[M8] reusable libraries: install layout + cargoxx-path deps

tests/lockfile_round_trip.cpp

@@ -118,6 +118,30 @@ TEST_CASE("write round-trips lockfile recipe fields", "[lockfile]") {
     REQUIRE(round_trip(l) == l);
 }
 
+TEST_CASE("write round-trips cargoxx-path source fields", "[lockfile]") {
+    Lockfile l{
+        .version = 1,
+        .packages = {
+            LockfilePackage{
+                .name = "mylib",
+                .version = "*",
+                .dependencies = {},
+                .nixpkgs_attr = std::nullopt,
+                .nixpkgs_rev = std::nullopt,
+                .linkdb_source = "cargoxx-path",
+                .find_package = "mylib CONFIG REQUIRED",
+                .targets = {"mylib::mylib"},
+                .pkg_config_module = std::nullopt,
+                .brute_force_libs = {},
+                .brute_force_includes = {},
+                .source_kind = "cargoxx-path",
+                .source_path = "../mylib",
+            },
+        },
+    };
+    REQUIRE(round_trip(l) == l);
+}
+
 TEST_CASE("Lockfile::nixpkgs_rev returns the shared rev", "[lockfile]") {
     Lockfile l{
         .version = 1,