chore(vendor): add anyhow crate

third_party/crates/clap-4.6.7/examples/pacman.md

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+[`pacman`](https://wiki.archlinux.org/index.php/pacman) defines subcommands via flags.
+
+Here, `-S` is a short flag subcommand:
+```console
+$ pacman -S package
+Installing package...
+
+```
+
+Here `--sync` is a long flag subcommand:
+```console
+$ pacman --sync package
+Installing package...
+
+```
+
+Now the short flag subcommand (`-S`) with a long flag:
+```console
+$ pacman -S --search name
+Searching for name...
+
+```
+
+And the various forms of short flags that work:
+```console
+$ pacman -S -s name
+Searching for name...
+
+$ pacman -Ss name
+Searching for name...
+
+```
+*(users can "stack" short subcommands with short flags or with other short flag subcommands)*
+
+In the help, this looks like:
+```console
+$ pacman -h
+package manager utility
+
+Usage: pacman[EXE] <COMMAND>
+
+Commands:
+  query, -Q, --query  Query the package database.
+  sync, -S, --sync    Synchronize packages.
+  help                Print this message or the help of the given subcommand(s)
+
+Options:
+  -h, --help     Print help
+  -V, --version  Print version
+
+$ pacman -S -h
+Synchronize packages.
+
+Usage: pacman[EXE] {sync|--sync|-S} [OPTIONS] [package]...
+
+Arguments:
+  [package]...  packages
+
+Options:
+  -s, --search <search>...  search remote repositories for matching strings
+  -i, --info                view package information
+  -h, --help                Print help
+
+```
+
+And errors:
+```console
+$ pacman -S -s foo -i bar
+? failed
+error: the argument '--search <search>...' cannot be used with '--info'
+
+Usage: pacman[EXE] {sync|--sync|-S} --search <search>... <package>...
+
+For more information, try '--help'.
+
+```
+
+<div class="warning">
+
+**NOTE:** Keep in mind that subcommands, flags, and long flags are *case sensitive*: `-Q` and `-q` are different flags/subcommands. For example, you can have both `-Q` subcommand and `-q` flag, and they will be properly disambiguated.
+Let's make a quick program to illustrate.
+
+</div>
+
+## Reviewing help output
+
+The test renders every command's long help.
+Each Markdown heading contains the complete command path.
+Generated `help` subcommands are skipped.
+`term_width(0)` prevents terminal-dependent wrapping.
+
+[`snapbox`](https://docs.rs/snapbox) compares this output with a snapshot.
+The resulting diff makes CLI changes easy to review.
+Set `SNAPSHOTS=overwrite` to accept intentional changes.