Add git_diff_commit and last-changed examplerb/commit-modified-file

This adds a new diff API `git_diff_commit` which makes it easy to
generate a `git_diff` object that represents the changes in a given
commit.  It follows the core Git rules for considering changes in
a merge commit - i.e. if a file has an exact match in any parent
of the commit, then the file is considered unmodified by the merge.

This also adds a new example program "last-changed" which takes a
list of filenames and for each one displays the SHA of the last
commit that changed that file.

1 files changed, 19 insertions, 0 deletions

diff --git a/include/git2/diff.h b/include/git2/diff.h
index a0cfbc918..450fc3c79 100644
--- a/include/git2/diff.h
+++ b/include/git2/diff.h
@@ -775,6 +775,25 @@ GIT_EXTERN(int) git_diff_tree_to_workdir_with_index(
 	const git_diff_options *opts); /**< can be NULL for defaults */
 
 /**
+ * Create a diff of the changes between a commit and its parent(s).
+ *
+ * This generates a diff list between a commit and its parents.  For a
+ * non-merge commit, this is simply a shortcut for `git_diff_tree_to_tree`
+ * between the commit tree and the parent tree.  For a parent-less commit,
+ * this will generate a diff with the content of the commit tree.  For a
+ * merge commit, this generates a diff that contains only files that do
+ * not match any of the parents' trees.
+ *
+ * @param diff A pointer to a git_diff pointer that will be allocated.
+ * @param commit A git_commit object to diff from
+ * @param opts Structure with options to influence diff or NULL for defaults.
+ */
+GIT_EXTERN(int) git_diff_commit(
+	git_diff **diff,
+	git_commit *commit,
+	const git_diff_options *opts); /**< can be NULL for defaults */
+
+/**
  * Merge one diff into another.
  *
  * This merges items from the "from" list into the "onto" list.  The