Support named captures in hooks

Fixes #2857

doc/pages/hooks.asciidoc

@@ -189,7 +189,9 @@ vars are available:
 
 * `kak_hook_param`: filtering text passed to the currently executing hook
 
-* `kak_hook_param_capture_N`: text captured by the hook filter regex capture N
+* `kak_hook_param_capture_N`: text captured by the hook filter regex capturing
+    group N, N can either be the capturing group number, or its name
+    (See <<regex#groups,`:doc regex groups`>>).
 
 == Disabling Hooks
 

src/hook_manager.cc

@@ -117,6 +117,9 @@ void HookManager::run_hook(Hook hook, StringView param, Context& context)
             for (size_t i = 0; i < to_run.captures.size(); ++i)
                 env_vars.insert({format("hook_param_capture_{}", i),
                                  {to_run.captures[i].first, to_run.captures[i].second}});
+            for (auto& c : to_run.hook->filter.impl()->named_captures)
+                env_vars.insert({format("hook_param_capture_{}", c.name),
+                                 {to_run.captures[c.index].first, to_run.captures[c.index].second}});
 
             CommandManager::instance().execute(to_run.hook->commands, context,
                                                { {}, std::move(env_vars) });

test/compose/hook-named-captures/cmd

@@ -0,0 +1 @@
+i<ret><esc>

test/compose/hook-named-captures/in

@@ -0,0 +1 @@
+

test/compose/hook-named-captures/out

@@ -0,0 +1 @@
+ret

test/compose/hook-named-captures/rc

@@ -0,0 +1 @@
+hook global InsertKey '<(?<name>\w+)>' %{ exec "<backspace>%val(hook_param_capture_name)" }