add mypy to style checks; rename `spack flake8` to `spack style` (#20384)

I lost my mind a bit after getting the completion stuff working and
decided to get Mypy working for spack as well. This adds a 
`.mypy.ini` that checks all of the spack and llnl modules, though
not yet packages, and fixes all of the identified missing types and
type issues for the spack library.

In addition to these changes, this includes:

* rename `spack flake8` to `spack style`

Aliases flake8 to style, and just runs flake8 as before, but with
a warning.  The style command runs both `flake8` and `mypy`,
in sequence. Added --no-<tool> options to turn off one or the
other, they are on by default.  Fixed two issues caught by the tools.

* stub typing module for python2.x

We don't support typing in Spack for python 2.x. To allow 2.x to
support `import typing` and `from typing import ...` without a
try/except dance to support old versions, this adds a stub module
*just* for python 2.x.  Doing it this way means we can only reliably
use all type hints in python3.7+, and mypi.ini has been updated to
reflect that.

* add non-default black check to spack style

This is a first step to requiring black.  It doesn't enforce it by
default, but it will check it if requested.  Currently enforcing the
line length of 79 since that's what flake8 requires, but it's a bit odd
for a black formatted project to be quite that narrow.  All settings are
in the style command since spack has no pyproject.toml and I don't
want to add one until more discussion happens. Also re-format
`style.py` since it no longer passed the black style check
with the new length.

* use style check in github action

Update the style and docs action to use `spack style`, adding in mypy
and black to the action even if it isn't running black right now.

3 files changed, 17 insertions, 4 deletions

diff --git a/share/spack/qa/run-flake8-tests b/share/spack/qa/run-style-tests
index d6077fceb8..b91834f9d8 100755
--- a/share/spack/qa/run-flake8-tests
+++ b/share/spack/qa/run-style-tests
@@ -15,10 +15,10 @@
 #     run-flake8-tests
 #
 . "$(dirname $0)/setup.sh"
-check_dependencies flake8
+check_dependencies flake8 mypy
 
 # verify that the code style is correct
-spack flake8
+spack style
 
 # verify that the license headers are present
 spack license verify
diff --git a/share/spack/qa/setup.sh b/share/spack/qa/setup.sh
index e614bae909..3940d497c2 100755
--- a/share/spack/qa/setup.sh
+++ b/share/spack/qa/setup.sh
@@ -66,6 +66,10 @@ check_dependencies() {
                     spack_package=py-flake8
                     pip_package=flake8
                     ;;
+                mypy)
+                    spack_package=py-mypy
+                    pip_package=mypy
+                    ;;
                 dot)
                     spack_package=graphviz
                     ;;
diff --git a/share/spack/spack-completion.bash b/share/spack/spack-completion.bash
index cbe59bc90a..36880dfdef 100755
--- a/share/spack/spack-completion.bash
+++ b/share/spack/spack-completion.bash
@@ -333,7 +333,7 @@ _spack() {
     then
         SPACK_COMPREPLY="-h --help -H --all-help --color -C --config-scope -d --debug --timestamp --pdb -e --env -D --env-dir -E --no-env --use-env-repo -k --insecure -l --enable-locks -L --disable-locks -m --mock -p --profile --sorted-profile --lines -v --verbose --stacktrace -V --version --print-shell-vars"
     else
-        SPACK_COMPREPLY="activate add arch blame build-env buildcache cd checksum ci clean clone commands compiler compilers concretize config containerize create deactivate debug dependencies dependents deprecate dev-build develop docs edit env extensions external fetch find flake8 gc gpg graph help info install license list load location log-parse maintainers mark mirror module patch pkg providers pydoc python reindex remove rm repo resource restage setup solve spec stage test test-env tutorial undevelop uninstall unit-test unload url verify versions view"
+        SPACK_COMPREPLY="activate add arch blame build-env buildcache cd checksum ci clean clone commands compiler compilers concretize config containerize create deactivate debug dependencies dependents deprecate dev-build develop docs edit env extensions external fetch find flake8 gc gpg graph help info install license list load location log-parse maintainers mark mirror module patch pkg providers pydoc python reindex remove rm repo resource restage setup solve spec stage style test test-env tutorial undevelop uninstall unit-test unload url verify versions view"
     fi
 }
 
@@ -913,7 +913,7 @@ _spack_find() {
 _spack_flake8() {
     if $list_options
     then
-        SPACK_COMPREPLY="-h --help -b --base -a --all -o --output -r --root-relative -U --no-untracked"
+        SPACK_COMPREPLY="-h --help -b --base -a --all -o --output -r --root-relative -U --no-untracked --no-flake8 --no-mypy --black"
     else
         SPACK_COMPREPLY=""
     fi
@@ -1513,6 +1513,15 @@ _spack_stage() {
     fi
 }
 
+_spack_style() {
+    if $list_options
+    then
+        SPACK_COMPREPLY="-h --help -b --base -a --all -o --output -r --root-relative -U --no-untracked --no-flake8 --no-mypy --black"
+    else
+        SPACK_COMPREPLY=""
+    fi
+}
+
 _spack_test() {
     if $list_options
     then