gh-142714: Strip hidden parts of the PEG grammar in all builders

Apply PEGLexer's stripping to peg literal blocks before the i18n transform,
so the catalogs (and the text builder) only get what the rendered page shows.

This also stops the hidden rules from showing on translated pages, which
happens when the "rules for invalid syntax" comment is translated (as on
zh-tw).

Author: Aurora-NICExq

Doc/tools/extensions/lexers/__init__.py

@@ -1,12 +1,33 @@
+from docutils import nodes
+from sphinx.transforms import SphinxTransform
+
 from .asdl_lexer import ASDLLexer
 from .peg_lexer import PEGLexer
 
 
+class StripPEGBlocks(SphinxTransform):
+    # Strip PEG blocks like PEGLexer does when highlighting them, so that
+    # other builders (gettext in particular) get the text the page shows.
+    # Must run before the i18n Locale transform (20).
+    default_priority = 10
+
+    def apply(self):
+        lexer = PEGLexer()
+        for node in self.document.findall(nodes.literal_block):
+            if node.get("language") != "peg":
+                continue
+            tokens = lexer.get_tokens_unprocessed(node.rawsource)
+            text = "".join(value for _, _, value in tokens)
+            node.rawsource = text
+            node[:] = [nodes.Text(text)]
+
+
 def setup(app):
     # Used for highlighting Parser/Python.asdl in library/ast.rst
     app.add_lexer("asdl", ASDLLexer)
     # Used for highlighting Grammar/python.gram in reference/grammar.rst
     app.add_lexer("peg", PEGLexer)
+    app.add_transform(StripPEGBlocks)
 
     return {
         "version": "1.0",