Hookup explain command (#427)

gitoxide-core/src/repository/mod.rs

@@ -12,6 +12,8 @@ pub mod tree;
 
 pub mod commit;
 
+pub mod revision;
+
 pub mod verify;
 
 pub mod odb;

gitoxide-core/src/repository/revision/explain.rs

@@ -0,0 +1,11 @@
+use git_repository as git;
+use std::ffi::OsString;
+
+pub fn explain(
+    _repo: git::Repository,
+    _spec: OsString,
+    mut _out: impl std::io::Write,
+    mut _err: impl std::io::Write,
+) -> anyhow::Result<()> {
+    Ok(())
+}

gitoxide-core/src/repository/revision/mod.rs

@@ -0,0 +1,2 @@
+mod explain;
+pub use explain::explain;

src/plumbing/main.rs

@@ -161,7 +161,16 @@ pub fn main() -> Result<()> {
             let repository = git::ThreadSafeRepository::discover(repository)?;
             match cmd {
                 repo::Subcommands::Revision { cmd } => match cmd {
-                    repo::revision::Subcommands::Explain { spec: _ } => todo!("describe spec"),
+                    repo::revision::Subcommands::Explain { spec } => prepare_and_run(
+                        "repository-commit-describe",
+                        verbose,
+                        progress,
+                        progress_keep_open,
+                        None,
+                        move |_progress, out, err| {
+                            core::repository::revision::explain(repository.into(), spec, out, err)
+                        },
+                    ),
                 },
                 repo::Subcommands::Commit { cmd } => match cmd {
                     repo::commit::Subcommands::Describe {