checker, cgen: fix generic empty interface to multi struct (#14132)

vlib/v/checker/if.v

@@ -296,7 +296,7 @@ fn (mut c Checker) smartcast_if_conds(node ast.Expr, mut scope ast.Scope) {
 			c.smartcast_if_conds(node.right, mut scope)
 		} else if node.op == .key_is {
 			right_expr := node.right
-			mut right_type := match right_expr {
+			right_type := match right_expr {
 				ast.TypeNode {
 					right_expr.typ
 				}
@@ -308,11 +308,10 @@ fn (mut c Checker) smartcast_if_conds(node ast.Expr, mut scope ast.Scope) {
 					ast.Type(0)
 				}
 			}
-			right_type = c.unwrap_generic(right_type)
 			if right_type != ast.Type(0) {
 				left_sym := c.table.sym(node.left_type)
 				right_sym := c.table.sym(right_type)
-				mut expr_type := c.unwrap_generic(c.expr(node.left))
+				mut expr_type := c.expr(node.left)
 				if left_sym.kind == .aggregate {
 					expr_type = (left_sym.info as ast.Aggregate).sum_type
 				}
@@ -322,7 +321,7 @@ fn (mut c Checker) smartcast_if_conds(node ast.Expr, mut scope ast.Scope) {
 					} else {
 						return
 					}
-				} else if !c.check_types(right_type, expr_type) {
+				} else if !c.check_types(right_type, expr_type) && left_sym.kind != .sum_type {
 					expect_str := c.table.type_to_str(right_type)
 					expr_str := c.table.type_to_str(expr_type)
 					c.error('cannot use type `$expect_str` as type `$expr_str`', node.pos)

vlib/v/checker/return.v

@@ -34,7 +34,7 @@ pub fn (mut c Checker) return_stmt(mut node ast.Return) {
 	mut got_types := []ast.Type{}
 	mut expr_idxs := []int{}
 	for i, expr in node.exprs {
-		typ := c.expr(expr)
+		mut typ := c.expr(expr)
 		if typ == ast.void_type {
 			c.error('`$expr` used as value', node.pos)
 		}
@@ -46,6 +46,13 @@ pub fn (mut c Checker) return_stmt(mut node ast.Return) {
 				expr_idxs << i
 			}
 		} else {
+			if expr is ast.Ident {
+				if expr.obj is ast.Var {
+					if expr.obj.smartcasts.len > 0 {
+						typ = c.unwrap_generic(expr.obj.smartcasts.last())
+					}
+				}
+			}
 			got_types << typ
 			expr_idxs << i
 		}

vlib/v/gen/c/cgen.v

@@ -3286,7 +3286,7 @@ fn (mut g Gen) selector_expr(node ast.SelectorExpr) {
 						if field_sym.kind == .sum_type {
 							g.write('*')
 						}
-						cast_sym := g.table.sym(typ)
+						cast_sym := g.table.sym(g.unwrap_generic(typ))
 						if i != 0 {
 							dot := if field.typ.is_ptr() { '->' } else { '.' }
 							sum_type_deref_field += ')$dot'

vlib/v/gen/c/fn.v

@@ -941,7 +941,7 @@ fn (mut g Gen) method_call(node ast.CallExpr) {
 					g.gen_expr_to_string(node.left, rec_type)
 					return
 				} else if node.left.obj.smartcasts.len > 0 {
-					rec_type = node.left.obj.smartcasts.last()
+					rec_type = g.unwrap_generic(node.left.obj.smartcasts.last())
 					cast_sym := g.table.sym(rec_type)
 					if cast_sym.info is ast.Aggregate {
 						rec_type = cast_sym.info.types[g.aggregate_type_idx]
@@ -1331,7 +1331,7 @@ fn (mut g Gen) fn_call(node ast.CallExpr) {
 					if expr.obj is ast.Var {
 						typ = expr.obj.typ
 						if expr.obj.smartcasts.len > 0 {
-							typ = expr.obj.smartcasts.last()
+							typ = g.unwrap_generic(expr.obj.smartcasts.last())
 							cast_sym := g.table.sym(typ)
 							if cast_sym.info is ast.Aggregate {
 								typ = cast_sym.info.types[g.aggregate_type_idx]

vlib/v/gen/c/str_intp.v

@@ -156,7 +156,7 @@ fn (mut g Gen) str_val(node ast.StringInterLiteral, i int) {
 				if g.comptime_var_type_map.len > 0 || g.comptime_for_method.len > 0 {
 					exp_typ = expr.obj.typ
 				} else if expr.obj.smartcasts.len > 0 {
-					exp_typ = expr.obj.smartcasts.last()
+					exp_typ = g.unwrap_generic(expr.obj.smartcasts.last())
 					cast_sym := g.table.sym(exp_typ)
 					if cast_sym.info is ast.Aggregate {
 						exp_typ = cast_sym.info.types[g.aggregate_type_idx]

vlib/v/tests/generic_empty_interface_to_multi_struct_test.v

@@ -0,0 +1,30 @@
+interface Any {}
+
+struct ConcreteA {
+	a int
+}
+
+struct ConcreteB {
+	b int
+}
+
+struct Container {
+	concrete_a Any
+	concrete_b Any
+}
+
+fn cast_struct<T>(any_struct Any) &T {
+	if any_struct is T {
+		return any_struct
+	}
+	panic('cannot cast')
+}
+
+fn test_generic_empty_interface_to_multi_struct() {
+	concrete_a := cast_struct<ConcreteA>(ConcreteA{12345})
+	concrete_b := cast_struct<ConcreteB>(ConcreteB{54321})
+	println(concrete_a.a)
+	println(concrete_b.b)
+	assert concrete_a.a == 12345
+	assert concrete_b.b == 54321
+}