Allow inline message for but describe

Add an optional -m/--message flag to the describe command so users can
supply a new commit message or branch name on the command line instead
of opening an editor. This change threads the optional message through
the describe handlers and uses it to validate and apply the supplied
value, when absent it falls back to the existing editor-based flow.

Author: mtsgrd

crates/but/src/args/mod.rs

@@ -345,6 +345,9 @@ pub enum Subcommands {
     Describe {
         /// Commit ID to edit the message for, or branch ID to rename
         target: String,
+        /// The new commit message or branch name. If not provided, opens an editor.
+        #[clap(short = 'm', long = "message")]
+        message: Option<String>,
     },
 
     /// Show operation history.

crates/but/src/command/legacy/describe.rs

@@ -9,6 +9,7 @@ pub(crate) fn describe_target(
     project: &Project,
     out: &mut OutputChannel,
     target: &str,
+    message: Option<&str>,
 ) -> Result<()> {
     let mut ctx = Context::new_from_legacy_project(project.clone())?;
 
@@ -31,10 +32,10 @@ pub(crate) fn describe_target(
 
     match cli_id {
         CliId::Branch { name, .. } => {
-            edit_branch_name(&ctx, project, name, out)?;
+            edit_branch_name(&ctx, project, name, out, message)?;
         }
         CliId::Commit { oid } => {
-            edit_commit_message_by_id(&ctx, project, *oid, out)?;
+            edit_commit_message_by_id(&ctx, project, *oid, out, message)?;
         }
         _ => {
             bail!("Target must be a commit ID, not {}", cli_id.kind());
@@ -49,6 +50,7 @@ fn edit_branch_name(
     project: &Project,
     branch_name: &str,
     out: &mut OutputChannel,
+    message: Option<&str>,
 ) -> Result<()> {
     // Find which stack this branch belongs to
     let stacks = but_api::legacy::workspace::stacks(
@@ -62,7 +64,17 @@ fn edit_branch_name(
         }
 
         if let Some(sid) = stack_entry.id {
-            let new_name = get_branch_name_from_editor(branch_name)?;
+            let new_name = if let Some(msg) = message {
+                // Use provided message, trim and validate
+                let trimmed = msg.trim();
+                if trimmed.is_empty() {
+                    bail!("Aborting due to empty branch name");
+                }
+                trimmed.to_string()
+            } else {
+                // Fall back to editor
+                get_branch_name_from_editor(branch_name)?
+            };
             but_api::legacy::stack::update_branch_name(
                 project.id,
                 sid,
@@ -84,6 +96,7 @@ fn edit_commit_message_by_id(
     project: &Project,
     commit_oid: gix::ObjectId,
     out: &mut OutputChannel,
+    message: Option<&str>,
 ) -> Result<()> {
     // Find which stack this commit belongs to
     let stacks = but_api::legacy::workspace::stacks(project.id, None)?;
@@ -132,15 +145,25 @@ fn edit_commit_message_by_id(
     let stack_id = stack_id
         .ok_or_else(|| anyhow::anyhow!("Could not find stack for commit {}", commit_oid))?;
 
-    // Get the files changed in this commit using but_api
-    let commit_details = but_api::legacy::diff::commit_details(project.id, commit_oid.into())?;
-    let changed_files = get_changed_files_from_commit_details(&commit_details);
-
     // Get current commit message
     let current_message = commit_message.to_string();
 
-    // Open editor with current message and file list
-    let new_message = get_commit_message_from_editor(&current_message, &changed_files)?;
+    // Get new message from provided argument or editor
+    let new_message = if let Some(msg) = message {
+        // Use provided message, trim and validate
+        let trimmed = msg.trim();
+        if trimmed.is_empty() {
+            bail!("Aborting due to empty commit message");
+        }
+        trimmed.to_string()
+    } else {
+        // Get the files changed in this commit using but_api
+        let commit_details = but_api::legacy::diff::commit_details(project.id, commit_oid.into())?;
+        let changed_files = get_changed_files_from_commit_details(&commit_details);
+
+        // Open editor with current message and file list
+        get_commit_message_from_editor(&current_message, &changed_files)?
+    };
 
     if new_message.trim() == current_message.trim() {
         bail!("No changes to commit message.");

crates/but/src/lib.rs

@@ -364,9 +364,9 @@ async fn match_subcommand(
                 .emit_metrics(metrics_ctx)
         }
         #[cfg(feature = "legacy")]
-        Subcommands::Describe { target } => {
+        Subcommands::Describe { target, message } => {
             let project = legacy::get_or_init_non_bare_project(&args)?;
-            command::legacy::describe::describe_target(&project, out, &target)
+            command::legacy::describe::describe_target(&project, out, &target, message.as_deref())
                 .emit_metrics(metrics_ctx)
         }
         #[cfg(feature = "legacy")]

crates/but/tests/but/command/describe.rs

@@ -0,0 +1,154 @@
+use snapbox::str;
+
+use crate::utils::{Sandbox, setup_metadata};
+
+#[test]
+fn describe_commit_with_message_flag() -> anyhow::Result<()> {
+    let env = Sandbox::init_scenario_with_target_and_default_settings("one-stack")?;
+    insta::assert_snapshot!(env.git_log()?, @r"
+    * edd3eb7 (HEAD -> gitbutler/workspace) GitButler Workspace Commit
+    * 9477ae7 (A) add A
+    * 0dc3733 (origin/main, origin/HEAD, main) add M
+    ");
+
+    setup_metadata(&env, &["A"])?;
+
+    // Use describe with -m flag to change commit message (using commit ID)
+    env.but("describe 9477ae7 -m 'Updated commit message'")
+        .assert()
+        .success()
+        .stdout_eq(str![[r#"
+Updated commit message for [..] (now [..])
+
+"#]]);
+
+    // Verify the commit message was updated
+    let log = env.git_log()?;
+    assert!(log.contains("Updated commit message"));
+    assert!(!log.contains("add A"));
+
+    Ok(())
+}
+
+// Note: Branch rename test is omitted because the test scenario uses single-character
+// branch names ("A") which don't meet the 2-character minimum requirement for CLI IDs.
+// The branch rename functionality with -m flag is tested manually and works correctly.
+
+#[test]
+fn describe_with_empty_message_fails() -> anyhow::Result<()> {
+    let env = Sandbox::init_scenario_with_target_and_default_settings("one-stack")?;
+    insta::assert_snapshot!(env.git_log()?, @r"
+    * edd3eb7 (HEAD -> gitbutler/workspace) GitButler Workspace Commit
+    * 9477ae7 (A) add A
+    * 0dc3733 (origin/main, origin/HEAD, main) add M
+    ");
+
+    setup_metadata(&env, &["A"])?;
+
+    // Try to describe commit with empty message
+    env.but("describe 9477ae7 -m ''")
+        .assert()
+        .failure()
+        .stderr_eq(str![[r#"
+Error: Aborting due to empty commit message
+
+"#]]);
+
+    Ok(())
+}
+
+#[test]
+fn describe_with_whitespace_only_message_fails() -> anyhow::Result<()> {
+    let env = Sandbox::init_scenario_with_target_and_default_settings("one-stack")?;
+    insta::assert_snapshot!(env.git_log()?, @r"
+    * edd3eb7 (HEAD -> gitbutler/workspace) GitButler Workspace Commit
+    * 9477ae7 (A) add A
+    * 0dc3733 (origin/main, origin/HEAD, main) add M
+    ");
+
+    setup_metadata(&env, &["A"])?;
+
+    // Try to describe commit with whitespace-only message
+    env.but("describe 9477ae7 -m '   '")
+        .assert()
+        .failure()
+        .stderr_eq(str![[r#"
+Error: Aborting due to empty commit message
+
+"#]]);
+
+    Ok(())
+}
+
+#[test]
+fn describe_commit_with_same_message_fails() -> anyhow::Result<()> {
+    let env = Sandbox::init_scenario_with_target_and_default_settings("one-stack")?;
+    insta::assert_snapshot!(env.git_log()?, @r"
+    * edd3eb7 (HEAD -> gitbutler/workspace) GitButler Workspace Commit
+    * 9477ae7 (A) add A
+    * 0dc3733 (origin/main, origin/HEAD, main) add M
+    ");
+
+    setup_metadata(&env, &["A"])?;
+
+    // Try to describe with the same message
+    env.but("describe 9477ae7 -m 'add A'")
+        .assert()
+        .failure()
+        .stderr_eq(str![[r#"
+Error: No changes to commit message.
+
+"#]]);
+
+    Ok(())
+}
+
+#[test]
+fn describe_nonexistent_target_fails() -> anyhow::Result<()> {
+    let env = Sandbox::init_scenario_with_target_and_default_settings("one-stack")?;
+    insta::assert_snapshot!(env.git_log()?, @r"
+    * edd3eb7 (HEAD -> gitbutler/workspace) GitButler Workspace Commit
+    * 9477ae7 (A) add A
+    * 0dc3733 (origin/main, origin/HEAD, main) add M
+    ");
+
+    setup_metadata(&env, &["A"])?;
+
+    // Try to describe a nonexistent target
+    env.but("describe nonexistent -m 'new message'")
+        .assert()
+        .failure()
+        .stderr_eq(str![[r#"
+Error: ID 'nonexistent' not found
+
+"#]]);
+
+    Ok(())
+}
+
+#[test]
+fn describe_commit_with_multiline_message() -> anyhow::Result<()> {
+    let env = Sandbox::init_scenario_with_target_and_default_settings("one-stack")?;
+    insta::assert_snapshot!(env.git_log()?, @r"
+    * edd3eb7 (HEAD -> gitbutler/workspace) GitButler Workspace Commit
+    * 9477ae7 (A) add A
+    * 0dc3733 (origin/main, origin/HEAD, main) add M
+    ");
+
+    setup_metadata(&env, &["A"])?;
+
+    // Use describe with multiline message
+    env.but("describe 9477ae7 -m 'First line\n\nSecond paragraph with details'")
+        .assert()
+        .success()
+        .stdout_eq(str![[r#"
+Updated commit message for [..] (now [..])
+
+"#]]);
+
+    // Verify the commit message was updated with multiline content
+    let log = env.git_log()?;
+    assert!(log.contains("First line"));
+
+    Ok(())
+}

crates/but/tests/but/command/mod.rs

@@ -3,6 +3,8 @@
 mod branch;
 #[cfg(feature = "legacy")]
 mod commit;
+#[cfg(feature = "legacy")]
+mod describe;
 mod format;
 mod help;
 #[cfg(feature = "legacy")]