docs: enable Sphinx nitpicky

.github/workflows/ci-rtfd.yml

@@ -0,0 +1,16 @@
+name: RTFD Preview
+on:
+  pull_request_target:
+    types:
+      - opened
+
+permissions:
+  pull-requests: write
+
+jobs:
+  documentation-links:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: readthedocs/actions/preview@v1
+        with:
+          project-slug: "torchmetrics"

.github/workflows/docs-build.yml

@@ -21,6 +21,7 @@ env:
   PYPI_CACHE: "_ci-cache_PyPI"
   PROTOCOL_BUFFERS_PYTHON_IMPLEMENTATION: 'python'
   TOKENIZERS_PARALLELISM: false
+  SPHINX_FETCH_ASSETS: 1  # todo: consider not downloading on PRs
 
 jobs:
   docs-check:

docs/source/conf.py

@@ -264,9 +264,11 @@ def _set_root_image_path(page_path: str):
     "python": ("https://docs.python.org/3", None),
     "torch": ("https://pytorch.org/docs/stable/", None),
     "numpy": ("https://numpy.org/doc/stable/", None),
+    "matplotlib": ("http://matplotlib.org/stable", None),
 }
+nitpicky = True
 
-# -- Options for todo extension ----------------------------------------------
+# -- Options for to-do extension ----------------------------------------------
 
 # If true, `todo` and `todoList` produce output, else they produce nothing.
 todo_include_todos = True