Delete the ghost-paths fallback the record reader now makes loud

include/pup/core/string_id.hpp

@@ -13,6 +13,7 @@ namespace pup {
 enum class StringId : std::uint32_t { Empty = 0 };
 
 /// Check if StringId represents the empty string
+/// Only the empty string interns to Empty, so a guard may test the handle instead (#391).
 [[nodiscard]]
 constexpr auto is_empty(StringId id) -> bool
 {

src/cli/cmd_build.cpp

@@ -1287,22 +1287,10 @@ auto merge_out_of_scope_commands(
 
     auto new_lookup = index_command_lookup(ctx.index);
 
-    // Vestigial since the ghost arm began registering its own path (#386): every entry with a
-    // path is now in path_to_id, so this finds nothing. Kept pending its own removal.
-    auto ghost_paths = PathIdMap {};
-    for (auto const& file : ctx.index.files()) {
-        if (!pup::is_empty(file.path) && !ctx.path_to_id.find(file.path)) {
-            ghost_paths.insert(file.path, file.id);
-        }
-    }
-
     auto find_new_id_by_path = [&](StringId path) -> pup::NodeId {
         if (auto found = ctx.path_to_id.find(path)) {
             return *found;
         }
-        if (auto found = ghost_paths.find(path)) {
-            return *found;
-        }
         return pup::INVALID_NODE_ID;
     };
 

test/unit/test_string_pool.cpp

@@ -2,6 +2,7 @@
 // Copyright (c) 2024 Putup authors
 
 #include "catch_amalgamated.hpp"
+#include "pup/core/string_id.hpp"
 #include "pup/core/string_pool.hpp"
 
 #include <cstdio>
@@ -112,3 +113,11 @@ TEST_CASE("StringPool Robin Hood index", "[string_pool]")
         REQUIRE(moved.find("before_move") == id);
     }
 }
+
+TEST_CASE("Interning the empty string yields the empty handle", "[string_pool]")
+{
+    auto pool = pup::StringPool {};
+    REQUIRE(pup::is_empty(pool.intern("")));
+    REQUIRE_FALSE(pup::is_empty(pool.intern("a")));
+    REQUIRE(pup::is_empty(pool.intern("")));
+}