Making --debug more configurable for the pytest user (#8955)

Close #8954

src/_pytest/helpconfig.py

@@ -80,10 +80,14 @@ def pytest_addoption(parser: Parser) -> None:
     )
     group.addoption(
         "--debug",
-        action="store_true",
+        action="store",
+        nargs="?",
+        const="pytestdebug.log",
         dest="debug",
-        default=False,
-        help="store internal tracing debug information in 'pytestdebug.log'.",
+        metavar="DEBUG_FILE_NAME",
+        help="store internal tracing debug information in this log file.\n"
+        "This file is opened with 'w' and truncated as a result, care advised.\n"
+        "Defaults to 'pytestdebug.log'.",
     )
     group._addoption(
         "-o",
@@ -98,8 +102,10 @@ def pytest_addoption(parser: Parser) -> None:
 def pytest_cmdline_parse():
     outcome = yield
     config: Config = outcome.get_result()
+
     if config.option.debug:
-        path = os.path.abspath("pytestdebug.log")
+        # --debug | --debug <file.log> was provided.
+        path = config.option.debug
         debugfile = open(path, "w")
         debugfile.write(
             "versions pytest-%s, py-%s, "
@@ -114,11 +120,11 @@ def pytest_cmdline_parse():
         )
         config.trace.root.setwriter(debugfile.write)
         undo_tracing = config.pluginmanager.enable_tracing()
-        sys.stderr.write("writing pytestdebug information to %s\n" % path)
+        sys.stderr.write("writing pytest debug information to %s\n" % path)
 
         def unset_tracing() -> None:
             debugfile.close()
-            sys.stderr.write("wrote pytestdebug information to %s\n" % debugfile.name)
+            sys.stderr.write("wrote pytest debug information to %s\n" % debugfile.name)
             config.trace.root.setwriter(None)
             undo_tracing()