fast-export: do not copy from modified file

When run with the "-C" option, fast-export writes 'C' commands in its
output whenever the internal diff mechanism detects a file copy,
indicating that fast-import should copy the given existing file to the
given new filename. However, the diff mechanism works against the
prior version of the file, whereas fast-import uses whatever is current.
This causes issues when a commit both modifies a file and uses it as the
source for a copy.

Therefore, teach fast-export to refrain from writing 'C' when it has
already written a modification command for a file.

An existing test in t9350-fast-export is also fixed in this patch. The
existing line "C file6 file7" copies the wrong version of file6, but it
has coincidentally worked because file7 was subsequently overridden.

Reported-by: Juraj Oršulić <juraj.orsulic@fer.hr>
Signed-off-by: Jonathan Tan <jonathantanmy@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/fast-export.c

@@ -342,6 +342,7 @@ static void show_filemodify(struct diff_queue_struct *q,
 			    struct diff_options *options, void *data)
 {
 	int i;
+	struct string_list *changed = data;
 
 	/*
 	 * Handle files below a directory first, in case they are all deleted
@@ -357,20 +358,31 @@ static void show_filemodify(struct diff_queue_struct *q,
 		case DIFF_STATUS_DELETED:
 			printf("D ");
 			print_path(spec->path);
+			string_list_insert(changed, spec->path);
 			putchar('\n');
 			break;
 
 		case DIFF_STATUS_COPIED:
 		case DIFF_STATUS_RENAMED:
+			/*
+			 * If a change in the file corresponding to ospec->path
+			 * has been observed, we cannot trust its contents
+			 * because the diff is calculated based on the prior
+			 * contents, not the current contents.  So, declare a
+			 * copy or rename only if there was no change observed.
+			 */
+			if (!string_list_has_string(changed, ospec->path)) {
 				printf("%c ", q->queue[i]->status);
 				print_path(ospec->path);
 				putchar(' ');
 				print_path(spec->path);
+				string_list_insert(changed, spec->path);
 				putchar('\n');
 
 				if (!oidcmp(&ospec->oid, &spec->oid) &&
 				    ospec->mode == spec->mode)
 					break;
+			}
 			/* fallthrough */
 
 		case DIFF_STATUS_TYPE_CHANGED:
@@ -391,6 +403,7 @@ static void show_filemodify(struct diff_queue_struct *q,
 				       get_object_mark(object));
 			}
 			print_path(spec->path);
+			string_list_insert(changed, spec->path);
 			putchar('\n');
 			break;
 
@@ -526,7 +539,8 @@ static void anonymize_ident_line(const char **beg, const char **end)
 	*end = out->buf + out->len;
 }
 
-static void handle_commit(struct commit *commit, struct rev_info *rev)
+static void handle_commit(struct commit *commit, struct rev_info *rev,
+			  struct string_list *paths_of_changed_objects)
 {
 	int saved_output_format = rev->diffopt.output_format;
 	const char *commit_buffer;
@@ -613,6 +627,7 @@ static void handle_commit(struct commit *commit, struct rev_info *rev)
 	if (full_tree)
 		printf("deleteall\n");
 	log_tree_diff_flush(rev);
+	string_list_clear(paths_of_changed_objects, 0);
 	rev->diffopt.output_format = saved_output_format;
 
 	printf("\n");
@@ -628,14 +643,15 @@ static void *anonymize_tag(const void *old, size_t *len)
 	return strbuf_detach(&out, len);
 }
 
-static void handle_tail(struct object_array *commits, struct rev_info *revs)
+static void handle_tail(struct object_array *commits, struct rev_info *revs,
+			struct string_list *paths_of_changed_objects)
 {
 	struct commit *commit;
 	while (commits->nr) {
 		commit = (struct commit *)commits->objects[commits->nr - 1].item;
 		if (has_unshown_parent(commit))
 			return;
-		handle_commit(commit, revs);
+		handle_commit(commit, revs, paths_of_changed_objects);
 		commits->nr--;
 	}
 }
@@ -975,6 +991,7 @@ int cmd_fast_export(int argc, const char **argv, const char *prefix)
 	char *export_filename = NULL, *import_filename = NULL;
 	uint32_t lastimportid;
 	struct string_list refspecs_list = STRING_LIST_INIT_NODUP;
+	struct string_list paths_of_changed_objects = STRING_LIST_INIT_DUP;
 	struct option options[] = {
 		OPT_INTEGER(0, "progress", &progress,
 			    N_("show progress after <n> objects")),
@@ -1047,14 +1064,15 @@ int cmd_fast_export(int argc, const char **argv, const char *prefix)
 	if (prepare_revision_walk(&revs))
 		die("revision walk setup failed");
 	revs.diffopt.format_callback = show_filemodify;
+	revs.diffopt.format_callback_data = &paths_of_changed_objects;
 	DIFF_OPT_SET(&revs.diffopt, RECURSIVE);
 	while ((commit = get_revision(&revs))) {
 		if (has_unshown_parent(commit)) {
 			add_object_array(&commit->object, NULL, &commits);
 		}
 		else {
-			handle_commit(commit, &revs);
-			handle_tail(&commits, &revs);
+			handle_commit(commit, &revs, &paths_of_changed_objects);
+			handle_tail(&commits, &revs, &paths_of_changed_objects);
 		}
 	}
 

t/t9350-fast-export.sh

@@ -234,7 +234,7 @@ test_expect_success 'fast-export -C -C | fast-import' '
 	mkdir new &&
 	git --git-dir=new/.git init &&
 	git fast-export -C -C --signed-tags=strip --all > output &&
-	grep "^C file6 file7\$" output &&
+	grep "^C file2 file4\$" output &&
 	cat output |
 	(cd new &&
 	 git fast-import &&
@@ -522,4 +522,22 @@ test_expect_success 'delete refspec' '
 	test_cmp expected actual
 '
 
+test_expect_success 'when using -C, do not declare copy when source of copy is also modified' '
+	test_create_repo src &&
+	echo a_line >src/file.txt &&
+	git -C src add file.txt &&
+	git -C src commit -m 1st_commit &&
+
+	cp src/file.txt src/file2.txt &&
+	echo another_line >>src/file.txt &&
+	git -C src add file.txt file2.txt &&
+	git -C src commit -m 2nd_commit &&
+
+	test_create_repo dst &&
+	git -C src fast-export --all -C | git -C dst fast-import &&
+	git -C src show >expected &&
+	git -C dst show >actual &&
+	test_cmp expected actual
+'
+
 test_done