From c5f77c595172d27165f88c2baee869bf5cd0ed59 Mon Sep 17 00:00:00 2001
From: Raheman Vaiya <r.vaiya@gmail.com>
Date: Mon, 24 Jan 2022 14:30:30 -0500
Subject: [PATCH] Allow mapping to modifier keycodes

---
 src/descriptor.c |  7 +++----
 src/keyd.c       | 25 +++++++++++++------------
 t/layer4.t       | 13 +++++++++++++
 t/run.sh         |  2 +-
 t/test.conf      |  1 +
 5 files changed, 31 insertions(+), 17 deletions(-)
 create mode 100644 t/layer4.t

diff --git a/src/descriptor.c b/src/descriptor.c
index ef0baa8..4b17aa8 100644
--- a/src/descriptor.c
+++ b/src/descriptor.c
@@ -236,10 +236,9 @@ int parse_descriptor(char *s,
 	if (!parse_key_sequence(s, &seq)) {
 		desc->op = OP_KEYSEQ;
 
-		if (keycode_to_mod(seq.code)) {
-			err("modifier keycodes are not directly mappable, you probably want layer(<modifier name>) (e.g layer(alt))");
-			return -1;
-		}
+		if (keycode_to_mod(seq.code))
+			fprintf(stderr,
+				"WARNING: mapping modifier keycodes directly may produce unintended results, you probably want layer(<modifier name>) instead\n");
 
 		desc->args[0].sequence = seq;
 	} else if (!parse_macro_fn(&config->macros[macro_idx], s)) {
diff --git a/src/keyd.c b/src/keyd.c
index f622190..3e05b11 100644
--- a/src/keyd.c
+++ b/src/keyd.c
@@ -226,22 +226,23 @@ static void send_repetitions()
 
 void set_mods(uint16_t mods)
 {
+	static uint16_t state = 0;
 	size_t i;
 
-	for (i = 0; i < sizeof modifier_table / sizeof modifier_table[0]; i++) {
-		struct modifier_table_ent *m = &modifier_table[i];
+	uint16_t diff = mods ^ state;
 
-		if (m->mask & mods) {
-			if (!keystate[m->code1] && !keystate[m->code2])
-				send_key(m->code1, 1);
-		} else {
-			if (keystate[m->code1])
-				send_key(m->code1, 0);
+	if (MOD_CTRL & diff)
+		send_key(KEY_LEFTCTRL, !!(MOD_CTRL & mods));
+	if (MOD_ALT_GR & diff)
+		send_key(KEY_RIGHTALT, !!(MOD_ALT_GR & mods));
+	if (MOD_SHIFT & diff)
+		send_key(KEY_LEFTSHIFT, !!(MOD_SHIFT & mods));
+	if (MOD_SUPER & diff)
+		send_key(KEY_LEFTMETA, !!(MOD_SUPER & mods));
+	if (MOD_ALT & diff)
+		send_key(KEY_LEFTALT, !!(MOD_ALT & mods));
 
-			if (keystate[m->code2])
-				send_key(m->code2, 0);
-		}
-	}
+	state = mods;
 }
 
 /* Block on the given keyboard nodes until no keys are depressed. */
diff --git a/t/layer4.t b/t/layer4.t
new file mode 100644
index 0000000..02a7ef8
--- /dev/null
+++ b/t/layer4.t
@@ -0,0 +1,13 @@
+s down
+meta down
+c down
+c up
+meta up
+s up
+
+shift down
+meta down
+c down
+c up
+meta up
+shift up
diff --git a/t/run.sh b/t/run.sh
index ced6f21..cb1f958 100755
--- a/t/run.sh
+++ b/t/run.sh
@@ -4,7 +4,7 @@
 
 cleanup() {
 	sudo pkill keyd
-	sleep .5s
+	sleep 1s
 	sudo systemctl restart keyd
 
 	trap - EXIT
diff --git a/t/test.conf b/t/test.conf
index 0a3b6db..b01133d 100644
--- a/t/test.conf
+++ b/t/test.conf
@@ -23,6 +23,7 @@ l = layer(test)
 t = overload(o, esc, 2)
 m = macro(C-h one)
 - = layout(layout2)
+s = leftshift
 
 [layout2:layout]