users_guide: fix sphinx error caused by non-explicit override

Encouter following error when `make`:

```
Extension error:
The 'ghc-flag' directive is already registered to domain std
```

as we register `ghc-flag` to `std` in `add_object_type` first and then
overtride it in `add_directive_to_domain`.

Test Plan:
  make -C utils/haddock/doc html SPHINX_BUILD=/usr/bin/sphinx-build

Reviewers: austin, bgamari, patrickdoc

Subscribers: rwbarton, carter

Differential Revision: https://phabricator.haskell.org/D5161

1 files changed, 5 insertions, 12 deletions

diff --git a/docs/users_guide/flags.py b/docs/users_guide/flags.py
index 284b5e06cc..0e56bdfcc3 100644
--- a/docs/users_guide/flags.py
+++ b/docs/users_guide/flags.py
@@ -48,8 +48,6 @@ from docutils import nodes
 from docutils.parsers.rst import Directive, directives
 from sphinx import addnodes
 from sphinx.domains.std import GenericObject
-from sphinx.domains import ObjType
-from sphinx.roles import XRefRole
 from sphinx.errors import SphinxError
 from utils import build_table_from_list
 
@@ -601,20 +599,15 @@ def purge_flags(app, env, docname):
 ### Initialization
 
 def setup(app):
-    # Yuck: We can't use app.add_object_type since we need to provide the
-    # Directive instance ourselves.
-    std_object_types = app.registry.domain_object_types.setdefault('std', {})
 
     # Add ghc-flag directive, and override the class with our own
-    app.add_directive_to_domain('std', 'ghc-flag', Flag)
-    app.add_role_to_domain('std', 'ghc-flag', XRefRole())
-    std_object_types['ghc-flag'] = ObjType('ghc-flag', 'ghc-flag')
+    app.add_object_type('ghc-flag', 'ghc-flag')
+    app.add_directive_to_domain('std', 'ghc-flag', Flag, override=True)
 
     # Add extension directive, and override the class with our own
-    app.add_directive_to_domain('std', 'extension', LanguageExtension)
-    app.add_role_to_domain('std', 'extension', XRefRole())
-    std_object_types['extension'] = ObjType('ghc-flag', 'ghc-flag')
-
+    app.add_object_type('extension', 'extension')
+    app.add_directive_to_domain('std', 'extension', LanguageExtension,
+            override=True)
     # NB: language-extension would be misinterpreted by sphinx, and produce
     # lang="extensions" XML attributes