Refactor coverage CI workflow (#9361)

This relaxes the constraint on `coverage` added in #9305.  The issue
there is actually the now unmaintained `coveragepy-lcov` package is not
compatible with Coverage.py 7.0.  However, we only needed
`coveragepy-lcov` to convert Coverage's format into LCOV, which is a
feature Coverage has had itself since version 6.0.

This commit also updates some parts of the coverage workflow that were
old:

- there are new versions of the Actions `checkout` and `setup-python`,
  which swap to using Node 16 rather than Node 12, which is deprecated
  in GHA
- `grcov` is packaged and installable from `cargo` now, rather than
  needing a manual hard-coded pull from GitHub
- we can have `grcov` only keep the parts we care about immediately,
  rather than converting everything and later discarding it

Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

.github/workflows/coverage.yml

@@ -11,49 +11,54 @@ jobs:
     name: Coverage
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2
-      - uses: actions/setup-python@v2
+      - uses: actions/checkout@v3
+      - uses: actions/setup-python@v4
         name: Install Python
         with:
           python-version: '3.8'
+
       - name: Install Rust toolchain
         uses: actions-rs/toolchain@v1
         with:
           toolchain: stable
           override: true
           profile: default
           components: llvm-tools-preview
+
       - name: Install dependencies
         run: |
-            pip install coveragepy-lcov
+            cargo install grcov
             sudo apt-get install lcov
-      - name: Download grcov for rust coverage
-        run: curl -L https://github.com/mozilla/grcov/releases/download/v0.8.11/grcov-x86_64-unknown-linux-gnu.tar.bz2 | tar xj
+
       - name: Build and install qiskit-terra
         run: pip install -e .
         env:
           CARGO_INCREMENTAL: 0
           RUSTFLAGS: "-Cinstrument-coverage"
           LLVM_PROFILE_FILE: "qiskit-%p-%m.profraw"
           SETUPTOOLS_ENABLE_FEATURES: "legacy-editable"
+
       - name: Generate unittest coverage report
         run: |
           set -e
           pip install -r requirements-dev.txt qiskit-aer
           stestr run
-          ./grcov . --binary-path ./target/debug/ -s . --llvm --parallel -t lcov --branch --ignore-not-existing --ignore "/*" -o ./rust_unittest.info
-          rm *profraw
+          # We set the --source-dir to '.' because we want all paths to appear relative to the repo
+          # root (we need to combine them with the Python ones), but we only care about `grcov`
+          # keeping the `src/*` files; we don't care about coverage in dependencies.
+          grcov . --binary-path target/debug/ --source-dir . --output-type lcov --output-path rust.info --llvm --branch --parallel --keep-only 'src/*'
         env:
           QISKIT_TEST_CAPTURE_STREAMS: 1
           QISKIT_PARALLEL: FALSE
-          PYTHON: "coverage3 run --source qiskit --parallel-mode"
+          PYTHON: "coverage run --source qiskit --parallel-mode"
+
       - name: Convert to lcov and combine data
         run: |
           set -e
-          coverage3 combine
-          coveragepy-lcov --output_file_path python.info
-          lcov --add-tracefile python.info -a rust_unittest.info -o combined.info
-          lcov --remove combined.info "target/*" -o coveralls.info
+          coverage combine
+          coverage lcov -o python.info
+          lcov --add-tracefile python.info --add-tracefile rust.info --output-file coveralls.info
+
       - name: Coveralls
         uses: coverallsapp/github-action@master
         with:

constraints.txt

@@ -10,8 +10,3 @@ jupyter-core==4.11.2
 # ipywidgets 8.0.3 started emitting deprecation warnings via a seaborn import.
 # This pin can be removed when compatibility with those packages is fixed.
 ipywidgets<8.0.3
-
-# coverage 7.0.0 breaks with Python 3.8.15 upon the import
-#   from coverage.files import FnmatchMatcher
-# since this is in Python 3.8 itself and not Qiskit, pinning this for now.
-coverage<7.0