simplify response file parsing

[jonsequitur]

Response file parsing can currently be customized by a developer using System.CommandLine using the CommandLineBuilder.ParseRespondFilesAs(ResponseFileHandling) method. The ResponseFileHandling enum provides two modes (in addition to Disabled) but the behavior is not apparent to end users, and is occasionally surprising.

The proposal is to support only a single response file parsing behavior by removing the existing methods and supporting only enable/disable. The new behavior would follow these rules:

• Multiple-line files will be parsed treating newlines as equivalent to spaces.
• Multiple tokens on a single line will be parsed as though passed verbatim on the command line.
  • Including a space within a token will now require enclosing the token in quotes, e.g. "this is one token".
  • Shell-specific escaping of quotes will not be required.
• Allow comment lines using a # prefix at the beginning of the line

Open questions:

• How should quotation marks be escaped?

[KathleenDollard]

What's the prior art. Multiple double quotes in C# and & in HTML?

[jonsequitur]

It's inconsistent, with minor differences even among Microsoft implementations. Documentation is a bit sparse. I couldn't find any mention of escape syntax.

https://docs.microsoft.com/en-us/dotnet/visual-basic/reference/command-line-compiler/specify-response-file
https://docs.microsoft.com/en-us/cpp/build/reference/at-specify-a-compiler-response-file?view=msvc-170
https://docs.microsoft.com/en-us/visualstudio/msbuild/msbuild-response-files?view=vs-2022
https://docs.microsoft.com/en-us/visualstudio/install/automated-installation-with-response-file?view=vs-2022
https://docs.microsoft.com/en-us/windows/win32/midl/response-files#:~:text=A%20response%20file%20is%20a,convenience%20for%20your%20build%20process.

[marek-safar]

This is a breaking change that breaks .net6 servicing builds. Was it really intentional when there is no version bump?