Incorrect space sanitization for shell creation

[sqlrob]

Environment

> [Environment]::OSVersion

Platform ServicePack Version      VersionString
-------- ----------- -------      -------------
 Win32NT             10.0.18363.0 Microsoft Windows NT 10.0.18363.0

Terminal version 0.8.10091.0

Steps to reproduce

1. Create a file C:\Program, contents irrelevant; this applies to en-us, other languages will have different names.
2. Open a powershell tab (other shells may have the issue, didn't check)

Expected behavior

Tab opens with a usable Powershell

Actual behavior

Window opens with the message

[error 0x800700c1 when launching `powershell.exe']

[DHowett-MSFT]

(For the shell,)
This is, and always will be, how CreateProcess with search path expansion works. Sorry.

• We're relying on the system to do PATH resolution
• If we implement our own heuristics here, we have to expand PATH and PATHEXT to properly populate the first arg to CreateProcess.
• Even if we fix this, other applications will fail in the same way.
• You need to be an admin to make a file there; there are far easier ways to break Terminal

(For the console host,)
This was fixed by #4172, which will be in the next servicing update... which may make this a /dup of #4061

[ghost]

Hi! We've identified this issue as a duplicate of another one that already exists on this Issue Tracker. This specific instance is being closed in favor of tracking the concern over on the referenced thread. Thanks for your report!

[sqlrob]

Shells are in well defined locations. Why is PATH even being used?

[DHowett-MSFT]

I'm not sure I agree that shells are in well-defined locations- A user's entitled to reorganize PATH such that their preferred instance of pwsh.exe comes first, or so that they can set version priorities for OpenSSH. Shells are wherever the user wants to put them!

[eryksun]

* If we implement our own heuristics here, we have to expand `PATH` _and_ `PATHEXT` to properly populate the first arg to `CreateProcess`.

CreateProcessW doesn't use PATHEXT. It calls SearchPathW with an optional ".EXE" extension.

[DHowett-MSFT]

Fair enough.