cli: Fix ahead/behind and diff behavior

In certain cases, eg. after a rebase, or when patches are stacked, the
"ahead/behind" and/or the diff stats can be wrong.

This fixes it.

.gitignore

@@ -1 +1,2 @@
 /target
+/radicle-cli/target

radicle-cli/examples/rad-patch-ahead-behind.md

@@ -0,0 +1,118 @@
+In this example, we explore how the `ahead/behind` indicator works, and what is
+shown as diffs in the case of divergent branches.
+
+First we add the `CONTRIBUTORS` file to `master`, which contains one entry:
+```
+$ git checkout -q master
+$ git add CONTRIBUTORS
+$ git commit -a -q -m "Add contributors"
+$ git push rad master
+$ cat CONTRIBUTORS
+Alice Jones
+```
+
+Then we create a feature branch which adds another entry:
+```
+$ git checkout -q -b feature/1
+$ sed -i '$a Alan K' CONTRIBUTORS
+$ git commit -a -q -m "Add Alan"
+```
+
+We go back to master, and add a different second entry, essentially forking
+the history:
+```
+$ git checkout -q master
+$ sed -i '$a Jason Bourne' CONTRIBUTORS
+$ git commit -a -q -m "Add Jason"
+$ git push rad master
+$ git log --graph --decorate --abbrev-commit --pretty=oneline --all
+* 5c88a79 (feature/1) Add Alan
+| * e101a99 (HEAD -> master, rad/master) Add Jason
+|/ [..]
+* f64fb2c Add contributors
+* f2de534 Second commit
+* 08c788d Initial commit
+```
+
+Then we create a patch from `feature/1`:
+``` (stderr)
+$ git push rad feature/1:refs/patches
+✓ Patch 866f59c001cd4d78a151f444b34265566c83c264 opened
+To rad://z42hL2jL4XNk6K8oHQaSWfMgCL7ji/z6MknSLrJoTcukLrE435hVNQT4JUhbvWLX4kUzqkEStBU8Vi
+ * [new reference]   feature/1 -> refs/patches
+```
+
+When listing, we see that it has one addition:
+```
+$ rad patch list
+╭─────────────────────────────────────────────────────────────────────────────╮
+│ ●  ID       Title     Author                  Head     +   -   Updated      │
+├─────────────────────────────────────────────────────────────────────────────┤
+│ ●  866f59c  Add Alan  z6MknSL…StBU8Vi  (you)  5c88a79  +1  -0  [   ...    ] │
+╰─────────────────────────────────────────────────────────────────────────────╯
+```
+
+When showing the patch, we see that it is `ahead 1, behind 1`, since master has
+diverged by one commit:
+```
+$ rad patch show -p 866f59c
+╭────────────────────────────────────────────────────────────────────╮
+│ Title     Add Alan                                                 │
+│ Patch     866f59c001cd4d78a151f444b34265566c83c264                 │
+│ Author    did:key:z6MknSLrJoTcukLrE435hVNQT4JUhbvWLX4kUzqkEStBU8Vi │
+│ Head      5c88a79d75f5c2b4cc51ee6f163d2db91ee198d7                 │
+│ Branches  feature/1                                                │
+│ Commits   ahead 1, behind 1                                        │
+│ Status    open                                                     │
+├────────────────────────────────────────────────────────────────────┤
+│ 5c88a79 Add Alan                                                   │
+├────────────────────────────────────────────────────────────────────┤
+│ ● opened by (you) (z6MknSL…StBU8Vi) [              ...           ] │
+╰────────────────────────────────────────────────────────────────────╯
+
+commit 5c88a79d75f5c2b4cc51ee6f163d2db91ee198d7
+Author: radicle <radicle@localhost>
+Date:   Thu Dec 15 17:28:04 2022 +0000
+
+    Add Alan
+
+diff --git a/CONTRIBUTORS b/CONTRIBUTORS
+index 3f60d25..6829c43 100644
+--- a/CONTRIBUTORS
++++ b/CONTRIBUTORS
+@@ -1 +1,2 @@
+ Alice Jones
++Alan K
+
+```
+
+Then, we stack another change onto `feature/1`, adding another contributor:
+``` (stderr)
+$ git checkout -q -b feature/2 feature/1
+$ sed -i '$a Mel Farna' CONTRIBUTORS
+$ git commit -a -q -m "Add Mel"
+$ git push -o patch.message="Add Mel" rad HEAD:refs/patches
+✓ Patch 57cb9b2758518e547de324456ac967fda456c6c1 opened
+To rad://z42hL2jL4XNk6K8oHQaSWfMgCL7ji/z6MknSLrJoTcukLrE435hVNQT4JUhbvWLX4kUzqkEStBU8Vi
+ * [new reference]   HEAD -> refs/patches
+```
+
+When we look at the patch, we see that it has both commits, because this new
+patch uses the same base as the previous patch:
+```
+$ rad patch show 57cb9b2758518e547de324456ac967fda456c6c1
+╭────────────────────────────────────────────────────────────────────╮
+│ Title     Add Mel                                                  │
+│ Patch     57cb9b2758518e547de324456ac967fda456c6c1                 │
+│ Author    did:key:z6MknSLrJoTcukLrE435hVNQT4JUhbvWLX4kUzqkEStBU8Vi │
+│ Head      7f63fcbcf23fc39eea784c091ad3d20d7e4bd005                 │
+│ Branches  feature/2                                                │
+│ Commits   ahead 2, behind 1                                        │
+│ Status    open                                                     │
+├────────────────────────────────────────────────────────────────────┤
+│ 7f63fcb Add Mel                                                    │
+│ 5c88a79 Add Alan                                                   │
+├────────────────────────────────────────────────────────────────────┤
+│ ● opened by (you) (z6MknSL…StBU8Vi) 5 months ago                   │
+╰────────────────────────────────────────────────────────────────────╯
+```

radicle-cli/src/commands/patch/common.rs

@@ -1,6 +1,6 @@
 use anyhow::{anyhow, Context};
 
-use radicle::cob::patch::{Clock, MergeTarget, Patch, PatchId, Patches};
+use radicle::cob::patch::{Clock, Patch, PatchId, Patches};
 use radicle::git;
 use radicle::git::raw::Oid;
 use radicle::prelude::*;
@@ -52,22 +52,6 @@ pub fn get_merge_target(
     Ok((get_branch(qualified_ref), (*target_oid).into()))
 }
 
-/// Return the [`Oid`] of the merge target.
-pub fn patch_merge_target_oid(target: MergeTarget, repository: &Repository) -> anyhow::Result<Oid> {
-    match target {
-        MergeTarget::Delegates => {
-            if let Ok((_, target)) = repository.head() {
-                Ok(*target)
-            } else {
-                anyhow::bail!(
-                    "failed to determine default branch head for project {}",
-                    repository.id,
-                );
-            }
-        }
-    }
-}
-
 /// Get the diff stats between two commits.
 pub fn diff_stats(
     repo: &git::raw::Repository,

radicle-cli/src/commands/patch/list.rs

@@ -98,7 +98,8 @@ pub fn row(
 ) -> anyhow::Result<[term::Line; 9]> {
     let state = patch.state();
     let (_, revision) = patch.latest();
-    let stats = common::diff_stats(repository.raw(), revision.base(), &revision.head())?;
+    let (from, to) = patch.range(repository)?;
+    let stats = common::diff_stats(repository.raw(), &from, &to)?;
     let author = patch.author().id;
 
     Ok([

radicle-cli/src/commands/patch/show.rs

@@ -10,17 +10,15 @@ use radicle_term::{
 
 use crate::terminal as term;
 
-use super::common::*;
 use super::*;
 
-fn show_patch_diff(patch: &patch::Patch, storage: &Repository) -> anyhow::Result<()> {
-    let target_head = patch_merge_target_oid(patch.target(), storage)?;
-    let base_oid = storage.raw().merge_base(target_head, **patch.head())?;
-    let diff = format!("{}..{}", base_oid, patch.head());
+fn show_patch_diff(patch: &patch::Patch, stored: &Repository) -> anyhow::Result<()> {
+    let (from, to) = patch.range(stored)?;
+    let range = format!("{}..{}", from, to);
 
     process::Command::new("git")
-        .current_dir(storage.path())
-        .args(["log", "--patch", &diff])
+        .current_dir(stored.path())
+        .args(["log", "--patch", &range])
         .stdout(process::Stdio::inherit())
         .stderr(process::Stdio::inherit())
         .spawn()?
@@ -30,7 +28,8 @@ fn show_patch_diff(patch: &patch::Patch, storage: &Repository) -> anyhow::Result
 }
 
 fn patch_commits(patch: &patch::Patch, stored: &Repository) -> anyhow::Result<Vec<term::Line>> {
-    let range = format!("{}..{}", patch.base(), patch.head());
+    let (from, to) = patch.range(stored)?;
+    let range = format!("{}..{}", from, to);
 
     let mut revwalk = stored.revwalk(*patch.head())?;
     let mut lines = Vec::new();
@@ -67,8 +66,11 @@ pub fn run(
     let (_, revision) = patch.latest();
     let state = patch.state();
     let branches = common::branches(&revision.head(), workdir)?;
-    let target_head = common::patch_merge_target_oid(patch.target(), stored)?;
-    let ahead_behind = common::ahead_behind(stored.raw(), revision.head().into(), target_head)?;
+    let ahead_behind = common::ahead_behind(
+        stored.raw(),
+        *revision.head(),
+        *patch.target().head(stored)?,
+    )?;
 
     let mut attrs = Table::<2, term::Line>::new(TableOptions {
         spacing: 2,

radicle-cli/tests/commands.rs

@@ -1,6 +1,6 @@
-use std::env;
 use std::path::Path;
 use std::str::FromStr;
+use std::{env, fs};
 use std::{thread, time};
 
 use radicle::git;
@@ -276,6 +276,28 @@ fn rad_patch() {
     test("examples/rad-patch.md", working.path(), Some(home), []).unwrap();
 }
 
+#[test]
+fn rad_patch_ahead_behind() {
+    let mut environment = Environment::new();
+    let profile = environment.profile("alice");
+    let working = tempfile::tempdir().unwrap();
+    let home = &profile.home;
+
+    // Setup a test repository.
+    fixtures::repository(working.path());
+
+    fs::write(working.path().join("CONTRIBUTORS"), "Alice Jones\n").unwrap();
+
+    test("examples/rad-init.md", working.path(), Some(home), []).unwrap();
+    test(
+        "examples/rad-patch-ahead-behind.md",
+        working.path(),
+        Some(home),
+        [],
+    )
+    .unwrap();
+}
+
 #[test]
 fn rad_patch_draft() {
     let mut environment = Environment::new();

radicle/src/cob/patch.rs

@@ -24,6 +24,7 @@ use crate::cob::thread::Thread;
 use crate::cob::{store, ActorId, EntryId, ObjectId, TypeName};
 use crate::crypto::{PublicKey, Signer};
 use crate::git;
+use crate::identity;
 use crate::identity::doc::DocError;
 use crate::identity::PayloadError;
 use crate::prelude::*;
@@ -155,6 +156,18 @@ pub enum MergeTarget {
     Delegates,
 }
 
+impl MergeTarget {
+    /// Get the head of the target branch.
+    pub fn head<R: ReadRepository>(&self, repo: &R) -> Result<git::Oid, identity::IdentityError> {
+        match self {
+            MergeTarget::Delegates => {
+                let (_, target) = repo.head()?;
+                Ok(target)
+            }
+        }
+    }
+}
+
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub struct Patch {
     /// Title of the patch.
@@ -290,6 +303,28 @@ impl Patch {
         &self.latest().1.base
     }
 
+    /// Get the merge base of this patch.
+    pub fn merge_base<R: ReadRepository>(&self, repo: &R) -> Result<git::Oid, git::ext::Error> {
+        let target = self.target().head(repo).map_err(|_| {
+            git::ext::Error::NotFound(git::ext::NotFound::NoSuchBranch(String::from("HEAD")))
+        })?;
+        let base = repo.merge_base(&target, self.head())?;
+
+        Ok(base)
+    }
+
+    /// Get the commit range of this patch.
+    pub fn range<R: ReadRepository>(
+        &self,
+        repo: &R,
+    ) -> Result<(git::Oid, git::Oid), git::ext::Error> {
+        if self.is_merged() {
+            Ok((*self.base(), *self.head()))
+        } else {
+            Ok((self.merge_base(repo)?, *self.head()))
+        }
+    }
+
     /// Index of latest revision in the revisions list.
     pub fn version(&self) -> RevisionIx {
         self.revisions
@@ -320,6 +355,11 @@ impl Patch {
         self.latest().1.timestamp()
     }
 
+    /// Check if the patch is merged.
+    pub fn is_merged(&self) -> bool {
+        matches!(self.state(), State::Merged { .. })
+    }
+
     /// Check if the patch is open.
     pub fn is_open(&self) -> bool {
         matches!(self.state(), State::Open { .. })

radicle/src/storage.rs

@@ -437,6 +437,9 @@ pub trait ReadRepository {
 
     /// Get the repository's identity document at a specific commit.
     fn identity_doc_at(&self, head: Oid) -> Result<identity::Doc<Unverified>, DocError>;
+
+    /// Get the merge base of two commits.
+    fn merge_base(&self, left: &Oid, right: &Oid) -> Result<Oid, git::ext::Error>;
 }
 
 /// Allows read-write access to a repository.

radicle/src/storage/git.rs

@@ -595,6 +595,13 @@ impl ReadRepository for Repository {
         }
         Ok(longest.into())
     }
+
+    fn merge_base(&self, left: &Oid, right: &Oid) -> Result<Oid, ext::Error> {
+        self.backend
+            .merge_base(**left, **right)
+            .map(Oid::from)
+            .map_err(ext::Error::from)
+    }
 }
 
 impl WriteRepository for Repository {

radicle/src/test/storage.rs

@@ -233,6 +233,10 @@ impl ReadRepository for MockRepository {
     fn canonical_identity_head(&self) -> Result<Oid, IdentityError> {
         Ok(Oid::from_str("cccccccccccccccccccccccccccccccccccccccc").unwrap())
     }
+
+    fn merge_base(&self, _left: &Oid, _right: &Oid) -> Result<Oid, git::ext::Error> {
+        todo!()
+    }
 }
 
 impl WriteRepository for MockRepository {