feat: add gix free discover to inform about repository discovery.

It's mainly to better understand what's causing certain failures
if a repository can't be opened, in different modes of operations.

gitoxide-core/src/discover.rs

@@ -0,0 +1,59 @@
+use std::path::Path;
+
+pub fn discover(repo: &Path, mut out: impl std::io::Write) -> anyhow::Result<()> {
+    let mut has_err = false;
+    writeln!(out, "open (strict) {}:", repo.display())?;
+    has_err |= print_result(
+        &mut out,
+        gix::open_opts(repo, gix::open::Options::default().strict_config(true)),
+    )?;
+
+    if has_err {
+        writeln!(out, "open (lenient) {}:", repo.display())?;
+        has_err |= print_result(
+            &mut out,
+            gix::open_opts(repo, gix::open::Options::default().strict_config(false)),
+        )?;
+    }
+
+    writeln!(out)?;
+    writeln!(out, "discover from {}:", repo.display())?;
+    has_err |= print_result(&mut out, gix::discover(repo))?;
+
+    writeln!(out)?;
+    writeln!(out, "discover (plumbing) from {}:", repo.display())?;
+    has_err |= print_result(&mut out, gix::discover::upwards(repo))?;
+
+    if has_err {
+        writeln!(out)?;
+        anyhow::bail!("At least one operation failed")
+    }
+
+    Ok(())
+}
+
+fn print_result<T, E>(mut out: impl std::io::Write, res: Result<T, E>) -> std::io::Result<bool>
+where
+    T: std::fmt::Debug,
+    E: std::error::Error + Send + Sync + 'static,
+{
+    let mut has_err = false;
+    let to_print = match res {
+        Ok(good) => {
+            format!("{good:#?}")
+        }
+        Err(err) => {
+            has_err = true;
+            format!("{:?}", anyhow::Error::from(err))
+        }
+    };
+    indent(&mut out, to_print)?;
+    Ok(has_err)
+}
+
+fn indent(mut out: impl std::io::Write, msg: impl Into<String>) -> std::io::Result<()> {
+    for line in msg.into().lines() {
+        writeln!(out, "\t{line}")?;
+    }
+    Ok(())
+}

gitoxide-core/src/lib.rs

@@ -79,5 +79,8 @@ pub mod pack;
 pub mod query;
 pub mod repository;
 
+mod discover;
+pub use discover::discover;
+
 #[cfg(all(feature = "async-client", feature = "blocking-client"))]
 compile_error!("Cannot set both 'blocking-client' and 'async-client' features as they are mutually exclusive");

src/plumbing/main.rs

@@ -72,6 +72,7 @@ pub fn main() -> Result<()> {
     let object_hash = args.object_hash;
     let config = args.config;
     let repository = args.repository;
+    let repository_path = repository.clone();
     enum Mode {
         Strict,
         StrictWithGitInstallConfig,
@@ -449,6 +450,15 @@ pub fn main() -> Result<()> {
         )
         .map(|_| ()),
         Subcommands::Free(subcommands) => match subcommands {
+            free::Subcommands::Discover => prepare_and_run(
+                "discover",
+                trace,
+                verbose,
+                progress,
+                progress_keep_open,
+                None,
+                move |_progress, out, _err| core::discover(&repository_path, out),
+            ),
             free::Subcommands::CommitGraph(cmd) => match cmd {
                 free::commitgraph::Subcommands::Verify { path, statistics } => prepare_and_run(
                     "commitgraph-verify",

src/plumbing/options/free.rs

@@ -14,6 +14,8 @@ pub enum Subcommands {
     Pack(pack::Subcommands),
     /// Subcommands for interacting with a worktree index, typically at .git/index
     Index(index::Platform),
+    /// Show information about repository discovery and when opening a repository at the current path.
+    Discover,
 }
 
 ///