break and continue in loops

examples/programs/break_continue/main.bro

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+# Milestone 18: `break` and `continue`.
+#
+# `break` exits the innermost loop; `continue` skips to that loop's next
+# iteration (running the update / index increment first). Both target the
+# innermost enclosing loop. Each section returns a distinct code on failure so
+# a regression points at the broken behaviour; success falls through to 42.
+
+main :: func() i32 {
+	# 1. `break` out of a `while` once i reaches 5.
+	i i32 = 0
+	a i32 = 0
+	while i < 100 : i += 1 {
+		if (i == 5) break
+		a += 1
+	}
+	if (a != 5) return 101
+
+	# 2. `continue` past n == 3 while summing 0..9 (45 - 3 = 42).
+	b i32 = 0
+	for 0..10 |n| {
+		if (n == 3) continue
+		b = b + n
+	}
+	if (b != 42) return 102
+
+	# 3. Nested loops: the inner `break` exits only the inner loop, so the outer
+	#    loop still runs all three iterations (each contributing one y == 0 pass).
+	c i32 = 0
+	for 0..3 |x| {
+		for 0..3 |y| {
+			if (y == 1) break
+			c += 1
+		}
+		_ = x
+	}
+	if (c != 3) return 103
+
+	# 4. `continue` on the final element of an inclusive range bounded by the
+	#    element type's maximum must exit cleanly, not overflow the increment.
+	hi u8 :: 255
+	d i32 = 0
+	for 0..=hi |v| {
+		if (v == 255) continue
+		d += 1
+	}
+	if (d != 255) return 104
+
+	# 5. `while true` is exitable via `break` (so it is not an infinite loop and
+	#    the code after it is reachable).
+	e i32 = 0
+	while true {
+		e += 1
+		if (e == 7) break
+	}
+	if (e != 7) return 105
+
+	return 42
+}