Sphinx 3.4+ required for correct reference target linking

lib/spack/docs/conf.py

@@ -97,7 +97,7 @@ def setup(sphinx):
 # -- General configuration -----------------------------------------------------
 
 # If your documentation needs a minimal Sphinx version, state it here.
-needs_sphinx = '1.8'
+needs_sphinx = '3.4'
 
 # Add any Sphinx extension module names here, as strings. They can be extensions
 # coming with Sphinx (named 'sphinx.ext.*') or your custom ones.

lib/spack/docs/requirements.txt

@@ -1,7 +1,7 @@
 # These dependencies should be installed using pip in order
 # to build the documentation.
 
-sphinx
+sphinx>=3.4
 sphinxcontrib-programoutput
 sphinx-rtd-theme
 python-levenshtein

lib/spack/docs/spack.yaml

@@ -14,6 +14,6 @@
 #
 spack:
   specs:
-  - py-sphinx
+  - "py-sphinx@3.4:"
   - py-sphinxcontrib-programoutput
   - py-sphinx-rtd-theme