Create til::env to help with refreshing environment variables

[miniksa]

Summary of the Pull Request

References

PR Checklist

• Closes #xxx
• CLA signed. If not, go over here and sign the CLA
• Tests added/passed
• Documentation updated. If checked, please file a pull request on our docs repo and link it here: #xxx
• Schema updated.
• I've discussed this with core contributors already. If not checked, I'm ready to accept this work might be rejected in favor of a different grand plan. Issue number where discussion took place: #xxx

Detailed Description of the Pull Request / Additional comments

Validation Steps Performed

[miniksa]

@lhecker this can be yours now if you want it.

[github-actions]

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[ianjoneill]

I've added a commit to this on my fork of the terminal that no longer extends from std::map - https://github.com/ianjoneill/terminal/tree/dev/miniksa/env. Should I open another MR or is there some way of linking my branch with this MR?

[ianjoneill]

I take it this method needs implementing as follows - or is this too naive?

Iterate through the string - append characters to a "return" buffer until you find a percent character. At this point start appending the characters to a "key" buffer instead. When you find a "closing" percent, look the key up in the map. If found, append the looked up value to the return buffer, otherwise append the key as was (including the percent characters), then reset the state. If at the end there's stuff left in the key buffer, append it to the return buffer (including a literal percent character at the beginning).

Test cases:

1. "Foo%ENV%Baz" with an environment variable %ENV% defined as "Bar" would result in the string "FooBarBaz".
2. "Foo%ENV%Baz" with no %ENV% variable would result in the string "Foo%ENV%Baz".
3. "Foo%ENV" would result in the string "Foo%ENV".

[KalleOlaviNiemitalo]

How about "Foo%Baz%ENV%" with an %ENV% variable but no %Baz% variable? CMD seems to expand %ENV% in that situation, but I don't know what ExpandEnvironmentStringsW does.

[zadjii-msft]

I've added a commit to this on my fork of the terminal that no longer extends from std::map - ianjoneill/terminal@dev/miniksa/env. Should I open another MR or is there some way of linking my branch with this MR?

Honestly, I'd recommend just filing a new one, I think that'd be the easiest way to iterate and get this in. Thanks!

[DHowett]

Superseded by @ianjoneill's (excellent) work. Thanks Michael!