docs: kernel_feat.py: add build dependencies

Ensure that the feature files will be regenerated if any
changes happen at the Documentation/features files that were
processed by gen_feat.pl.

Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>
Link: https://lore.kernel.org/r/5cdf7a8300019129dcc09d4c2557f75908754445.1648290305.git.mchehab@kernel.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Author: mchehab

Documentation/sphinx/kernel_feat.py

@@ -33,6 +33,7 @@
 
 import codecs
 import os
+import re
 import subprocess
 import sys
 
@@ -82,7 +83,7 @@ def run(self):
 
         env = doc.settings.env
         cwd = path.dirname(doc.current_source)
-        cmd = "get_feat.pl rest --dir "
+        cmd = "get_feat.pl rest --enable-fname --dir "
         cmd += self.arguments[0]
 
         if len(self.arguments) > 1:
@@ -102,7 +103,22 @@ def run(self):
         shell_env["srctree"] = srctree
 
         lines = self.runCmd(cmd, shell=True, cwd=cwd, env=shell_env)
-        nodeList = self.nestedParse(lines, fname)
+
+        line_regex = re.compile("^\.\. FILE (\S+)$")
+
+        out_lines = ""
+
+        for line in lines.split("\n"):
+            match = line_regex.search(line)
+            if match:
+                fname = match.group(1)
+
+                # Add the file to Sphinx build dependencies
+                env.note_dependency(os.path.abspath(fname))
+            else:
+                out_lines += line + "\n"
+
+        nodeList = self.nestedParse(out_lines, fname)
         return nodeList
 
     def runCmd(self, cmd, **kwargs):