cli:converge: new jj converge command

CHANGELOG.md

@@ -24,6 +24,12 @@ to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
   jj workspace can have its own Git HEAD. Existing repositories are migrated
   automatically.
 
+* The new `jj converge` command attempts to automatically resolve divergence by
+  creating a new commit that replaces the divergent commits. It applies
+  heuristics to try to automatically come up with a good solution, and falls
+  back to prompting the user if the heuristics are inconclusive. It can also run
+  in non-interactive mode, which aborts if prompting would be needed.
+
 ### Fixed bugs
 
 * The default pager flags now include `-K` (`--quit-on-intr`), so pressing

cli/src/command_error.rs

@@ -28,6 +28,7 @@ use jj_lib::config::ConfigFileSaveError;
 use jj_lib::config::ConfigGetError;
 use jj_lib::config::ConfigLoadError;
 use jj_lib::config::ConfigMigrateError;
+use jj_lib::converge::ConvergeError;
 use jj_lib::dsl_util::Diagnostics;
 use jj_lib::evolution::WalkPredecessorsError;
 use jj_lib::fileset::FilePatternParseError;
@@ -427,6 +428,19 @@ impl From<WalkPredecessorsError> for CommandError {
     }
 }
 
+impl From<ConvergeError> for CommandError {
+    fn from(err: ConvergeError) -> Self {
+        match err {
+            ConvergeError::Backend(err) => err.into(),
+            ConvergeError::Index(err) => err.into(),
+            ConvergeError::RevsetEvaluation(err) => err.into(),
+            ConvergeError::WalkPredecessors(err) => err.into(),
+            ConvergeError::IO(err) => err.into(),
+            ConvergeError::Other(err) => internal_error(err),
+        }
+    }
+}
+
 impl From<DiffEditError> for CommandError {
     fn from(err: DiffEditError) -> Self {
         user_error_with_message("Failed to edit diff", err)
@@ -507,6 +521,12 @@ impl From<TempTextEditError> for CommandError {
     }
 }
 
+impl From<TempTextEditError> for ConvergeError {
+    fn from(err: TempTextEditError) -> Self {
+        Self::Other(Box::new(err))
+    }
+}
+
 impl From<TrailerParseError> for CommandError {
     fn from(err: TrailerParseError) -> Self {
         user_error(err)
@@ -936,7 +956,9 @@ fn revset_resolution_error_hints(err: &RevsetResolutionError) -> Vec<String> {
             kind: _,
             symbol: _,
             targets,
-        } => vec![multiple_targets_hint(targets)],
+        } => {
+            vec![multiple_targets_hint(targets)]
+        }
         RevsetResolutionError::EmptyString
         | RevsetResolutionError::WorkspaceMissingWorkingCopy { .. }
         | RevsetResolutionError::AmbiguousCommitIdPrefix(_)