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