Fix Codecov integration and improve coverage reporting (#602)

* Initial plan

* Update Codecov integration to v5 and add codecov.yml config

Co-authored-by: pancetta <7158893+pancetta@users.noreply.github.com>

* Improve code coverage documentation with multiple viewing options

Co-authored-by: pancetta <7158893+pancetta@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: pancetta <7158893+pancetta@users.noreply.github.com>

Author: Copilot

.github/workflows/postprocess.yml

@@ -39,9 +39,12 @@ jobs:
         run: |
           genbadge coverage -i coverage.xml -o htmlcov/coverage-badge.svg
       - name: Upload coverage reports to Codecov
-        uses: codecov/codecov-action@v4
+        uses: codecov/codecov-action@v5
         with:
-          token: ${{ secrets.CODECOV }}
+          token: ${{ secrets.CODECOV_TOKEN }}
+          files: ./coverage.xml
+          fail_ci_if_error: false
+          verbose: true
 
 #      - name: Generate benchmark report
 #        uses: pancetta/github-action-benchmark@v1

codecov.yml

@@ -0,0 +1,36 @@
+codecov:
+  require_ci_to_pass: yes
+  notify:
+    wait_for_ci: yes
+
+coverage:
+  precision: 2
+  round: down
+  range: "70...100"
+  status:
+    project:
+      default:
+        target: auto
+        threshold: 1%
+        base: auto
+    patch:
+      default:
+        target: auto
+        threshold: 1%
+        base: auto
+
+comment:
+  layout: "reach,diff,flags,tree,reach"
+  behavior: default
+  require_changes: false
+  require_base: false
+  require_head: true
+
+ignore:
+  - "pySDC/tests/**"
+  - "pySDC/playgrounds/**"
+  - "pySDC/projects/deprecated/**"
+  - "data/**"
+  - "docs/**"
+  - "etc/**"
+  - "setup.py"

docs/contrib/02_continuous_integration.md

@@ -162,7 +162,30 @@ This stage allows to checks how much of the `pySDC` code is tested by the previo
 - `pySDC/tutorial`
 
 This analysis is done in parallel to the test each time a pull is done on any branch (main repository or fork).
-You can look at the current [coverage report for the master branch](https://parallel-in-time.org/pySDC/coverage/index.html) or [compare the results with previous builds](https://app.codecov.io/gh/Parallel-in-Time/pySDC). Codecov will also comment on any pull request, indicating the change of coverage.
+
+### Viewing Coverage Reports
+
+There are multiple ways to view test coverage for pySDC:
+
+1. **HTML Coverage Report** (recommended for detailed analysis)
+   - View the current [coverage report for the master branch](https://parallel-in-time.org/pySDC/coverage/index.html)
+   - Shows line-by-line coverage with color coding
+   - Updated automatically with each push to master
+
+2. **Codecov Dashboard** (for trends and PR analysis)
+   - [Compare results with previous builds](https://app.codecov.io/gh/Parallel-in-Time/pySDC)
+   - View coverage trends over time
+   - See coverage impact of specific commits
+   - Codecov automatically comments on pull requests with coverage changes
+
+3. **Coverage Badge** (quick status check)
+   - Displayed in the [README](../../README.md)
+   - Shows current coverage percentage for master branch
+
+4. **PR Coverage Comments** (for contributors)
+   - Codecov comments on each pull request
+   - Shows coverage changes introduced by the PR
+   - Highlights uncovered lines in modified files
 
 During developments, you can also run the coverage tests locally, using :
 
@@ -186,6 +209,11 @@ This will generate the coverage report in a `htmlcov` folder, and you can open t
 
 ### Coverage exceptions
 
+The coverage configuration is defined in two places:
+
+1. **Runtime configuration** (`pyproject.toml`) - Controls what coverage measures during test execution
+2. **Codecov configuration** (`codecov.yml`) - Controls how Codecov reports and displays coverage
+
 Some types of code lines will be ignored by the coverage analysis (_e.g_ lines starting with `raise`, ...), see the `[tool.coverage.report]` section in `pyproject.toml`.
 Part of code (functions, conditionaly, for loops, etc ...) can be ignored by coverage analysis using the `# pragma: no cover`, for instance