Add submodule caching

pygit2/_run.py

@@ -91,14 +91,15 @@
 
 C_HEADER_SRC = '\n'.join(h_source)
 
+C_PREAMBLE = """\
+#include <git2.h>
+#include <git2/sys/repository.h>
+"""
+
 # ffi
 _, libgit2_kw = get_libgit2_paths()
 ffi = FFI()
-ffi.set_source(
-    "pygit2._libgit2",
-    "#include <git2.h>", # preamble
-    **libgit2_kw
-)
+ffi.set_source("pygit2._libgit2", C_PREAMBLE, **libgit2_kw)
 ffi.cdef(C_HEADER_SRC)
 
 

pygit2/decl/repository.h

@@ -87,3 +87,6 @@ int git_repository_ident(const char **name, const char **email, const git_reposi
 int git_repository_set_ident(git_repository *repo, const char *name, const char *email);
 int git_repository_index(git_index **out, git_repository *repo);
 git_repository_state_t git_repository_state(git_repository *repo);
+
+int git_repository_submodule_cache_all(git_repository *repo);
+int git_repository_submodule_cache_clear(git_repository *repo);

pygit2/repository.py

@@ -252,6 +252,31 @@ def update_submodules(
         for submodule in instances:
             submodule.update(init, callbacks)
 
+    def submodule_cache_all(self):
+        """
+        Load and cache all submodules in the repository.
+
+        Because the `.gitmodules` file is unstructured, loading submodules is an
+        O(N) operation.  Any operation that requires accessing all submodules is O(N^2)
+        in the number of submodules, if it has to look each one up individually.
+        This function loads all submodules and caches them so that subsequent calls to
+        `lookup_submodule` are O(1).
+        """
+        err = C.git_repository_submodule_cache_all(self._repo)
+        check_error(err)
+
+    def submodule_cache_clear(self):
+        """
+        Clear the submodule cache populated by `submodule_cache_all`.
+        If there is no cache, do nothing.
+
+        The cache incorporates data from the repository's configuration, as well
+        as the state of the working tree, the index, and HEAD. So any time any
+        of these has changed, the cache might become invalid.
+        """
+        err = C.git_repository_submodule_cache_clear(self._repo)
+        check_error(err)
+
     #
     # Mapping interface
     #

test/test_submodule.py

@@ -132,3 +132,17 @@ def test_add_submodule(repo):
     assert sm_repo_path == sm.path
     assert SUBM_URL == sm.url
     assert not sm_repo.is_empty
+
+def test_submodule_cache(repo):
+    # When the cache is turned on, looking up the same submodule twice must return the same git_submodule object
+    repo.submodule_cache_all()
+    sm1 = repo.lookup_submodule(SUBM_NAME)
+    sm2 = repo.lookup_submodule(SUBM_NAME)
+    assert sm1._subm == sm2._subm
+
+    # After turning off the cache, each lookup must return a new git_submodule object
+    repo.submodule_cache_clear()
+    sm3 = repo.lookup_submodule(SUBM_NAME)
+    sm4 = repo.lookup_submodule(SUBM_NAME)
+    assert sm1._subm != sm3._subm
+    assert sm3._subm != sm4._subm