94 lines
3.8 KiB
Go
94 lines
3.8 KiB
Go
package funcs
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import (
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"strconv"
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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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// MakeToFunc constructs a "to..." function, like "tostring", which converts
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// its argument to a specific type or type kind.
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//
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// The given type wantTy can be any type constraint that cty's "convert" package
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// would accept. In particular, this means that you can pass
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// cty.List(cty.DynamicPseudoType) to mean "list of any single type", which
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// will then cause cty to attempt to unify all of the element types when given
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// a tuple.
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func MakeToFunc(wantTy cty.Type) function.Function {
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return function.New(&function.Spec{
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Params: []function.Parameter{
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{
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Name: "v",
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// We use DynamicPseudoType rather than wantTy here so that
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// all values will pass through the function API verbatim and
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// we can handle the conversion logic within the Type and
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// Impl functions. This allows us to customize the error
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// messages to be more appropriate for an explicit type
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// conversion, whereas the cty function system produces
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// messages aimed at _implicit_ type conversions.
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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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Type: func(args []cty.Value) (cty.Type, error) {
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gotTy := args[0].Type()
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if gotTy.Equals(wantTy) {
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return wantTy, nil
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}
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conv := convert.GetConversionUnsafe(args[0].Type(), wantTy)
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if conv == nil {
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// We'll use some specialized errors for some trickier cases,
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// but most we can handle in a simple way.
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switch {
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case gotTy.IsTupleType() && wantTy.IsTupleType():
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return cty.NilType, function.NewArgErrorf(0, "incompatible tuple type for conversion: %s", convert.MismatchMessage(gotTy, wantTy))
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case gotTy.IsObjectType() && wantTy.IsObjectType():
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return cty.NilType, function.NewArgErrorf(0, "incompatible object type for conversion: %s", convert.MismatchMessage(gotTy, wantTy))
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default:
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return cty.NilType, function.NewArgErrorf(0, "cannot convert %s to %s", gotTy.FriendlyName(), wantTy.FriendlyNameForConstraint())
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}
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}
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// If a conversion is available then everything is fine.
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return wantTy, nil
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},
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Impl: func(args []cty.Value, retType cty.Type) (cty.Value, error) {
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// We didn't set "AllowUnknown" on our argument, so it is guaranteed
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// to be known here but may still be null.
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ret, err := convert.Convert(args[0], retType)
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if err != nil {
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// Because we used GetConversionUnsafe above, conversion can
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// still potentially fail in here. For example, if the user
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// asks to convert the string "a" to bool then we'll
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// optimistically permit it during type checking but fail here
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// once we note that the value isn't either "true" or "false".
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gotTy := args[0].Type()
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switch {
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case args[0].ContainsMarked():
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// Generic message so we won't inadvertently disclose
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// information about sensitive values.
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return cty.NilVal, function.NewArgErrorf(0, "cannot convert this sensitive %s to %s", gotTy.FriendlyName(), wantTy.FriendlyNameForConstraint())
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case gotTy == cty.String && wantTy == cty.Bool:
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what := "string"
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if !args[0].IsNull() {
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what = strconv.Quote(args[0].AsString())
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}
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return cty.NilVal, function.NewArgErrorf(0, `cannot convert %s to bool; only the strings "true" or "false" are allowed`, what)
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case gotTy == cty.String && wantTy == cty.Number:
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what := "string"
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if !args[0].IsNull() {
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what = strconv.Quote(args[0].AsString())
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}
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return cty.NilVal, function.NewArgErrorf(0, `cannot convert %s to number; given string must be a decimal representation of a number`, what)
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default:
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return cty.NilVal, function.NewArgErrorf(0, "cannot convert %s to %s", gotTy.FriendlyName(), wantTy.FriendlyNameForConstraint())
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}
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}
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return ret, nil
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},
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})
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}
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