fix: roundtrip BODY JSON FROM \$var on consumed REST operations

Rest\$JsonBody.Value was always written as the empty string and never
read back, so DESCRIBE REST CLIENT showed an empty BODY clause after
roundtrip. Pass the body expression through serializeRestBody and read
it back in parseRestBody so 'BODY JSON FROM \$JsonBody' survives a
write/read cycle and Mendix mx check reports 0 errors.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: ako

sdk/mpr/parser_rest.go

@@ -227,8 +227,12 @@ func parseRestBody(bodyVal any, op *model.RestClientOperation) {
 		op.BodyType = "JSON"
 	case "Rest$JsonBody":
 		op.BodyType = "JSON"
+		op.BodyVariable = extractString(bodyMap["Value"])
 	case "Rest$StringBody":
 		op.BodyType = "FILE" // StringBody with template is used for file uploads
+		if vt := extractBsonMap(bodyMap["ValueTemplate"]); vt != nil {
+			op.BodyVariable = extractString(vt["Value"])
+		}
 	}
 }
 

sdk/mpr/writer_rest.go

@@ -177,7 +177,7 @@ func serializeRestMethod(op *model.RestClientOperation) bson.M {
 			"$Type":      "Rest$RestOperationMethodWithBody",
 			"HttpMethod": httpMethod,
 		}
-		doc["Body"] = serializeRestBody(op.BodyType)
+		doc["Body"] = serializeRestBody(op.BodyType, op.BodyVariable)
 		return doc
 	}
 
@@ -189,7 +189,7 @@ func serializeRestMethod(op *model.RestClientOperation) bson.M {
 			"$Type":      "Rest$RestOperationMethodWithBody",
 			"HttpMethod": httpMethod,
 		}
-		doc["Body"] = serializeRestBody("JSON")
+		doc["Body"] = serializeRestBody("JSON", op.BodyVariable)
 		return doc
 	}
 
@@ -204,25 +204,29 @@ func serializeRestMethod(op *model.RestClientOperation) bson.M {
 // serializeRestBody creates a polymorphic Body field.
 // Uses Rest$JsonBody instead of Rest$ImplicitMappingBody to avoid CE7247/CE0061
 // (ImplicitMappingBody requires entity mapping which isn't supported yet).
-func serializeRestBody(bodyType string) bson.M {
+//
+// bodyExpr is a Mendix expression (typically "$variableName") that produces
+// the JSON or file body at call time. It is stored verbatim in the BSON Value
+// field so a roundtrip preserves it.
+func serializeRestBody(bodyType, bodyExpr string) bson.M {
 	switch strings.ToUpper(bodyType) {
 	case "JSON":
 		return bson.M{
 			"$ID":   idToBsonBinary(generateUUID()),
 			"$Type": "Rest$JsonBody",
-			"Value": "",
+			"Value": bodyExpr,
 		}
 	case "FILE":
 		return bson.M{
 			"$ID":           idToBsonBinary(generateUUID()),
 			"$Type":         "Rest$StringBody",
-			"ValueTemplate": serializeValueTemplate(""),
+			"ValueTemplate": serializeValueTemplate(bodyExpr),
 		}
 	default:
 		return bson.M{
 			"$ID":   idToBsonBinary(generateUUID()),
 			"$Type": "Rest$JsonBody",
-			"Value": "",
+			"Value": bodyExpr,
 		}
 	}
 }