ast: reduce memory usage of ast.ScopeObject and ast.Ident instances (#24704)

cmd/tools/vast/vast.v

@@ -385,8 +385,8 @@ fn (t Tree) objects(so map[string]ast.ScopeObject) &Node {
 }
 
 fn (t Tree) scope_object(node ast.ScopeObject) &Node {
-	mut obj := create_object()
-	match node {
+	obj := match node {
+		ast.EmptyScopeObject { create_object() }
 		ast.ConstField { t.const_field(node) }
 		ast.GlobalField { t.global_field(node) }
 		ast.Var { t.var(node) }

vlib/v/ast/ast.v

@@ -117,7 +117,13 @@ pub type Stmt = AsmStmt
 	| StructDecl
 	| TypeDecl
 
-pub type ScopeObject = AsmRegister | ConstField | GlobalField | Var
+pub struct EmptyScopeObject {
+pub mut:
+	name string
+	typ  Type
+}
+
+pub type ScopeObject = EmptyScopeObject | AsmRegister | ConstField | GlobalField | Var
 
 // TODO: replace Param
 pub type Node = CallArg
@@ -209,6 +215,7 @@ pub:
 pub const empty_expr = Expr(EmptyExpr(0))
 pub const empty_stmt = Stmt(EmptyStmt{})
 pub const empty_node = Node(EmptyNode{})
+pub const empty_scope_object = ScopeObject(EmptyScopeObject{'empty_scope_object', 0})
 pub const empty_comptime_const_value = ComptTimeConstValue(EmptyExpr(0))
 
 // `{stmts}` or `unsafe {stmts}`
@@ -1076,8 +1083,8 @@ pub:
 	mut_pos  token.Pos
 	comptime bool
 pub mut:
-	scope          &Scope = unsafe { nil }
-	obj            ScopeObject
+	scope          &Scope      = unsafe { nil }
+	obj            ScopeObject = empty_scope_object
 	mod            string
 	name           string
 	full_name      string
@@ -1115,7 +1122,7 @@ pub fn (i &Ident) is_auto_heap() bool {
 pub fn (i &Ident) is_mut() bool {
 	match i.obj {
 		Var { return i.obj.is_mut }
-		ConstField { return false }
+		ConstField, EmptyScopeObject { return false }
 		AsmRegister, GlobalField { return true }
 	}
 }
@@ -2403,7 +2410,7 @@ pub fn (node Node) pos() token.Pos {
 				ConstField, GlobalField, Var {
 					return node.pos
 				}
-				AsmRegister {
+				EmptyScopeObject, AsmRegister {
 					return token.Pos{
 						len:       -1
 						line_nr:   -1
@@ -2551,7 +2558,7 @@ pub fn (node Node) children() []Node {
 	} else if node is ScopeObject {
 		match node {
 			GlobalField, ConstField, Var { children << node.expr }
-			AsmRegister {}
+			AsmRegister, EmptyScopeObject {}
 		}
 	} else {
 		match node {

vlib/v/ast/scope.v

@@ -111,8 +111,21 @@ pub fn (s &Scope) find_const(name string) ?&ConstField {
 }
 
 pub fn (s &Scope) known_var(name string) bool {
-	s.find_var(name) or { return false }
-	return true
+	if s == unsafe { nil } {
+		return false
+	}
+	for sc := unsafe { s }; true; sc = sc.parent {
+		if name in sc.objects {
+			obj := unsafe { sc.objects[name] or { empty_scope_object } }
+			if obj is Var {
+				return true
+			}
+		}
+		if sc.dont_lookup_parent() {
+			break
+		}
+	}
+	return false
 }
 
 pub fn (s &Scope) known_global(name string) bool {

vlib/v/checker/checker.v

@@ -4639,7 +4639,7 @@ fn (mut c Checker) find_obj_definition(obj ast.ScopeObject) !ast.Expr {
 	// TODO: remove once we have better type inference
 	mut name := ''
 	match obj {
-		ast.Var, ast.ConstField, ast.GlobalField, ast.AsmRegister { name = obj.name }
+		ast.EmptyScopeObject, ast.Var, ast.ConstField, ast.GlobalField, ast.AsmRegister { name = obj.name }
 	}
 	mut expr := ast.empty_expr
 	if obj is ast.Var {

vlib/v/gen/native/gen.v

@@ -906,6 +906,7 @@ fn (mut g Gen) is_fp_type(typ ast.Type) bool {
 
 fn (mut g Gen) get_sizeof_ident(ident ast.Ident) i32 {
 	typ := match ident.obj {
+		ast.EmptyScopeObject { ident.obj.typ }
 		ast.AsmRegister { ast.i64_type }
 		ast.ConstField { ident.obj.typ }
 		ast.GlobalField { ident.obj.typ }