Add ObjectDescription.get_field_type_map()

Conceal caching mechanism of Field classes to ObjectDescription class.
This deprecates DocFieldTransformer.preprocess_field_types().

CHANGES

@@ -36,6 +36,7 @@ Deprecated
 * ``sphinx.ext.autodoc.importer.MockLoader``
 * ``sphinx.ext.autodoc.importer.mock()``
 * ``sphinx.ext.autosummary.autolink_role()``
+* ``sphinx.util.docfields.DocFieldTransformer.preprocess_fieldtypes()``
 * ``sphinx.util.node.find_source_node()``
 * ``sphinx.util.i18n.find_catalog()``
 * ``sphinx.util.i18n.find_catalog_files()``

doc/extdev/deprecated.rst

@@ -141,6 +141,11 @@ The following is a list of deprecated interfaces.
      - 4.0
      - ``sphinx.ext.autosummary.AutoLink``
 
+   * - ``sphinx.util.docfields.DocFieldTransformer.preprocess_fieldtypes()``
+     - 2.1
+     - 4.0
+     - ``sphinx.directives.ObjectDescription.get_field_type_map()``
+
    * - ``sphinx.util.node.find_source_node()``
      - 2.1
      - 4.0

sphinx/directives/__init__.py

@@ -17,12 +17,12 @@ from docutils.parsers.rst import directives, roles
 from sphinx import addnodes
 from sphinx.deprecation import RemovedInSphinx40Warning, deprecated_alias
 from sphinx.util import docutils
-from sphinx.util.docfields import DocFieldTransformer
+from sphinx.util.docfields import DocFieldTransformer, TypedField
 from sphinx.util.docutils import SphinxDirective
 
 if False:
     # For type annotation
-    from typing import Any, Dict  # NOQA
+    from typing import Any, Dict, Tuple  # NOQA
     from sphinx.application import Sphinx  # NOQA
     from sphinx.util.docfields import Field  # NOQA
     from sphinx.util.typing import DirectiveOption  # NOQA
@@ -67,6 +67,23 @@ class ObjectDescription(SphinxDirective):
     objtype = None          # type: str
     indexnode = None        # type: addnodes.index
 
+    # Warning: this might be removed in future version. Don't touch this from extensions.
+    _doc_field_type_map = {}  # type: Dict[str, Tuple[Field, bool]]
+
+    def get_field_type_map(self):
+        # type: () -> Dict[str, Tuple[Field, bool]]
+        if self._doc_field_type_map == {}:
+            for field in self.doc_field_types:
+                for name in field.names:
+                    self._doc_field_type_map[name] = (field, False)
+
+                if field.is_typed:
+                    typed_field = cast(TypedField, field)
+                    for name in typed_field.typenames:
+                        self._doc_field_type_map[name] = (field, True)
+
+        return self._doc_field_type_map
+
     def get_signatures(self):
         # type: () -> List[str]
         """

sphinx/util/docfields.py

@@ -9,15 +9,18 @@
     :license: BSD, see LICENSE for details.
 """
 
+import warnings
 from typing import List, Tuple, cast
 
 from docutils import nodes
 
 from sphinx import addnodes
+from sphinx.deprecation import RemovedInSphinx40Warning
 
 if False:
     # For type annotation
     from typing import Any, Dict, Type, Union  # NOQA
+    from sphinx.directive import ObjectDescription  # NOQA
     from sphinx.environment import BuildEnvironment  # NOQA
     from sphinx.util.typing import TextlikeNode  # NOQA
 
@@ -244,15 +247,14 @@ class DocFieldTransformer:
     typemap = None  # type: Dict[str, Tuple[Field, bool]]
 
     def __init__(self, directive):
-        # type: (Any) -> None
+        # type: (ObjectDescription) -> None
         self.directive = directive
-        if '_doc_field_type_map' not in directive.__class__.__dict__:
+        self.typemap = directive.get_field_type_map()
-            directive.__class__._doc_field_type_map = \
-                self.preprocess_fieldtypes(directive.__class__.doc_field_types)
-        self.typemap = directive._doc_field_type_map
 
     def preprocess_fieldtypes(self, types):
         # type: (List[Field]) -> Dict[str, Tuple[Field, bool]]
+        warnings.warn('DocFieldTransformer.preprocess_fieldtypes() is deprecated.',
+                      RemovedInSphinx40Warning)
         typemap = {}
         for fieldtype in types:
             for name in fieldtype.names: