all: fix mutability after if-smartcast (#6129)

vlib/v/checker/checker.v

@@ -2550,7 +2550,7 @@ pub fn (mut c Checker) ident(mut ident ast.Ident) table.Type {
 		return info.typ
 	} else if ident.kind == .unresolved {
 		// first use
-		start_scope := c.file.scope.innermost(ident.pos.pos)
+		start_scope := c.file.scope.innermost(ident.pos.pos + 1)
 		if obj1 := start_scope.find(ident.name) {
 			match mut obj1 as obj {
 				ast.GlobalDecl {
@@ -2985,8 +2985,11 @@ pub fn (mut c Checker) if_expr(mut node ast.IfExpr) table.Type {
 					left_sym := c.table.get_type_symbol(infix.left_type)
 					if left_sym.kind == .sum_type && branch.left_as_name.len > 0 {
 						mut is_mut := false
-						if infix.left is ast.Ident {
-							is_mut = (infix.left as ast.Ident).is_mut
+						mut scope := c.file.scope.innermost(branch.body_pos.pos)
+						if infix.left is ast.Ident as infix_left {
+							if var := scope.find_var(infix_left.name) {
+								is_mut = var.is_mut
+							}
 						} else if infix.left is ast.SelectorExpr {
 							selector := infix.left as ast.SelectorExpr
 							field := c.table.struct_find_field(left_sym, selector.field_name) or {
@@ -2994,7 +2997,6 @@ pub fn (mut c Checker) if_expr(mut node ast.IfExpr) table.Type {
 							}
 							is_mut = field.is_mut
 						}
-						mut scope := c.file.scope.innermost(branch.body_pos.pos)
 						scope.register(branch.left_as_name, ast.Var{
 							name: branch.left_as_name
 							typ: right_expr.typ.to_ptr()

vlib/v/gen/cgen.v

@@ -1826,6 +1826,11 @@ fn (mut g Gen) expr(node ast.Expr) {
 				g.write(')')
 			} else if sym.kind == .sum_type {
 				g.expr_with_cast(node.expr, node.expr_type, node.typ)
+			} else if sym.kind == .struct_ && !node.typ.is_ptr() && !(sym.info as table.Struct).is_typedef {
+				styp := g.typ(node.typ)
+				g.write('*(($styp *)(&')
+				g.expr(node.expr)
+				g.write('))')
 			} else {
 				// styp := g.table.Type_to_str(it.typ)
 				styp := g.typ(node.typ)

vlib/v/parser/if_match.v

@@ -118,7 +118,7 @@ fn (mut p Parser) if_expr() ast.IfExpr {
 			cond: cond
 			stmts: stmts
 			pos: start_pos.extend(end_pos)
-			body_pos: body_pos.extend(p.tok.position())
+			body_pos: body_pos.extend(p.prev_tok.position())
 			comments: comments
 			left_as_name: left_as_name
 		}

vlib/v/tests/if_smartcast_test.v

@@ -51,7 +51,7 @@ fn test_mutable_with_struct() {
 	mut x := Test{Abc{'test'}}
 	if x.abc is Abc as test {
 		mut ttt := test
-		assert u64(ttt) == u64(ttt)        
+		assert u64(ttt) == u64(ttt)
 		ttt.val = 'test'
 		assert ttt.val == 'test'
 	}
@@ -63,3 +63,26 @@ fn test_as_cast_with_struct() {
 		assert test.val == 'test'
 	}
 }
+
+struct CellStr { str string }
+struct CellInt { itg i64 }
+struct CellFloat { flt f64 }
+type Cell = CellStr | CellInt | CellFloat
+fn test_mutability() {
+	my_str := 'the quick brown fox jumps over the lazy dog.'
+	my_itg := -1234567890
+	my_flt := 3.14159265358979323846
+	my_u32 := u32(4294967296)
+	cell_str := CellStr{ str: my_str }
+	cell_itg := CellInt{ itg: my_itg }
+	cell_flt := CellFloat{ flt: my_flt }
+	mut cell := Cell{}
+	cell = cell_str
+	if cell is CellStr {
+		println('$cell.str')
+	}
+	cell = cell_itg
+	if cell is CellInt {
+		println('$cell.itg')
+	}
+}