Extend hcl2 support with more functions

Signed-off-by: CrazyMax <crazy-max@users.noreply.github.com>

vendor/github.com/zclconf/go-cty/cty/convert/conversion_object.go

@@ -11,17 +11,29 @@ import (
 // type, meaning that each attribute of the output type has a corresponding
 // attribute in the input type where a recursive conversion is available.
 //
+// If the "out" type has any optional attributes, those attributes may be
+// absent in the "in" type, in which case null values will be used in their
+// place in the result.
+//
 // Shallow object conversions work the same for both safe and unsafe modes,
 // but the safety flag is passed on to recursive conversions and may thus
 // limit the above definition of "subset".
 func conversionObjectToObject(in, out cty.Type, unsafe bool) conversion {
 	inAtys := in.AttributeTypes()
 	outAtys := out.AttributeTypes()
+	outOptionals := out.OptionalAttributes()
 	attrConvs := make(map[string]conversion)
 
 	for name, outAty := range outAtys {
 		inAty, exists := inAtys[name]
 		if !exists {
+			if _, optional := outOptionals[name]; optional {
+				// If it's optional then we'll skip inserting an
+				// attribute conversion and then deal with inserting
+				// the default value in our overall conversion logic
+				// later.
+				continue
+			}
 			// No conversion is available, then.
 			return nil
 		}
@@ -71,6 +83,13 @@ func conversionObjectToObject(in, out cty.Type, unsafe bool) conversion {
 			attrVals[name] = val
 		}
 
+		for name := range outOptionals {
+			if _, exists := attrVals[name]; !exists {
+				wantTy := outAtys[name]
+				attrVals[name] = cty.NullVal(wantTy)
+			}
+		}
+
 		return cty.ObjectVal(attrVals), nil
 	}
 }