Add support for literals in inspect alternatives

Author: filipsajdak

source/cppfront.cpp

@@ -1282,8 +1282,11 @@ class cppfront
 
             auto id = std::string{};
             printer.emit_to_string(&id);
-            assert(alt->id_expression);
-            emit(*alt->id_expression);
+            assert(alt->id_expression || alt->literal);
+            if (alt->id_expression)
+                emit(*alt->id_expression);
+            else if (alt->literal)
+                emit(*alt->literal);
             printer.emit_to_string();
 
             assert (*alt->is_as_keyword == "is" || *alt->is_as_keyword == "as");

source/parse.h

@@ -667,6 +667,7 @@ struct alternative_node
     std::unique_ptr<id_expression_node>  id_expression;
     source_position                      equal_sign;
     std::unique_ptr<statement_node>      statement;
+    token const*                         literal;
 
     auto position() const -> source_position
     {
@@ -776,8 +777,11 @@ auto alternative_node::visit(auto& v, int depth) -> void
     }
     assert (is_as_keyword);
     v.start(*is_as_keyword, depth+1);
-    assert (id_expression);
-    id_expression->visit(v, depth+1);
+    assert (id_expression || literal);
+    if (id_expression)
+        id_expression->visit(v, depth+1);
+    else if (literal)
+        literal->visit(v, depth+1);
     assert (statement);
     statement->visit(v, depth+1);
     v.end(*this, depth);
@@ -2346,8 +2350,12 @@ class parser
         if (auto id = id_expression()) {
             n->id_expression = std::move(id);
         }
+        else if (is_literal(curr().type())) {
+            n->literal = &curr();
+            next();
+        }
         else {
-            error("expected id-expression after 'is' in inspect alternative");
+            error("expected id-expression or literal after 'is' in inspect alternative");
             return {};
         }