Whitelist TERMINFO environment variable

[jacwah]

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The TERMINFO environment variable is used by ncurses et al to find files describing current terminal's capabilities (see e.g. man ncurses). When the variable is filtered out, code using ncurses down the line gets confused if the terminal is not included in the default termcap database. An example of this is the "Cannot read termcap database; using dumb terminal settings" message described in #4527. This is written by libedit, loaded from irb, loaded from debrew. With this patch the message is not printed any more.

An alternative solution is to place termcap files under ~/.terminfo instead. Some terminals do not do this by default, for instance Kitty.

[MikeMcQuaid]

Can you provide the exact reproduction case for this?

[jacwah]

To reproduce:

1. Use a terminal that does not have its termcap database distributed with ncurses, but has a termcap database located at $TERMINFO. In my case, I am using Kitty with TERMINFO=/Applications/kitty.app/Contents/Frameworks/kitty/terminfo. This is the default setup for this particular terminal emulator.
2. Run a Homebrew install command, for instance brew install (without arguments).
3. The message "Cannot read termcap database; using dumb terminal settings" is written to stderr.

If readline was actually being used, this would probably lead to weird behavior like backspace not working etc, as ncurses would not know how to interact with the terminal.

When TERMINFO is whitelisted, this message does not appear.

I traced this message to the initialization of libedit (terminal.c). As you can see, it is written when ncurses does not find a termcap for the current $TERM. On my machine, the ruby readline module uses libedit under the hood:

> Readline::VERSION
=> "EditLine wrapper"

As mentioned in the OP, readline is transitively required by debrew.rb.

[MikeMcQuaid]

Which if any of those variables are customised from the application default values?

[jacwah]

No variables are customized. As I said, I am using the default setup for the application.

[MikeMcQuaid]

Cool, seems reasonable. Thanks so much for your first contribution! Without people like you submitting PRs we couldn't run this project. You rock, @jacwah!

[smancill]

@jacwah TERMINFO_DIRS should also be whitelisted. Otherwise the error mentioned in #4527 doesn't go away on all possible cases.

[maxim-belkin]

@smancill, if you can provide a reproducible scenario when this is necessary -- submit a PR! 😉