bookmark: Make moving a bookmark onto a hidden commit a warning

cli/src/commands/bookmark/create.rs

@@ -12,6 +12,8 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+use std::ops::Deref;
+
 use clap::builder::NonEmptyStringValueParser;
 use jj_lib::object_id::ObjectId as _;
 use jj_lib::op_store::RefTarget;
@@ -46,7 +48,9 @@ pub fn cmd_bookmark_create(
     let mut workspace_command = command.workspace_helper(ui)?;
     let target_commit = workspace_command
         .resolve_single_rev(ui, args.revision.as_ref().unwrap_or(&RevisionArg::AT))?;
+    let repo = workspace_command.repo();
     let view = workspace_command.repo().view();
+    let is_hidden = target_commit.is_hidden(repo.deref())?;
     let bookmark_names = &args.names;
     for name in bookmark_names {
         if view.get_local_bookmark(name).is_present() {
@@ -87,6 +91,14 @@ pub fn cmd_bookmark_create(
         writeln!(ui.hint_default(), "Use -r to specify the target revision.")?;
     }
 
+    if is_hidden {
+        writeln!(
+            ui.status(),
+            "Created {} bookmarks onto a hidden commit, use `jj new` to unhide it.",
+            bookmark_names.len()
+        )?;
+    }
+
     tx.finish(
         ui,
         format!(

cli/src/commands/bookmark/move.rs

@@ -12,6 +12,8 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+use std::ops::Deref;
+
 use clap_complete::ArgValueCandidates;
 use itertools::Itertools as _;
 use jj_lib::object_id::ObjectId as _;
@@ -91,6 +93,7 @@ pub fn cmd_bookmark_move(
     let repo = workspace_command.repo().clone();
 
     let target_commit = workspace_command.resolve_single_rev(ui, &args.to)?;
+    let is_hidden = target_commit.is_hidden(repo.deref())?;
     let matched_bookmarks = {
         let is_source_ref: Box<dyn Fn(&RefTarget) -> _> = if !args.from.is_empty() {
             let is_source_commit = workspace_command
@@ -168,6 +171,13 @@ pub fn cmd_bookmark_move(
         )?;
     }
 
+    if is_hidden {
+        writeln!(
+            ui.hint_default(),
+            "Moved a bookmark onto a hidden commit, use `jj new` to unhide it"
+        )?;
+    }
+
     tx.finish(
         ui,
         format!(

cli/src/commands/bookmark/set.rs

@@ -56,6 +56,7 @@
         .resolve_single_rev(ui, args.revision.as_ref().unwrap_or(&RevisionArg::AT))?;
     let repo = workspace_command.repo().as_ref();
     let bookmark_names = &args.names;
+    let is_hidden = target_commit.is_hidden(repo)?;
     let mut new_bookmark_count = 0;
     let mut moved_bookmark_count = 0;
     for name in bookmark_names {
@@ -101,6 +102,14 @@
     if bookmark_names.len() > 1 && args.revision.is_none() {
         writeln!(ui.hint_default(), "Use -r to specify the target revision.")?;
     }
+    // TODO: Emit a warning here to `jj new -r <old>` to revive the commmit if it
+    // was hidden.
+    if is_hidden {
+        writeln!(
+            ui.hint_default(),
+            "Moved a bookmark onto a hidden commit, use `jj new` to unhide it."
+        )?;
+    }
     if new_bookmark_count > 0 {
         // TODO: delete this hint in jj 0.25+
         writeln!(

cli/src/commit_templater.rs

@@ -752,8 +752,8 @@ fn builtin_commit_methods<'repo>() -> CommitTemplateBuildMethodFnMap<'repo, Comm
             function.expect_no_arguments()?;
             let repo = language.repo;
             let out_property = self_property.map(|commit| {
-                let maybe_entries = repo.resolve_change_id(commit.change_id());
-                maybe_entries.map_or(true, |entries| !entries.contains(commit.id()))
+                let value = commit.is_hidden(repo);
+                value.unwrap_or_default()
             });
             Ok(L::wrap_boolean(out_property))
         },

cli/tests/test_bookmark_command.rs

@@ -1898,6 +1898,21 @@ fn test_bookmark_list_conflicted() {
     "###);
 }
 
+#[test]
+fn test_bookmark_create_onto_hidden_warning() {
+    // TODO: write
+}
+
+#[test]
+fn test_bookmark_move_onto_hidden_warning() {
+    // TODO: write
+}
+
+#[test]
+fn test_bookmark_set_onto_hidden_warning() {
+    // TODO: write
+}
+
 fn get_log_output(test_env: &TestEnvironment, cwd: &Path) -> String {
     let template = r#"bookmarks ++ " " ++ commit_id.short()"#;
     test_env.jj_cmd_success(cwd, &["log", "-T", template])

lib/src/commit.rs

@@ -162,6 +162,12 @@ impl Commit {
         &self.data.committer
     }
 
+    ///  A commit is hidden, if its commit id is not in the predecessor set.
+    pub fn is_hidden(&self, repo: &dyn Repo) -> BackendResult<bool> {
+        let maybe_entries = repo.resolve_change_id(self.change_id());
+        Ok(maybe_entries.map_or(true, |entries| !entries.contains(&self.id)))
+    }
+
     /// A commit is discardable if it has no change from its parent, and an
     /// empty description.
     pub fn is_discardable(&self, repo: &dyn Repo) -> BackendResult<bool> {