checker/cgen: put `shared` struct always on heap (#8492)

vlib/v/checker/checker.v

@@ -2511,7 +2511,11 @@ pub fn (mut c Checker) assign_stmt(mut assign_stmt ast.AssignStmt) {
 					}
 					mut ident_var_info := left.info as ast.IdentVar
 					if ident_var_info.share == .shared_t {
+						if left_type.nr_muls() > 1 {
+							c.error('shared cannot be multi level reference', left.pos)
+						}
 						left_type = left_type.set_flag(.shared_f)
+						left_type = left_type.set_nr_muls(1)
 					}
 					if ident_var_info.share == .atomic_t {
 						left_type = left_type.set_flag(.atomic_f)
@@ -2590,7 +2594,8 @@ pub fn (mut c Checker) assign_stmt(mut assign_stmt ast.AssignStmt) {
 				c.error('cannot assign to `$left`: ' +
 					c.expected_msg(right_type_unwrapped, left_type_unwrapped), right.position())
 			}
-			if (right is ast.StructInit || !right_is_ptr) && !right_sym.is_number() {
+			if (right is ast.StructInit || !right_is_ptr) && !(right_sym.is_number()
+				|| left_type.has_flag(.shared_f)) {
 				left_name := c.table.type_to_str(left_type_unwrapped)
 				mut rtype := right_type_unwrapped
 				if rtype.is_ptr() {

vlib/v/gen/cgen.v

@@ -4693,13 +4693,13 @@ fn (mut g Gen) struct_init(struct_init ast.StructInit) {
 	g.is_amp = false // reset the flag immediately so that other struct inits in this expr are handled correctly
 	if is_amp {
 		g.out.go_back(1) // delete the `&` already generated in `prefix_expr()
+	}
 	if g.is_shared {
 		mut shared_typ := struct_init.typ.set_flag(.shared_f)
 		shared_styp = g.typ(shared_typ)
 		g.writeln('($shared_styp*)__dup${shared_styp}(&($shared_styp){.val = ($styp){')
-		} else {
+	} else if is_amp {
 		g.write('($styp*)memdup(&($styp){')
-		}
 	} else if struct_init.typ.is_ptr() {
 		basetyp := g.typ(struct_init.typ.set_nr_muls(0))
 		if is_multiline {
@@ -4708,10 +4708,7 @@ fn (mut g Gen) struct_init(struct_init ast.StructInit) {
 			g.write('&($basetyp){')
 		}
 	} else {
-		if g.is_shared {
-			// TODO: non-ref shared should be forbidden
-			g.writeln('{.val = {')
-		} else if is_multiline {
+		if is_multiline {
 			g.writeln('($styp){')
 		} else {
 			g.write('($styp){')
@@ -4870,10 +4867,7 @@ fn (mut g Gen) struct_init(struct_init ast.StructInit) {
 	}
 	g.write('}')
 	if g.is_shared {
-		g.write('}')
-		if is_amp {
-			g.write(', sizeof($shared_styp))')
-		}
+		g.write('}, sizeof($shared_styp))')
 	} else if is_amp {
 		g.write(', sizeof($styp))')
 	}

vlib/v/tests/shared_lock_test.v

@@ -19,13 +19,13 @@ fn f(shared x St, shared y St, shared z St) {
 }
 
 fn test_shared_lock() {
-	shared x := &St{
+	shared x := St{
 		a: 5
 	}
 	shared y := &St{
 		a: 7
 	}
-	shared z := &St{
+	shared z := St{
 		a: 1
 	}
 	go f(shared x, shared y, shared z)