cgen: if smartcast part 3 (#5755)

vlib/v/checker/checker.v

@@ -2635,6 +2635,13 @@ pub fn (mut c Checker) if_expr(mut node ast.IfExpr) table.Type {
 							is_used: true
 							is_mut: left_expr.is_mut
 						})
+						scope.register(left_expr.name, ast.Var{
+							name: left_expr.name
+							typ: right_expr.typ.to_ptr()
+							pos: left_expr.pos
+							is_used: true
+							is_mut: left_expr.is_mut
+						})
 						node.branches[i].smartcast = true
 					}
 				}

vlib/v/gen/cgen.v

@@ -963,9 +963,17 @@ fn (mut g Gen) expr_with_cast(expr ast.Expr, got_type, expected_type table.Type)
 			got_styp := g.typ(got_type)
 			exp_styp := g.typ(expected_type)
 			got_idx := got_type.idx()
+			if got_type.is_ptr() {
+				g.write('/* sum type cast */ ($exp_styp) {.obj = ')
+				g.expr(expr)
+				g.write(', .typ = $got_idx /* $got_sym.name */}')
+			}
+			else {
 				g.write('/* sum type cast */ ($exp_styp) {.obj = memdup(&($got_styp[]) {')
 				g.expr(expr)
 				g.write('}, sizeof($got_styp)), .typ = $got_idx /* $got_sym.name */}')
+			}
+
 			return
 		}
 	}
@@ -2314,6 +2322,7 @@ fn (mut g Gen) if_expr(node ast.IfExpr) {
 			infix := branch.cond as ast.InfixExpr
 			right_type := infix.right as ast.Type
 			left_type := infix.left_type
+			left_expr := infix.left as ast.Ident
 			it_type := g.typ(right_type.typ)
 			g.write('\t$it_type* it = ($it_type*)')
 			g.expr(infix.left)
@@ -2323,6 +2332,7 @@ fn (mut g Gen) if_expr(node ast.IfExpr) {
 				g.write('.')
 			}
 			g.writeln('obj;')
+			g.writeln('\t$it_type* $left_expr.name = it;')
 		}
 		g.stmts(branch.stmts)
 	}

vlib/v/tests/sum_type_test.v

@@ -110,7 +110,7 @@ fn test_nested_sumtype() {
 	mut a := Node{}
 	mut b := Node{}
 	a = StructDecl{pos: 1}
-	b = IfExpr {pos: 1}
+	b = IfExpr{pos: 1}
 	match a {
 		StructDecl {
 			assert true
@@ -127,6 +127,18 @@ fn test_nested_sumtype() {
 	else {
 		assert false
 	}
+	c := Node(Expr(IfExpr{pos:1}))
+	if c is Expr {
+		if c is IfExpr {
+			assert true
+		}
+		else {
+			assert false
+		}
+	}
+	else {
+		assert false
+	}
 }
 
 type Abc = int | string