Prevent parseUTF8 from overwriting srcfile attribute

[meztez]

Fix #916, related to parseUTF8 return value attribute srcfile on Windows.

PR task list:

• Update NEWS
• Add tests
• Update documentation with devtools::document()

[ArcadeAntics]

This fixes the issue of the source file pointing to the correct file, but on other operating systems you've basically made a srcfilecopy just for parse to overwrite it with the exact same input. You need to directly supply keep.source = FALSE always, on every OS, for all possible encodings. You're losing all the work done by readUTF8 by throwing out those lines.

[ArcadeAntics]

Yes, perfect! Thank you so much!

[meztez]

This fixes the issue of the source file pointing to the correct file, but you've basically made a srcfilecopy just for parse to overwrite it with the exact same input. You need to directly supply keep.source = FALSE always.

I saw that, I thought maybe there was a reason for it? I will let @schloerke comment on this behaviour since it seems the line came from a commit he authored. I've taken your comment into account for this PR.

Shiny has keep.source set to FALSE with similar instructions in sourceUTF8.
https://github.com/rstudio/shiny/blob/b1297395a9365c97972f243ee492232d70af281f/R/utils.R#L1355

[schloerke]

Yes, this puts us back to parity with Shiny's implementation. Don't know why I deviated in the first place.

Thank you!