Fix sphinx-doc#7301: Allow . and _ for node_id

In development 3.0, Sphinx has obeyed to the rule of "Identifier
Normalization" of docutils.  This extends it to allow dots(".") and
underscores("_") for node identifier.

It allows Sphinx to generate node identifier from source string as
possible as it is (bacause dots and underscores are usually used in
many programming langauges).

This change will keep not to break hyperlinks as possible.

sphinx/domains/python.py

@@ -370,7 +370,7 @@ def add_target_and_index(self, name_cls: Tuple[str, str], sig: str,
                              signode: desc_signature) -> None:
         modname = self.options.get('module', self.env.ref_context.get('py:module'))
         fullname = (modname + '.' if modname else '') + name_cls[0]
-        node_id = make_id(self.env, self.state.document, modname or '', name_cls[0])
+        node_id = make_id(self.env, self.state.document, '', fullname)
         signode['ids'].append(node_id)
 
         # Assign old styled node_id(fullname) not to break old hyperlinks (if possible)

sphinx/util/nodes.py

@@ -9,6 +9,7 @@
 """
 
 import re
+import unicodedata
 import warnings
 from typing import Any, Callable, Iterable, List, Set, Tuple
 from typing import cast
@@ -436,6 +437,79 @@ def inline_all_toctrees(builder: "Builder", docnameset: Set[str], docname: str,
     return tree
 
 
+def _make_id(string: str) -> str:
+    """Convert `string` into an identifier and return it.
+
+    This function is a modified version of ``docutils.nodes.make_id()`` of
+    docutils-0.16.
+
+    Changes:
+
+    * Allow to use dots (".") and underscores ("_") for an identifier
+      without a leading character.
+
+    # Author: David Goodger <goodger@python.org>
+    # Maintainer: docutils-develop@lists.sourceforge.net
+    # Copyright: This module has been placed in the public domain.
+    """
+    id = string.lower()
+    id = id.translate(_non_id_translate_digraphs)
+    id = id.translate(_non_id_translate)
+    # get rid of non-ascii characters.
+    # 'ascii' lowercase to prevent problems with turkish locale.
+    id = unicodedata.normalize('NFKD', id).encode('ascii', 'ignore').decode('ascii')
+    # shrink runs of whitespace and replace by hyphen
+    id = _non_id_chars.sub('-', ' '.join(id.split()))
+    id = _non_id_at_ends.sub('', id)
+    return str(id)
+
+
+_non_id_chars = re.compile('[^a-z0-9._]+')
+_non_id_at_ends = re.compile('^[-0-9._]+|-+$')
+_non_id_translate = {
+    0x00f8: u'o',       # o with stroke
+    0x0111: u'd',       # d with stroke
+    0x0127: u'h',       # h with stroke
+    0x0131: u'i',       # dotless i
+    0x0142: u'l',       # l with stroke
+    0x0167: u't',       # t with stroke
+    0x0180: u'b',       # b with stroke
+    0x0183: u'b',       # b with topbar
+    0x0188: u'c',       # c with hook
+    0x018c: u'd',       # d with topbar
+    0x0192: u'f',       # f with hook
+    0x0199: u'k',       # k with hook
+    0x019a: u'l',       # l with bar
+    0x019e: u'n',       # n with long right leg
+    0x01a5: u'p',       # p with hook
+    0x01ab: u't',       # t with palatal hook
+    0x01ad: u't',       # t with hook
+    0x01b4: u'y',       # y with hook
+    0x01b6: u'z',       # z with stroke
+    0x01e5: u'g',       # g with stroke
+    0x0225: u'z',       # z with hook
+    0x0234: u'l',       # l with curl
+    0x0235: u'n',       # n with curl
+    0x0236: u't',       # t with curl
+    0x0237: u'j',       # dotless j
+    0x023c: u'c',       # c with stroke
+    0x023f: u's',       # s with swash tail
+    0x0240: u'z',       # z with swash tail
+    0x0247: u'e',       # e with stroke
+    0x0249: u'j',       # j with stroke
+    0x024b: u'q',       # q with hook tail
+    0x024d: u'r',       # r with stroke
+    0x024f: u'y',       # y with stroke
+}
+_non_id_translate_digraphs = {
+    0x00df: u'sz',      # ligature sz
+    0x00e6: u'ae',      # ae
+    0x0153: u'oe',      # ligature oe
+    0x0238: u'db',      # db digraph
+    0x0239: u'qp',      # qp digraph
+}
+
+
 def make_id(env: "BuildEnvironment", document: nodes.document,
             prefix: str = '', term: str = None) -> str:
     """Generate an appropriate node_id for given *prefix* and *term*."""
@@ -447,12 +521,12 @@ def make_id(env: "BuildEnvironment", document: nodes.document,
 
     # try to generate node_id by *term*
     if prefix and term:
-        node_id = nodes.make_id(idformat % term)
+        node_id = _make_id(idformat % term)
         if node_id == prefix:
             # *term* is not good to generate a node_id.
             node_id = None
     elif term:
-        node_id = nodes.make_id(term)
+        node_id = _make_id(term)
         if node_id == '':
             node_id = None  # fallback to None
 

tests/test_util_nodes.py

@@ -189,9 +189,9 @@ def test_clean_astext():
         ('', '', 'id0'),
         ('term', '', 'term-0'),
         ('term', 'Sphinx', 'term-sphinx'),
-        ('', 'io.StringIO', 'io-stringio'),   # contains a dot
-        ('', 'sphinx.setup_command', 'sphinx-setup-command'),  # contains a dot
-        ('', '_io.StringIO', 'io-stringio'),  # starts with underscore
+        ('', 'io.StringIO', 'io.stringio'),   # contains a dot
+        ('', 'sphinx.setup_command', 'sphinx.setup_command'),  # contains a dot & underscore
+        ('', '_io.StringIO', 'io.stringio'),  # starts with underscore
         ('', 'ｓｐｈｉｎｘ', 'sphinx'),  # alphabets in unicode fullwidth characters
         ('', '悠好', 'id0'),  # multibytes text (in Chinese)
         ('', 'Hello=悠好=こんにちは', 'hello'),  # alphabets and multibytes text