Change conflict hint depending on state of working commit.

To avoid always printing the rebase instructions to fix a conflict
even when a child commit to fix the conflict already exists, implement
the following:

* If working commit has conflicts:
  * if any decendants are conflict free: "Conflict fixed in <decendant>". For
    this, print the short_change_hash of the first decendant without conflicts.
  * if no decendants are conflict free: Print the existing message we print today.

* If working commit has no conflicts:
  * If any parent has conflicts: "Conflict in parent is resolved in working copy".
    Explicitly not printing the "conflicting parent" here, since a merge commit
    could have conflict in multiple parents.
  * If no parent has any conflicts: exit quietly.

* Rename existing unittest
* Also update Changelog here

CHANGELOG.md

@@ -101,6 +101,10 @@ to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ### Fixed bugs
 
+* `jj status` will show different messages in a conflicted tree, depending
+  on the state of the working commit. In particular, if a child commit has
+  fixed the conflict, this will be reflected in the hint provided by `jj status`
+
 * `jj diff --git` no longer shows the contents of binary files.
 
 * Windows binaries no longer require `vcruntime140.dll` to be installed

cli/src/commands/status.rs

@@ -17,7 +17,7 @@ use jj_lib::repo::Repo;
 use jj_lib::revset::{RevsetExpression, RevsetFilterPredicate};
 use tracing::instrument;
 
-use crate::cli_util::{print_conflicted_paths, CommandHelper};
+use crate::cli_util::{print_conflicted_paths, short_change_hash, CommandHelper};
 use crate::command_error::CommandError;
 use crate::diff_util::DiffFormat;
 use crate::revset_util;
@@ -91,21 +91,54 @@ pub(crate) fn cmd_status(
             writeln!(formatter)?;
         }
 
-        let wc_revset = RevsetExpression::commit(wc_commit.id().clone());
-        // Ancestors with conflicts, excluding the current working copy commit.
-        let ancestors_conflicts = workspace_command
-            .attach_revset_evaluator(
-                wc_revset
-                    .parents()
-                    .ancestors()
-                    .filtered(RevsetFilterPredicate::HasConflict)
-                    .minus(&revset_util::parse_immutable_expression(
-                        &workspace_command.revset_parse_context(),
-                    )?),
-            )?
-            .evaluate_to_commit_ids()?
-            .collect();
-        workspace_command.report_repo_conflicts(formatter, repo, ancestors_conflicts)?;
+        if wc_commit.has_conflict()? {
+            let wc_revset = RevsetExpression::commit(wc_commit.id().clone());
+
+            if let Some(first_descendant_no_conflict) = workspace_command
+                .attach_revset_evaluator(
+                    wc_revset
+                        .children()
+                        .descendants()
+                        .filtered(RevsetFilterPredicate::HasNoConflict),
+                )?
+                .evaluate_to_commits()?
+                .collect::<Vec<_>>()
+                .pop()
+            {
+                writeln!(
+                    formatter.labeled("conflict"),
+                    "Conflict has been resolved in descendants: {}",
+                    short_change_hash(first_descendant_no_conflict?.change_id())
+                )?;
+            } else {
+                // Ancestors with conflicts, excluding the current working copy commit.
+                let ancestors_conflicts: Vec<_> = workspace_command
+                    .attach_revset_evaluator(
+                        wc_revset
+                            .parents()
+                            .ancestors()
+                            .filtered(RevsetFilterPredicate::HasConflict)
+                            .minus(&revset_util::parse_immutable_expression(
+                                &workspace_command.revset_parse_context(),
+                            )?),
+                    )?
+                    .evaluate_to_commit_ids()?
+                    .collect();
+
+                workspace_command.report_repo_conflicts(formatter, repo, ancestors_conflicts)?;
+            }
+        } else {
+            for parent in wc_commit.parents() {
+                let parent = parent?;
+                if parent.has_conflict()? {
+                    writeln!(
+                        formatter.labeled("conflict"),
+                        "Conflict in parent commit has been resolved in working copy"
+                    )?;
+                    break;
+                }
+            }
+        }
     } else {
         writeln!(formatter, "No working copy")?;
     }