commit fdf3c2d3876d076bf098461a4d147227126588b4
from: Stefan Sperling <stsp@stsp.name>
date: Thu Jun 17 09:01:05 2021 UTC

use Patience diff for merging during cherrypick/backout/histedit/rebase

This has been shown to prevent mis-merges in some cases. It's probably
not a final solution. We should look at what Git's "recursive merge"
is doing and implement something similar.

Keep using Myers during update/unstage. The advantage of Myers is that
it produces smaller conflict chunks, and there are no known cases of
mis-merges which affect update/unstage.

commit - 1d0f405485b02cc4480ea188879e4122e0ea32bd
commit + fdf3c2d3876d076bf098461a4d147227126588b4
blob - b8c328a2f9b853caabcc322afe5c68eefd3b4ccb
blob + fa402b0446d11c215371183b598bd9573467a1d0
--- lib/diff3.c
+++ lib/diff3.c
@@ -197,7 +197,8 @@ diff_output(BUF *diffbuf, const char *fmt, ...)
 }
 
 static const struct got_error*
-diffreg(BUF **d, const char *path1, const char *path2)
+diffreg(BUF **d, const char *path1, const char *path2,
+    enum got_diff_algorithm diff_algo)
 {
 	const struct got_error *err = NULL;
 	FILE *f1 = NULL, *f2 = NULL, *outfile = NULL;
@@ -222,8 +223,7 @@ diffreg(BUF **d, const char *path1, const char *path2)
 	if (err)
 		goto done;
 
-	err = got_diffreg(&diffreg_result, f1, f2,
-	    GOT_DIFF_ALGORITHM_MYERS, 0, 1);
+	err = got_diffreg(&diffreg_result, f1, f2, diff_algo, 0, 1);
 	if (err)
 		goto done;
 
@@ -262,7 +262,8 @@ done:
  */
 const struct got_error *
 got_merge_diff3(int *overlapcnt, int outfd, FILE *f1, FILE *f2,
-    FILE *f3, const char *label1, const char *label2, const char *label3)
+    FILE *f3, const char *label1, const char *label2, const char *label3,
+    enum got_diff_algorithm diff_algo)
 {
 	const struct got_error *err = NULL;
 	char *dp13, *dp23, *path1, *path2, *path3;
@@ -321,14 +322,14 @@ got_merge_diff3(int *overlapcnt, int outfd, FILE *f1, 
 	buf_free(b2);
 	b2 = NULL;
 
-	err = diffreg(&d1, path1, path3);
+	err = diffreg(&d1, path1, path3, diff_algo);
 	if (err) {
 		buf_free(diffb);
 		diffb = NULL;
 		goto out;
 
 	}
-	err = diffreg(&d2, path2, path3);
+	err = diffreg(&d2, path2, path3, diff_algo);
 	if (err) {
 		buf_free(diffb);
 		diffb = NULL;
blob - c056426dd1569f33cd5459cba2caaa263be5224d
blob + 6262295fc0820142511469142f7dfe853a485953
--- lib/got_lib_diff.h
+++ lib/got_lib_diff.h
@@ -63,7 +63,7 @@ const struct got_error *got_diffreg_close(FILE *, char
     FILE *, char *, size_t);
 
 const struct got_error *got_merge_diff3(int *, int, FILE *, FILE *, FILE *,
-    const char *, const char *, const char *);
+    const char *, const char *, const char *, enum got_diff_algorithm);
 
 const struct got_error *got_diff_files(struct got_diffreg_result **, FILE *,
     const char *, FILE *, const char *, int, int, int, FILE *);
blob - 522c2fe12ca9c96345952c0586dcca8194d69202
blob + 77e9ecb628d437b68e991e2de6d272b5053ad9e0
--- lib/worktree.c
+++ lib/worktree.c
@@ -771,7 +771,7 @@ merge_file(int *local_changes_subsumed, struct got_wor
     FILE *f_orig, FILE *f_deriv, FILE *f_deriv2, const char *ondisk_path,
     const char *path, uint16_t st_mode,
     const char *label_orig, const char *label_deriv, const char *label_deriv2,
-    struct got_repository *repo,
+    enum got_diff_algorithm diff_algo, struct got_repository *repo,
     got_worktree_checkout_cb progress_cb, void *progress_arg)
 {
 	const struct got_error *err = NULL;
@@ -797,7 +797,7 @@ merge_file(int *local_changes_subsumed, struct got_wor
 		goto done;
 
 	err = got_merge_diff3(&overlapcnt, merged_fd, f_deriv, f_orig,
-	    f_deriv2, label_deriv, label_orig, label_deriv2);
+	    f_deriv2, label_deriv, label_orig, label_deriv2, diff_algo);
 	if (err)
 		goto done;
 
@@ -1182,7 +1182,7 @@ merge_blob(int *local_changes_subsumed, struct got_wor
 
 	err = merge_file(local_changes_subsumed, worktree, f_orig, f_deriv,
 	    f_deriv2, ondisk_path, path, st_mode, label_orig, label_deriv,
-	    NULL, repo, progress_cb, progress_arg);
+	    NULL, GOT_DIFF_ALGORITHM_MYERS, repo, progress_cb, progress_arg);
 done:
 	if (f_orig && fclose(f_orig) == EOF && err == NULL)
 		err = got_error_from_errno("fclose");
@@ -2922,7 +2922,8 @@ merge_file_cb(void *arg, struct got_blob_object *blob1
 			err = merge_file(&local_changes_subsumed, a->worktree,
 			    f_orig, f_deriv, f_deriv2, ondisk_path, path2,
 			    sb.st_mode, a->label_orig, NULL, label_deriv2,
-			    repo, a->progress_cb, a->progress_arg);
+			    GOT_DIFF_ALGORITHM_PATIENCE, repo,
+			    a->progress_cb, a->progress_arg);
 		}
 	} else if (blob1) {
 		ie = got_fileindex_entry_get(a->fileindex, path1,
@@ -7875,7 +7876,7 @@ unstage_hunks(struct got_object_id *staged_blob_id,
 		err = merge_file(&local_changes_subsumed, worktree,
 		    f_base, f, f_deriv2, ondisk_path, ie->path,
 		    got_fileindex_perms_to_st(ie),
-		    label_orig, "unstaged", NULL,
+		    label_orig, "unstaged", NULL, GOT_DIFF_ALGORITHM_MYERS,
 		    repo, progress_cb, progress_arg);
 	}
 	if (err)