Remove support for running with Python 2.7 (#33063)

* Remove CI jobs related to Python 2.7

* Remove Python 2.7 specific code from Spack core

* Remove externals for Python 2 only

* Remove llnl.util.compat

.github/workflows/bootstrap.yml

@@ -214,7 +214,7 @@ jobs:
       - name: Bootstrap clingo
         run: |
           set -ex
-          for ver in '2.7' '3.6' '3.7' '3.8' '3.9' '3.10' ; do
+          for ver in '3.6' '3.7' '3.8' '3.9' '3.10' ; do
             not_found=1
             ver_dir="$(find $RUNNER_TOOL_CACHE/Python -wholename "*/${ver}.*/*/bin" | grep . || true)"
             echo "Testing $ver_dir"

.github/workflows/ci.yaml

@@ -20,12 +20,6 @@ jobs:
     uses: ./.github/workflows/valid-style.yml
     with:
       with_coverage: ${{ needs.changes.outputs.core }}
-  audit-ancient-python:
-    uses: ./.github/workflows/audit.yaml
-    needs: [ changes ]
-    with:
-      with_coverage: ${{ needs.changes.outputs.core }}
-      python_version: 2.7
   all-prechecks:
     needs: [ prechecks ]
     runs-on: ubuntu-latest
@@ -85,7 +79,7 @@ jobs:
     needs: [ prechecks ]
     uses: ./.github/workflows/windows_python.yml
   all:
-    needs: [ windows, unit-tests, bootstrap, audit-ancient-python ]
+    needs: [ windows, unit-tests, bootstrap ]
     runs-on: ubuntu-latest
     steps:
     - name: Success

.github/workflows/unit_tests.yaml

@@ -14,14 +14,11 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        python-version: ['2.7', '3.6', '3.7', '3.8', '3.9', '3.10', '3.11']
+        python-version: ['3.6', '3.7', '3.8', '3.9', '3.10', '3.11']
         concretizer: ['clingo']
         on_develop:
         - ${{ github.ref == 'refs/heads/develop' }}
         include:
-        - python-version: 2.7
-          concretizer: original
-          on_develop: ${{ github.ref == 'refs/heads/develop' }}
         - python-version: '3.11'
           concretizer: original
           on_develop: ${{ github.ref == 'refs/heads/develop' }}
@@ -66,10 +63,6 @@ jobs:
           if python -c 'import sys; sys.exit(not sys.version_info >= (3, 6))'; then
               pip install --upgrade flake8 "isort>=4.3.5" "mypy>=0.900" "click==8.0.4" "black<=21.12b0"
           fi
-    - name: Pin pathlib for Python 2.7
-      if: ${{ matrix.python-version == 2.7 }}
-      run: |
-          pip install -U pathlib2==2.3.6 toml
     - name: Setup git configuration
       run: |
           # Need this for the git tests to succeed.
@@ -89,7 +82,7 @@ jobs:
           SPACK_TEST_SOLVER: ${{ matrix.concretizer }}
           SPACK_TEST_PARALLEL: 2
           COVERAGE: true
-          UNIT_TEST_COVERAGE: ${{ (matrix.python-version == '3.11') }}
+          UNIT_TEST_COVERAGE: ${{ matrix.python-version == '3.11' }}
       run: |
           share/spack/qa/run-unit-tests
     - uses: codecov/codecov-action@d9f34f8cd5cb3b3eb79b3e4b5dae3a16df499a70

.github/workflows/valid-style.yml

@@ -28,9 +28,9 @@ jobs:
         pip install --upgrade pip
         pip install --upgrade vermin
     - name: vermin (Spack's Core)
-      run: vermin --backport argparse --violations --backport typing -t=2.7- -t=3.6- -vvv lib/spack/spack/ lib/spack/llnl/ bin/
+      run: vermin --backport importlib --backport argparse --violations --backport typing -t=3.6- -vvv lib/spack/spack/ lib/spack/llnl/ bin/
     - name: vermin (Repositories)
-      run: vermin --backport argparse --violations --backport typing -t=2.7- -t=3.6- -vvv var/spack/repos
+      run: vermin --backport importlib --backport argparse --violations --backport typing -t=3.6- -vvv var/spack/repos
   # Run style checks on the files that have been changed
   style:
     runs-on: ubuntu-latest
@@ -44,7 +44,7 @@ jobs:
         cache: 'pip'
     - name: Install Python packages
       run: |
-        python3 -m pip install --upgrade pip six setuptools types-six click==8.0.2 'black==21.12b0' mypy isort clingo flake8
+        python3 -m pip install --upgrade pip six setuptools types-six black mypy isort clingo flake8
     - name: Setup git configuration
       run: |
         # Need this for the git tests to succeed.