This introduces a syntax for `command` and `initial-command` that allows
the user to specify whether it should be run via `/bin/sh -c` or not.
The syntax is a prefix `direct:` or `shell:` prior to the command,
with no prefix implying a default behavior as documented.
Previously, we unconditionally ran commands via `/bin/sh -c`, primarily
to avoid having to do any shell expansion ourselves. We also leaned on
it as a crutch for PATH-expansion but this is an easy problem compared
to shell expansion.
For the principle of least surprise, this worked well for configurations
specified via the config file, and is still the default. However, these
configurations are also set via the `-e` special flag to the CLI, and it
is very much not the principle of least surprise to have the command run via
`/bin/sh -c` in that scenario since a shell has already expanded all the
arguments and given them to us in a nice separated format. But we had no
way to toggle this behavior.
This commit introduces the ability to do this, and changes the defaults
so that `-e` doesn't shell expand. Further, we also do PATH lookups
ourselves for the non-shell expanded case because thats easy (using
execvpe style extensions but implemented as part of the Zig stdlib). We don't
do path expansion (e.g. `~/`) because thats a shell expansion.
So to be clear, there are no two polar opposite behavioes here with
clear semantics:
1. Direct commands are passed to `execvpe` directly, space separated.
This will not handle quoted strings, environment variables, path
expansion (e.g. `~/`), command expansion (e.g. `$()`), etc.
2. Shell commands are passed to `/bin/sh -c` and will be shell expanded
as per the shell's rules. This will handle everything that `sh`
supports.
In doing this work, I also stumbled upon a variety of smaller
improvements that could be made:
- A number of allocations have been removed from the startup path that
only existed to add a null terminator to various strings. We now
have null terminators from the beginning since we are almost always
on a system that's going to need it anyways.
- For bash shell integration, we no longer wrap the new bash command
in a shell since we've formed a full parsed command line.
- The process of creating the command to execute by termio is now unit
tested, so we can test the various complex cases particularly on
macOS of wrapping commands in the login command.
- `xdg-terminal-exec` on Linux uses the `direct:` method by default
since it is also assumed to be executed via a shell environment.