C API: add nix_locked_flake_get_path for flake path retreival

Author: RossComputerGuy

src/libflake-c/nix_api_flake.cc

@@ -206,4 +206,15 @@ nix_value * nix_locked_flake_get_output_attrs(
     NIXC_CATCH_ERRS_NULL
 }
 
+nix_err nix_locked_flake_get_path(
+    nix_c_context * context, nix_locked_flake * lockedFlake, nix_get_string_callback callback, void * user_data)
+{
+    nix_clear_err(context);
+    try {
+        auto v = lockedFlake->lockedFlake->flake.path.parent().to_string();
+        return call_nix_get_string_callback(v, callback, user_data);
+    }
+    NIXC_CATCH_ERRS
+}
+
 } // extern "C"

src/libflake-c/nix_api_flake.h

@@ -238,6 +238,18 @@ void nix_flake_reference_free(nix_flake_reference * store);
 nix_value * nix_locked_flake_get_output_attrs(
     nix_c_context * context, nix_flake_settings * settings, EvalState * evalState, nix_locked_flake * lockedFlake);
 
+/**
+ * @brief Get the root path of a flake.
+ * @note The callback borrows the string only for the duration of the call.
+ *
+ * @param[out] context Optional, stores error information
+ * @param[in] locked_flake the flake to get the path for
+ * @param[in] callback The callback to call with the string
+ * @param[in] user_data Additional data to pass for the callback
+ */
+nix_err nix_locked_flake_get_path(
+    nix_c_context * context, nix_locked_flake * lockedFlake, nix_get_string_callback callback, void * user_data);
+
 #ifdef __cplusplus
 } // extern "C"
 #endif