Implement stack_v3 as hypothetical substitute for stack, using new head_info().

Also, refactor `stacks()` related code into its own module to shrink `lib.rs`.

Author: Byron

crates/but-workspace/src/branch_details.rs

@@ -6,6 +6,7 @@ use but_core::RefMetadata;
 use gitbutler_command_context::CommandContext;
 use gitbutler_error::error::Code;
 use gitbutler_oxidize::OidExt;
+use gix::reference::Category;
 use gix::remote::Direction;
 use std::collections::HashSet;
 use std::path::Path;
@@ -145,7 +146,8 @@ pub fn branch_details(
 /// This branch is assumed to not be in the workspace, but it will still be assumed to want to integrate with the workspace target reference if set.
 ///
 /// ### Implementation
-#[allow(unused_variables)]
+///
+/// Note that not all possible [`PushStatus`] status are respected.
 pub fn branch_details_v3(
     repo: &gix::Repository,
     name: &gix::refs::FullNameRef,
@@ -197,24 +199,26 @@ pub fn branch_details_v3(
         )?;
         // TODO: have a test that shows why this must/should be last. Then maybe make it easy to do
         //       the right thing whenever the mergebase with the integration branch is needed.
-        merge_bases.last().map(|id| id.detach())
+        merge_bases
+            .last()
+            .map(|id| id.detach())
+            .with_context(|| format!("No merge-base found between {name} and the integration branch {integration_ref_name}", name = name.as_bstr()))?
     };
 
-    todo!()
-    // Ok(ui::BranchDetails {
-    //     name: name.as_bstr().into(),
-    //     remote_tracking_branch: remote_tracking_branch.map(|b| b.name().as_bstr().to_owned()),
-    //     description: meta.description.clone(),
-    //     pr_number: meta.review.pull_request,
-    //     review_id: meta.review.review_id.clone(),
-    //     base_commit: todo!(),
-    //     push_status,
-    //     last_updated_at: todo!(),
-    //     authors: todo!(),
-    //     is_conflicted: todo!(),
-    //     commits: todo!(),
-    //     upstream_commits: todo!(),
-    //     tip: branch_target_id.detach(),
-    //     is_remote_head: name.category() == Some(Category::RemoteBranch),
-    // })
+    Ok(ui::BranchDetails {
+        name: name.as_bstr().into(),
+        remote_tracking_branch: remote_tracking_branch.map(|b| b.name().as_bstr().to_owned()),
+        description: meta.description.clone(),
+        pr_number: meta.review.pull_request,
+        review_id: meta.review.review_id.clone(),
+        base_commit,
+        push_status,
+        last_updated_at: todo!(),
+        authors: todo!(),
+        is_conflicted: todo!(),
+        commits: todo!(),
+        upstream_commits: todo!(),
+        tip: branch_target_id.detach(),
+        is_remote_head: name.category() == Some(Category::RemoteBranch),
+    })
 }