markused: fix x := t.wait(), when t := go fn () string { (fix #24577) (#24580)

Author: felipensp

vlib/v/ast/table.v

@@ -32,6 +32,7 @@ pub mut:
 	map_update       bool            // {...foo}
 	interpolation    bool            // '${foo} ${bar}'
 	option_or_result bool            // has panic call
+	waiter           bool            // has thread waiter
 	print_types      map[int]bool    // print() idx types
 	used_fns         map[string]bool // filled in by markused
 	used_consts      map[string]bool // filled in by markused

vlib/v/checker/fn.v

@@ -2726,6 +2726,9 @@ fn (mut c Checker) spawn_expr(mut node ast.SpawnExpr) ast.Type {
 		c.error('option handling cannot be done in `spawn` call. Do it when calling `.wait()`',
 			node.call_expr.or_block.pos)
 	}
+	if node.is_expr {
+		c.table.used_features.waiter = true
+	}
 	// Make sure there are no mutable arguments
 	for arg in node.call_expr.args {
 		if arg.is_mut && !arg.typ.is_ptr() {
@@ -2761,6 +2764,9 @@ fn (mut c Checker) go_expr(mut node ast.GoExpr) ast.Type {
 		c.error('option handling cannot be done in `go` call. Do it when calling `.wait()`',
 			node.call_expr.or_block.pos)
 	}
+	if node.is_expr {
+		c.table.used_features.waiter = true
+	}
 	// Make sure there are no mutable arguments
 	for arg in node.call_expr.args {
 		if arg.is_mut && !arg.typ.is_ptr() {

vlib/v/markused/markused.v

@@ -168,6 +168,9 @@ pub fn mark_used(mut table ast.Table, mut pref_ pref.Preferences, ast_files []&a
 				builderptr_idx + '.write_rune',
 			]
 		}
+		if table.used_features.waiter {
+			core_fns << 'free'
+		}
 		if !table.used_features.arr_init {
 			table.used_features.arr_init = table.used_features.print_types.keys().any(table.type_to_str(it).contains('[]'))
 		}

vlib/v/tests/skip_unused/thread_waiter.run.out

@@ -0,0 +1,2 @@
+string
+hi

vlib/v/tests/skip_unused/thread_waiter.skip_unused.run.out

@@ -0,0 +1,2 @@
+string
+hi

vlib/v/tests/skip_unused/thread_waiter.vv

@@ -0,0 +1,10 @@
+module main
+
+fn main() {
+	t := go fn () string {
+		return 'hi'
+	}()
+	x := t.wait()
+	println(typeof(x).name)
+	println(x)
+}