Code completion

[deepayan]

R has a built-in code completion mechanism (see ?utils::rc.settings) which is not used by RStudio (making it of limited general interest) but is used by several other front-ends, including the Windows / Mac GUIs, ESS, and Jupyter (via the IRkernel package).

The current state of affairs could be improved in many small ways:

• Rgui on Windows does not currently support "fuzzy" completion. This is a backend problem which is conceptually easy to fix but needs some low-level GraphApp coding.

• Completion inside quotes and backquotes could be improved, as can completion involving non-syntactic names; for example, see PR#18479. A solution that works perfectly for all backends may not be feasible, but it would help to at least make a list of what kinds of behaviour would be useful in different contexts, and have settings to activate them.

• There is scope to extend the currently available types of completions, e.g., to support pipeline operators and some kinds of non-standard evaluation (here is a very prelimiary prototype). It is perhaps best to implement this (mostly) as an add-on package, but it would be useful to at least understand what kind of API at the R level will be most useful.