Check datasource validity on loading.

[xCodeMuse]

The Problem

Currently the dynamic fn [in case of datasource as fn] script of task is not evaluated/compiled beforehand, when it uses inputs or outputs like references which are available during a workflow call (runtime only).
But for other cases where datasource name is statically given or the dynamic fn uses mappings or config we can evaluate and check validaity of those in the load time itself. generating the fn in functionloader to check if datasource is available or not.

The Solution

Evaluate script beforehand and check if datasource is present in fn as datasource of tasks of a workflow.

How will we solve

• Make changes in the core functionloader.ts file and make required changes to evaluate the fn script before checking the datasource validation success. [ commented the code for now ]
• Ensure that loaded datasource is a valid datasource (load time checks). The cases to cover are
  • fn: <js% datasource.<% config.hello %>.dynamodb.listTables %>
  • fn: datasource.<% config.hello %>.dynamodb.listTables
  • fn: <% mappings.datasourcename.for.dbcall %> fn: <% config.datasourcename.for.dbcall %>
  • fn: datasource.<%mappings[outputs.create_lender_api_request.data.request_data.headers['pl-product']][outputs.create_lender_api_request.data.request_data.headers['pl-lender']].lender_api_suit[outputs.create_lender_api_request.data.request_data.params?.wrapper_event].datasource%>.get.<%outputs.path_params_url.data.updated_url%>
• In expandVariables during loadTime, when an error occurs in script evaluation, check whether the script was using outputs. or inputs. don't log this - because this will be evaluated in runtime. Otherwise process.exit(1) with a fatal log message.

[ghost]

@xCodeMuse Please follow this design to check these cases:

Step-1: check if task.fn starts with 'datasource.'
    step 1.1: if <% %> is present in task.fn then do expandVariable
    step 1.2: check if <% %> is still present in the expanded variable. 
        step 1.2.1: If yes, then skip checking datasource name, as the expanded variable might have dynamic variables like inputs/outputs.
        step 1.2.2: else check datasource name and return false if datasource name not found in the datasources.
Step-2: else
    step 2.1: if <% %> is present task.fn, then do expandVariable
    step 2.2: After expandVariable, check if task.fn starts with 'datasource.' 
        step 2.2.1: If yes, then repeat Step-1 for this case.
return true