Reject negative log_auto_indent values

changelog/14586.bugfix.rst

@@ -0,0 +1 @@
+Negative values passed to ``log_auto_indent`` now correctly fall back to no indentation, matching the documented behavior.

src/_pytest/logging.py

@@ -186,10 +186,10 @@ def _get_auto_indent(auto_indent_option: int | str | bool | None) -> int:
             case True:
                 return -1
             case int():
-                return auto_indent_option
+                return max(auto_indent_option, 0)
             case str():
                 try:
-                    return int(auto_indent_option)
+                    return max(int(auto_indent_option), 0)
                 except ValueError:
                     pass
                 try:

testing/logging/test_formatter.py

@@ -149,6 +149,18 @@ def test_multiline_message() -> None:
         "dummypath                   10 INFO     Test Message line1\n     line2"
     )
 
+    record.auto_indent = "-5"
+    output = ai_off_style.format(record)
+    assert output == (
+        "dummypath                   10 INFO     Test Message line1\nline2"
+    )
+
+    record.auto_indent = -5
+    output = ai_off_style.format(record)
+    assert output == (
+        "dummypath                   10 INFO     Test Message line1\nline2"
+    )
+
 
 def test_colored_short_level() -> None:
     logfmt = "%(levelname).1s %(message)s"