Support 'else' blocks on for and while loops

src/compiler.c

@@ -1879,6 +1879,23 @@ static void continueStatement(void) {
 	current->continues[current->continueCount++] = (struct LoopExit){emitJump(OP_JUMP),parser.previous};
 }
 
+static void optionalElse(size_t blockWidth) {
+	KrkScanner scannerBefore = krk_tellScanner();
+	Parser  parserBefore = parser;
+	if (blockWidth == 0 || (check(TOKEN_INDENTATION) && (parser.current.length == blockWidth))) {
+		if (blockWidth) advance();
+		if (match(TOKEN_ELSE)) {
+			consume(TOKEN_COLON, "Expected ':' after 'else'.");
+			beginScope();
+			block(blockWidth,"else");
+			endScope();
+		} else {
+			krk_rewindScanner(scannerBefore);
+			parser = parserBefore;
+		}
+	}
+}
+
 static void whileStatement(void) {
 	size_t blockWidth = (parser.previous.type == TOKEN_INDENTATION) ? parser.previous.length : 0;
 	advance();
@@ -1900,6 +1917,7 @@ static void whileStatement(void) {
 	emitLoop(loopStart);
 	patchJump(exitJump);
 	emitByte(OP_POP);
+	optionalElse(blockWidth);
 	patchBreaks(loopStart);
 }
 
@@ -1992,8 +2010,8 @@ static void forStatement(void) {
 	emitLoop(loopStart);
 	patchJump(exitJump);
 	emitByte(OP_POP);
+	optionalElse(blockWidth);
 	patchBreaks(loopStart);
-
 	endScope();
 }
 

test/testLoopElse.krk

@@ -0,0 +1,32 @@
+
+def func(breakPoint):
+    let j = 0
+    for i in range(20):
+        if i == breakPoint:
+            break
+        j += 1
+    else:
+        print('finished for')
+    print('out of for')
+    return j
+
+print(func(20))
+print(func(15))
+print(func(20))
+print(func(15))
+
+def func2(breakPoint):
+    let i = 0
+    while i < 20:
+        if i == breakPoint:
+            break
+        i++
+    else:
+        print('finished while')
+    print('out of while')
+    return i
+
+print(func2(20))
+print(func2(15))
+print(func2(20))
+print(func2(15))

test/testLoopElse.krk.expect

@@ -0,0 +1,20 @@
+finished for
+out of for
+20
+out of for
+15
+finished for
+out of for
+20
+out of for
+15
+finished while
+out of while
+20
+out of while
+15
+finished while
+out of while
+20
+out of while
+15