but branch show command

for insepecting a branch
Show conflicting files and their modifying commits in branch merge check

Previously the merge check listed upstream commits that conflicted, which hid which files were actually in conflict and which commits on each side touched those files. Replace the conflicting-commits model with a conflicting-files model that lists each conflicting file and the commits from the branch and from upstream that modified that file. This improves the merge-check output by focusing on problematic files and showing the concrete commits on both sides that caused the conflict.

Author: schacon

crates/but/src/args.rs

@@ -209,6 +209,68 @@ For examples see `but rub --help`."
     },
 }
 
+impl Subcommands {
+    pub fn to_metrics_command(&self) -> CommandName {
+        use CommandName::*;
+        match self {
+            Subcommands::Log => Log,
+            Subcommands::Status { .. } => Status,
+            Subcommands::Stf { .. } => Stf,
+            Subcommands::Rub { .. } => Rub,
+            Subcommands::Base(base::Platform { cmd }) => match cmd {
+                base::Subcommands::Update => BaseUpdate,
+                base::Subcommands::Check => BaseCheck,
+            },
+            Subcommands::Branch(branch::Platform { cmd }) => match cmd {
+                None | Some(branch::Subcommands::List { .. }) => BranchList,
+                Some(branch::Subcommands::New { .. }) => BranchNew,
+                Some(branch::Subcommands::Delete { .. }) => BranchDelete,
+                Some(branch::Subcommands::Unapply { .. }) => BranchUnapply,
+                Some(branch::Subcommands::Apply { .. }) => BranchApply,
+                Some(branch::Subcommands::Show { .. }) => BranchShow,
+            },
+            Subcommands::Worktree(crate::worktree::Platform { cmd: _ }) => Worktree,
+            Subcommands::Mark { .. } => Mark,
+            Subcommands::Unmark => Unmark,
+            Subcommands::Gui => Gui,
+            Subcommands::Commit { .. } => Commit,
+            Subcommands::Push(_) => Push,
+            Subcommands::New { .. } => New,
+            Subcommands::Describe { .. } => Describe,
+            Subcommands::Oplog { .. } => Oplog,
+            Subcommands::Restore { .. } => Restore,
+            Subcommands::Undo => Undo,
+            Subcommands::Snapshot { .. } => Snapshot,
+            Subcommands::Claude(claude::Platform { cmd }) => match cmd {
+                claude::Subcommands::PreTool => ClaudePreTool,
+                claude::Subcommands::PostTool => ClaudePostTool,
+                claude::Subcommands::Stop => ClaudeStop,
+                claude::Subcommands::Last { .. }
+                | claude::Subcommands::PermissionPromptMcp { .. } => Unknown,
+            },
+            Subcommands::Cursor(cursor::Platform { cmd }) => match cmd {
+                cursor::Subcommands::AfterEdit => CursorAfterEdit,
+                cursor::Subcommands::Stop { .. } => CursorStop,
+            },
+            Subcommands::Forge(forge::integration::Platform { cmd }) => match cmd {
+                forge::integration::Subcommands::Auth => ForgeAuth,
+                forge::integration::Subcommands::Forget { .. } => ForgeForget,
+                forge::integration::Subcommands::ListUsers => ForgeListUsers,
+            },
+            Subcommands::Review(forge::review::Platform { cmd }) => match cmd {
+                forge::review::Subcommands::Publish { .. } => PublishReview,
+                forge::review::Subcommands::Template { .. } => ReviewTemplate,
+            },
+            Subcommands::Completions { .. } => Completions,
+            Subcommands::Absorb { .. } => Absorb,
+            Subcommands::Metrics { .. }
+            | Subcommands::Actions(_)
+            | Subcommands::Mcp { .. }
+            | Subcommands::Init { .. } => Unknown,
+        }
+    }
+}
+
 #[derive(Debug, Clone, Copy, clap::ValueEnum, Default)]
 pub enum CommandName {
     Log,
@@ -231,6 +293,7 @@ pub enum CommandName {
     BranchNew,
     BranchDelete,
     BranchList,
+    BranchShow,
     BranchUnapply,
     BranchApply,
     ClaudePreTool,

crates/but/src/branch/mod.rs

@@ -11,6 +11,7 @@ use crate::{
 
 mod apply;
 mod list;
+mod show;
 
 mod json {
     use serde::Serialize;
@@ -133,6 +134,26 @@ pub enum Subcommands {
         #[clap(long)]
         no_check: bool,
     },
+    /// Show commits ahead of base for a specific branch
+    Show {
+        /// CLI ID or name of the branch to show
+        branch_id: String,
+        /// Fetch and display review information
+        #[clap(short, long)]
+        review: bool,
+        /// Disable pager output
+        #[clap(long)]
+        no_pager: bool,
+        /// Show files modified in each commit with line counts
+        #[clap(short, long)]
+        files: bool,
+        /// Generate AI summary of the branch changes
+        #[clap(long)]
+        ai: bool,
+        /// Check if the branch merges cleanly into upstream and identify conflicting commits
+        #[clap(long)]
+        check: bool,
+    },
     /// Apply a branch to the workspace
     Apply {
         /// Name of the branch to apply
@@ -152,6 +173,7 @@ pub async fn handle(
     cmd: Option<Subcommands>,
     ctx: &but_ctx::Context,
     out: &mut OutputChannel,
+    json: bool,
 ) -> anyhow::Result<serde_json::Value> {
     let legacy_project = &ctx.legacy_project;
     match cmd {
@@ -173,7 +195,8 @@ pub async fn handle(
                 json,
                 check,
             )
-            .await
+            .await?;
+            Ok(we_need_proper_json_output_here())
         }
         Some(Subcommands::List {
             filter,
@@ -197,9 +220,30 @@ pub async fn handle(
                 json,
                 check,
             )
-            .await
+            .await?;
+            Ok(we_need_proper_json_output_here())
+        }
+        Some(Subcommands::Show {
+            branch_id,
+            review,
+            no_pager,
+            files,
+            ai,
+            check,
+        }) => {
+            show::show(
+                legacy_project,
+                &branch_id,
+                json,
+                review,
+                !no_pager,
+                files,
+                ai,
+                check,
+            )
+            .await?;
+            Ok(we_need_proper_json_output_here())
         }
-        Some(Subcommands::List { local }) => list::list(legacy_project, local, out).await,
         Some(Subcommands::New {
             branch_name,
             anchor,