basic infrastructure for delegate implementation (#427)

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

@@ -1,11 +1,69 @@
+use git::revision::spec::parse::{delegate, Delegate};
 use git_repository as git;
+use git_repository::bstr::BStr;
+use git_repository::hash::Prefix;
+use git_repository::revision::spec::parse::delegate::{PeelTo, ReflogLookup, SiblingBranch, Traversal};
+use git_repository::revision::spec::Kind;
 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(())
+struct Explain<'a> {
+    out: &'a mut dyn std::io::Write,
+}
+
+impl<'a> delegate::Revision for Explain<'a> {
+    fn find_ref(&mut self, name: &BStr) -> Option<()> {
+        todo!()
+    }
+
+    fn disambiguate_prefix(&mut self, prefix: Prefix) -> Option<()> {
+        todo!()
+    }
+
+    fn reflog(&mut self, query: ReflogLookup) -> Option<()> {
+        todo!()
+    }
+
+    fn nth_checked_out_branch(&mut self, branch_no: usize) -> Option<()> {
+        todo!()
+    }
+
+    fn sibling_branch(&mut self, kind: SiblingBranch) -> Option<()> {
+        todo!()
+    }
+}
+
+impl<'a> delegate::Navigate for Explain<'a> {
+    fn traverse(&mut self, kind: Traversal) -> Option<()> {
+        todo!()
+    }
+
+    fn peel_until(&mut self, kind: PeelTo<'_>) -> Option<()> {
+        todo!()
+    }
+
+    fn find(&mut self, regex: &BStr, negated: bool) -> Option<()> {
+        todo!()
+    }
+
+    fn index_lookup(&mut self, path: &BStr, stage: u8) -> Option<()> {
+        todo!()
+    }
+}
+
+impl<'a> delegate::Kind for Explain<'a> {
+    fn kind(&mut self, kind: Kind) -> Option<()> {
+        todo!()
+    }
+}
+
+impl<'a> Delegate for Explain<'a> {
+    fn done(&mut self) {
+        todo!()
+    }
+}
+
+pub fn explain(_repo: git::Repository, spec: OsString, mut out: impl std::io::Write) -> anyhow::Result<()> {
+    let mut explain = Explain { out: &mut out };
+    let spec = git::path::os_str_into_bstr(&spec)?;
+    git::revision::spec::parse(spec, &mut explain).map_err(anyhow::Error::from)
 }

src/plumbing/main.rs

@@ -167,9 +167,7 @@ pub fn main() -> Result<()> {
                         progress,
                         progress_keep_open,
                         None,
-                        move |_progress, out, err| {
-                            core::repository::revision::explain(repository.into(), spec, out, err)
-                        },
+                        move |_progress, out, _err| core::repository::revision::explain(repository.into(), spec, out),
                     ),
                 },
                 repo::Subcommands::Commit { cmd } => match cmd {