git: restore support for git.push-branch-prefix config but deprecate it

CHANGELOG.md

@@ -29,6 +29,9 @@ to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
   that describes them better, and they also behave similar to Mercurial's 
   bookmarks. 
 
+* The `git.push-branch-prefix` config has been deprecated in favor of
+  `git.push-bookmark-prefix`.
+
 ### New features
 
 * The new config option `snapshot.auto-track` lets you automatically track only

cli/src/commands/git/push.rs

@@ -193,12 +193,19 @@ pub fn cmd_git_push(
         let mut seen_bookmarks: HashSet<&str> = HashSet::new();
 
         // Process --change bookmarks first because matching bookmarks can be moved.
-        let change_bookmark_names = update_change_bookmarks(
-            ui,
-            &mut tx,
-            &args.change,
-            &command.settings().push_bookmark_prefix(),
-        )?;
+        // TODO: Drop support support for git.push-branch-prefix in 0.28.0+
+        let bookmark_prefix = if let Some(prefix) = command.settings().push_branch_prefix() {
+            writeln!(
+                ui.warning_default(),
+                "Config git.push-branch-prefix is deprecated. Please switch to \
+                 git.push-bookmark-prefix",
+            )?;
+            prefix
+        } else {
+            command.settings().push_bookmark_prefix()
+        };
+        let change_bookmark_names =
+            update_change_bookmarks(ui, &mut tx, &args.change, &bookmark_prefix)?;
         let change_bookmarks = change_bookmark_names.iter().map(|bookmark_name| {
             let targets = LocalAndRemoteRef {
                 local_target: tx.repo().view().get_local_bookmark(bookmark_name),

cli/tests/test_git_push.rs

@@ -679,6 +679,25 @@ fn test_git_push_changes() {
     Bookmark changes to push to origin:
       Add bookmark test-yostqsxwqrlt to 38cb417ce3a6
     "###);
+
+    // Test deprecation warning for `git.push-branch-prefix`
+    let (stdout, stderr) = test_env.jj_cmd_ok(
+        &workspace_root,
+        &[
+            "git",
+            "push",
+            "--config-toml",
+            r"git.push-branch-prefix='branch-'",
+            "--change=@",
+        ],
+    );
+    insta::assert_snapshot!(stdout, @"");
+    insta::assert_snapshot!(stderr, @r###"
+  Warning: Config git.push-branch-prefix is deprecated. Please switch to git.push-bookmark-prefix
+  Creating bookmark branch-yostqsxwqrlt for revision yostqsxwqrlt
+  Bookmark changes to push to origin:
+    Add bookmark branch-yostqsxwqrlt to 38cb417ce3a6
+  "###);
 }
 
 #[test]

lib/src/settings.rs

@@ -196,6 +196,10 @@ impl UserSettings {
             .unwrap_or_else(|_| "push-".to_string())
     }
 
+    pub fn push_branch_prefix(&self) -> Option<String> {
+        self.config.get_string("git.push-branch-prefix").ok()
+    }
+
     pub fn default_description(&self) -> String {
         self.config()
             .get_string("ui.default-description")