Include "metplus" in autodoc_mock_imports list in the configuration f…

…ile for sphinx (conf.py) (this will give sphinx access to METplus); remove definition of METPLUS_ROOT as an environment variable from the Makefile for the docs and instead define it in conf.py (as just a null string since it isn't actually used to load METplus).

doc/Makefile

@@ -1,12 +1,10 @@
 # Makefile for Sphinx documentation
 
-#SPHINXOPTS    = -a -n -W
-SPHINXOPTS    = -a -n
+SPHINXOPTS    = -a -n -W
 SPHINXBUILD   = sphinx-build
 SOURCEDIR     = .
 BUILDDIR      = build
 LINKCHECKDIR  = $(BUILDDIR)/linkcheck
-METPLUSROOT   = /scratch1/NCEPDEV/nems/role.epic/spack-stack/spack-stack-1.6.0/envs/upp-addon-env/install/intel/2021.5.0/metplus-5.1.0-eznr7ze
 
 .PHONY: help Makefile linkcheck
 
@@ -16,8 +14,8 @@ help:
 
 doc:
 	make clean
-	export METPLUS_ROOT=$(METPLUSROOT) ; $(MAKE) linkcheck
-	export METPLUS_ROOT=$(METPLUSROOT) ; $(MAKE) html
+	$(MAKE) linkcheck
+	$(MAKE) html
 
 linkcheck:
 	$(SPHINXBUILD) -b linkcheck $(SPHINXOPTS) $(SOURCEDIR) $(LINKCHECKDIR)

doc/conf.py

@@ -253,7 +253,7 @@ def setup(app):
 # -- Options for autodoc extension ---------------------------------------
 
 autodoc_mock_imports = ["f90nml","cartopy","mpl_toolkits.basemap","fill_jinja_template",
-   "matplotlib","numpy","uwtools","mpl_toolkits",
+   "matplotlib","numpy","uwtools","mpl_toolkits","metplus",
    ]
 
 logger = logging.getLogger(__name__)
@@ -310,3 +310,11 @@ def warn_undocumented_members(app, what, name, obj, options, lines):
             'fire-ug': ('https://fire-behavior.readthedocs.io/en/latest/%s', '%s'),
             }
 
+# Define environment variables that need to exist when running the top-level code in python
+# files (outside of functions, classes, etc.).
+#
+# METPLUS_ROOT just needs to exist in the environment; its value is not important since for
+# the purpose of building the documentation, METplus is loaded by including "metplus" in
+# the autodoc_mock_imports list above, not via use of the METPLUS_ROOT environment variable.
+os.environ["METPLUS_ROOT"] = ""
+