57 lines
2.4 KiB
Go
57 lines
2.4 KiB
Go
|
// Package customdecode contains a HCL extension that allows, in certain
|
||
|
|
// contexts, expression evaluation to be overridden by custom static analysis.
|
||
|
|
//
|
||
|
|
// This mechanism is only supported in certain specific contexts where
|
||
|
|
// expressions are decoded with a specific target type in mind. For more
|
||
|
|
// information, see the documentation on CustomExpressionDecoder.
|
||
|
|
package customdecode
|
||
|
|
|
||
|
|
import (
|
||
|
|
"github.com/hashicorp/hcl/v2"
|
||
|
|
"github.com/zclconf/go-cty/cty"
|
||
|
|
)
|
||
|
|
|
||
|
|
type customDecoderImpl int
|
||
|
|
|
||
|
|
// CustomExpressionDecoder is a value intended to be used as a cty capsule
|
||
|
|
// type ExtensionData key for capsule types whose values are to be obtained
|
||
|
|
// by static analysis of an expression rather than normal evaluation of that
|
||
|
|
// expression.
|
||
|
|
//
|
||
|
|
// When a cooperating capsule type is asked for ExtensionData with this key,
|
||
|
|
// it must return a non-nil CustomExpressionDecoderFunc value.
|
||
|
|
//
|
||
|
|
// This mechanism is not universally supported; instead, it's handled in a few
|
||
|
|
// specific places where expressions are evaluated with the intent of producing
|
||
|
|
// a cty.Value of a type given by the calling application.
|
||
|
|
//
|
||
|
|
// Specifically, this currently works for type constraints given in
|
||
|
|
// hcldec.AttrSpec and hcldec.BlockAttrsSpec, and it works for arguments to
|
||
|
|
// function calls in the HCL native syntax. HCL extensions implemented outside
|
||
|
|
// of the main HCL module may also implement this; consult their own
|
||
|
|
// documentation for details.
|
||
|
|
const CustomExpressionDecoder = customDecoderImpl(1)
|
||
|
|
|
||
|
|
// CustomExpressionDecoderFunc is the type of value that must be returned by
|
||
|
|
// a capsule type handling the key CustomExpressionDecoder in its ExtensionData
|
||
|
|
// implementation.
|
||
|
|
//
|
||
|
|
// If no error diagnostics are returned, the result value MUST be of the
|
||
|
|
// capsule type that the decoder function was derived from. If the returned
|
||
|
|
// error diagnostics prevent producing a value at all, return cty.NilVal.
|
||
|
|
type CustomExpressionDecoderFunc func(expr hcl.Expression, ctx *hcl.EvalContext) (cty.Value, hcl.Diagnostics)
|
||
|
|
|
||
|
|
// CustomExpressionDecoderForType takes any cty type and returns its
|
||
|
|
// custom expression decoder implementation if it has one. If it is not a
|
||
|
|
// capsule type or it does not implement a custom expression decoder, this
|
||
|
|
// function returns nil.
|
||
|
|
func CustomExpressionDecoderForType(ty cty.Type) CustomExpressionDecoderFunc {
|
||
|
|
if !ty.IsCapsuleType() {
|
||
|
|
return nil
|
||
|
|
}
|
||
|
|
if fn, ok := ty.CapsuleExtensionData(CustomExpressionDecoder).(CustomExpressionDecoderFunc); ok {
|
||
|
|
return fn
|
||
|
|
}
|
||
|
|
return nil
|
||
|
|
}
|