ci: Add job for pushing coverity reports

This job does:
1. Download the coverity bundle and untar it
2. Build mutter using clang and the coverity tool
3. Compress the coverity report
4. Upload for analysis

Things to note:
- Analysis are throttled, as per https://scan.coverity.com/faq#frequency
  we qualify for 21 weekly builds, 3 daily. Mutter is sometimes a busy
  project, so it seems we'd get often those consumed early in the day.
  This is something we can resign to, but the times we'll try to upload
  a report to have it rejected make the operation kinda pointless and
  probably better throttled by ourselves.
- The task is manual, given the restrictions above.
- The task only applies on master, as the envvar holding the coverity
  token is protected in gitlab.
- I had to use clang as the coverity tool doesn't seem to work ATM with
  gcc as per recent Fedora.
- The coverity tarball is 1.2GB in size, which is a bit too big to have
  it downloaded each time. As per their upload instructions, the tarball
  gets updated twice yearly, so this is cached to minimize downloads.
- The coverity token for mutter is kept private/hidden in gitlab CI
  settings.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1100>

.gitlab-ci.yml

@@ -7,14 +7,14 @@ stages:
  - prepare
  - build
  - test
- - coverage
+ - analyze
 
 .mutter.fedora:34@common:
   variables:
     FDO_DISTRIBUTION_VERSION: 34
-    BASE_TAG: '2021-07-07.1'
+    BASE_TAG: '2021-07-09.1'
     FDO_UPSTREAM_REPO: GNOME/mutter
-    FDO_DISTRIBUTION_PACKAGES: 'gdm gnome-shell xorg-x11-server-Xvfb sassc gcovr'
+    FDO_DISTRIBUTION_PACKAGES: 'gdm gnome-shell xorg-x11-server-Xvfb sassc gcovr clang'
 
     FDO_DISTRIBUTION_EXEC: |
       dnf install -y 'dnf-command(builddep)' &&
@@ -226,7 +226,7 @@ test-mutter@aarch64:
 .test-mutter-coverage:
   extends:
     - .fdo.distribution-image@fedora
-  stage: coverage
+  stage: analyze
   script:
     - ninja -C build coverage
     - cat build/meson-logs/coverage.txt
@@ -262,3 +262,29 @@ can-build-gnome-shell@x86_64:
     - .gitlab-ci/checkout-gnome-shell.sh
     - meson gnome-shell gnome-shell/build --prefix /usr -Dman=false
     - ninja -C gnome-shell/build install
+
+test-mutter-coverity:
+  rules:
+    - if: '$CI_PIPELINE_SOURCE == "schedule" && $MUTTER_SCHEDULED_JOB == "coverity"'
+      when: always
+    - when: manual
+  extends:
+    - .fdo.distribution-image@fedora
+    - .mutter.fedora:34@x86_64
+  needs:
+    - build-fedora-container@x86_64
+  stage: analyze
+  allow_failure: true
+  script:
+    - .gitlab-ci/download-coverity-tarball.sh
+    - CC=clang meson coverity-build -Dprofiler=false
+    - ./coverity/cov-analysis-linux64-*/bin/cov-build --dir cov-int ninja -C coverity-build
+    - tar czf cov-int.tar.gz cov-int
+    - curl https://scan.coverity.com/builds?project=mutter
+      --form token=$COVERITY_TOKEN --form email=carlosg@gnome.org
+      --form file=@cov-int.tar.gz --form version="`git describe --tags`"
+      --form description="GitLab CI build"
+  cache:
+    key: coverity-tarball
+    paths:
+      - coverity

.gitlab-ci/download-coverity-tarball.sh

@@ -0,0 +1,38 @@
+#!/usr/bin/bash
+
+# We need a coverity token to fetch the tarball
+if [ -x $COVERITY_TOKEN ]
+then
+  echo "No coverity token. Run this job from a protected branch."
+  exit -1
+fi
+
+mkdir -p coverity
+
+# Download and check MD5 first
+curl https://scan.coverity.com/download/linux64 \
+  --data "token=$COVERITY_TOKEN&project=mutter&md5=1" \
+  --output /tmp/coverity_tool.md5
+
+diff /tmp/coverity_tool.md5 coverity/coverity_tool.md5 >/dev/null 2>&1
+
+if [ $? -eq 0 -a -d coverity/cov-analysis* ]
+then
+  echo "Coverity tarball is up-to-date"
+  exit 0
+fi
+
+# Download and extract coverity tarball
+curl https://scan.coverity.com/download/linux64 \
+  --data "token=$COVERITY_TOKEN&project=mutter" \
+  --output /tmp/coverity_tool.tgz
+
+rm -rf ./coverity/cov-analysis*
+
+tar zxf /tmp/coverity_tool.tgz -C coverity/
+if [ $? -eq 0 ]
+then
+  mv /tmp/coverity_tool.md5 coverity/
+fi
+
+rm /tmp/coverity_tool.tgz