Use R files for background process

[ElianHugh]

Resolves #781

• Moves R process commands from inline text to R scripts
• Use environment variables to pass values to the scripts (as per @renkun-ken's suggestion)
• No user-facing changes

Why?

In general, easier to maintain:

• Easier to read
• Easier to test!
• Less pain re: quoting
• More extensible

Changes

• Move R-related session files to R/session
• Move getAliases.R to R/help
• New file helpServer.R in R/help
• New file knit.R in R/rmarkdown
• New file preview.R in R/rmarkdown

---

• I looked at other uses of childProcesses, but I'm not 100% at what point we should use a file vs. inline text.
• Tested on WSL (Ubuntu) and Arch Linux

[renkun-ken]

Should we also make it for the R help server at

vscode-R/src/helpViewer/helpProvider.ts

Lines 42 to 45 in 4d6a663

	const cmd = (
	`${this.rPath} --silent --slave --no-save --no-restore -e ` +
	`"cat('${lim}', tools::startDynamicHelp(), '${lim}', sep=''); while(TRUE) Sys.sleep(1)" `
	);

[ElianHugh]

Should we also make it for the R help server at

vscode-R/src/helpViewer/helpProvider.ts

Lines 42 to 45 in 4d6a663

	const cmd = (
	`${this.rPath} --silent --slave --no-save --no-restore -e ` +
	`"cat('${lim}', tools::startDynamicHelp(), '${lim}', sep=''); while(TRUE) Sys.sleep(1)" `
	);

I wasn't sure at what point/complexity we should create files. Do we think all background processes?

[renkun-ken]

I think we should put a script if the command line has multiple expressions or needs quoting.

[renkun-ken]

Also, do we really need the background folder? Will the following look better or more confusing?

• R/help/getAliases.R
• R/help/server.R
• R/rmarkdown/knit.R
• R/rmarkdown/preview.R

[ElianHugh]

Also, do we really need the background folder? Will the following look better or more confusing?

* `R/help/getAliases.R`

* `R/help/server.R`

* `R/rmarkdown/knit.R`

* `R/rmarkdown/preview.R`

I was thinking the background folder, because I wanted to distinguish it from the session-watcher related files. Would it make more sense to have the following?

• R/rmarkdown/
• R/help/
• R/session/

[renkun-ken]

Would it make more sense to have the following?

Makes good sense.

[ElianHugh]

I've moved the session files to R/session! Everything should work as before -- just double checking if I caught everything

[renkun-ken]

Everything works well.
LGTM