gh-127833: Fix grammar snippet formatting for help() output

Doc/tools/extensions/grammar_snippet.py

@@ -36,6 +36,12 @@ def __init__(
         self['classes'].append('sx')
 
 
+class grammar_snippet(nodes.literal_block):  # noqa: N801 (snake_case)
+    """Node for a grammar snippet"""
+
+    grammar_snippet_content: Sequence[str]
+
+
 class GrammarSnippetBase(SphinxDirective):
     """Common functionality for GrammarSnippetDirective & CompatProductionList."""
 
@@ -58,11 +64,14 @@ def make_grammar_snippet(
         # To get around this, we set it to this non-empty string:
         rawsource = 'You should not see this.'
 
-        literal = nodes.literal_block(
+        literal = grammar_snippet(
             rawsource,
             '',
             classes=['highlight'],
         )
+        # Save a copy of the "input" content. For plain text, we want to
+        # output this verbatim.
+        literal.grammar_snippet_content = list(content)
 
         grammar_re = re.compile(
             r"""

Doc/tools/extensions/pydoc_topics.py

@@ -1,17 +1,18 @@
 """Support for building "topic help" for pydoc."""
 
 from __future__ import annotations
 
 from time import asctime
 from typing import TYPE_CHECKING
 
 from sphinx.builders.text import TextBuilder
 from sphinx.util import logging
 from sphinx.util.display import status_iterator
 from sphinx.util.docutils import new_document
 from sphinx.writers.text import TextTranslator
+from docutils import nodes
 
 if TYPE_CHECKING:
     from collections.abc import Sequence, Set
 
     from sphinx.application import Sphinx
@@ -102,6 +103,14 @@
     "yield",
 })
 
+class PydocTextTranslator(TextTranslator):
+    def visit_grammar_snippet(self, node: Element) -> None:
+        """For grammar snippets, return the "input" as is."""
+        self.new_state()
+        self.add_text(self.nl.join(node.grammar_snippet_content))
+        self.end_state(wrap=False)
+        raise nodes.SkipNode
+
 
 class PydocTopicsBuilder(TextBuilder):
     name = "pydoc-topics"
@@ -141,7 +150,7 @@
             for topic_label, label_id in label_ids:
                 document = new_document("<section node>")
                 document.append(doc_ids[label_id])
-                visitor = TextTranslator(document, builder=self)
+                visitor = PydocTextTranslator(document, builder=self)
                 document.walkabout(visitor)
                 self.topics[topic_label] = visitor.body