engine: a mode switch shows the mode it switched to

Ctrl+S, Ctrl+N and the rest changed the mode with nothing to see; the
next key was the only way to tell.  The popup now shows A, 한, あ, ア, or
ă until a key is typed, beside the ☺ and 漢 a search already shows.

README.md

@@ -17,6 +17,9 @@ compatibility mode.
 | `Ctrl+E` | Emoji and symbol search |
 | `Ctrl+H` | One-shot Hanja search |
 
+Switching mode shows the mode switched to — `A`, `한`, `あ`, `ア`, `ă` — in
+the popup until the next key.
+
 A Korean keyboard's 한/영 key toggles Korean and English, and its 한자 key
 is `Ctrl+H`; a Japanese keyboard's 半角/全角 toggles Japanese and English,
 ひらがな/カタカナ switches between the two kana modes, 変換 turns Japanese

strans.c

@@ -7,6 +7,7 @@ static void *lostowner;	/* the context the engine was taken from */
 static Str lost;
 static int clientpre;	/* the owner draws its own preedit */
 static Caret caret;
+static Rune modemark;	/* the mode the last key switched to */
 static Drawcmd lastdraw;
 static Emit transjp(Im*, Rune);
 static void backjp(Im*);
@@ -197,6 +198,8 @@ snapshot(Drawcmd *dc)
 		dc->pre = pre;
 	if(search.lang && pre.n == 0)	/* a search just begun shows itself */
 		sputr(&dc->pre, search.lang == LangEMOJI ? L'☺' : L'漢');
+	else if(modemark != 0 && pre.n == 0 && im.nkouho == 0)
+		sputr(&dc->pre, modemark);
 	first = pagefirst();
 	n = im.nkouho - first;
 	if(n > Maxdisp) n = Maxdisp;
@@ -336,6 +339,19 @@ katakouho(void)
 		addkouho(&k);
 }
 
+/* What the popup shows for a moment when the mode changes. */
+static Rune
+langmark(int lang)
+{
+	switch(lang){
+	case LangJP:	return L'あ';
+	case LangJPK:	return L'ア';
+	case LangKO:	return L'한';
+	case LangVI:	return L'ă';
+	}
+	return L'A';
+}
+
 static int
 setlang(int c)
 {
@@ -344,6 +360,8 @@ setlang(int c)
 	l = getlang(c);
 	if(l == nil)
 		return 0;
+	if(l != im.l)
+		modemark = langmark(l->lang);
 	im.l = l;
 	return 1;
 }
@@ -783,6 +801,7 @@ transition(u32int ks, u32int mod, Str *com)
 	int n;
 	Rune c;
 
+	modemark = 0;	/* any key after the switch takes its mark away */
 	if(im.l->lang == LangKO)
 		ks = kokey(ks, mod);
 	else if(isjp(&im))
@@ -897,6 +916,7 @@ init(void)
 	im.sel = -1;
 	memset(&search, 0, sizeof search);
 	memset(&caret, 0, sizeof caret);
+	modemark = 0;
 	activeowner = nil;
 	lostowner = nil;
 	clientpre = 0;

tests/engine_test.c

@@ -565,11 +565,25 @@ engine_korean_modifiers_and_backspace(struct ct *t)
 void
 engine_direct_language_modes(struct ct *t)
 {
+	Drawcmd dc;
 	Str com;
 
 	init();
+	draindraw(nil);
 	sclear(&com);
 	CT_EQ_INT(t, LangEN, im.l->lang);
+	/* A switch shows the mode it switched to until the next key. */
+	CT_CHECK(t, keystroke('s', Mctrl, &com));
+	if(CT_CHECK(t, draindraw(&dc) > 0))
+		checkstr(t, "mode mark", "한", &dc.pre);
+	CT_CHECK(t, keystroke('t', Mctrl, &com));
+	if(CT_CHECK(t, draindraw(&dc) > 0))
+		checkstr(t, "mode mark", "A", &dc.pre);
+	CT_CHECK(t, !keystroke('a', 0, &com));
+	if(CT_CHECK(t, draindraw(&dc) > 0))
+		CT_EQ_INT(t, 0, dc.pre.n);
+	CT_CHECK(t, !keystroke('a', 0, &com));
+	CT_EQ_INT(t, 0, draindraw(nil));
 	CT_EQ_PTR(t, nil, im.l->mapname);
 	CT_EQ_PTR(t, nil, im.l->map);
 	CT_EQ_PTR(t, nil, im.l->trans);