feat(cli): Support -C

src/bin/git-stack/args.rs

@@ -58,6 +58,20 @@ pub struct Args {
     #[clap(long, group = "mode")]
     pub protect: Option<String>,
 
+    /// Run as if git was started in `PATH` instead of the current working directory.
+    ///
+    /// When multiple -C options are given, each subsequent
+    /// non-absolute -C <path> is interpreted relative to the preceding -C <path>. If <path> is present but empty, e.g.  -C "", then the
+    /// current working directory is left unchanged.
+    ///
+    /// This option affects options that expect path name like --git-dir and --work-tree in that their interpretations of the path names
+    /// would be made relative to the working directory caused by the -C option. For example the following invocations are equivalent:
+    ///
+    ///     git --git-dir=a.git --work-tree=b -C c status
+    ///     git --git-dir=c/a.git --work-tree=c/b status
+    #[clap(short = 'C', hide = true, value_name = "PATH", parse(from_os_str))]
+    pub current_dir: Option<Vec<std::path::PathBuf>>,
+
     /// Write the current configuration to file with `-` for stdout
     #[clap(long, parse(from_os_str), group = "mode")]
     pub dump_config: Option<std::path::PathBuf>,

src/bin/git-stack/main.rs

@@ -3,6 +3,7 @@
 #![allow(clippy::if_same_then_else)]
 
 use clap::Parser;
+use proc_exit::WithCodeResultExt;
 
 mod args;
 mod config;
@@ -35,6 +36,16 @@ fn run() -> proc_exit::ExitResult {
 
     logger::init_logging(args.verbose.clone(), colored_stderr);
 
+    if let Some(current_dir) = args.current_dir.as_deref() {
+        let current_dir = current_dir
+            .iter()
+            .fold(std::path::PathBuf::new(), |current, next| {
+                current.join(next)
+            });
+        log::trace!("CWD={}", current_dir.display());
+        std::env::set_current_dir(current_dir).with_code(proc_exit::Code::USAGE_ERR)?;
+    }
+
     if let Some(output_path) = args.dump_config.as_deref() {
         config::dump_config(&args, output_path)?;
     } else if let Some(ignore) = args.protect.as_deref() {