repo: Add wrapper function for setting devino cache on checkout opts

I was trying to use this with pygobject for an OCI+ostree project, and pygobject
rejected simply assigning to the field (understandably, since it can't bind the
lifetime together).

Add a wrapper function, which is still unsafe, but hides that unsafety
where most people shouldn't find it.  And if they do...well, sorry,
Rust wasn't invented when ostree was started.

Closes: #1295
Approved by: pwithnall

apidoc/ostree-sections.txt

@@ -371,6 +371,8 @@ ostree_repo_write_commit
 ostree_repo_write_commit_with_time
 ostree_repo_read_commit_detached_metadata
 ostree_repo_write_commit_detached_metadata
+OstreeRepoCheckoutAtOptions
+ostree_repo_checkout_at_options_set_devino
 OstreeRepoCheckoutMode
 OstreeRepoCheckoutOverwriteMode
 ostree_repo_checkout_tree

src/libostree/libostree-devel.sym

@@ -21,6 +21,7 @@
 LIBOSTREE_2017.13 {
 global:
   ostree_checksum_file_at;
+  ostree_repo_checkout_at_options_set_devino;
 } LIBOSTREE_2017.12;
 
 /* Stub section for the stable release *after* this development one; don't

src/libostree/ostree-repo-checkout.c

@@ -1210,6 +1210,24 @@ ostree_repo_checkout_at (OstreeRepo                        *self,
   return TRUE;
 }
 
+/**
+ * ostree_repo_checkout_at_options_set_devino:
+ * @opts: Checkout options
+ * @cache: (transfer none) (nullable): Devino cache
+ *
+ * This function simply assigns @cache to the `devino_to_csum_cache` member of
+ * @opts; it's only useful for introspection.
+ *
+ * Note that cache does *not* have its refcount incremented - the lifetime of
+ * @cache must be equal to or greater than that of @opts.
+ */
+void
+ostree_repo_checkout_at_options_set_devino (OstreeRepoCheckoutAtOptions *opts,
+                                            OstreeRepoDevInoCache *cache)
+{
+  opts->devino_to_csum_cache = cache;
+}
+
 static guint
 devino_hash (gconstpointer a)
 {

src/libostree/ostree-repo-commit.c

@@ -3415,6 +3415,8 @@ ostree_repo_commit_modifier_set_sepolicy (OstreeRepoCommitModifier
  *
  * This function will add a reference to @cache without copying - you
  * should avoid further mutation of the cache.
+ *
+ * Since: 2017.13
  */
 void
 ostree_repo_commit_modifier_set_devino_cache (OstreeRepoCommitModifier              *modifier,

src/libostree/ostree-repo.h

@@ -911,6 +911,9 @@ OstreeRepoDevInoCache * ostree_repo_devino_cache_ref (OstreeRepoDevInoCache *cac
 _OSTREE_PUBLIC
 void ostree_repo_devino_cache_unref (OstreeRepoDevInoCache *cache);
 
+_OSTREE_PUBLIC
+void ostree_repo_checkout_at_options_set_devino (OstreeRepoCheckoutAtOptions *opts, OstreeRepoDevInoCache *cache);
+
 _OSTREE_PUBLIC
 gboolean ostree_repo_checkout_at (OstreeRepo                         *self,
                                   OstreeRepoCheckoutAtOptions        *options,