C API: Add query_from_hash_part to Store API

doc/manual/rl-next/c-api-new-store-methods.md

@@ -0,0 +1,8 @@
+---
+synopsis: "C API: New store API methods"
+prs: [14766]
+---
+
+The C API now includes additional methods:
+
+- `nix_store_query_path_from_hash_part()` - Get the full store path given its hash part

src/libstore-c/nix_api_store.cc

@@ -338,4 +338,20 @@ nix_derivation * nix_store_drv_from_store_path(nix_c_context * context, Store *
     NIXC_CATCH_ERRS_NULL
 }
 
+StorePath * nix_store_query_path_from_hash_part(nix_c_context * context, Store * store, const char * hash)
+{
+    if (context)
+        context->last_err_code = NIX_OK;
+    try {
+        std::optional<nix::StorePath> s = store->ptr->queryPathFromHashPart(hash);
+
+        if (!s.has_value()) {
+            return nullptr;
+        }
+
+        return new StorePath{std::move(s.value())};
+    }
+    NIXC_CATCH_ERRS_NULL
+}
+
 } // extern "C"

src/libstore-c/nix_api_store.h

@@ -259,6 +259,17 @@ nix_err nix_store_get_fs_closure(
  */
 nix_derivation * nix_store_drv_from_store_path(nix_c_context * context, Store * store, const StorePath * path);
 
+/**
+ * @brief Query the full store path given the hash part of a valid store
+ * path, or empty if no matching path is found.
+ *
+ * @param[out] context Optional, stores error information
+ * @param[in] store nix store reference
+ * @param[in] hash Hash part of path as a string
+ * @return Store path reference, NULL if no matching path is found.
+ */
+StorePath * nix_store_query_path_from_hash_part(nix_c_context * context, Store * store, const char * hash);
+
 // cffi end
 #ifdef __cplusplus
 }