xim: dead keys and Compose

Xlib does no local composing for a client on an input method server,
so under XIM a dead key was forwarded as a bare keysym and vanished.
The XIM frontend now feeds keys through xkbcommon's Compose table for
the daemon's locale and commits the composed character itself.

xim/xim.c

@@ -2,10 +2,12 @@
 #include "fn.h"
 
 #include <errno.h>
+#include <locale.h>
 #include <poll.h>
 #include <xcb/xcb.h>
 #include <xcb/xkb.h>
 #include <xkbcommon/xkbcommon.h>
+#include <xkbcommon/xkbcommon-compose.h>
 #include <xkbcommon/xkbcommon-x11.h>
 #include <xcb-imdkit/imdkit.h>
 #include <xcb-imdkit/encoding.h>
@@ -38,6 +40,7 @@ enum
 static xcb_connection_t *conn;
 static xcb_im_t *xim;
 static struct xkb_state *kstate;
+static struct xkb_compose_state *compose;
 static uint8_t xkbevent;
 static xcb_window_t rootwin;
 static Ic *ics;
@@ -96,6 +99,26 @@ out:
 	return ok;
 }
 
+/* Dead keys and Compose: Xlib leaves them to the input method server. */
+static void
+cinit(void)
+{
+	struct xkb_context *context;
+	struct xkb_compose_table *table;
+	char *locale;
+
+	locale = setlocale(LC_CTYPE, "");
+	context = xkb_context_new(XKB_CONTEXT_NO_FLAGS);
+	if(context == nil)
+		return;
+	table = xkb_compose_table_new_from_locale(context,
+		locale != nil ? locale : "C", XKB_COMPOSE_COMPILE_NO_FLAGS);
+	if(table != nil)
+		compose = xkb_compose_state_new(table, XKB_COMPOSE_STATE_NO_FLAGS);
+	xkb_compose_table_unref(table);
+	xkb_context_unref(context);
+}
+
 static void
 kwatch(void)
 {
@@ -361,11 +384,25 @@ kpress(Ic *state, xcb_key_press_event_t *ev)
 {
 	Keyres res;
 	char buf[Maxutf];
-	u32int key;
+	u32int key, sym;
-	int n, wasvalid;
+	int composed, n, wasvalid;
 
-	key = keymaplookup(kstate, ev->detail, ev->state);
+	sym = keymaplookup(kstate, ev->detail, ev->state);
-	key = ipckeysym(key, xkb_keysym_to_utf32(key));
+	composed = 0;
+	if(compose != nil &&
+	   xkb_compose_state_feed(compose, sym) == XKB_COMPOSE_FEED_ACCEPTED)
+		switch(xkb_compose_state_get_status(compose)){
+		case XKB_COMPOSE_COMPOSING:
+		case XKB_COMPOSE_CANCELLED:
+			return;
+		case XKB_COMPOSE_COMPOSED:
+			sym = xkb_compose_state_get_one_sym(compose);
+			composed = 1;
+			break;
+		default:
+			break;
+		}
+	key = ipckeysym(sym, xkb_keysym_to_utf32(sym));
 	if(keymeaningful(key)){
 		wasvalid = state->caret.valid;
 		place(state);
@@ -376,7 +413,13 @@ kpress(Ic *state, xcb_key_press_event_t *ev)
 	n = stoutf(&res.commit, buf, sizeof buf);
 	commit(state, buf, n);
 	updatepreedit(state, &res.preedit);
-	if(!res.eaten)
+	if(res.eaten)
+		;
+	else if(composed){
+		/* The event holds the last key of the sequence, not its result. */
+		n = xkb_keysym_to_utf8(sym, buf, sizeof buf);
+		commit(state, buf, max(n - 1, 0));
+	}else
 		xcb_im_forward_event(xim, state->xic, ev);
 	xcb_flush(conn);
 }
@@ -498,6 +541,7 @@ ximinit(void)
 		ximlog("cannot read keyboard mapping");
 		return -1;
 	}
+	cinit();
 	kwatch();
 	win = xcb_generate_id(conn);
 	xcb_create_window(conn, XCB_COPY_FROM_PARENT, win, screen->root,