src/tox.ini (coverage.py-html): Split out from coverage.py for better…

… help display

src/doc/en/developer/tools.rst

@@ -62,7 +62,7 @@ available::
         codespell              -- check for misspelled words in source code
         rst                    -- validate Python docstrings markup as reStructuredText
         coverage.py            -- run the Sage doctester with Coverage.py
-                                  (use "sage --tox -e coverage.py-html" to generate HTML report)
+        coverage.py-html       -- run the Sage doctester with Coverage.py, generate HTML report
         pyright                -- run the static typing checker pyright
         pycodestyle            -- check against the Python style conventions of PEP8
         cython-lint            -- check Cython files for code style

src/tox.ini

@@ -51,11 +51,10 @@ allowlist_externals = {[sagedirect]allowlist_externals}
 commands =
     {env:SAGE} -t -p 0 {posargs:--all}
 
-[testenv:coverage.py{,-html}]
+[testenv:coverage.py]
 # https://coverage.readthedocs.io/en/latest/index.html
 description =
     run the Sage doctester with Coverage.py
-    (use "sage --tox -e coverage.py-html" to generate HTML report)
 ## This toxenv bypasses the virtual environment set up by tox.
 passenv = {[sagedirect]passenv}
 setenv  = {[sagedirect]setenv}
@@ -68,7 +67,24 @@ commands =
 commands_post =
     {env:SAGE} --python -m coverage combine
     {env:SAGE} --python -m coverage report
-    html: {env:SAGE} --python -m coverage html -d "{envdir}"
+
+[testenv:coverage.py-html]
+# https://coverage.readthedocs.io/en/latest/index.html
+description =
+    run the Sage doctester with Coverage.py, generate HTML report
+## This toxenv bypasses the virtual environment set up by tox.
+passenv = {[sagedirect]passenv}
+setenv  = {[sagedirect]setenv}
+envdir  = {[sagedirect]envdir}
+allowlist_externals = {[sagedirect]allowlist_externals}
+commands_pre =
+    {env:SAGE} -pip install -U coverage
+commands =
+    {env:SAGE} --python -m coverage run "{toxinidir}/../venv/bin/sage-runtests" -p 0 {posargs:--all}
+commands_post =
+    {env:SAGE} --python -m coverage combine
+    {env:SAGE} --python -m coverage report
+    {env:SAGE} --python -m coverage html -d "{envdir}"
 
 [testenv:coverage]
 description =