Remove backslash stripping in domains.

Adds several ways to reinstate the old behaviour.

Fixes sphinx-doc/sphinx#6462

CHANGES

@@ -42,6 +42,12 @@ Incompatible changes
   The existing ones are now more strict, resulting in new warnings.
 * The attribute ``sphinx_cpp_tagname`` in the ``desc_signature_line`` node
   has been renamed to ``sphinx_line_type``.
+* #6462: double backslashes in domain directives are no longer replaced by
+  single backslashes as default. Each class derived from ObjectDescription
+  may reenable the stripping for it self. A new configuration value
+  :confval:`signature_backslash_strip_domain_override` can be used by users
+  to reenable it per domain as well. Setting it to ``[]`` will reinstate the
+  old behaviour with backslash stripping in every domain.
 
 Deprecated
 ----------

doc/usage/configuration.rst

@@ -634,6 +634,17 @@ General configuration
    .. versionchanged:: 1.1
       Now also removes ``<BLANKLINE>``.
 
+.. confval:: signature_backslash_strip_domain_override
+
+    A list of domain names for which to forcibly reinstate backslash stripping.
+    The value ``None`` means "no domains" while ``[]`` means every domain
+    (i.e., the behaviour before version 3.0).
+    Default is ``None``.
+    When backslash stripping is enabled then every occurrence of ``\\`` in a domain
+    directive will be changed to ``\``, even within string literals.
+
+    .. versionadded:: 3.0
+
 
 .. _intl-options:
 

sphinx/directives/__init__.py

@@ -60,6 +60,7 @@ class ObjectDescription(SphinxDirective):
     required_arguments = 1
     optional_arguments = 0
     final_argument_whitespace = True
+    strip_backslashes = None
     option_spec = {
         'noindex': directives.flag,
     }  # type: Dict[str, DirectiveOption]
@@ -95,8 +96,28 @@ class ObjectDescription(SphinxDirective):
         Backslash-escaping of newlines is supported.
         """
         lines = nl_escape_re.sub('', self.arguments[0]).split('\n')
-        # remove backslashes to support (dummy) escapes; helps Vim highlighting
-        return [strip_backslash_re.sub(r'\1', line.strip()) for line in lines]
+
+        # Stripping of backslashes can be overridden by the user config,
+        # otherwise the object it self may have an opinion, and
+        # otherwise we don't do stripping.
+        do_stripping = False
+        conf_stripping = self.env.config.signature_backslash_strip_domain_override
+        if conf_stripping is None:
+            # no user config override, use the object opinion if any
+            if self.strip_backslashes is not None:
+                do_stripping = self.strip_backslashes
+        else:
+            # could be overridden by the user
+            if len(conf_stripping) == 0:
+                # override always (i.e., the old behaviour)
+                do_stripping = True
+            elif self.domain is not None:
+                do_stripping = self.domain in conf_stripping
+        if do_stripping:
+            # remove backslashes to support (dummy) escapes; helps Vim highlighting
+            return [strip_backslash_re.sub(r'\1', line.strip()) for line in lines]
+        else:
+            return [line.strip() for line in lines]
 
     def handle_signature(self, sig: str, signode: desc_signature) -> Any:
         """
@@ -297,6 +318,7 @@ deprecated_alias('sphinx.directives',
 
 
 def setup(app: "Sphinx") -> Dict[str, Any]:
+    app.add_config_value("signature_backslash_strip_domain_override", None, 'env')
     directives.register_directive('default-role', DefaultRole)
     directives.register_directive('default-domain', DefaultDomain)
     directives.register_directive('describe', ObjectDescription)