lx: Rewrite logic to make the four cases explicit, fix dead code.

This was previously ending up with a useless call to the current zone
after returning the token ("case S1: return TOK_UNKNOWN; lx->z(lx);"),
which led to a warning in CI [-Werror=implicit-fallthrough=].

Author: silentbicycle

src/lx/print/c.c

@@ -190,20 +190,28 @@ accept_c(FILE *f, const struct fsm_options *opt,
 	}
 
 	fprintf(f, "return ");
-	if (m->to != NULL) {
-		fprintf(f, "lx->z = z%u, ", zindexof(ast, m->to));
-	} else if (m->to == NULL && m->token == NULL) {
-		/* If accept-ing here doesn't actually map to a token or
-		 * a different zone, then it's stuck in the middle of a
-		 * pattern pair like `'//' .. /\n/ -> $nl;` with an EOF,
-		 * so tokenization should still fail. */
-		fprintf(f, "%sUNKNOWN; ", prefix.tok);
-	}
-	if (m->token != NULL) {
-		fprintf(f, "%s", prefix.tok);
-		esctok(f, m->token->s);
+	if (m->to == NULL) {
+		if (m->token == NULL) {
+			/* If accept-ing here doesn't actually map to a token or
+			 * a different zone, then it's stuck in the middle of a
+			 * pattern pair like `'//' .. /\n/ -> $nl;` with an EOF,
+			 * so tokenization should still fail. */
+			fprintf(f, "%sUNKNOWN", prefix.tok);
+		} else {
+			/* yield a token */
+			fprintf(f, "%s", prefix.tok);
+			esctok(f, m->token->s);
+		}
 	} else {
-		fprintf(f, "lx->z(lx)");
+		if (m->token == NULL) {
+			/* update to a different zone, then call to it */
+			fprintf(f, "lx->z = z%u, lx->z(lx)", zindexof(ast, m->to));
+		} else {
+			/* update zone, then yield a token */
+			fprintf(f, "lx->z = z%u, ", zindexof(ast, m->to));
+			fprintf(f, "%s", prefix.tok);
+			esctok(f, m->token->s);
+		}
 	}
 	fprintf(f, ";");
 	return 0;