docs: kdoc: fix logic to handle unissued warnings

Changeset 469c1c9 ("kernel-doc: Issue warnings that were silently discarded")
didn't properly addressed the missing messages behavior, as
it was calling directly python logger low-level function,
instead of using the expected method to emit warnings.

Basically, there are two methods to log messages:

- self.config.log.warning() - This is the raw level to emit a
  warning. It just writes the a message at stderr, via python
  logging, as it is initialized as:

    self.config.log = logging.getLogger("kernel-doc")

- self.config.warning() - This is where we actually consider a
  message as a warning, properly incrementing error count.

Due to that, several parsing error messages are internally considered
as success, causing -Werror to not work on such messages.

While here, ensure that the last ignored entry will also be handled
by adding an extra check at the end of the parse handler.

Fixes: 469c1c9 ("kernel-doc: Issue warnings that were silently discarded")
Closes: https://lore.kernel.org/linux-doc/20260112091053.00cee29a@foz.lan/
Cc: stable@vger.kernel.org
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Acked-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Message-ID: <95109a6585171da4d6900049deaa2634b41ee743.1768823489.git.mchehab+huawei@kernel.org>

Author: mchehab

tools/lib/python/kdoc/kdoc_parser.py

@@ -295,7 +295,7 @@ def contents(self):
 
     # TODO: rename to emit_message after removal of kernel-doc.pl
     def emit_msg(self, ln, msg, *, warning=True):
-        """Emit a message"""
+        """Emit a message."""
 
         log_msg = f"{self.fname}:{ln} {msg}"
 
@@ -448,18 +448,37 @@ def output_declaration(self, dtype, name, **args):
 
         self.config.log.debug("Output: %s:%s = %s", dtype, name, pformat(args))
 
+    def emit_unused_warnings(self):
+        """
+        When the parser fails to produce a valid entry, it places some
+        warnings under `entry.warnings` that will be discarded when resetting
+        the state.
+
+        Ensure that those warnings are not lost.
+
+        .. note::
+
+              Because we are calling `config.warning()` here, those
+              warnings are not filtered by the `-W` parameters: they will all
+              be produced even when `-Wreturn`, `-Wshort-desc`, and/or
+              `-Wcontents-before-sections` are used.
+
+              Allowing those warnings to be filtered is complex, because it
+              would require storing them in a buffer and then filtering them
+              during the output step of the code, depending on the
+              selected symbols.
+        """
+        if self.entry and self.entry not in self.entries:
+            for log_msg in self.entry.warnings:
+                self.config.warning(log_msg)
+
     def reset_state(self, ln):
         """
         Ancillary routine to create a new entry. It initializes all
         variables used by the state machine.
         """
 
-        #
-        # Flush the warnings out before we proceed further
-        #
-        if self.entry and self.entry not in self.entries:
-            for log_msg in self.entry.warnings:
-                self.config.log.warning(log_msg)
+        self.emit_unused_warnings()
 
         self.entry = KernelEntry(self.config, self.fname, ln)
 
@@ -1741,6 +1760,8 @@ def parse_kdoc(self):
                         # Hand this line to the appropriate state handler
                         self.state_actions[self.state](self, ln, line)
 
+            self.emit_unused_warnings()
+
         except OSError:
             self.config.log.error(f"Error: Cannot open file {self.fname}")