Allow implicit conversions from String => os.*Path to allow multiple segments if the string is a literal (500USD Bounty)

[lihaoyi]

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From the maintainer Li Haoyi: I'm putting a 500USD bounty on this issue, payable by bank transfer on a merged PR implementing this.

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Currently, os.pwd / "foo/bar/baz" fails. We do this to guard against people accidentally doing os.pwd / myStringValue and accidentally getting path traversal problems and such, and for people to explicitly say os.pwd / os.SubPath(myStringValue) or os.pwd / os.RelPath(myStringValue).

But if the RHS of the / is a literal string, there is no risk, and we should allow people to say os.pwd / "foo/bar/baz" instead of the more verbose os.pwd / "foo" / "bar" / "baz". This can be done by making the implicit conversion from String to SubPath/RelPath a macro that checks whether the RHS is a literal, and if so goes through a different code path that allows it to contain multiple segments automatically

[pawelsadlo]

I will take a look

[pawelsadlo]

@lihaoyi I think it might be possible to do by utilizing scala.ValueOf, and Singleton upper bound, do you require it to be implemented with macro?

[lihaoyi]

@pawelsadlo I'd be ok with non-macro implementations. The main requirement is that it only work for literal strings and that it give some kind of useful error message when used on non-literal strings