cli: make operation to undo or restore to a positional argument

I originally made the operation argument a named argument
(`--operation`) to allow for a change ID to be passed as a positional
argument, matching e.g. `hg revert -r <rev> <path>`. However, even if
we add support for undoing changes only to certain change IDs, it's
going to be done much less frequently than full undo/restore. We can
therefore make that a named argument if we ever add it.

CHANGELOG.md

@@ -7,6 +7,12 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Breaking changes
+
+* `jj [op] undo` and `jj op restore` used to take the operation to undo or
+  restore to as an argument to `-o/--operation`. It is now a positional
+  argument instead (i.e. `jj undo -o abc123` is now written `jj undo abc123`).
+
 ### New features
 
 * `jj rebase` now accepts a `--branch/-b <revision>` argument, which can be used

src/commands.rs

@@ -1527,7 +1527,7 @@ struct OperationLogArgs {}
 #[derive(clap::Args, Clone, Debug)]
 struct OperationRestoreArgs {
     /// The operation to restore to
-    #[clap(long, alias = "op", short, default_value = "@")]
+    #[clap(default_value = "@")]
     operation: String,
 }
 
@@ -1535,7 +1535,7 @@ struct OperationRestoreArgs {
 #[derive(clap::Args, Clone, Debug)]
 struct OperationUndoArgs {
     /// The operation to undo
-    #[clap(long, alias = "op", short, default_value = "@")]
+    #[clap(default_value = "@")]
     operation: String,
 }
 

tests/test_undo.rs

@@ -35,7 +35,7 @@ fn test_undo_rewrite_with_child() {
     o modified
     o 
     "###);
-    test_env.jj_cmd_success(&repo_path, &["undo", "-o", &op_id_hex]);
+    test_env.jj_cmd_success(&repo_path, &["undo", &op_id_hex]);
 
     // Since we undid the description-change, the child commit should now be on top
     // of the initial commit