Assure we can use different merge bases when showing branch details.

Alternatively, correct the assumption that there is a difference.

crates/gitbutler-branch-actions/src/base.rs

@@ -314,11 +314,12 @@ fn _print_tree(repo: &git2::Repository, tree: &git2::Tree) -> Result<()> {
     Ok(())
 }
 
-// try to update the target branch
-// this means that we need to:
-// determine if what the target branch is now pointing to is mergeable with our current working directory
-// merge the target branch into our current working directory
-// update the target sha
+/// try to update the target branch
+/// this means that we need to:
+/// - determine if what the target branch is now pointing to is mergeable with our current working directory,
+/// - merge the target branch into our current working directory
+/// - update the target sha
+/// - return all conflicting references that were unapplied to avoid the conflict
 pub(crate) fn update_base_branch(
     ctx: &CommandContext,
     perm: &mut WorktreeWritePermission,

crates/gitbutler-branch-actions/src/branch.rs

@@ -428,7 +428,7 @@ pub fn get_branch_listing_details(
     let repo = ctx.repository();
     let branches = list_branches(ctx, None, Some(branch_names))?;
 
-    let (default_target_upstream_commit_id, default_target_merge_base) = {
+    let (default_target_current_upstream_commit_id, default_target_seen_at_last_update) = {
         let target = ctx
             .project()
             .virtual_branches()
@@ -446,12 +446,12 @@ pub fn get_branch_listing_details(
     for branch in branches {
         let other_branch_commit_id = if let Some(virtual_branch) = branch.virtual_branch {
             if virtual_branch.in_workspace {
-                default_target_merge_base
+                default_target_seen_at_last_update
             } else {
-                default_target_upstream_commit_id
+                default_target_current_upstream_commit_id
             }
         } else {
-            default_target_upstream_commit_id
+            default_target_current_upstream_commit_id
         };
         let Ok(base) = repo.merge_base(other_branch_commit_id, branch.head) else {
             continue;

crates/gitbutler-branch-actions/tests/fixtures/for-details.sh

@@ -49,4 +49,7 @@ git clone remote complex-repo
     echo non-virtual-feature >> file
     git commit -am "non-virtual-feat-$round"
   done
+
+  # pretend the remote is at the same state as our local `main`
+  git update-ref refs/remotes/origin/main main
 )

crates/gitbutler-branch-actions/tests/virtual_branches/list_details.rs

@@ -52,12 +52,13 @@ fn many_commits_in_all_branch_types() -> anyhow::Result<()> {
         list[0],
         BranchListingDetails {
             name: "feature".into(),
-            lines_added: 100 + 5,
+            lines_added: 100,
             lines_removed: 0,
             number_of_files: 1,
-            number_of_commits: 100 + 5, /* local tracking branch is merge base */
+            number_of_commits: 100,
             authors: vec![default_author()],
-        }
+        },
+        "local branches use the *current* local tracking branch…"
     );
     assert_eq!(
         list[1],
@@ -66,21 +67,24 @@ fn many_commits_in_all_branch_types() -> anyhow::Result<()> {
             lines_added: 15,
             lines_removed: 0,
             number_of_files: 1,
-            // TODO(ST): why is it also going against the local tracking branch instead of the local `main`?
             number_of_commits: 10 + 5,
             authors: vec![default_author()],
-        }
+        },
+        "…while virtual branches use the 'target' stored when the workspace was last updated.\
+        That way the 'update' of the workspace performs the calculation to put it back on top of \
+        the local tracking branch."
     );
     assert_eq!(
         list[2],
         BranchListingDetails {
             name: "non-virtual-feature".into(),
-            lines_added: 55,
+            lines_added: 50,
             lines_removed: 0,
             number_of_files: 1,
-            number_of_commits: 50 + 5,
+            number_of_commits: 50,
             authors: vec![default_author()],
-        }
+        },
+        "This is a non-virtual brnach, so it sees the local tracking branch as well"
     );
     Ok(())
 }

crates/gitbutler-branch/src/target.rs

@@ -5,12 +5,19 @@ use serde::{ser::SerializeStruct, Deserialize, Deserializer, Serialize, Serializ
 pub struct Target {
     /// The combination of remote name and branch name, i.e. `origin` and `main`.
     /// The remote name is the one used to fetch from.
+    /// It's equivalent to e.g. `refs/remotes/origin/main` , and the type `RemoteRefName`
+    /// stores it as `<remote>` and `<suffix>` so that finding references named `<remote>/<suffix>`
+    /// will typically find the local tracking branch unambiguously.
     pub branch: RemoteRefname,
     /// The URL of the remote behind the symbolic name.
     pub remote_url: String,
-    /// The merge-base between `branch` and the current worktree `HEAD`.
-    // TODO(ST): is it safe/correct to rename this to `merge_base_commit_id`?
-    //           It seems like it, but why was it named just `sha` in the first place?
+    /// The merge-base between `branch` and the current worktree `HEAD` upon first creation,
+    /// but then it's the set to the new destination of e.g. `refs/remotes/origin/main` after
+    /// the remote was fetched. This value is used to determine if there was a change,
+    /// and if the *workspace* needs to be recalculated/rebased against the new commit.
+    // TODO(ST): is it safe/correct to rename this to `branch_target_id`? Should be!
+    //           It's just a bit strange it starts life as merge-base, but maybe it ends
+    //           up the same anyway? Definitely could use a test then.
     pub sha: git2::Oid,
     /// The name of the remote to push to.
     pub push_remote_name: Option<String>,

crates/gitbutler-cli/src/args.rs

@@ -71,6 +71,8 @@ pub mod vbranch {
         },
         /// List all branches that can be relevant.
         ListAll,
+        /// After fetching the target (i.e. local tracking branch), recompute our workspace against it.
+        UpdateTarget,
     }
 }
 

crates/gitbutler-cli/src/command/vbranch.rs

@@ -8,6 +8,11 @@ use gitbutler_project::Project;
 
 use crate::command::debug_print;
 
+pub fn update_target(project: Project) -> Result<()> {
+    let unapplied = VirtualBranchActions.update_base_branch(&project)?;
+    debug_print(unapplied)
+}
+
 pub fn list_all(project: Project) -> Result<()> {
     let ctx = CommandContext::open(&project)?;
     debug_print(list_branches(&ctx, None, None)?)

crates/gitbutler-cli/src/main.rs

@@ -36,6 +36,9 @@ fn main() -> Result<()> {
                     command::vbranch::details(project, names)
                 }
                 Some(vbranch::SubCommands::ListAll) => command::vbranch::list_all(project),
+                Some(vbranch::SubCommands::UpdateTarget) => {
+                    command::vbranch::update_target(project)
+                }
                 None => command::vbranch::list(project),
             }
         }