ci: add a GitHub workflow to submit Coverity scans

Coverity is a static analysis tool that detects and generates reports on
various security and code quality issues.

It is particularly useful when diagnosing memory safety issues which may
be used as part of exploiting a security vulnerability.

Coverity's website provides a service that accepts "builds" (which
contains the object files generated during a standard build as well as a
database generated by Coverity's scan tool).

Let's add a GitHub workflow to automate all of this. To avoid running it
without appropriate Coverity configuration (e.g. the token required to
use Coverity's services), the job only runs when the repository variable
"ENABLE_COVERITY_SCAN_FOR_BRANCHES" has been configured accordingly (see
https://docs.github.com/en/actions/learn-github-actions/variables for
details how to configure repository variables): It is expected to be a
valid JSON array of branch strings, e.g. `["main", "next"]`.

In addition, this workflow requires two repository secrets:

- COVERITY_SCAN_EMAIL: the email to send the report to, and

- COVERITY_SCAN_TOKEN: the Coverity token (look in the Project Settings
  tab of your Coverity project).

Note: The initial version of this patch used
`vapier/coverity-scan-action` to benefit from that Action's caching of
the Coverity tool, which is rather large. Sadly, that Action only
supports Linux, and we want to have the option of building on Windows,
too. Besides, in the meantime Coverity requires `cov-configure` to be
runantime, and that Action was not adjusted accordingly, i.e. it seems
not to be maintained actively. Therefore it would seem prudent to
implement the steps manually instead of using that Action.

Initial-patch-by: Taylor Blau <[email protected]>
Signed-off-by: Johannes Schindelin <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: dscho

.github/workflows/coverity.yml

@@ -0,0 +1,58 @@
+name: Coverity
+
+# This GitHub workflow automates submitting builds to Coverity Scan. To enable it,
+# set the repository variable `ENABLE_COVERITY_SCAN_FOR_BRANCHES` (for details, see
+# https://docs.github.com/en/actions/learn-github-actions/variables) to a JSON
+# string array containing the names of the branches for which the workflow should be
+# run, e.g. `["main", "next"]`.
+#
+# In addition, two repository secrets must be set (for details how to add secrets, see
+# https://docs.github.com/en/actions/security-guides/using-secrets-in-github-actions):
+# `COVERITY_SCAN_EMAIL` and `COVERITY_SCAN_TOKEN`. The former specifies the
+# email to which the Coverity reports should be sent and the latter can be
+# obtained from the Project Settings tab of the Coverity project).
+
+on:
+  push:
+
+jobs:
+  coverity:
+    if: contains(fromJSON(vars.ENABLE_COVERITY_SCAN_FOR_BRANCHES || '[""]'), github.ref_name)
+    runs-on: ubuntu-latest
+    env:
+      COVERITY_PROJECT: git
+      COVERITY_LANGUAGE: cxx
+      COVERITY_PLATFORM: linux64
+    steps:
+      - uses: actions/checkout@v3
+      - run: ci/install-dependencies.sh
+        env:
+          runs_on_pool: ubuntu-latest
+
+      - name: download the Coverity Build Tool (${{ env.COVERITY_LANGUAGE }} / ${{ env.COVERITY_PLATFORM}})
+        run: |
+          curl https://scan.coverity.com/download/$COVERITY_LANGUAGE/$COVERITY_PLATFORM \
+            --fail --no-progress-meter \
+            --output $RUNNER_TEMP/cov-analysis.tgz \
+            --form token='${{ secrets.COVERITY_SCAN_TOKEN }}' \
+            --form project="$COVERITY_PROJECT"
+      - name: extract the Coverity Build Tool
+        run: |
+          mkdir $RUNNER_TEMP/cov-analysis &&
+          tar -xzf $RUNNER_TEMP/cov-analysis.tgz --strip 1 -C $RUNNER_TEMP/cov-analysis
+      - name: build with cov-build
+        run: |
+          export PATH="$RUNNER_TEMP/cov-analysis/bin:$PATH" &&
+          cov-configure --gcc &&
+          cov-build --dir cov-int make -j$(nproc)
+      - name: package the build
+        run: tar -czvf cov-int.tgz cov-int
+      - name: submit the build to Coverity Scan
+        run: |
+          curl \
+            --fail \
+            --form token='${{ secrets.COVERITY_SCAN_TOKEN }}' \
+            --form email='${{ secrets.COVERITY_SCAN_EMAIL }}' \
+            --form [email protected] \
+            --form version='${{ github.sha }}' \
+            "https://scan.coverity.com/builds?project=$COVERITY_PROJECT"