pkgdown::deploy_to_branch creates malformed URLs

[jwimberl]

The function pkgdown::deploy_to_branch modifes the URL provided by the user by extending it by the specified build subdirectory:

https://github.com/r-lib/pkgdown/blob/c40ba2c989e786bbb2829b431114d26375bbe19a/R/deploy-site.R#L147-L149

When the URL starts with a protocol, as it should, the fs::path method will replace the double forward slash with a single one, turning a valid URL like https://www.hostname.org into http:/www.hostname.org.

I think the behavior of automatically appending the subdir argument to the URL is also an issue:

• This equates the documented intent of subdir, a filesystem directory within the gh-pages branch in which the generated code tracked, with the URL location at which the documentation will be served. A user may very well want to keep the documentation in a docs/ subfolder in the gh-pages branch, but not serve the documentation at a URL that has to end in /docs/
• This leads to inconsistent behavior with pkgdown::build_site(...) and other methods: a setting for url that works for one will generate incorrect absolute URLs with the other. I think there are various good reasons that the generated HTML and links should be identical whichever build method is used. For one, build_site(...) is useful for checking for issues before calling deploy_to_branch(...), since the latter makes a git commit before the generated HTML could be previewed.