engine: Backspace deletes the last kana shown; Tab converts like Space

Backspace undid a keystroke: な became ん, かんじ became かんj, きゃ
became ky.  Like every Japanese IME it now deletes the last kana as
shown — な goes, かんじ becomes かん, きゃ becomes き — while a romaji
letter that never became kana still goes one at a time.  Tab stepped
through candidates in a search and committed in Japanese; it steps
through them there too, with Space, and Shift+Tab steps back.

README.md

@@ -24,11 +24,12 @@ or `Super` held it commits what is pending and goes to the application, so
 `Ctrl+Shift+V` still pastes.
 
 A complete Japanese reading shows its Kanji candidates with none chosen.
-`Space` chooses the first and then steps on, wrapping (`Shift+Space` steps
+`Space` or `Tab` chooses the first and then steps on, wrapping (with
-back); `Up`/`Down` and `PageUp`/`PageDown` move without wrapping. An
+`Shift`, back); `Up`/`Down` and `PageUp`/`PageDown` move without wrapping.
-unmodified `1`-`9` commits that row of the current page. `Enter` and `Tab`
+An unmodified `1`-`9` commits that row of the current page. `Enter`
-commit the chosen candidate, or the reading when none is chosen, as `0`
+commits the chosen candidate, or the 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.
 Japanese consumes the confirming key; Korean and Vietnamese pass it on to
 the application. `Space` adds the reading in Katakana as the last
 candidate, so a word the dictionary lacks converts to Katakana with one

strans.c

@@ -356,13 +356,20 @@ commitim(Im *p, Str *com)
 	sclear(&p->raw);
 }
 
+/* Deletes the last kana as shown, not the last key: kya loses ゃ. */
 static void
 backjp(Im *p)
 {
-	if(p->raw.n != 0)
+	Str v;
-		spopr(&p->raw);
+
-	else
+	if(p->raw.n == 0)
 		spopr(&p->pre);
+	else if(mapget(p->l->map, &p->raw, &v)){
+		spopr(&v);
+		sappend(&p->pre, &v);
+		sclear(&p->raw);
+	}else
+		spopr(&p->raw);
 }
 
 /*
@@ -800,9 +807,10 @@ transition(u32int ks, u32int mod, Str *com)
 		reset();
 		return 1;
 	}
-	if(ks == ' ' && isjp(&im) && haspre(&im) && !(mod & ~Mshift)){
+	if((ks == ' ' || ks == Ktab) && isjp(&im) && haspre(&im) &&
-		/* Space converts: it steps through the candidates, Katakana
+	   !(mod & ~Mshift)){
-		 * last; a reading with none is committed. */
+		/* Space and Tab convert: they step through the candidates,
+		 * Katakana last; a reading with none is committed. */
 		katakouho();
 		if(im.nkouho != 0)
 			cyclekouho(mod & Mshift ? -1 : 1);

tests/engine_test.c

@@ -120,9 +120,9 @@ engine_backspace_clears_candidates(struct ct *t)
 	checkstr(t, "chosen candidate backspace", "na", &im.raw);
 	CT_CHECK(t, keystroke(Kback, 0, &com));
 	checkstr(t, "backspace commit", "", &com);
-	checkstr(t, "pending romaji after backspace", "n", &im.raw);
+	checkstr(t, "backspace deletes the kana shown", "", &im.raw);
 	impre(&im, &shown);
-	checkstr(t, "shown preedit after backspace", "ん", &shown);
+	checkstr(t, "shown preedit after backspace", "", &shown);
 	CT_EQ_INT(t, 0, im.nkouho);
 	CT_EQ_INT(t, -1, im.sel);
 }
@@ -852,21 +852,28 @@ engine_candidate_page_movement(struct ct *t)
 void
 engine_candidate_completion(struct ct *t)
 {
-	static Rune keys[] = { Kret, Ktab };
 	Str com;
-	int i;
 
-	for(i = 0; i < nelem(keys); i++){
+	init();
-		init();
+	im.l = getlang(LangJP);
-		im.l = getlang(LangJP);
+	im.pre = mkstr("reading");
-		im.pre = mkstr("reading");
+	setcandidates(1);
-		setcandidates(1);
+	sclear(&com);
-		sclear(&com);
+	CT_CHECK(t, keystroke(Kret, 0, &com));
-		CT_CHECK(t, keystroke(keys[i], 0, &com));
+	checkstr(t, "unselected candidate commits reading", "reading", &com);
-		checkstr(t, "unselected candidate commits reading",
+	CT_EQ_INT(t, 0, im.nkouho);
-			"reading", &com);
+
-		CT_EQ_INT(t, 0, im.nkouho);
+	init();
-	}
+	im.l = getlang(LangJP);
+	im.pre = mkstr("reading");
+	setcandidates(2);
+	sclear(&com);
+	CT_CHECK(t, keystroke(Ktab, 0, &com));
+	CT_EQ_INT(t, 0, im.sel);
+	CT_CHECK(t, keystroke(Ktab, Mshift, &com));
+	CT_EQ_INT(t, 1, im.sel);
+	CT_CHECK(t, keystroke(Kret, 0, &com));
+	checkstr(t, "Tab steps through the candidates", "c2", &com);
 
 	candidatebegin(2);
 	im.pre = mkstr("reading");
@@ -1250,8 +1257,6 @@ engine_japanese_candidates(struct ct *t)
 	if(!typekeys(t, "kanji", &com))
 		goto cleanup;
 	CT_CHECK(t, keystroke(Kback, 0, &com));
-	CT_EQ_INT(t, 0, im.nkouho);
-	CT_CHECK(t, keystroke(Kback, 0, &com));
 	if(CT_EQ_INT(t, 1, im.nkouho))
 		checkstr(t, "shorter reading candidate", "缶", &im.kouho[0]);
 cleanup:
@@ -1270,13 +1275,18 @@ engine_japanese_backspace_and_boundaries(struct ct *t)
 	if(typekeys(t, "kanji", &com)){
 		CT_CHECK(t, keystroke(Kback, 0, &com));
 		impre(&im, &shown);
-		checkstr(t, "backspace pending i", "かんj", &shown);
+		checkstr(t, "backspace deletes じ", "かん", &shown);
 		CT_CHECK(t, keystroke(Kback, 0, &com));
 		impre(&im, &shown);
-		checkstr(t, "backspace pending j", "かん", &shown);
+		checkstr(t, "backspace deletes ん", "か", &shown);
-		CT_CHECK(t, keystroke(Kback, 0, &com));
+		if(typekeys(t, "kyu", &com)){
-		impre(&im, &shown);
+			CT_CHECK(t, keystroke(Kback, 0, &com));
-		checkstr(t, "backspace accumulated kana", "か", &shown);
+			impre(&im, &shown);
+			checkstr(t, "backspace deletes ゅ", "かき", &shown);
+			CT_CHECK(t, keystroke(Kback, 0, &com));
+			CT_CHECK(t, keystroke(Kback, 0, &com));
+			CT_CHECK(t, !haspre(&im));
+		}
 	}
 
 	init();