helix: Add support for line length in reflow command (#52152)

* Add `editor::RewrapOptions::line_length` to, optionally, override the
  line length used when rewrapping text.
* Update `editor::Editor::rewrap_impl` to prefer
  `editor::RewrapOptions::line_length`, when set.
* Add a `line_length` field to the `vim::rewrap::Rewrap` action.
* Update the `:reflow` vim command with `vim::command::VimCommand::args`
  so as to be able to parse the provided argument as `usize`, ensuring
  that no effect is taken if the argument can't be parsed as such.

Release Notes:

- N/A

crates/vim/src/command.rs

@@ -1726,7 +1726,15 @@ fn generate_commands(_: &App) -> Vec<VimCommand> {
         )
         .range(wrap_count),
         VimCommand::new(("j", "oin"), JoinLines).range(select_range),
-        VimCommand::new(("reflow", ""), Rewrap).range(select_range),
+        VimCommand::new(("reflow", ""), Rewrap { line_length: None })
+            .range(select_range)
+            .args(|_action, args| {
+                args.parse::<usize>().map_or(None, |length| {
+                    Some(Box::new(Rewrap {
+                        line_length: Some(length),
+                    }))
+                })
+            }),
         VimCommand::new(("fo", "ld"), editor::actions::FoldSelectedRanges).range(act_on_range),
         VimCommand::new(("foldo", "pen"), editor::actions::UnfoldLines)
             .bang(editor::actions::UnfoldRecursive)
@@ -3550,7 +3558,7 @@ mod test {
 
         cx.set_state(
             indoc! {"
-                ˇ0123456789 0123456789 0123456789 0123456789
+                ˇ0123456789 0123456789
             "},
             Mode::Normal,
         );
@@ -3560,8 +3568,6 @@ mod test {
 
         cx.assert_state(
             indoc! {"
-                0123456789
-                0123456789
                 0123456789
                 ˇ0123456789
             "},
@@ -3570,22 +3576,59 @@ mod test {
 
         cx.set_state(
             indoc! {"
-                «0123456789 0123456789ˇ»
-                0123456789 0123456789
+                ˇ0123456789 0123456789
             "},
             Mode::VisualLine,
         );
 
-        cx.simulate_keystrokes(": reflow");
+        cx.simulate_keystrokes("shift-v : reflow");
         cx.simulate_keystrokes("enter");
 
         cx.assert_state(
             indoc! {"
-                ˇ0123456789
                 0123456789
-                0123456789 0123456789
+                ˇ0123456789
             "},
             Mode::Normal,
         );
+
+        cx.set_state(
+            indoc! {"
+                ˇ0123 4567 0123 4567
+            "},
+            Mode::VisualLine,
+        );
+
+        cx.simulate_keystrokes(": reflow space 7");
+        cx.simulate_keystrokes("enter");
+
+        cx.assert_state(
+            indoc! {"
+                ˇ0123
+                4567
+                0123
+                4567
+            "},
+            Mode::Normal,
+        );
+
+        // Assert that, if `:reflow` is invoked with an invalid argument, it
+        // does not actually have any effect in the buffer's contents.
+        cx.set_state(
+            indoc! {"
+                ˇ0123 4567 0123 4567
+            "},
+            Mode::VisualLine,
+        );
+
+        cx.simulate_keystrokes(": reflow space a");
+        cx.simulate_keystrokes("enter");
+
+        cx.assert_state(
+            indoc! {"
+                ˇ0123 4567 0123 4567
+            "},
+            Mode::VisualLine,
+        );
     }
 }