Add the start change id to error message when no descandants are found.

If movement commands don't find a target commit, they fail. However,
it's usually not intuitive why they fail because in non-edit mode the
start commit is the parent of the working commit.

Adding the start commit change hash to the error message makes it easier
for the user to figure out what is going on.

Part of #3947

cli/src/movement_util.rs

@@ -16,12 +16,12 @@ use std::io::Write;
 use std::rc::Rc;
 
 use itertools::Itertools;
-use jj_lib::backend::CommitId;
+use jj_lib::backend::{BackendError, CommitId};
 use jj_lib::commit::Commit;
 use jj_lib::repo::Repo;
 use jj_lib::revset::{RevsetExpression, RevsetFilterPredicate, RevsetIteratorExt};
 
-use crate::cli_util::WorkspaceCommandHelper;
+use crate::cli_util::{short_change_hash, WorkspaceCommandHelper};
 use crate::command_error::{user_error, CommandError};
 use crate::ui::{MovementEditMode, Ui};
 
@@ -53,20 +53,11 @@ impl Direction {
 
     fn get_target_revset(
         &self,
-        working_commit_id: &CommitId,
-        edit: bool,
+        working_revset: &Rc<RevsetExpression>,
+        start_revset: &Rc<RevsetExpression>,
         has_conflict: bool,
         change_offset: u64,
     ) -> Result<Rc<RevsetExpression>, CommandError> {
-        let wc_revset = RevsetExpression::commit(working_commit_id.clone());
-        // If we're editing, start at the working-copy commit. Otherwise, start from
-        // its direct parent(s).
-        let start_revset = if edit {
-            wc_revset.clone()
-        } else {
-            wc_revset.parents()
-        };
-
         let target_revset = match self {
             Direction::Next => if has_conflict {
                 start_revset
@@ -77,7 +68,7 @@ impl Direction {
             } else {
                 start_revset.descendants_at(change_offset)
             }
-            .minus(&wc_revset),
+            .minus(working_revset),
 
             Direction::Prev => {
                 if has_conflict {
@@ -115,8 +106,27 @@ pub fn get_target_commit(
     has_conflict: bool,
     change_offset: u64,
 ) -> Result<Commit, CommandError> {
+    let wc_revset = RevsetExpression::commit(working_commit_id.clone());
+    // If we're editing, start at the working-copy commit. Otherwise, start from
+    // its direct parent(s).
+    let start_revset = if edit {
+        wc_revset.clone()
+    } else {
+        wc_revset.parents()
+    };
+
+    let start_commit: Commit = start_revset
+        .clone()
+        .evaluate_programmatic(workspace_command.repo().as_ref())?
+        .iter()
+        .commits(workspace_command.repo().store())
+        .collect::<Result<Vec<_>, BackendError>>()?
+        .pop()
+        .unwrap();
+
     let target_revset =
-        direction.get_target_revset(working_commit_id, edit, has_conflict, change_offset)?;
+        direction.get_target_revset(&wc_revset, &start_revset, has_conflict, change_offset)?;
+
     let targets: Vec<Commit> = target_revset
         .evaluate_programmatic(workspace_command.repo().as_ref())?
         .iter()
@@ -128,11 +138,12 @@ pub fn get_target_commit(
         [] => {
             // We found no descendant.
             return Err(user_error(format!(
-                "No {} found {} commit{} {}",
+                "No {} found {} commit{} {} from {}",
                 direction.next_node_type(),
                 change_offset,
                 if change_offset > 1 { "s" } else { "" },
                 direction.direction(),
+                short_change_hash(start_commit.change_id()),
             )));
         }
         commits => choose_commit(ui, workspace_command, &direction, commits)?,

cli/tests/test_next_prev_commands.rs

@@ -201,7 +201,7 @@ fn test_next_exceeding_history() {
     let stderr = test_env.jj_cmd_failure(&repo_path, &["next", "3"]);
     // `jj next` beyond existing history fails.
     insta::assert_snapshot!(stderr, @r###"
-    Error: No descendant found 3 commits forward
+    Error: No descendant found 3 commits forward from rlvkpnrzqnoo
     "###);
 }
 
@@ -594,7 +594,7 @@ fn test_prev_beyond_root_fails() {
     // @- is at "fourth", and there is no parent 5 commits behind it.
     let stderr = test_env.jj_cmd_failure(&repo_path, &["prev", "5"]);
     insta::assert_snapshot!(stderr,@r###"
-    Error: No ancestor found 5 commits back
+    Error: No ancestor found 5 commits back from zsuskulnrvyr
     "###);
 }
 
@@ -860,12 +860,12 @@ fn test_next_conflict_head() {
     "###);
     let stderr = test_env.jj_cmd_failure(&repo_path, &["next", "--conflict"]);
     insta::assert_snapshot!(stderr, @r###"
-    Error: No descendant found 1 commit forward
+    Error: No descendant found 1 commit forward from zzzzzzzzzzzz
     "###);
 
     let stderr = test_env.jj_cmd_failure(&repo_path, &["next", "--conflict", "--edit"]);
     insta::assert_snapshot!(stderr, @r###"
-    Error: No descendant found 1 commit forward
+    Error: No descendant found 1 commit forward from rlvkpnrzqnoo
     "###);
 }