Restore original TTY state after Sandbox

[sullivan-sean]

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Fixes #11984

This PR switches from the current method of using raw! and then cooked! to reset the Sandbox TTY to just using raw which automatically restores the original TTY state (and also is the recommended method in the docs). Using this approach the TTY state should always be properly restored, including the echonl and istrip flags that are not currently reset in all cases.

[MikeMcQuaid]

Thanks, looks good so far! Could you add more comments here explaining what's being done and why? Thanks!

[sullivan-sean]

To add some more context, the current behavior on 3.2.10 is that the TTY state is modified by the sandbox when installing a package with brew install and are not properly reset afterwards. This can result in unexpected artifacts in a user's terminal after running brew install, such as an extra newline being printed before running each command.

Current behavior

On my machine I see the following differences in stty -a before and after running brew install:

% stty -a | grep echonl
lflags: icanon isig iexten echo echoe echok echoke -echonl echoctl
% brew install tree-sitter
==> Downloading https://ghcr.io/v2/homebrew/core/tree-sitter/manifests/0.20.0-1
Already downloaded: /Users/seansullivan/Library/Caches/Homebrew/downloads/caf4df26418c0c4664fed59578fe8257f590731241bbbc342433585a2bab3694--tree-sitter-0.20.0-1.bottle_manifest.json
==> Downloading https://ghcr.io/v2/homebrew/core/tree-sitter/blobs/sha256:cbf44029649cea921fe333454
Already downloaded: /Users/seansullivan/Library/Caches/Homebrew/downloads/e30e408fcc1bd5715be4a06aefd102e2e64d2209249d2fec6f41c7d3d115b0c1--tree-sitter--0.20.0.arm64_big_sur.bottle.1.tar.gz
==> Pouring tree-sitter--0.20.0.arm64_big_sur.bottle.1.tar.gz
🍺  /opt/homebrew/Cellar/tree-sitter/0.20.0: 18 files, 12.6MB
% stty -a | grep echonl

lflags: icanon isig iexten echo echoe echok echoke echonl echoctl

The echonl flag is OFF (-echonl) in the stty -a output before hand and ON afterwards, which has the side effect of an extra newline before the output of every command in this TTY after running brew install.

Proposed Solution

In tracking down the source of this changed behavior in 3.2.10, I found it was related to the io/console Ruby gem, which was not used by Homebrew until #11914. In particular, the change to start the sandbox in a PTY requires setting the parent TTY to "raw" mode to be able to pass through input such as terminal escape codes directly to the parent TTY. The approach in #11914 is to set the TTY to "raw" mode with io.raw! method and to restore the original TTY state with the io.cooked! method.

This PR changes the Sandbox PTY to use the io.raw method from io/console instead of io.raw!. The documentation for io.raw! highlights io.raw as the preferred method for properly restoring the original TTY state.

While the current approach with io.raw! might work in some cases (i.e. when the original TTY state exactly matches that of io.cooked!), using io.raw will work in all cases.

[carlocab]

Thanks for the clear explanation -- can we summarise that a little and add that in comments in the code?

[MikeMcQuaid]

Thanks so much for your first contribution! Without people like you submitting PRs we couldn't run this project. You rock, @sullivan-sean!