feat: implement physical and logical cwd

[39555]

After diving into the system's paths rabbit hole for a while, I've implemented cross-platform cwd handling for the shell, along with support for cd -L -P and pwd -L -P.

Closes: #202

With this PR, the shell now maintains the logical current working directory alongside with the physical one. To correctly create an absolute path and expand all .. and . from the logical path, the functions have been added to the brush_core::sys::fs crate:

• expand_tilde_with_home - expands the tilde using the given home directory
• make_absolute - makes the path absolute based on the given base path.
• normalize_lexically - performs canonicalization without touching the filesystem.

Posix notes:

There is a special handling for paths with double slashes, such as //users/home

If a pathname begins with two successive characters, the first component following the leading characters may be interpreted in an implementation-defined manner, although more than two leading characters shall be treated as a single character.

See: https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap04.html#tag_04_13

Windows notes

There is a lot of special handling for Windows weird path formats:

• UNC \\server\share\my_dir.
• Verbatim paths \\?\C$\super_path, this paths must not be normalized.
• Device namespace \\.\Pipe and UNC with the device namespace \\.\UNC\.
• volume relative C:iamrelative.

See: https://learn.microsoft.com/en-us/dotnet/standard/io/file-path-formats
See: The book of windows file path: https://chrisdenton.github.io/omnipath/

I've written a lot of tests, trying to cover all the special cases.

[github-actions]

Performance Benchmark Report

Benchmark name	Baseline (μs)	Test/PR (μs)	Delta (μs)	Delta %
expand_one_string	3.42 μs	3.57 μs	0.15 μs	🟠 +4.27%
instantiate_shell	59.72 μs	70.61 μs	10.89 μs	🟠 +18.24%
instantiate_shell_with_init_scripts	31137.02 μs	30989.98 μs	-147.04 μs	⚪ Unchanged
parse_bash_completion	2829.91 μs	2702.85 μs	-127.05 μs	⚪ Unchanged
parse_sample_script	4.31 μs	4.16 μs	-0.15 μs	🟢 -3.48%
run_echo_builtin_command	90.77 μs	102.49 μs	11.72 μs	🟠 +12.91%
run_one_builtin_command	109.48 μs	122.58 μs	13.10 μs	🟠 +11.97%
run_one_external_command	1991.67 μs	1956.48 μs	-35.19 μs	🟢 -1.77%
run_one_external_command_directly	1017.00 μs	1017.80 μs	0.80 μs	⚪ Unchanged

Code Coverage Report: Only Changed Files listed

Package	Base Coverage	New Coverage	Difference
brush-core/src/builtins/cd.rs	🟢 81.82%	🟢 82.61%	🟢 0.79%
brush-core/src/builtins/dirs.rs	🟢 85.71%	🟢 88.1%	🟢 2.39%
brush-core/src/builtins/pwd.rs	🟢 80.95%	🟢 83.33%	🟢 2.38%
brush-core/src/interp.rs	🟢 90.02%	🟢 90.01%	🔴 -0.01%
brush-core/src/patterns.rs	🟢 97.77%	🟢 97.78%	🟢 0.01%
brush-core/src/shell.rs	🟢 77.97%	🟢 80.03%	🟢 2.06%
brush-core/src/sys/fs.rs	🔴 0%	🟢 97.04%	🟢 97.04%
brush-shell/src/main.rs	🟢 90.2%	🟢 90.85%	🟢 0.65%
Overall Coverage	🟢 73.41%	🟢 74.13%	🟢 0.72%

Minimum allowed coverage is 70%, this run produced 74.13%

[reubeno]

Thanks for diving deep into this; I'll need a bit of time to review the changes here. Is there a reasonable way to break this up into multiple, smaller changes?

[39555]

I don't think so, maybe cd and pwd, but they just call the new shell api Shell.set_current_working_dir_from_logical.

All changes are based on the new Cwd type instead of PathBuf for Shell.working_dir. Cwd contains both a physical PathBuf and a logical PathBuf. When we set a new cwd with Shell.set_current_working_dir_from_logical, the path should be normalized but without using syscalls (for preserving symlinks):

1. expand tilde
2. make it absolute based on our current physical or logical cwd
3. expand dots

For startup cwd Inside Shell::new, we try to get the logical path from the PWD environment variable if it is present.

In other changed files, such as dirs or interp, I fixed the usage of working_dir to use the physical path for now. This should be addressed in other PRs if completion needs the logical path instead.