[PATCH v2 1/4] merge-ort: barebones API of new merge strategy with empty implementation

From: Elijah Newren via GitGitGadget <gitgitgadget@gmail.com>
Date: Oct 26, 2020, 16:57 UTC
Message-ID: <b9e73975eab1f349be678779ff57155feb4c3501.1603731448.git.gitgitgadget@gmail.com>
In-Reply-To: <pull.895.v2.git.git.1603731448.gitgitgadget@gmail.com>

From: Elijah Newren <newren@gmail.com>

This is the beginning of a new merge strategy. While there are some API differences, and the implementation has some differences in behavior, it is essentially meant as an eventual drop-in replacement for merge-recursive.c. However, it is being built to exist side-by-side with merge-recursive so that we have plenty of time to find out how those differences pan out in the real world while people can still fall back to merge-recursive. (Also, I intend to avoid modifying merge-recursive during this process, to keep it stable.)

The primary difference noticable here is that the updating of the working tree and index is not done simultaneously with the merge algorithm, but is a separate post-processing step. The new API is designed so that one can do repeated merges (e.g. during a rebase or cherry-pick) and only update the index and working tree one time at the end instead of updating it with every intermediate result. Also, one can perform a merge between two branches, neither of which match the index or the working tree, without clobbering the index or working tree.

The next three commits will demonstrate various uses of this new API.

Signed-off-by: Elijah Newren <newren@gmail.com>
---
 Makefile    |  1 +
 merge-ort.c | 52 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 merge-ort.h | 49 +++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 102 insertions(+)
 create mode 100644 merge-ort.c
 create mode 100644 merge-ort.h

diff --git a/Makefile b/Makefile
index 95571ee3fc..088770c2ae 100644
--- a/Makefile
+++ b/Makefile
@@ -921,6 +921,7 @@ LIB_OBJS += mailmap.o
 LIB_OBJS += match-trees.o
 LIB_OBJS += mem-pool.o
 LIB_OBJS += merge-blobs.o
+LIB_OBJS += merge-ort.o
 LIB_OBJS += merge-recursive.o
 LIB_OBJS += merge.o
 LIB_OBJS += mergesort.o
diff --git a/merge-ort.c b/merge-ort.c
new file mode 100644
index 0000000000..5230364a8d
--- /dev/null
+++ b/merge-ort.c
@@ -0,0 +1,52 @@
+/*
+ * "Ostensibly Recursive's Twin" merge strategy, or "ort" for short.  Meant
+ * as a drop-in replacement for the "recursive" merge strategy, allowing one
+ * to replace
+ *
+ *   git merge [-s recursive]
+ *
+ * with
+ *
+ *   git merge -s ort
+ *
+ * Note: git's parser allows the space between '-s' and its argument to be
+ * missing.  (Should I have backronymed "ham", "alsa", "kip", "nap, "alvo",
+ * "cale", "peedy", or "ins" instead of "ort"?)
+ */
+
+#include "cache.h"
+#include "merge-ort.h"
+
+void merge_switch_to_result(struct merge_options *opt,
+			    struct tree *head,
+			    struct merge_result *result,
+			    int update_worktree_and_index,
+			    int display_update_msgs)
+{
+	die("Not yet implemented");
+	merge_finalize(opt, result);
+}
+
+void merge_finalize(struct merge_options *opt,
+		    struct merge_result *result)
+{
+	die("Not yet implemented");
+}
+
+void merge_inmemory_nonrecursive(struct merge_options *opt,
+				 struct tree *merge_base,
+				 struct tree *side1,
+				 struct tree *side2,
+				 struct merge_result *result)
+{
+	die("Not yet implemented");
+}
+
+void merge_inmemory_recursive(struct merge_options *opt,
+			      struct commit_list *merge_bases,
+			      struct commit *side1,
+			      struct commit *side2,
+			      struct merge_result *result)
+{
+	die("Not yet implemented");
+}
diff --git a/merge-ort.h b/merge-ort.h
new file mode 100644
index 0000000000..47d30cf538
--- /dev/null
+++ b/merge-ort.h
@@ -0,0 +1,49 @@
+#ifndef MERGE_ORT_H
+#define MERGE_ORT_H
+
+#include "merge-recursive.h"
+
+struct commit;
+struct tree;
+
+struct merge_result {
+	/* whether the merge is clean */
+	int clean;
+
+	/* Result of merge.  If !clean, represents what would go in worktree */
+	struct tree *tree;
+
+	/*
+	 * Additional metadata used by merge_switch_to_result() or future calls
+	 * to merge_inmemory_*().  Not for external use.
+	 */
+	void *priv;
+	unsigned ate;
+};
+
+/* rename-detecting three-way merge with recursive ancestor consolidation. */
+void merge_inmemory_recursive(struct merge_options *opt,
+			      struct commit_list *merge_bases,
+			      struct commit *side1,
+			      struct commit *side2,
+			      struct merge_result *result);
+
+/* rename-detecting three-way merge, no recursion. */
+void merge_inmemory_nonrecursive(struct merge_options *opt,
+				 struct tree *merge_base,
+				 struct tree *side1,
+				 struct tree *side2,
+				 struct merge_result *result);
+
+/* Update the working tree and index from head to result after inmemory merge */
+void merge_switch_to_result(struct merge_options *opt,
+			    struct tree *head,
+			    struct merge_result *result,
+			    int update_worktree_and_index,
+			    int display_update_msgs);
+
+/* Do needed cleanup when not calling merge_switch_to_result() */
+void merge_finalize(struct merge_options *opt,
+		    struct merge_result *result);
+
+#endif

-- 
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