Support externally supplying a terminal width when running outside a tty

[Nemo157]

Please complete the following tasks

• I have searched the discussions
• I have searched the open and rejected issues

Clap Version

v3.2.20

Describe your use case

I am attempting to verify my readme contains the latest version of the help text from my utility. To do so I need an appropriately widthed help text to compare against (and auto-update from).

Describe the solution you'd like

I'm not sure what the best interface for this would be. One thought I had was to obey the COLUMNS variable if that is set and the output is not a tty, that would make text="$(COLUMNS=60 cargo run -- --help)" work fine.

Alternatives, if applicable

Locally I found a way to get a sub-tty with a limited width

script -q -c 'sh -c "stty cols 60 && cargo run -q -- --help"' $(mktemp)

but unfortunately that doesn't work in GitHub Actions for some unknown reason.

Additional Context

No response

[epage]

Already terminal_size doesn't do detection if STDOUT is not a tty:

Another option is to not use If STDOUT is not a tty, returns None

Is that sufficient or something going wrong with it? Or are you wanting a different fallback terminal width?

Also, as a workaround, you can implement this all yourself by calling terminal_size directly and setting term_width under the specific circumstances for your app.

[Nemo157]

Or are you wanting a different fallback terminal width?

Yes, this; I want to override the fallback terminal width in my script to have a consistent width no matter what terminal I'm running under.

Also, as a workaround, you can implement this all yourself

Yep, it doesn't seem too hard (just misses out on a lot of the Parser nicities to be able to override the derive). I just feel like it's pretty common to include --help output into a readme, where the default 100 column fallback is far too wide, so surely there must be other people running into this.

[epage]

Yes, this; I want to override the fallback terminal width in my script to have a consistent width no matter what terminal I'm running under.

In my initial research on this, it sounded like COLUMNS isn't actually env-variable but is instead something built directly into some shells that some users forward on to the environment and that application support is very half-hazard. This made me less interested in supporting it.

Then I saw it suggested in https://clig.dev and saw it used in git which makes me feel more comfortable in supporting it.

The question is what should the level of precedence be?

1. COLUMNS
2. `terminal_size``
3. default

or

1. `terminal_size``
2. COLUMNS
3. default

[epage]

Also, I feel safer putting this into clap v4 rather than clap v3 (if we make the release window)