terraform-provider-gitea/vendor/github.com/zclconf/go-cty/cty/convert/unify.go

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2022-04-03 04:07:16 +00:00
package convert
import (
"github.com/zclconf/go-cty/cty"
)
// The current unify implementation is somewhat inefficient, but we accept this
// under the assumption that it will generally be used with small numbers of
// types and with types of reasonable complexity. However, it does have a
// "happy path" where all of the given types are equal.
//
// This function is likely to have poor performance in cases where any given
// types are very complex (lots of deeply-nested structures) or if the list
// of types itself is very large. In particular, it will walk the nested type
// structure under the given types several times, especially when given a
// list of types for which unification is not possible, since each permutation
// will be tried to determine that result.
func unify(types []cty.Type, unsafe bool) (cty.Type, []Conversion) {
if len(types) == 0 {
// Degenerate case
return cty.NilType, nil
}
// If all of the given types are of the same structural kind, we may be
// able to construct a new type that they can all be unified to, even if
// that is not one of the given types. We must try this before the general
// behavior below because in unsafe mode we can convert an object type to
// a subset of that type, which would be a much less useful conversion for
// unification purposes.
{
mapCt := 0
listCt := 0
setCt := 0
objectCt := 0
tupleCt := 0
dynamicCt := 0
for _, ty := range types {
switch {
case ty.IsMapType():
mapCt++
case ty.IsListType():
listCt++
case ty.IsSetType():
setCt++
case ty.IsObjectType():
objectCt++
case ty.IsTupleType():
tupleCt++
case ty == cty.DynamicPseudoType:
dynamicCt++
default:
break
}
}
switch {
case mapCt > 0 && (mapCt+dynamicCt) == len(types):
return unifyCollectionTypes(cty.Map, types, unsafe, dynamicCt > 0)
case mapCt > 0 && (mapCt+objectCt+dynamicCt) == len(types):
// Objects often contain map data, but are not directly typed as
// such due to language constructs or function types. Try to unify
// them as maps first before falling back to heterogeneous type
// conversion.
ty, convs := unifyObjectsAsMaps(types, unsafe)
// If we got a map back, we know the unification was successful.
if ty.IsMapType() {
return ty, convs
}
case listCt > 0 && (listCt+dynamicCt) == len(types):
return unifyCollectionTypes(cty.List, types, unsafe, dynamicCt > 0)
case listCt > 0 && (listCt+tupleCt+dynamicCt) == len(types):
// Tuples are often lists in disguise, and we may be able to
// unify them as such.
ty, convs := unifyTuplesAsList(types, unsafe)
// if we got a list back, we know the unification was successful.
// Otherwise we will fall back to the heterogeneous type codepath.
if ty.IsListType() {
return ty, convs
}
case setCt > 0 && (setCt+dynamicCt) == len(types):
return unifyCollectionTypes(cty.Set, types, unsafe, dynamicCt > 0)
case objectCt > 0 && (objectCt+dynamicCt) == len(types):
return unifyObjectTypes(types, unsafe, dynamicCt > 0)
case tupleCt > 0 && (tupleCt+dynamicCt) == len(types):
return unifyTupleTypes(types, unsafe, dynamicCt > 0)
case objectCt > 0 && tupleCt > 0:
// Can never unify object and tuple types since they have incompatible kinds
return cty.NilType, nil
}
}
prefOrder := sortTypes(types)
// sortTypes gives us an order where earlier items are preferable as
// our result type. We'll now walk through these and choose the first
// one we encounter for which conversions exist for all source types.
conversions := make([]Conversion, len(types))
Preferences:
for _, wantTypeIdx := range prefOrder {
wantType := types[wantTypeIdx]
for i, tryType := range types {
if i == wantTypeIdx {
// Don't need to convert our wanted type to itself
conversions[i] = nil
continue
}
if tryType.Equals(wantType) {
conversions[i] = nil
continue
}
if unsafe {
conversions[i] = GetConversionUnsafe(tryType, wantType)
} else {
conversions[i] = GetConversion(tryType, wantType)
}
if conversions[i] == nil {
// wantType is not a suitable unification type, so we'll
// try the next one in our preference order.
continue Preferences
}
}
return wantType, conversions
}
// If we fall out here, no unification is possible
return cty.NilType, nil
}
// unifyTuplesAsList attempts to first see if the tuples unify as lists, then
// re-unifies the given types with the list in place of the tuples.
func unifyTuplesAsList(types []cty.Type, unsafe bool) (cty.Type, []Conversion) {
var tuples []cty.Type
var tupleIdxs []int
for i, t := range types {
if t.IsTupleType() {
tuples = append(tuples, t)
tupleIdxs = append(tupleIdxs, i)
}
}
ty, tupleConvs := unifyTupleTypesToList(tuples, unsafe)
if !ty.IsListType() {
return cty.NilType, nil
}
// the tuples themselves unified as a list, get the overall
// unification with this list type instead of the tuple.
// make a copy of the types, so we can fallback to the standard
// codepath if something went wrong
listed := make([]cty.Type, len(types))
copy(listed, types)
for _, idx := range tupleIdxs {
listed[idx] = ty
}
newTy, convs := unify(listed, unsafe)
if !newTy.IsListType() {
return cty.NilType, nil
}
// we have a good conversion, wrap the nested tuple conversions.
// We know the tuple conversion is not nil, because we went from tuple to
// list
for i, idx := range tupleIdxs {
listConv := convs[idx]
tupleConv := tupleConvs[i]
if listConv == nil {
convs[idx] = tupleConv
continue
}
convs[idx] = func(in cty.Value) (out cty.Value, err error) {
out, err = tupleConv(in)
if err != nil {
return out, err
}
return listConv(in)
}
}
return newTy, convs
}
// unifyObjectsAsMaps attempts to first see if the objects unify as maps, then
// re-unifies the given types with the map in place of the objects.
func unifyObjectsAsMaps(types []cty.Type, unsafe bool) (cty.Type, []Conversion) {
var objs []cty.Type
var objIdxs []int
for i, t := range types {
if t.IsObjectType() {
objs = append(objs, t)
objIdxs = append(objIdxs, i)
}
}
ty, objConvs := unifyObjectTypesToMap(objs, unsafe)
if !ty.IsMapType() {
return cty.NilType, nil
}
// the objects themselves unified as a map, get the overall
// unification with this map type instead of the object.
// Make a copy of the types, so we can fallback to the standard codepath if
// something went wrong without changing the original types.
mapped := make([]cty.Type, len(types))
copy(mapped, types)
for _, idx := range objIdxs {
mapped[idx] = ty
}
newTy, convs := unify(mapped, unsafe)
if !newTy.IsMapType() {
return cty.NilType, nil
}
// we have a good conversion, so wrap the nested object conversions.
// We know the object conversion is not nil, because we went from object to
// map.
for i, idx := range objIdxs {
mapConv := convs[idx]
objConv := objConvs[i]
if mapConv == nil {
convs[idx] = objConv
continue
}
convs[idx] = func(in cty.Value) (out cty.Value, err error) {
out, err = objConv(in)
if err != nil {
return out, err
}
return mapConv(in)
}
}
return newTy, convs
}
func unifyCollectionTypes(collectionType func(cty.Type) cty.Type, types []cty.Type, unsafe bool, hasDynamic bool) (cty.Type, []Conversion) {
// If we had any dynamic types in the input here then we can't predict
// what path we'll take through here once these become known types, so
// we'll conservatively produce DynamicVal for these.
if hasDynamic {
return unifyAllAsDynamic(types)
}
elemTypes := make([]cty.Type, 0, len(types))
for _, ty := range types {
elemTypes = append(elemTypes, ty.ElementType())
}
retElemType, _ := unify(elemTypes, unsafe)
if retElemType == cty.NilType {
return cty.NilType, nil
}
retTy := collectionType(retElemType)
conversions := make([]Conversion, len(types))
for i, ty := range types {
if ty.Equals(retTy) {
continue
}
if unsafe {
conversions[i] = GetConversionUnsafe(ty, retTy)
} else {
conversions[i] = GetConversion(ty, retTy)
}
if conversions[i] == nil {
// Shouldn't be reachable, since we were able to unify
return cty.NilType, nil
}
}
return retTy, conversions
}
func unifyObjectTypes(types []cty.Type, unsafe bool, hasDynamic bool) (cty.Type, []Conversion) {
// If we had any dynamic types in the input here then we can't predict
// what path we'll take through here once these become known types, so
// we'll conservatively produce DynamicVal for these.
if hasDynamic {
return unifyAllAsDynamic(types)
}
// There are two different ways we can succeed here:
// - If all of the given object types have the same set of attribute names
// and the corresponding types are all unifyable, then we construct that
// type.
// - If the given object types have different attribute names or their
// corresponding types are not unifyable, we'll instead try to unify
// all of the attribute types together to produce a map type.
//
// Our unification behavior is intentionally stricter than our conversion
// behavior for subset object types because user intent is different with
// unification use-cases: it makes sense to allow {"foo":true} to convert
// to emptyobjectval, but unifying an object with an attribute with the
// empty object type should be an error because unifying to the empty
// object type would be suprising and useless.
firstAttrs := types[0].AttributeTypes()
for _, ty := range types[1:] {
thisAttrs := ty.AttributeTypes()
if len(thisAttrs) != len(firstAttrs) {
// If number of attributes is different then there can be no
// object type in common.
return unifyObjectTypesToMap(types, unsafe)
}
for name := range thisAttrs {
if _, ok := firstAttrs[name]; !ok {
// If attribute names don't exactly match then there can be
// no object type in common.
return unifyObjectTypesToMap(types, unsafe)
}
}
}
// If we get here then we've proven that all of the given object types
// have exactly the same set of attribute names, though the types may
// differ.
retAtys := make(map[string]cty.Type)
atysAcross := make([]cty.Type, len(types))
for name := range firstAttrs {
for i, ty := range types {
atysAcross[i] = ty.AttributeType(name)
}
retAtys[name], _ = unify(atysAcross, unsafe)
if retAtys[name] == cty.NilType {
// Cannot unify this attribute alone, which means that unification
// of everything down to a map type can't be possible either.
return cty.NilType, nil
}
}
retTy := cty.Object(retAtys)
conversions := make([]Conversion, len(types))
for i, ty := range types {
if ty.Equals(retTy) {
continue
}
if unsafe {
conversions[i] = GetConversionUnsafe(ty, retTy)
} else {
conversions[i] = GetConversion(ty, retTy)
}
if conversions[i] == nil {
// Shouldn't be reachable, since we were able to unify
return unifyObjectTypesToMap(types, unsafe)
}
}
return retTy, conversions
}
func unifyObjectTypesToMap(types []cty.Type, unsafe bool) (cty.Type, []Conversion) {
// This is our fallback case for unifyObjectTypes, where we see if we can
// construct a map type that can accept all of the attribute types.
var atys []cty.Type
for _, ty := range types {
for _, aty := range ty.AttributeTypes() {
atys = append(atys, aty)
}
}
ety, _ := unify(atys, unsafe)
if ety == cty.NilType {
return cty.NilType, nil
}
retTy := cty.Map(ety)
conversions := make([]Conversion, len(types))
for i, ty := range types {
if ty.Equals(retTy) {
continue
}
if unsafe {
conversions[i] = GetConversionUnsafe(ty, retTy)
} else {
conversions[i] = GetConversion(ty, retTy)
}
if conversions[i] == nil {
return cty.NilType, nil
}
}
return retTy, conversions
}
func unifyTupleTypes(types []cty.Type, unsafe bool, hasDynamic bool) (cty.Type, []Conversion) {
// If we had any dynamic types in the input here then we can't predict
// what path we'll take through here once these become known types, so
// we'll conservatively produce DynamicVal for these.
if hasDynamic {
return unifyAllAsDynamic(types)
}
// There are two different ways we can succeed here:
// - If all of the given tuple types have the same sequence of element types
// and the corresponding types are all unifyable, then we construct that
// type.
// - If the given tuple types have different element types or their
// corresponding types are not unifyable, we'll instead try to unify
// all of the elements types together to produce a list type.
firstEtys := types[0].TupleElementTypes()
for _, ty := range types[1:] {
thisEtys := ty.TupleElementTypes()
if len(thisEtys) != len(firstEtys) {
// If number of elements is different then there can be no
// tuple type in common.
return unifyTupleTypesToList(types, unsafe)
}
}
// If we get here then we've proven that all of the given tuple types
// have the same number of elements, though the types may differ.
retEtys := make([]cty.Type, len(firstEtys))
atysAcross := make([]cty.Type, len(types))
for idx := range firstEtys {
for tyI, ty := range types {
atysAcross[tyI] = ty.TupleElementTypes()[idx]
}
retEtys[idx], _ = unify(atysAcross, unsafe)
if retEtys[idx] == cty.NilType {
// Cannot unify this element alone, which means that unification
// of everything down to a map type can't be possible either.
return cty.NilType, nil
}
}
retTy := cty.Tuple(retEtys)
conversions := make([]Conversion, len(types))
for i, ty := range types {
if ty.Equals(retTy) {
continue
}
if unsafe {
conversions[i] = GetConversionUnsafe(ty, retTy)
} else {
conversions[i] = GetConversion(ty, retTy)
}
if conversions[i] == nil {
// Shouldn't be reachable, since we were able to unify
return unifyTupleTypesToList(types, unsafe)
}
}
return retTy, conversions
}
func unifyTupleTypesToList(types []cty.Type, unsafe bool) (cty.Type, []Conversion) {
// This is our fallback case for unifyTupleTypes, where we see if we can
// construct a list type that can accept all of the element types.
var etys []cty.Type
for _, ty := range types {
for _, ety := range ty.TupleElementTypes() {
etys = append(etys, ety)
}
}
ety, _ := unify(etys, unsafe)
if ety == cty.NilType {
return cty.NilType, nil
}
retTy := cty.List(ety)
conversions := make([]Conversion, len(types))
for i, ty := range types {
if ty.Equals(retTy) {
continue
}
if unsafe {
conversions[i] = GetConversionUnsafe(ty, retTy)
} else {
conversions[i] = GetConversion(ty, retTy)
}
if conversions[i] == nil {
// Shouldn't be reachable, since we were able to unify
return unifyObjectTypesToMap(types, unsafe)
}
}
return retTy, conversions
}
func unifyAllAsDynamic(types []cty.Type) (cty.Type, []Conversion) {
conversions := make([]Conversion, len(types))
for i := range conversions {
conversions[i] = func(cty.Value) (cty.Value, error) {
return cty.DynamicVal, nil
}
}
return cty.DynamicPseudoType, conversions
}