markused: improve the tracking of used closures (#25009)

cmd/tools/vast/vast.v

@@ -605,6 +605,7 @@ fn (t Tree) fn_decl(node ast.FnDecl) &Node {
 	obj.add_terse('is_unsafe', t.bool_node(node.is_unsafe))
 	obj.add_terse('is_markused', t.bool_node(node.is_markused))
 	obj.add_terse('is_file_translated', t.bool_node(node.is_file_translated))
+	obj.add_terse('is_closure', t.bool_node(node.is_closure))
 	obj.add_terse('receiver', t.struct_field(node.receiver))
 	obj.add('receiver_pos', t.pos(node.receiver_pos))
 	obj.add_terse('is_method', t.bool_node(node.is_method))

vlib/v/ast/ast.v

@@ -573,7 +573,7 @@ pub:
 pub struct AnonFn {
 pub mut:
 	decl           FnDecl
-	inherited_vars []Param
+	inherited_vars []Param         // note: closures have inherited_vars.len > 0
 	typ            Type            // the type of anonymous fn. Both .typ and .decl.name are auto generated
 	has_gen        map[string]bool // a map of the names of all generic anon functions, generated from it
 }
@@ -602,6 +602,7 @@ pub:
 	is_must_use           bool        // true, when @[must_use] is used on a fn. Calls to such functions, that ignore the return value, will cause warnings.
 	is_markused           bool        // true, when an explicit `@[markused]` tag was put on a fn; `-skip-unused` will not remove that fn
 	is_file_translated    bool        // true, when the file it resides in is `@[translated]`
+	is_closure            bool        // true, for actual closures like `fn [inherited] () {}` . It is false for normal anonymous functions, and for named functions/methods too.
 	receiver              StructField // TODO: this is not a struct field
 	receiver_pos          token.Pos   // `(u User)` in `fn (u User) name()` position
 	is_method             bool

vlib/v/ast/table.v

@@ -35,6 +35,7 @@ pub mut:
 	used_veb_types []Type          // veb context types, filled in by checker
 	used_maps      int             // how many times maps were used, filled in by markused
 	used_none      int             // how many times `none` was used, filled in by markused
+	used_closures  int             // number of used closures, either directly with `fn [state] () {}`, or indirectly (though `instance.method` promotions)
 	// json             bool            // json is imported
 	comptime_calls map[string]bool // resolved name to call on comptime
 	comptime_syms  map[Type]bool   // resolved syms (generic)

vlib/v/markused/markused.v

@@ -363,13 +363,15 @@ pub fn mark_used(mut table ast.Table, mut pref_ pref.Preferences, ast_files []&a
 	table.used_features.used_consts = walker.used_consts.move()
 	table.used_features.used_globals = walker.used_globals.move()
 	table.used_features.used_syms = walker.used_syms.move()
+	table.used_features.used_closures = walker.used_closures
 
 	if trace_skip_unused {
 		eprintln('>> t.used_fns: ${table.used_features.used_fns.keys()}')
 		eprintln('>> t.used_consts: ${table.used_features.used_consts.keys()}')
 		eprintln('>> t.used_globals: ${table.used_features.used_globals.keys()}')
 		eprintln('>> t.used_syms: ${table.used_features.used_syms.keys()}')
-		eprintln('>> walker.table.used_features.used_maps: ${walker.table.used_features.used_maps}')
+		eprintln('>> t.used_maps: ${table.used_features.used_maps}')
+		eprintln('>> t.used_closures: ${table.used_features.used_closures}')
 	}
 	if trace_skip_unused_just_unused_fns {
 		all_fns_keys := all_fns.keys()

vlib/v/markused/walker.v

@@ -21,6 +21,7 @@ pub mut:
 	used_option   int // _option_ok
 	used_result   int // _result_ok
 	used_panic    int // option/result propagation
+	used_closures int // fn [x] (){}, and `instance.method` used in an expression
 	pref          &pref.Preferences = unsafe { nil }
 mut:
 	all_fns       map[string]ast.FnDecl
@@ -712,6 +713,9 @@ fn (mut w Walker) expr(node_ ast.Expr) {
 			}
 			w.mark_by_type(node.typ)
 			w.or_block(node.or_block)
+			if node.has_hidden_receiver {
+				w.used_closures++
+			}
 		}
 		ast.SqlExpr {
 			w.expr(node.db_expr)
@@ -811,9 +815,6 @@ pub fn (mut w Walker) fn_decl(mut node ast.FnDecl) {
 	if w.used_fns[fkey] {
 		return
 	}
-	if node.no_body {
-		return
-	}
 	if w.trace_enabled {
 		w.level++
 		defer { w.level-- }
@@ -824,6 +825,12 @@ pub fn (mut w Walker) fn_decl(mut node ast.FnDecl) {
 		}
 		eprintln('>>>${'  '.repeat(w.level)}${receiver_name}${node.name} [decl]')
 	}
+	if node.is_closure {
+		w.used_closures++
+	}
+	if node.no_body {
+		return
+	}
 	if node.is_method {
 		w.mark_by_type(node.receiver.typ)
 	}

vlib/v/parser/fn.v

@@ -914,6 +914,7 @@ fn (mut p Parser) anon_fn() ast.AnonFn {
 			return_type_pos: return_type_pos
 			params:          params
 			is_variadic:     is_variadic
+			is_closure:      inherited_vars.len > 0
 			is_method:       false
 			generic_names:   generic_names
 			is_anon:         true