rebase: introduce git_commit_create_cb

Introduce a new mechanism for `git_rebase_commit` for callers to
customize the experience.  Instead of assuming that we produce the
commit for them, provide a commit creation callback that allows callers
to produce the commit themselves and return the resulting commit id.

2 files changed, 52 insertions, 0 deletions

diff --git a/include/git2/commit.h b/include/git2/commit.h
index e6c4656a9..650bf65a5 100644
--- a/include/git2/commit.h
+++ b/include/git2/commit.h
@@ -503,6 +503,43 @@ GIT_EXTERN(int) git_commit_create_with_signature(
 GIT_EXTERN(int) git_commit_dup(git_commit **out, git_commit *source);
 
 /**
+ * Commit creation callback: used when a function is going to create
+ * commits (for example, in `git_rebase_commit`) to allow callers to
+ * override the commit creation behavior.  For example, users may
+ * wish to sign commits by providing this information to
+ * `git_commit_create_buffer`, signing that buffer, then calling
+ * `git_commit_create_with_signature`.  The resultant commit id
+ * should be set in the `out` object id parameter.
+ *
+ * @param out pointer that this callback will populate with the object
+ *            id of the commit that is created
+ * @param author the author name and time of the commit
+ * @param committer the committer name and time of the commit
+ * @param message_encoding the encoding of the given message, or NULL
+ *                         to assume UTF8
+ * @param message the commit message
+ * @param tree the tree to be committed
+ * @param parent_count the number of parents for this commit
+ * @param parents the commit parents
+ * @param payload the payload pointer in the rebase options
+ * @return 0 if this callback has created the commit and populated the out
+ *         parameter, GIT_PASSTHROUGH if the callback has not created a
+ *         commit and wants the calling function to create the commit as
+ *         if no callback had been specified, any other value to stop
+ *         and return a failure
+ */
+typedef int (*git_commit_create_cb)(
+	git_oid *out,
+	const git_signature *author,
+	const git_signature *committer,
+	const char *message_encoding,
+	const char *message,
+	const git_tree *tree,
+	size_t parent_count,
+	const git_commit *parents[],
+	void *payload);
+
+/**
  * Commit signing callback.
  *
  * The callback will be called with the commit content, giving a user an
diff --git a/include/git2/rebase.h b/include/git2/rebase.h
index 99a02fef9..7d2d5de69 100644
--- a/include/git2/rebase.h
+++ b/include/git2/rebase.h
@@ -75,11 +75,26 @@ typedef struct {
 	git_checkout_options checkout_options;
 
 	/**
+	 * Optional callback that allows users to override commit
+	 * creation in `git_rebase_commit`.  If specified, users can
+	 * create their own commit and provide the commit ID, which
+	 * may be useful for signing commits or otherwise customizing
+	 * the commit creation.
+	 *
+	 * If this callback returns `GIT_PASSTHROUGH`, then
+	 * `git_rebase_commit` will continue to create the commit.
+	 */
+	git_commit_create_cb commit_create_cb;
+
+	/**
 	 * If provided, this will be called with the commit content, allowing
 	 * a signature to be added to the rebase commit. Can be skipped with
 	 * GIT_PASSTHROUGH. If GIT_PASSTHROUGH is returned, a commit will be made
 	 * without a signature.
 	 * This field is only used when performing git_rebase_commit.
+	 *
+	 * This callback is not invoked if a `git_commit_create_cb` is
+	 * specified.
 	 */
 	git_commit_signing_cb signing_cb;