Show a keybinding the way a person writes it, and let bind_repeat be described

Measured with dotfiles-1a, who own the launcher that displays these: `srd
keybindings` returned 84 bindings and 84 empty descriptions - 100% - so
every entry their launcher showed was a bare key combo with nothing to say
what it does. Two causes, one on each side of the boundary.

`srd.bind_repeat` never accepted a description. `srd.bind` has taken an
optional third argument all along, but its repeating sibling took only two,
and mlua drops a surplus argument silently rather than raising - so a
config that documented its repeat bindings got no error and no description.
It now takes one exactly like `bind`.

The combos themselves were reported in their internal dispatch form:
`Shift+Mod4+h`. `Mod4` is the X11 modifier's name, not a key's; nothing on
a keyboard is labelled Mod4, and the canonical Ctrl/Shift/Alt/Mod4 ordering
renders the owner's own `Super+Shift+h` binding back to them inside out.
`srd keybindings` now reports a display form - Super, and the order people
write - while everything internal keeps the canonical form it dispatches
on. The display form parses back to the same binding, so it can be pasted
into a config, and a test pins that round trip rather than trusting it.

The owner's own config now describes all 84 bindings; verified through the
real path, in a nested compositor running that config: 84 of 84 described,
zero occurrences of "Mod4".

2 files changed, 53 insertions, 1 deletions

diff --git a/crates/core/src/event.rs b/crates/core/src/event.rs
index 0bfadc0..f171f06 100644
--- a/crates/core/src/event.rs
+++ b/crates/core/src/event.rs
@@ -104,6 +104,37 @@ pub fn parse_key_combo(combo: &str) -> Option<(Modifiers, &str)> {
     Some((modifiers, key_name))
 }
 
+/// The form of a combo to *show a person*, as distinct from the canonical
+/// form everything internal is keyed by.
+///
+/// Two differences, both of which matter only on screen:
+///
+/// - `Mod4` is written `Super`. `Mod4` is the X11 modifier's name, not the
+///   key's; nothing on a keyboard is labelled Mod4, and a launcher listing
+///   "Mod4+Return" is showing an implementation detail.
+/// - Modifiers come out in the order people write them - Super, Ctrl, Alt,
+///   Shift - rather than the canonical Ctrl/Shift/Alt/Mod4 order, which
+///   renders the owner's own `Super+Shift+h` binding as `Shift+Mod4+h`.
+///
+/// Round-trips: [`parse_key_combo`] accepts `Super` and takes modifiers in
+/// any order, so a string from here can be pasted straight into a config.
+/// Nothing dispatches on this form - [`canonicalize_key_combo`] still owns
+/// what a binding is stored and looked up as.
+pub fn display_key_combo(combo: &str) -> String {
+    let Some((modifiers, key_name)) = parse_key_combo(combo) else { return combo.to_string() };
+    let mut out = String::new();
+    for (flag, name) in
+        [(Modifiers::SUPER, "Super"), (Modifiers::CTRL, "Ctrl"), (Modifiers::ALT, "Alt"), (Modifiers::SHIFT, "Shift")]
+    {
+        if modifiers.contains(flag) {
+            out.push_str(name);
+            out.push('+');
+        }
+    }
+    out.push_str(key_name);
+    out
+}
+
 /// Re-orders a combo string into the canonical form [`key_combo_string`]
 /// produces, regardless of what order its modifiers were written in, *and*
 /// normalizes the key name to the exact casing [`crate::keysyms::
@@ -180,6 +211,27 @@ pub enum Event {
 
 #[cfg(test)]
 mod tests {
+    /// A launcher shows this string to a person, so it has to read like the
+    /// key on the keyboard and like what the config author wrote.
+    #[test]
+    fn display_form_uses_super_and_the_order_people_write() {
+        assert_eq!(display_key_combo("Shift+Mod4+h"), "Super+Shift+h");
+        assert_eq!(display_key_combo("Ctrl+Mod4+k"), "Super+Ctrl+k");
+        assert_eq!(display_key_combo("Shift+Alt+Tab"), "Alt+Shift+Tab");
+        assert_eq!(display_key_combo("Mod4+Return"), "Super+Return");
+        assert_eq!(display_key_combo("Print"), "Print");
+    }
+
+    /// The display form must be pasteable back into a config, or telling
+    /// someone their binding is "Super+Shift+h" sends them to a string that
+    /// does not work.
+    #[test]
+    fn display_form_parses_back_to_the_same_binding() {
+        for combo in ["Shift+Mod4+h", "Ctrl+Mod4+k", "Shift+Alt+Tab", "Mod4+Return", "Mod4+1"] {
+            assert_eq!(canonicalize_key_combo(&display_key_combo(combo)), canonicalize_key_combo(combo));
+        }
+    }
+
     use super::*;
 
     #[test]
diff --git a/crates/core/src/lib.rs b/crates/core/src/lib.rs
index 9a2c3bc..755a00e 100644
--- a/crates/core/src/lib.rs
+++ b/crates/core/src/lib.rs
@@ -13,7 +13,7 @@ pub mod window;
 pub mod workspace;
 
 pub use context_menu::{ContextMenu, MenuAction};
-pub use event::{canonicalize_key_combo, key_combo_string, parse_key_combo, Event, MouseButton, Modifiers};
+pub use event::{canonicalize_key_combo, display_key_combo, key_combo_string, parse_key_combo, Event, MouseButton, Modifiers};
 pub use geometry::Rect;
 pub use layout::{Layout, MasterStackLayout, NoOpLayout, TilingConfig};
 pub use lock_config::LockConfig;