V7.0 dev ds.colnames

[timcadman]

Instructions & checklist for PR author

Description of changes

• Refactored ds.colnames to remove checks
• Added two helper functions in utils.r: .set_datasources and .check_df_name_provided
• Replaced checks in ds.colnames with these helper functions

Refactor instructions

• Removed exists and isDefined from clientside function and add appropriate checks on server-side function
• Removed any client-side code checking whether an object has been successfully created
• Reviewed code to determine if additional refactoring could reduce calls to server-side package
• Replaced check relating to datashield connections object with .set_datasources() (defined in utils.r)
• If relevant, replaced argument check that dataset name has been provided to .check_df_name_provided() (defined in utils.r)

Testing instructions

• Writen server-side unit tests for unhappy flow
• Run devtools::test(filter = "smk-|disc|arg") and check it passes
• Run devtools::check(args = '--no-tests') and check it passes (we run tests separately to skip performance checks)
• Run devtools::build() and check it builds without errors

Instructions & checklist for PR reviewers

• Run devtools::test(filter = "smk-|disc|arg") and check it passes
• Run devtools::check(args = '--no-tests') and check it passes (we run tests separately to skip performance checks)
• Run devtools::build() and check it builds without errors