Ensure that 0B changes are hidden from text diffs too.

src/borg/archiver/diff_cmd.py

@@ -19,17 +19,19 @@ class DiffMixIn:
     def do_diff(self, args, repository, manifest):
         """Diff contents of two archives"""
 
-        def print_json_output(diff):
-            def actual_change(j):
-                j = j.to_dict()
-                if j["type"] == "modified":
-                    # It's useful to show 0 added and 0 removed for text output
-                    # but for JSON this is essentially noise. Additionally, the
-                    # JSON key is "changes", and this is not actually a change.
-                    return not (j["added"] == 0 and j["removed"] == 0)
-                else:
-                    return True
+        def actual_change(j):
+            j = j.to_dict()
+            if j["type"] == "modified":
+                # Added/removed keys will not exist if chunker params differ
+                # between the two archives. Err on the side of caution and assume
+                # a real modification in this case (short-circuiting retrieving
+                # non-existent keys).
+                return not {"added", "removed"} <= j.keys() or not (j["added"] == 0 and j["removed"] == 0)
+            else:
+                # All other change types are indeed changes.
+                return True
 
+        def print_json_output(diff):
             print(
                 json.dumps(
                     {
@@ -45,6 +47,17 @@ def actual_change(j):
                 )
             )
 
+        def print_text_output(diff, formatter):
+            actual_changes = dict(
+                (name, change)
+                for name, change in diff.changes().items()
+                if actual_change(change) and (not args.content_only or (name not in DiffFormatter.METADATA))
+            )
+            diff._changes = actual_changes
+            res: str = formatter.format_item(diff)
+            if res.strip():
+                sys.stdout.write(res)
+
         if args.format is not None:
             format = args.format
         elif args.content_only:
@@ -85,9 +98,7 @@ def actual_change(j):
             if args.json_lines:
                 print_json_output(diff)
             else:
-                res: str = formatter.format_item(diff)
-                if res.strip():
-                    sys.stdout.write(res)
+                print_text_output(diff, formatter)
 
         for pattern in matcher.get_unmatched_include_patterns():
             self.print_warning_instance(IncludePatternNeverMatchedWarning(pattern))

src/borg/testsuite/archiver/__init__.py

@@ -358,6 +358,12 @@ def assert_line_exists(lines, expected_regexpr):
     assert any(re.search(expected_regexpr, line) for line in lines), f"no match for {expected_regexpr} in {lines}"
 
 
+def assert_line_not_exists(lines, expected_regexpr):
+    assert not any(
+        re.search(expected_regexpr, line) for line in lines
+    ), f"unexpected match for {expected_regexpr} in {lines}"
+
+
 def _assert_dirs_equal_cmp(diff, ignore_flags=False, ignore_xattrs=False, ignore_ns=False):
     assert diff.left_only == []
     assert diff.right_only == []

src/borg/testsuite/archiver/diff_cmd_test.py

@@ -7,7 +7,14 @@
 from ...constants import *  # NOQA
 from .. import are_symlinks_supported, are_hardlinks_supported
 from ...platformflags import is_win32, is_darwin
-from . import cmd, create_regular_file, RK_ENCRYPTION, assert_line_exists, generate_archiver_tests
+from . import (
+    cmd,
+    create_regular_file,
+    RK_ENCRYPTION,
+    assert_line_exists,
+    generate_archiver_tests,
+    assert_line_not_exists,
+)
 
 pytest_generate_tests = lambda metafunc: generate_archiver_tests(metafunc, kinds="local,remote,binary")  # NOQA
 
@@ -105,17 +112,20 @@ def do_asserts(output, can_compare_ids, content_only=False):
         # pointing to the file is not changed.
         change = "modified.*0 B" if can_compare_ids else r"modified:  \(can't get size\)"
         assert_line_exists(lines, f"{change}.*input/empty")
+
+        # Do not show a 0 byte change for a file whose contents weren't modified.
+        assert_line_not_exists(lines, "0 B.*input/file_touched")
+        if not content_only:
+            assert_line_exists(lines, "[cm]time:.*input/file_touched")
+        else:
+            # And if we're doing content-only, don't show the file at all.
+            assert "input/file_touched" not in output
+
         if are_hardlinks_supported():
             assert_line_exists(lines, f"{change}.*input/hardlink_contents_changed")
         if are_symlinks_supported():
             assert "input/link_target_contents_changed" not in output
 
-        # Show a 0 byte change for a file whose contents weren't modified for text output.
-        if content_only:
-            assert "input/file_touched" not in output
-        else:
-            assert_line_exists(lines, f"{change}.*input/file_touched")
-
         # Added a new file and a hard link to it. Both links to the same
         # inode should appear as separate files.
         assert "added:              2.05 kB input/file_added" in output
@@ -159,7 +169,7 @@ def get_changes(filename, data):
         # File unchanged
         assert not any(get_changes("input/file_unchanged", joutput))
 
-        # Do NOT show a 0 byte change for a file whose contents weren't modified for JSON output.
+        # Do not show a 0 byte change for a file whose contents weren't modified.
         unexpected = {"type": "modified", "added": 0, "removed": 0}
         assert unexpected not in get_changes("input/file_touched", joutput)
         if not content_only: