diff: only show states with values in summary (#6229)

* Fixed diff summary to only show states with values.

* Removed redundant comma by using join.

* Swithced for loop to generator for better readability.

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

dvc/command/diff.py

@@ -111,14 +111,12 @@ class CmdDiff(CmdBase):
         if not sum(summary.values()):
             return None
 
-        fmt = (
-            "files summary: {added} added, {deleted} deleted,"
-            " {renamed} renamed, {modified} modified"
+        states_summary = ", ".join(
+            f"{summary[state]} {state}"
+            for state in states
+            if summary[state] > 0
         )
-        if not hide_missing:
-            fmt += ", {not in cache} not in cache"
-
-        ui.write(fmt.format_map(summary))
+        ui.write("files summary:", states_summary)
 
     def run(self):
         from dvc.exceptions import DvcException

tests/unit/command/test_diff.py

@@ -48,8 +48,7 @@ def test_default(mocker, capsys):
         "Renamed:\n"
         "    data{sep}file_old -> data{sep}file_new\n"
         "\n"
-        "files summary: 1 added, 0 deleted, "
-        "1 renamed, 0 modified, 0 not in cache"
+        "files summary: 1 added, 1 renamed"
     ).format(sep=os.path.sep) in capsys.readouterr()[0]
 
 
@@ -99,8 +98,7 @@ def test_show_hash(mocker, capsys):
         "    CCCCCCCC..DDDDDDDD  file1\n"
         "    AAAAAAAA..BBBBBBBB  file2\n"
         "\n"
-        "files summary: 0 added, 2 deleted, "
-        "1 renamed, 2 modified, 0 not in cache"
+        "files summary: 2 deleted, 1 renamed, 2 modified"
     ) in out
 
 
@@ -350,6 +348,6 @@ def test_hide_missing(mocker, capsys):
         "Renamed:\n"
         "    file_old -> file_new\n"
         "\n"
-        "files summary: 1 added, 0 deleted, 1 renamed, 0 modified"
+        "files summary: 1 added, 1 renamed"
     ) in out
     assert "not in cache" not in out