mypy: move configuration to pyproject.toml (#24802)

This moves our `mypy` configuration from `.mypy.ini` to `.pyproject.toml`
and increases the minimum `mypy` version in the tests.

- [x] move `mypy` configuration to `pyproject.toml`
- [x] remove `.mypy.ini`
- [x] ensure that `mypy` version .900 or higher is used in tests

pyproject.toml

@@ -12,3 +12,47 @@ known_archspec = "archspec"
 known_llnl = "llnl"
 src_paths = "lib"
 honor_noqa = true
+
+[tool.mypy]
+python_version = 3.7
+files = ['lib/spack/llnl/**/*.py', 'lib/spack/spack/**/*.py']
+mypy_path = ['bin', 'lib/spack', 'lib/spack/external', 'var/spack/repos/builtin']
+
+# This and a generated import file allows supporting packages
+namespace_packages = true
+
+# To avoid re-factoring all the externals, ignore errors and missing imports
+# globally, then turn back on in spack and spack submodules
+ignore_errors = true
+ignore_missing_imports = true
+
+[[tool.mypy.overrides]]
+module = 'spack.*'
+ignore_errors = false
+ignore_missing_imports = false
+
+[[tool.mypy.overrides]]
+module = 'packages.*'
+ignore_errors = false
+ignore_missing_imports = false
+
+[[tool.mypy.overrides]]
+module = 'llnl.*'
+ignore_errors = false
+ignore_missing_imports = false
+
+[[tool.mypy.overrides]]
+module = 'spack.test.packages'
+ignore_errors = true
+
+# ignore errors in fake import path for packages
+[[tool.mypy.overrides]]
+module = 'spack.pkg.*'
+ignore_errors = true
+ignore_missing_imports = true
+
+# jinja has syntax in it that requires python3 and causes a parse error
+# skip importing it
+[[tool.mypy.overrides]]
+module = 'jinja2'
+follow_imports = 'skip'