package funcs import ( "fmt" "github.com/hashicorp/terraform/tfdiags" "github.com/zclconf/go-cty/cty" "github.com/zclconf/go-cty/cty/convert" "github.com/zclconf/go-cty/cty/function" ) // DefaultsFunc is a helper function for substituting default values in // place of null values in a given data structure. // // See the documentation for function Defaults for more information. var DefaultsFunc = function.New(&function.Spec{ Params: []function.Parameter{ { Name: "input", Type: cty.DynamicPseudoType, AllowNull: true, }, { Name: "defaults", Type: cty.DynamicPseudoType, }, }, Type: func(args []cty.Value) (cty.Type, error) { // The result type is guaranteed to be the same as the input type, // since all we're doing is replacing null values with non-null // values of the same type. retType := args[0].Type() defaultsType := args[1].Type() // This function is aimed at filling in object types or collections // of object types where some of the attributes might be null, so // it doesn't make sense to use a primitive type directly with it. // (The "coalesce" function may be appropriate for such cases.) if retType.IsPrimitiveType() { // This error message is a bit of a fib because we can actually // apply defaults to tuples too, but we expect that to be so // unusual as to not be worth mentioning here, because mentioning // it would require using some less-well-known Terraform language // terminology in the message (tuple types, structural types). return cty.DynamicPseudoType, function.NewArgErrorf(1, "only object types and collections of object types can have defaults applied") } defaultsPath := make(cty.Path, 0, 4) // some capacity so that most structures won't reallocate if err := defaultsAssertSuitableFallback(retType, defaultsType, defaultsPath); err != nil { errMsg := tfdiags.FormatError(err) // add attribute path prefix return cty.DynamicPseudoType, function.NewArgErrorf(1, "%s", errMsg) } return retType, nil }, Impl: func(args []cty.Value, retType cty.Type) (cty.Value, error) { if args[0].Type().HasDynamicTypes() { // If the types our input object aren't known yet for some reason // then we'll defer all of our work here, because our // interpretation of the defaults depends on the types in // the input. return cty.UnknownVal(retType), nil } v := defaultsApply(args[0], args[1]) return v, nil }, }) func defaultsApply(input, fallback cty.Value) cty.Value { const fallbackArgIdx = 1 wantTy := input.Type() if !(input.IsKnown() && fallback.IsKnown()) { return cty.UnknownVal(wantTy) } // For the rest of this function we're assuming that the given defaults // will always be valid, because we expect to have caught any problems // during the type checking phase. Any inconsistencies that reach here are // therefore considered to be implementation bugs, and so will panic. // Our strategy depends on the kind of type we're working with. switch { case wantTy.IsPrimitiveType(): // For leaf primitive values the rule is relatively simple: use the // input if it's non-null, or fallback if input is null. if !input.IsNull() { return input } v, err := convert.Convert(fallback, wantTy) if err != nil { // Should not happen because we checked in defaultsAssertSuitableFallback panic(err.Error()) } return v case wantTy.IsObjectType(): atys := wantTy.AttributeTypes() ret := map[string]cty.Value{} for attr, aty := range atys { inputSub := input.GetAttr(attr) fallbackSub := cty.NullVal(aty) if fallback.Type().HasAttribute(attr) { fallbackSub = fallback.GetAttr(attr) } ret[attr] = defaultsApply(inputSub, fallbackSub) } return cty.ObjectVal(ret) case wantTy.IsTupleType(): l := wantTy.Length() ret := make([]cty.Value, l) for i := 0; i < l; i++ { inputSub := input.Index(cty.NumberIntVal(int64(i))) fallbackSub := fallback.Index(cty.NumberIntVal(int64(i))) ret[i] = defaultsApply(inputSub, fallbackSub) } return cty.TupleVal(ret) case wantTy.IsCollectionType(): // For collection types we apply a single fallback value to each // element of the input collection, because in the situations this // function is intended for we assume that the number of elements // is the caller's decision, and so we'll just apply the same defaults // to all of the elements. ety := wantTy.ElementType() switch { case wantTy.IsMapType(): newVals := map[string]cty.Value{} for it := input.ElementIterator(); it.Next(); { k, v := it.Element() newVals[k.AsString()] = defaultsApply(v, fallback) } if len(newVals) == 0 { return cty.MapValEmpty(ety) } return cty.MapVal(newVals) case wantTy.IsListType(), wantTy.IsSetType(): var newVals []cty.Value for it := input.ElementIterator(); it.Next(); { _, v := it.Element() newV := defaultsApply(v, fallback) newVals = append(newVals, newV) } if len(newVals) == 0 { if wantTy.IsSetType() { return cty.SetValEmpty(ety) } return cty.ListValEmpty(ety) } if wantTy.IsSetType() { return cty.SetVal(newVals) } return cty.ListVal(newVals) default: // There are no other collection types, so this should not happen panic(fmt.Sprintf("invalid collection type %#v", wantTy)) } default: // We should've caught anything else in defaultsAssertSuitableFallback, // so this should not happen. panic(fmt.Sprintf("invalid target type %#v", wantTy)) } } func defaultsAssertSuitableFallback(wantTy, fallbackTy cty.Type, fallbackPath cty.Path) error { // If the type we want is a collection type then we need to keep peeling // away collection type wrappers until we find the non-collection-type // that's underneath, which is what the fallback will actually be applied // to. inCollection := false for wantTy.IsCollectionType() { wantTy = wantTy.ElementType() inCollection = true } switch { case wantTy.IsPrimitiveType(): // The fallback is valid if it's equal to or convertible to what we want. if fallbackTy.Equals(wantTy) { return nil } conversion := convert.GetConversionUnsafe(fallbackTy, wantTy) if conversion == nil { msg := convert.MismatchMessage(fallbackTy, wantTy) return fallbackPath.NewErrorf("invalid default value for %s: %s", wantTy.FriendlyName(), msg) } return nil case wantTy.IsObjectType(): if !fallbackTy.IsObjectType() { if inCollection { return fallbackPath.NewErrorf("the default value for a collection of an object type must itself be an object type, not %s", fallbackTy.FriendlyName()) } return fallbackPath.NewErrorf("the default value for an object type must itself be an object type, not %s", fallbackTy.FriendlyName()) } for attr, wantAty := range wantTy.AttributeTypes() { if !fallbackTy.HasAttribute(attr) { continue // it's always okay to not have a default value } fallbackSubpath := fallbackPath.GetAttr(attr) fallbackSubTy := fallbackTy.AttributeType(attr) err := defaultsAssertSuitableFallback(wantAty, fallbackSubTy, fallbackSubpath) if err != nil { return err } } for attr := range fallbackTy.AttributeTypes() { if !wantTy.HasAttribute(attr) { fallbackSubpath := fallbackPath.GetAttr(attr) return fallbackSubpath.NewErrorf("target type does not expect an attribute named %q", attr) } } return nil case wantTy.IsTupleType(): if !fallbackTy.IsTupleType() { if inCollection { return fallbackPath.NewErrorf("the default value for a collection of a tuple type must itself be a tuple type, not %s", fallbackTy.FriendlyName()) } return fallbackPath.NewErrorf("the default value for a tuple type must itself be a tuple type, not %s", fallbackTy.FriendlyName()) } wantEtys := wantTy.TupleElementTypes() fallbackEtys := fallbackTy.TupleElementTypes() if got, want := len(wantEtys), len(fallbackEtys); got != want { return fallbackPath.NewErrorf("the default value for a tuple type of length %d must also have length %d, not %d", want, want, got) } for i := 0; i < len(wantEtys); i++ { fallbackSubpath := fallbackPath.IndexInt(i) wantSubTy := wantEtys[i] fallbackSubTy := fallbackEtys[i] err := defaultsAssertSuitableFallback(wantSubTy, fallbackSubTy, fallbackSubpath) if err != nil { return err } } return nil default: // No other types are supported right now. return fallbackPath.NewErrorf("cannot apply defaults to %s", wantTy.FriendlyName()) } } // Defaults is a helper function for substituting default values in // place of null values in a given data structure. // // This is primarily intended for use with a module input variable that // has an object type constraint (or a collection thereof) that has optional // attributes, so that the receiver of a value that omits those attributes // can insert non-null default values in place of the null values caused by // omitting the attributes. func Defaults(input, defaults cty.Value) (cty.Value, error) { return DefaultsFunc.Call([]cty.Value{input, defaults}) }