Fix an incorrect warning about Borg placeholders being unsupported in a command hook (#1075).

NEWS

@@ -1,3 +1,6 @@
+2.0.4.dev0
+ * #1075: Fix an incorrect warning about Borg placeholders being unsupported in a command hook.
+
 2.0.3
  * #1065: Fix a regression in monitoring hooks in which an error pinged the finish state instead of
    the fail state.

borgmatic/borg/create.py

@@ -69,7 +69,7 @@ def collect_special_file_paths(
     '''
     # Omit "--exclude-nodump" from the Borg dry run command, because that flag causes Borg to open
     # files including any named pipe we've created. And omit "--filter" because that can break the
-    # paths output parsing below such that path lines no longer start with th expected "- ".
+    # paths output parsing below such that path lines no longer start with the expected "- ".
     paths_output = execute_command_and_capture_output(
         flags.omit_flag_and_value(flags.omit_flag(create_command, '--exclude-nodump'), '--filter')
         + ('--dry-run', '--list'),

borgmatic/hooks/command.py

@@ -13,6 +13,19 @@ logger = logging.getLogger(__name__)
 
 
 SOFT_FAIL_EXIT_CODE = 75
+BORG_PLACEHOLDERS = {
+    '{hostname}',
+    '{fqdn}',
+    '{reverse-fqdn}',
+    '{now}',
+    '{utcnow}',
+    '{user}',
+    '{pid}',
+    '{borgversion}',
+    '{borgmajor}',
+    '{borgminor}',
+    '{borgpatch}',
+}
 
 
 def interpolate_context(hook_description, command, context):
@@ -23,10 +36,13 @@ def interpolate_context(hook_description, command, context):
     for name, value in context.items():
         command = command.replace(f'{{{name}}}', shlex.quote(str(value)))
 
-    for unsupported_variable in re.findall(r'{\w+}', command):
-        logger.warning(
-            f"Variable '{unsupported_variable}' is not supported in {hook_description} hook"
-        )
+    for unsupported_variable in re.findall(r'\{\w+\}', command):
+        # Warn about variables unknown to borgmatic, but don't warn if the variable name happens to
+        # be a Borg placeholder, as Borg should hopefully consume it.
+        if unsupported_variable not in BORG_PLACEHOLDERS:
+            logger.warning(
+                f'Variable "{unsupported_variable}" is not supported in the {hook_description} hook'
+            )
 
     return command
 

pyproject.toml

@@ -1,6 +1,6 @@
 [project]
 name = "borgmatic"
-version = "2.0.3"
+version = "2.0.4.dev0"
 authors = [
   { name="Dan Helfman", email="witten@torsion.org" },
 ]

tests/unit/hooks/test_command.py

@@ -11,8 +11,16 @@ def test_interpolate_context_passes_through_command_without_variable():
     assert module.interpolate_context('pre-backup', 'ls', {'foo': 'bar'}) == 'ls'
 
 
-def test_interpolate_context_passes_through_command_with_unknown_variable():
+def test_interpolate_context_warns_and_passes_through_command_with_unknown_variable():
     command = 'ls {baz}'  # noqa: FS003
+    flexmock(module.logger).should_receive('warning').once()
+
+    assert module.interpolate_context('pre-backup', command, {'foo': 'bar'}) == command
+
+
+def test_interpolate_context_does_not_warn_and_passes_through_command_with_unknown_variable_matching_borg_placeholder():
+    command = 'ls {hostname}'  # noqa: FS003
+    flexmock(module.logger).should_receive('warning').never()
 
     assert module.interpolate_context('pre-backup', command, {'foo': 'bar'}) == command