From 86619338dd2955e1d58a8a365409221e386a00fe Mon Sep 17 00:00:00 2001
From: SheatNoisette <45624871+SheatNoisette@users.noreply.github.com>
Date: Sat, 3 Jan 2026 08:11:41 +0100
Subject: [PATCH] wasm: fix infinite loop using continue in C-like for loops
 (#26250)

---
 vlib/v/gen/wasm/gen.v                        | 29 +++++---
 vlib/v/gen/wasm/tests/control_flow.vv        | 54 ++++++++++++++
 vlib/v/gen/wasm/tests/control_flow.vv.out    |  8 +-
 vlib/v/gen/wasm/tests/labeled_for_inc.vv     | 78 ++++++++++++++++++++
 vlib/v/gen/wasm/tests/labeled_for_inc.vv.out |  9 +++
 5 files changed, 165 insertions(+), 13 deletions(-)
 create mode 100644 vlib/v/gen/wasm/tests/labeled_for_inc.vv
 create mode 100644 vlib/v/gen/wasm/tests/labeled_for_inc.vv.out

diff --git a/vlib/v/gen/wasm/gen.v b/vlib/v/gen/wasm/gen.v
index bd6f2d80c..d3abcc9e7 100644
--- a/vlib/v/gen/wasm/gen.v
+++ b/vlib/v/gen/wasm/gen.v
@@ -1093,26 +1093,31 @@ pub fn (mut g Gen) expr_stmt(node ast.Stmt, expected ast.Type) {
 
 				loop := g.func.c_loop([], [])
 				{
-					g.loop_breakpoint_stack << LoopBreakpoint{
-						c_continue: loop
-						c_break:    block
-						name:       node.label
-					}
+					continue_block := g.func.c_block([], [])
+					{
+						g.loop_breakpoint_stack << LoopBreakpoint{
+							c_continue: continue_block
+							c_break:    block
+							name:       node.label
+						}
 
-					if node.has_cond {
-						g.expr(node.cond, ast.bool_type)
-						g.func.eqz(.i32_t)
-						g.func.c_br_if(block) // !cond, goto end
-					}
+						if node.has_cond {
+							g.expr(node.cond, ast.bool_type)
+							g.func.eqz(.i32_t)
+							g.func.c_br_if(block) // !cond, goto end
+						}
 
-					g.expr_stmts(node.stmts, ast.void_type)
+						g.expr_stmts(node.stmts, ast.void_type)
+
+						g.loop_breakpoint_stack.pop()
+					}
+					g.func.c_end(continue_block)
 
 					if node.has_inc {
 						g.expr_stmt(node.inc, ast.void_type)
 					}
 
 					g.func.c_br(loop)
-					g.loop_breakpoint_stack.pop()
 				}
 				g.func.c_end(loop)
 			}
diff --git a/vlib/v/gen/wasm/tests/control_flow.vv b/vlib/v/gen/wasm/tests/control_flow.vv
index 19d32a89d..94838bfab 100644
--- a/vlib/v/gen/wasm/tests/control_flow.vv
+++ b/vlib/v/gen/wasm/tests/control_flow.vv
@@ -94,6 +94,51 @@ fn infcfor() int {
 	return 0
 }
 
+fn continuecfor() int {
+	mut val := 0
+
+	for i := 0; i < 10; i += 2 {
+		if i == 6 {
+			continue
+		}
+		val += i
+	}
+	return val
+}
+
+fn continuecfor_multiple() int {
+	mut val := 0
+
+	for i := 0; i < 10; i += 2 {
+		if i == 6 {
+			continue
+		}
+		// Two continues
+		if i == 2 {
+			continue
+		}
+		val += i
+	}
+	return val
+}
+
+fn continuec_twofor_multiple() int {
+	mut val := 0
+
+	for i := 0; i < 10; i += 2 {
+		if i == 6 {
+			continue
+		}
+		for j := -12; j < 10; j += 1 {
+			if j == 6 {
+				continue
+			}
+			val += i
+		}
+	}
+	return val
+}
+
 fn main() {
 	println('--- func()')
 	println(func(10, true))
@@ -121,4 +166,13 @@ fn main() {
 
 	println('--- infcfor()')
 	println(infcfor())
+
+	println('--- continuecfor()')
+	println(continuecfor())
+
+	println('--- continuecfor_multiple()')
+	println(continuecfor_multiple())
+
+	println('--- continuec_twofor_multiple()')
+	println(continuec_twofor_multiple())
 }
diff --git a/vlib/v/gen/wasm/tests/control_flow.vv.out b/vlib/v/gen/wasm/tests/control_flow.vv.out
index f990171f8..4c0fa8112 100644
--- a/vlib/v/gen/wasm/tests/control_flow.vv.out
+++ b/vlib/v/gen/wasm/tests/control_flow.vv.out
@@ -16,4 +16,10 @@
 100
 99
 --- infcfor()
-10
\ No newline at end of file
+10
+--- continuecfor()
+14
+--- continuecfor_multiple()
+12
+--- continuec_twofor_multiple()
+294
\ No newline at end of file
diff --git a/vlib/v/gen/wasm/tests/labeled_for_inc.vv b/vlib/v/gen/wasm/tests/labeled_for_inc.vv
new file mode 100644
index 000000000..f7ab4119d
--- /dev/null
+++ b/vlib/v/gen/wasm/tests/labeled_for_inc.vv
@@ -0,0 +1,78 @@
+fn labeled_break_continue_with_inc() int {
+	// Should not infinite loop
+	outer: for i := 4; true; i++ {
+		for {
+			if i < 7 {
+				continue outer
+			} else {
+				break outer
+			}
+		}
+	}
+	return 0
+}
+
+fn labeled_break_with_inc() int {
+	mut sum := 0
+	outer: for i := 0; i < 10; i++ {
+		for j := 0; j < 5; j++ {
+			sum += j
+			if i == 3 && j == 2 {
+				break outer
+			}
+		}
+		if sum == 10 {
+			return i
+		}
+	}
+	return sum
+}
+
+fn triple_nested_labeled_continue() (int, int) {
+	mut val1 := 0
+	mut val2 := 0
+	outer: for i := 0; i < 5; i++ {
+		middle: for j := 0; j < 3; j++ {
+			for k := 0; k < 2; k++ {
+				if i == 1 && j == 1 {
+					continue outer
+				}
+				val2 += 1
+				if i == 2 && j == 2 {
+					continue middle
+				}
+				val1 += 1
+			}
+		}
+	}
+	return val1, val2
+}
+
+fn labeled_continue_deep_nest() int {
+	mut result := 0
+	outer: for i := 0; i < 3; i++ {
+		for j := 0; j < 2; j++ {
+			for k := 0; k < 2; k++ {
+				if k == 1 && i < 2 {
+					result++
+					continue outer
+				}
+				result++
+			}
+		}
+	}
+	return result
+}
+
+fn main() {
+	println('--- labeled_break_continue_with_inc()')
+	println(labeled_break_continue_with_inc())
+	println('--- labeled_break_with_inc()')
+	println(labeled_break_with_inc())
+	println('--- triple_nested_labeled_continue()')
+	a, b := triple_nested_labeled_continue()
+	println(a)
+	println(b)
+	println('--- labeled_continue_deep_nest()')
+	println(labeled_continue_deep_nest())
+}
diff --git a/vlib/v/gen/wasm/tests/labeled_for_inc.vv.out b/vlib/v/gen/wasm/tests/labeled_for_inc.vv.out
new file mode 100644
index 000000000..dbffa6be6
--- /dev/null
+++ b/vlib/v/gen/wasm/tests/labeled_for_inc.vv.out
@@ -0,0 +1,9 @@
+--- labeled_break_continue_with_inc()
+0
+--- labeled_break_with_inc()
+0
+--- triple_nested_labeled_continue()
+24
+25
+--- labeled_continue_deep_nest()
+8
\ No newline at end of file
-- 
2.39.5