]interfaces.Expr)
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ordered := []string{}
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for _, x := range t1.Ord {
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// We *don't* need to solve unusedField
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unusedField := &interfaces.ExprAny{}
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mapped[x] = unusedField
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if x == field { // the one we care about
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mapped[x] = dummyOut
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}
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ordered = append(ordered, x)
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}
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// We map to dummyOut which is the return type
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// and has the same type of the field we want!
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mapped[field] = dummyOut // redundant =D
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invar = &interfaces.EqualityWrapStructInvariant{
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Expr1: dummyStruct,
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Expr2Map: mapped,
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Expr2Ord: ordered,
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}
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// We only want to add this weird thing if the
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// field actually exists. Otherwise ignore it.
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if _, exists := t1.Map[field]; field != "" && exists {
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invariants = append(invariants, invar)
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}
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}
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if t2 != nil {
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invar = &interfaces.EqualsInvariant{
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Expr: dummyOptional,
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Type: t2,
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}
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invariants = append(invariants, invar)
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invar = &interfaces.EqualsInvariant{
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Expr: dummyOut,
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Type: t2,
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}
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invariants = append(invariants, invar)
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}
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// XXX: if t1 or t2 are missing, we could also return a
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// new generator for later if we learn new information,
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// but we'd have to be careful to not do it infinitely.
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// TODO: do we return this relationship with ExprCall?
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invar = &interfaces.EqualityWrapCallInvariant{
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// TODO: should Expr1 and Expr2 be reversed???
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Expr1: cfavInvar.Expr,
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//Expr2Func: cfavInvar.Func, // same as below
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Expr2Func: expr,
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}
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invariants = append(invariants, invar)
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// TODO: are there any other invariants we should build?
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return invariants, nil // generator return
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}
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// We couldn't tell the solver anything it didn't already know!
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return nil, fmt.Errorf("couldn't generate new invariants")
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}
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invar = &interfaces.GeneratorInvariant{
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Func: fn,
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}
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invariants = append(invariants, invar)
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return invariants, nil
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}
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// Build is run to turn the polymorphic, undetermined function, into the
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// specific statically typed version. It is usually run after Unify completes,
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// and must be run before Info() and any of the other Func interface methods are
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// used. This function is idempotent, as long as the arg isn't changed between
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// runs.
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func (obj *StructLookupOptionalFunc) Build(typ *types.Type) (*types.Type, error) {
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// typ is the KindFunc signature we're trying to build...
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if typ.Kind != types.KindFunc {
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return nil, fmt.Errorf("input type must be of kind func")
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}
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if len(typ.Ord) != 3 {
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return nil, fmt.Errorf("the structlookup function needs exactly three args")
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}
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if typ.Out == nil {
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return nil, fmt.Errorf("return type of function must be specified")
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}
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if typ.Map == nil {
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return nil, fmt.Errorf("invalid input type")
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}
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tStruct, exists := typ.Map[typ.Ord[0]]
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if !exists || tStruct == nil {
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return nil, fmt.Errorf("first arg must be specified")
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}
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tField, exists := typ.Map[typ.Ord[1]]
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if !exists || tField == nil {
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return nil, fmt.Errorf("second arg must be specified")
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}
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if err := tField.Cmp(types.TypeStr); err != nil {
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return nil, errwrap.Wrapf(err, "field must be an str")
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}
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tOptional, exists := typ.Map[typ.Ord[2]]
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if !exists || tOptional == nil {
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return nil, fmt.Errorf("third arg must be specified")
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}
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if err := tOptional.Cmp(typ.Out); err != nil {
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return nil, errwrap.Wrapf(err, "optional arg must match return type")
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}
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// NOTE: We actually don't know which field this is, only its type! we
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// could have cached the discovered field during Polymorphisms(), but it
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// turns out it's not actually necessary for us to know it to build the
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// struct.
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obj.Type = tStruct // struct type
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obj.Out = typ.Out // type of return value
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return obj.sig(), nil
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}
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// Validate tells us if the input struct takes a valid form.
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func (obj *StructLookupOptionalFunc) Validate() error {
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if obj.Type == nil { // build must be run first
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return fmt.Errorf("type is still unspecified")
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}
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if obj.Type.Kind != types.KindStruct {
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return fmt.Errorf("type must be a kind of struct")
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}
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if obj.Out == nil {
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return fmt.Errorf("return type must be specified")
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}
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// TODO: can we do better and validate more aspects here?
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return nil
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}
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// Info returns some static info about itself. Build must be called before this
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// will return correct data.
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func (obj *StructLookupOptionalFunc) Info() *interfaces.Info {
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var sig *types.Type
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if obj.Type != nil { // don't panic if called speculatively
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// TODO: can obj.Out be nil (a partial) ?
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sig = obj.sig() // helper
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}
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return &interfaces.Info{
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Pure: true,
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Memo: false,
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Sig: sig, // func kind
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Err: obj.Validate(),
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}
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}
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// helper
|
||||
func (obj *StructLookupOptionalFunc) sig() *types.Type {
|
||||
return types.NewType(fmt.Sprintf("func(%s %s, %s str, %s %s) %s", structLookupOptionalArgNameStruct, obj.Type.String(), structLookupOptionalArgNameField, structLookupOptionalArgNameOptional, obj.Out.String(), obj.Out.String()))
|
||||
}
|
||||
|
||||
// Init runs some startup code for this function.
|
||||
func (obj *StructLookupOptionalFunc) Init(init *interfaces.Init) error {
|
||||
obj.init = init
|
||||
return nil
|
||||
}
|
||||
|
||||
// Stream returns the changing values that this func has over time.
|
||||
func (obj *StructLookupOptionalFunc) Stream(ctx context.Context) error {
|
||||
defer close(obj.init.Output) // the sender closes
|
||||
for {
|
||||
select {
|
||||
case input, ok := <-obj.init.Input:
|
||||
if !ok {
|
||||
return nil // can't output any more
|
||||
}
|
||||
//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
|
||||
|
||||
st := (input.Struct()[structLookupOptionalArgNameStruct]).(*types.StructValue)
|
||||
field := input.Struct()[structLookupOptionalArgNameField].Str()
|
||||
optional := input.Struct()[structLookupOptionalArgNameOptional]
|
||||
|
||||
if field == "" {
|
||||
return fmt.Errorf("received empty field")
|
||||
}
|
||||
if obj.field == "" {
|
||||
obj.field = field // store first field
|
||||
}
|
||||
if field != obj.field {
|
||||
return fmt.Errorf("input field changed from: `%s`, to: `%s`", obj.field, field)
|
||||
}
|
||||
|
||||
// We know the result of this lookup statically at
|
||||
// compile time, but for simplicity we check each time
|
||||
// here anyways. Maybe one day there will be a fancy
|
||||
// reason why this might vary over time.
|
||||
var result types.Value
|
||||
val, exists := st.Lookup(field)
|
||||
if exists {
|
||||
result = val
|
||||
} else {
|
||||
result = optional
|
||||
}
|
||||
|
||||
// if previous input was `2 + 4`, but now it
|
||||
// changed to `1 + 5`, the result is still the
|
||||
// same, so we can skip sending an update...
|
||||
if obj.result != nil && result.Cmp(obj.result) == nil {
|
||||
continue // result didn't change
|
||||
}
|
||||
obj.result = result // store new result
|
||||
|
||||
case <-ctx.Done():
|
||||
return nil
|
||||
}
|
||||
|
||||
select {
|
||||
case obj.init.Output <- obj.result: // send
|
||||
case <-ctx.Done():
|
||||
return nil
|
||||
}
|
||||
}
|
||||
}
|
||||
36
lang/interpret_test/TestAstFunc2/lookup1.txtar
Normal file
36
lang/interpret_test/TestAstFunc2/lookup1.txtar
Normal file
@@ -0,0 +1,36 @@
|
||||
-- main.mcl --
|
||||
$l1 = ["a", "b", "c",]
|
||||
|
||||
$l2 = [$l1, ["hello", "world",],]
|
||||
|
||||
test $l1[0] {}
|
||||
test $l1[2] {}
|
||||
test $l1[3] || "pass" {}
|
||||
test $l2[1] {}
|
||||
|
||||
$map1 map{int: str} = {42 => "hello1",}
|
||||
test $map1[42] {}
|
||||
|
||||
$map2 map{int: str} = {42 => "hello2",}
|
||||
test $map2[13] || "world2" {}
|
||||
|
||||
$map3 = {42 => "hello3",}
|
||||
test $map3[42] {}
|
||||
|
||||
$map4 = {42 => "hello4",}
|
||||
test $map4[13] || "world4" {}
|
||||
|
||||
$map5 = {"wow" => "pass1",}
|
||||
test $map5["wow"] {}
|
||||
|
||||
-- OUTPUT --
|
||||
Vertex: test[a]
|
||||
Vertex: test[c]
|
||||
Vertex: test[hello1]
|
||||
Vertex: test[hello3]
|
||||
Vertex: test[hello]
|
||||
Vertex: test[pass1]
|
||||
Vertex: test[pass]
|
||||
Vertex: test[world2]
|
||||
Vertex: test[world4]
|
||||
Vertex: test[world]
|
||||
24
lang/interpret_test/TestAstFunc2/lookup2.txtar
Normal file
24
lang/interpret_test/TestAstFunc2/lookup2.txtar
Normal file
@@ -0,0 +1,24 @@
|
||||
-- main.mcl --
|
||||
|
||||
$st1 = struct{
|
||||
a => 42,
|
||||
b => true,
|
||||
c => "pass1",
|
||||
}
|
||||
|
||||
test $st1->c || "default" {}
|
||||
test $st1->missing || "pass2" {}
|
||||
|
||||
$st2 = struct{
|
||||
a => 42,
|
||||
b => true,
|
||||
c => "pass3",
|
||||
}
|
||||
|
||||
test $st2->c {}
|
||||
#test $st2->missing + "fail" {} # this can't unify! (by design!)
|
||||
|
||||
-- OUTPUT --
|
||||
Vertex: test[pass1]
|
||||
Vertex: test[pass2]
|
||||
Vertex: test[pass3]
|
||||
14
lang/interpret_test/TestAstFunc2/lookup3.txtar
Normal file
14
lang/interpret_test/TestAstFunc2/lookup3.txtar
Normal file
@@ -0,0 +1,14 @@
|
||||
-- main.mcl --
|
||||
|
||||
$st = struct{
|
||||
a => 42,
|
||||
b => true,
|
||||
c => "wow",
|
||||
}
|
||||
|
||||
# Since there is no field named "missing", we can't guess what the zero value
|
||||
# would be for this field, and as a result, we can't unify or compile this code!
|
||||
test $st->missing + "fail" {} # this can't unify!
|
||||
|
||||
-- OUTPUT --
|
||||
# err: errUnify: 2 unconsumed generators
|
||||
Reference in New Issue
Block a user