checker: support nested labeled for statements (#21658)

vlib/v/checker/checker.v

@@ -105,7 +105,7 @@ mut:
 	cur_orm_ts                       ast.TypeSymbol
 	cur_anon_fn                      &ast.AnonFn = unsafe { nil }
 	vmod_file_content                string     // needed for @VMOD_FILE, contents of the file, *NOT its path**
-	loop_label                       string     // set when inside a labelled for loop
+	loop_labels                      []string   // filled, when inside labelled for loops: `a_label: for x in 0..10 {`
 	vweb_gen_types                   []ast.Type // vweb route checks
 	timers                           &util.Timers = util.get_timers()
 	comptime_info_stack              []comptime.ComptimeInfo // stores the values from the above on each $for loop, to make nesting them easier
@@ -183,7 +183,7 @@ fn (mut c Checker) reset_checker_state_at_start_of_new_file() {
 	c.inside_sql = false
 	c.cur_orm_ts = ast.TypeSymbol{}
 	c.prevent_sum_type_unwrapping_once = false
-	c.loop_label = ''
+	c.loop_labels = []
 	c.using_new_err_struct = false
 	c.inside_selector_expr = false
 	c.inside_interface_deref = false
@@ -2015,16 +2015,15 @@ fn (mut c Checker) check_enum_field_integer_literal(expr ast.IntegerLiteral, is_
 }
 
 @[inline]
-fn (mut c Checker) check_loop_label(label string, pos token.Pos) {
+fn (mut c Checker) check_loop_labels(label string, pos token.Pos) {
 	if label == '' {
-		// ignore
 		return
 	}
-	if c.loop_label.len != 0 {
+	if label in c.loop_labels {
-		c.error('nesting of labelled `for` loops is not supported', pos)
+		c.error('the loop label was already defined before', pos)
 		return
 	}
-	c.loop_label = label
+	c.loop_labels << label
 }
 
 fn (mut c Checker) stmt(mut node ast.Stmt) {
@@ -2231,7 +2230,7 @@ fn (mut c Checker) branch_stmt(node ast.BranchStmt) {
 		}
 	}
 	if node.label.len > 0 {
-		if node.label != c.loop_label {
+		if node.label !in c.loop_labels {
 			c.error('invalid label name `${node.label}`', node.pos)
 		}
 	}

vlib/v/checker/for.v

@@ -7,7 +7,7 @@ import v.token
 
 fn (mut c Checker) for_c_stmt(mut node ast.ForCStmt) {
 	c.in_for_count++
-	prev_loop_label := c.loop_label
+	prev_loop_labels := c.loop_labels
 	if node.has_init {
 		c.stmt(mut node.init)
 	}
@@ -22,15 +22,15 @@ fn (mut c Checker) for_c_stmt(mut node ast.ForCStmt) {
 		}
 		c.stmt(mut node.inc)
 	}
-	c.check_loop_label(node.label, node.pos)
+	c.check_loop_labels(node.label, node.pos)
 	c.stmts(mut node.stmts)
-	c.loop_label = prev_loop_label
+	c.loop_labels = prev_loop_labels
 	c.in_for_count--
 }
 
 fn (mut c Checker) for_in_stmt(mut node ast.ForInStmt) {
 	c.in_for_count++
-	prev_loop_label := c.loop_label
+	prev_loop_labels := c.loop_labels
 	mut typ := c.expr(mut node.cond)
 	if node.key_var.len > 0 && node.key_var != '_' {
 		c.check_valid_snake_case(node.key_var, 'variable name', node.pos)
@@ -259,15 +259,15 @@ fn (mut c Checker) for_in_stmt(mut node ast.ForInStmt) {
 			}
 		}
 	}
-	c.check_loop_label(node.label, node.pos)
+	c.check_loop_labels(node.label, node.pos)
 	c.stmts(mut node.stmts)
-	c.loop_label = prev_loop_label
+	c.loop_labels = prev_loop_labels
 	c.in_for_count--
 }
 
 fn (mut c Checker) for_stmt(mut node ast.ForStmt) {
 	c.in_for_count++
-	prev_loop_label := c.loop_label
+	prev_loop_labels := c.loop_labels
 	c.expected_type = ast.bool_type
 	if node.cond !is ast.EmptyExpr {
 		typ := c.expr(mut node.cond)
@@ -288,9 +288,9 @@ fn (mut c Checker) for_stmt(mut node ast.ForStmt) {
 	}
 	// TODO: update loop var type
 	// how does this work currently?
-	c.check_loop_label(node.label, node.pos)
+	c.check_loop_labels(node.label, node.pos)
 	c.stmts(mut node.stmts)
-	c.loop_label = prev_loop_label
+	c.loop_labels = prev_loop_labels
 	c.in_for_count--
 	if c.smartcast_mut_pos != token.Pos{} {
 		c.smartcast_mut_pos = token.Pos{}

vlib/v/checker/tests/labelled_break_continue.out

@@ -26,10 +26,3 @@ vlib/v/checker/tests/labelled_break_continue.vv:16:10: error: invalid label name
       |                   ~~~~~
    17 |         }
    18 |     }
-vlib/v/checker/tests/labelled_break_continue.vv:21:11: error: nesting of labelled `for` loops is not supported
-   19 |     // check nested loops (not supported ATM)
-   20 |     L3: for ;; i++ {
-   21 |         L4: for {
-      |                 ^
-   22 |             if i < 17 {continue L3}
-   23 |             else {break L3}

vlib/v/tests/nested_fors_with_labels_test.v

@@ -0,0 +1,91 @@
+const good = [
+	'> x: 0 | y: 0 | z: 0',
+	'> x: 0 | y: 0 | z: 1',
+	'> x: 0 | y: 1 | z: 0',
+	'> x: 0 | y: 1 | z: 1',
+	'> x: 1 | y: 0 | z: 0',
+	'> x: 1 | y: 0 | z: 1',
+	'> x: 1 | y: 1 | z: 0',
+	'> x: 1 | y: 1 | z: 1',
+]
+
+fn test_labeled_nested_loops_for_in() {
+	mut values := []string{}
+	abc: for x in 0 .. 2 {
+		def: for y in 0 .. 5 {
+			if y > 1 {
+				continue abc
+			}
+			xyz: for z in 0 .. 10 {
+				if z > 1 {
+					continue def
+				}
+				values << '> x: ${x} | y: ${y} | z: ${z}'
+			}
+		}
+	}
+	assert values == good
+}
+
+fn test_labeled_nested_loops_for_c_style() {
+	mut values := []string{}
+	abc: for x := 0; x < 2; x++ {
+		def: for y := 0; y < 5; y++ {
+			if y > 1 {
+				continue abc
+			}
+			xyz: for z := 0; z < 10; z++ {
+				if z > 1 {
+					continue def
+				}
+				values << '> x: ${x} | y: ${y} | z: ${z}'
+			}
+		}
+	}
+	assert values == good
+}
+
+fn test_labeled_nested_loops_for_in_array() {
+	mut values := []string{}
+	x_array := [0, 1]
+	y_array := [0, 1, 2, 3, 4]
+	z_array := [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
+	abc: for x in x_array {
+		def: for y in y_array {
+			if y > 1 {
+				continue abc
+			}
+			xyz: for z in y_array {
+				if z > 1 {
+					continue def
+				}
+				values << '> x: ${x} | y: ${y} | z: ${z}'
+			}
+		}
+	}
+	assert values == good
+}
+
+fn test_labeled_nested_loops_for_condition() {
+	mut values := []string{}
+	mut x := -1
+	abc: for x < 1 {
+		x++
+		mut y := -1
+		def: for y < 5 {
+			y++
+			if y > 1 {
+				continue abc
+			}
+			mut z := -1
+			xyz: for z < 10 {
+				z++
+				if z > 1 {
+					continue def
+				}
+				values << '> x: ${x} | y: ${y} | z: ${z}'
+			}
+		}
+	}
+	assert values == good
+}