checker: fix propagation checking in c-style for loop increment

vlib/v/checker/for.v

@@ -22,9 +22,22 @@ fn (mut c Checker) for_c_stmt(mut node ast.ForCStmt) {
 
 			for right in assign.right {
 				if right is ast.CallExpr {
-					if right.or_block.stmts.len > 0 {
-						c.error('options are not allowed in `for statement increment` (yet)',
-							right.pos)
+					match right.or_block.kind {
+						.block {
+							if right.or_block.stmts.len > 0 {
+								c.error('options are not allowed in `for statement increment` (yet)',
+									right.pos)
+							}
+						}
+						.propagate_result {
+							c.error('propagating errors in `for statement increment` is not allowed (yet)',
+								right.pos)
+						}
+						.propagate_option {
+							c.error('propagating options in `for statement increment` is not allowed (yet)',
+								right.pos)
+						}
+						.absent {}
 					}
 				}
 			}

vlib/v/checker/tests/for_c_stmt_with_option_propagation.out

@@ -0,0 +1,7 @@
+vlib/v/checker/tests/for_c_stmt_with_option_propagation.vv:8:24: error: propagating options in `for statement increment` is not allowed (yet)
+    6 |     mut pos := 0
+    7 | 
+    8 |     for ; pos > 10; pos = foo()? {
+      |                           ~~~~~
+    9 |         println(pos)
+   10 |     }

vlib/v/checker/tests/for_c_stmt_with_option_propagation.vv

@@ -0,0 +1,11 @@
+fn foo() ?int {
+	return 5
+}
+
+fn main() {
+	mut pos := 0
+
+	for ; pos > 10; pos = foo()? {
+		println(pos)
+	}
+}

vlib/v/checker/tests/for_c_stmt_with_result_propagation.out

@@ -0,0 +1,7 @@
+vlib/v/checker/tests/for_c_stmt_with_result_propagation.vv:8:24: error: propagating errors in `for statement increment` is not allowed (yet)
+    6 |     mut pos := 0
+    7 | 
+    8 |     for ; pos > 10; pos = foo()! {
+      |                           ~~~~~
+    9 |         println(pos)
+   10 |     }

vlib/v/checker/tests/for_c_stmt_with_result_propagation.vv

@@ -0,0 +1,11 @@
+fn foo() !int {
+	return 5
+}
+
+fn main() {
+	mut pos := 0
+
+	for ; pos > 10; pos = foo()! {
+		println(pos)
+	}
+}