Eliminate duplicated code in ParseEntityName{FromJson,FromExpression}

This patch introduces a templated ParseEntityName which can accept a
json or ExpressionPtr. Internally, performs a proper dispatch on these
cases

- isString
- isList
  - size == 2
  - size >= 3

A test is added for checking the proper handling of an empty list

1 files changed, 5 insertions, 0 deletions

diff --git a/test/buildtool/build_engine/base_maps/rule_map.test.cpp b/test/buildtool/build_engine/base_maps/rule_map.test.cpp
index c0e64675..8667c7a9 100644
--- a/test/buildtool/build_engine/base_maps/rule_map.test.cpp
+++ b/test/buildtool/build_engine/base_maps/rule_map.test.cpp
@@ -323,6 +323,11 @@ TEST_CASE("Malformed rule description", "[rule_map]") {
                          [](auto /*values*/) {
                              CHECK(false);  // should never be called
                          }));
+        CHECK_FALSE(
+            ReadUserRule({"", ".", "test_malformed_implicit_entity_name_2"},
+                         [](auto /*values*/) {
+                             CHECK(false);  // should never be called
+                         }));
     }
 
     SECTION("Malformed config_vars") {