engine: Shift on the okurigana asks for that reading, as SKK does

kaku offers the twenty-two readings of かく before 書く, because the SKK
dictionary keys a verb by its stem and gives no frequency to rank the two
lists by.  SKK's own answer is the shift key: kaKu says where the
okurigana starts, and that split now comes first — the reading's own
candidates still follow it.  Caps Lock sends no Shift, so it marks
nothing, and a word typed without Shift is unchanged.

README.md

@@ -39,6 +39,10 @@ current page; before that the digits type. `Enter` commits the chosen candidate,
 reading when none is chosen, as `0` always does; so does typing on, or any
 key that ends the composition. `Backspace` deletes the last kana shown;
 romaji that made no kana stays in the reading as typed until it is mended.
+The dictionary keys a verb or adjective by its stem, so `kaku` offers the
+readings of かく and then 書く and its kin; typing the okurigana with
+`Shift`, as SKK does — `kaKu` — asks for that split first.  Caps Lock is
+not `Shift` and marks nothing.
 `Backspace` and `Esc` on a chosen candidate go back to the reading, and
 `Esc` on the reading cancels it. Katakana mode does not perform Kanji
 conversion.

strans.c

@@ -8,6 +8,7 @@ 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 int okuriat = -1;	/* where Shift marked the okurigana, or -1 */
 static Drawcmd lastdraw;
 static Emit transjp(Im*, Rune);
 static void backjp(Im*);
@@ -279,21 +280,22 @@ okuriletter(Rune r)
 
 /*
  * SKK keys a verb or adjective by its stem and the letter of the
- * okurigana that follows (かk: 書, 描, ...).  Every split of the reading
+ * okurigana that follows (かk: 書, 描, ...).  The split the user marked
- * is tried, longest stem first, and the okurigana is put back; a っ
+ * is tried alone; otherwise every split is, longest stem first.  The
- * ending the stem (いっt: 言, 行) is written in kana too.
+ * okurigana is put back, and a っ ending the stem (いっt: 言, 行) is
+ * written in kana too.
  */
 static void
-dictqokuri(Str *reading)
+dictqokuri(Str *reading, int split)
 {
 	Str key, okuri, kouho[Maxkouho];
 	Rune c;
 	int i, j, n;
 
-	for(i = reading->n - 1; i > 0; i--){
+	for(i = split >= 0 ? split : reading->n - 1; i > 0; i--){
 		c = okuriletter(reading->r[i]);
 		if(c == 0)
-			continue;
+			break;
 		key = *reading;
 		key.n = i;
 		sputr(&key, c);
@@ -305,6 +307,8 @@ dictqokuri(Str *reading)
 			sappend(&kouho[j], &okuri);
 			addkouho(&kouho[j]);
 		}
+		if(split >= 0)
+			break;
 	}
 }
 
@@ -312,14 +316,20 @@ dictqokuri(Str *reading)
 static void
 dictqjp(void)
 {
-	Str reading;
+	Str reading, exact[Maxkouho];
+	int i, n;
 
 	clearkouho();
 	if(!isjp(&im) || !jpreading(im.l->map, &im.pre, &im.raw, &reading) ||
 	   reading.n == 0)
 		return;
-	im.nkouho = dictlookup(im.l->dict, &reading, im.kouho, Maxkouho);
+	/* What Shift marked comes first; the dictionary's own readings next. */
-	dictqokuri(&reading);
+	if(okuriat > 0 && okuriat < reading.n)
+		dictqokuri(&reading, okuriat);
+	n = dictlookup(im.l->dict, &reading, exact, Maxkouho);
+	for(i = 0; i < n; i++)
+		addkouho(&exact[i]);
+	dictqokuri(&reading, -1);
 }
 
 /* The reading in Katakana is the last candidate, as in every IME. */
@@ -663,6 +673,7 @@ reset(void)
 {
 	sclear(&im.pre);
 	sclear(&im.raw);
+	okuriat = -1;
 	endsearch();
 }
 
@@ -798,10 +809,16 @@ searchkey(u32int ks, u32int mod, Str *com)
 static int
 transition(u32int ks, u32int mod, Str *com)
 {
+	Str mark;
 	int n;
 	Rune c;
 
 	modemark = 0;	/* any key after the switch takes its mark away */
+	/* Shift on a romaji letter marks the okurigana, as SKK's capital does. */
+	if(isjp(&im) && (mod & Mshift) && ks >= 'A' && ks <= 'Z' && haspre(&im)){
+		impre(&im, &mark);
+		okuriat = mark.n;
+	}
 	if(im.l->lang == LangKO)
 		ks = kokey(ks, mod);
 	else if(isjp(&im))
@@ -917,6 +934,7 @@ init(void)
 	memset(&search, 0, sizeof search);
 	memset(&caret, 0, sizeof caret);
 	modemark = 0;
+	okuriat = -1;
 	activeowner = nil;
 	lostowner = nil;
 	clientpre = 0;

tests/engine_test.c

@@ -1223,6 +1223,18 @@ engine_japanese_candidates(struct ct *t)
 	if(CT_EQ_INT(t, 1, im.nkouho))
 		checkstr(t, "two-kana okurigana", "大きい", &im.kouho[0]);
 	CT_CHECK(t, keystroke(Kesc, 0, &com));
+	/* Shift on the okurigana asks for that split alone, first. */
+	sclear(&com);
+	if(!typekeys(t, "ka", &com))
+		goto cleanup;
+	CT_CHECK(t, keystroke('K', Mshift, &com));
+	CT_CHECK(t, keystroke('u', 0, &com));
+	if(CT_EQ_INT(t, 3, im.nkouho)){
+		checkstr(t, "marked okurigana first", "書く", &im.kouho[0]);
+		checkstr(t, "then the second", "描く", &im.kouho[1]);
+		checkstr(t, "then the reading's own", "確", &im.kouho[2]);
+	}
+	CT_CHECK(t, keystroke(Kesc, 0, &com));
 	setdict(jp->dict, "いt", "言 行");
 	setdict(jp->dict, "いっt", "言 行");
 	if(!typekeys(t, "itta", &com))