logging: Improve formatting of multiline message

Author: twmr

changelog/5312.feature.rst

@@ -0,0 +1 @@
+Improved formatting of multiline log messages.

src/_pytest/logging.py

@@ -71,6 +71,36 @@ def format(self, record):
         return super(ColoredLevelFormatter, self).format(record)
 
 
+if not six.PY2:
+
+    class PercentStyleMultiline(logging.PercentStyle):
+        """A logging style with special support for multiline messages.
+
+        If the message of a record consists of multiple lines, this style
+        formats the message as if each line were logged separately.
+        """
+
+        @staticmethod
+        def _update_message(record_dict, message):
+            tmp = record_dict.copy()
+            tmp["message"] = message
+            return tmp
+
+        def format(self, record):
+            if "\n" in record.message:
+                fmt = self._fmt
+                dct = record.__dict__
+
+                data_seq = [
+                    # fmt % {**dct, "message": line}
+                    fmt % self._update_message(dct, line)
+                    for line in record.message.splitlines()
+                ]
+                return "\n".join(data_seq)
+            else:
+                return self._fmt % record.__dict__
+
+
 def get_option_ini(config, *names):
     for name in names:
         ret = config.getoption(name)  # 'default' arg won't work as expected
@@ -438,6 +468,9 @@ def _create_formatter(self, log_format, log_date_format):
             )
         else:
             formatter = logging.Formatter(log_format, log_date_format)
+
+        if not six.PY2:
+            formatter._style = PercentStyleMultiline(formatter._style._fmt)
         return formatter
 
     def _setup_cli_logging(self):

testing/logging/test_formatter.py

@@ -1,7 +1,9 @@
 import logging
 
 import py.io
+import six
 
+import pytest
 from _pytest.logging import ColoredLevelFormatter
 
 
@@ -34,3 +36,31 @@ class option(object):
     formatter = ColoredLevelFormatter(tw, logfmt)
     output = formatter.format(record)
     assert output == ("dummypath                   10 INFO     Test Message")
+
+
+@pytest.mark.skipif(
+    six.PY2, reason="Formatter classes don't support format styles in PY2"
+)
+def test_multiline_message():
+    from _pytest.logging import PercentStyleMultiline
+
+    logfmt = "%(filename)-25s %(lineno)4d %(levelname)-8s %(message)s"
+
+    record = logging.LogRecord(
+        name="dummy",
+        level=logging.INFO,
+        pathname="dummypath",
+        lineno=10,
+        msg="Test Message line1\nline2",
+        args=(),
+        exc_info=False,
+    )
+    # this is called by logging.Formatter.format
+    record.message = record.getMessage()
+
+    style = PercentStyleMultiline(logfmt)
+    output = style.format(record)
+    assert output == (
+        "dummypath                   10 INFO     Test Message line1\n"
+        "dummypath                   10 INFO     line2"
+    )