REPL shell mode for Windows

[musm]

supersedes https://github.com/JuliaLang/julia/pull/31490/files

[vtjnash]

Could you help land #30614? That’s generally what has prevented this PR from happening thus far.

[mgkuhn]

I'm note sure my code in #30614 is actually applicable for passing a command-line to CMD.EXE itself. It is only of use to get strings past CMD.EXE, to one of the EXE applications that then parse the command-line they received using the Microsoft C (CommandLineToArgvW) conventions (including Julia.EXE). The code in #30614 is not at all of use for passing shell command lines to any other applications that do not use CommandLineToArgvW, including for example all built-in commands of CMD.EXE itself.

Rather than playing around with escaping, I suspect REPL Shell mode needs to work fundamentally different on platforms (such as Windows) that invoke other processes with a single command line, rather than an ARGV array. I suspect this misunderstanding may have stalled progress here.

[musm]

@mgkuhn Your comment is a bit confusing to me.

Let me try to clarify my interpretation of how things should and do work. Feel free to correct me if I have said something incorrect.

The repl shell mode in julia essentially is supposed to act like running commands through the julia function run(Cmd("hello") or more simply run(command). As such it has to first go through Base.shell_split and other machinery to interpolate julia variables (in particular).

Now to have a reasonably functioning "repl" mode (I put it in quotes, since it's not a true repl mode in the sense of opening up cmd.exe and running commands in there). We need to join these arguments back into a single string according to the "inverse" rules that CommandLineToArgvW uses, which is now implemented by the function winsomely in #33465 . This then gives us a single string we can pass to cmd.exe, but we also need to take care to escape special characters for cmd.exe to avoid any security issues that the julia "repl" mode could have by users messing around in the environment, such as modifying environment variables etc. and thus we sanitize the input my running the single string through other escaping function that are specific to cmd.exe or powershell.exe .