CI: Add a test coverage job

This uses grcov internally to generate the HTML report.  We use grcov
instead of, say, lcov, because grcov actually generates accessible
pages.

We use the gnome-build-meta:core-nightly container image.  It doesn't
contain grcov by default, but we download the binary from its github
page.  We can change this later to build a custom container image for
gnome-calendar's own CI.

This will publish the report on

  https://gnome.pages.gitlab.gnome.org/gnome-calendar/coverage/

.gitlab-ci.yml

@@ -18,6 +18,7 @@ variables:
 stages:
   - check
   - build
+  - analysis
   - deploy
 
 style-check-diff:
@@ -48,3 +49,42 @@ nightly-aarch64:
   extends: '.publish_nightly'
   needs: ['build-flatpak-aarch64']
   when: manual
+
+coverage:
+  stage: analysis
+  image: quay.io/gnome_infrastructure/gnome-build-meta:core-nightly
+  needs:
+    - job: build-flatpak
+      artifacts: false
+  script:
+    - .gitlab-ci/install-grcov.sh
+    - .gitlab-ci/build-with-coverage.sh
+    - .gitlab-ci/gen-coverage.sh
+  coverage: '/Coverage: \d+\.\d+/'
+  artifacts:
+    name: "gnome-calendar-${CI_JOB_NAME}-${CI_COMMIT_REF_NAME}"
+    expire_in: 2 days
+    when: always
+    reports:
+      coverage_report:
+        coverage_format: cobertura
+        path: public/coverage.xml
+    paths:
+      - "_build/meson-logs"
+      - public
+  
+pages:
+  stage: deploy
+  needs: [ coverage ]
+  script:
+    # No-op, just to gitlab thinks there's something to do.
+    # The jobs that this job depends on have already populated public/
+    - echo
+  artifacts:
+    paths:
+      - public
+  rules:
+    # Restrict to the main branch so not every branch tries to deploy the web site
+    - if: ($CI_DEFAULT_BRANCH == $CI_COMMIT_BRANCH)
+    # Alternatively, restrict it to the GNOME namespace to avoid every fork pushing a set of pages by default
+    # - if: ($CI_DEFAULT_BRANCH == $CI_COMMIT_BRANCH && $CI_PROJECT_NAMESPACE == "GNOME")

.gitlab-ci/build-with-coverage.sh

@@ -0,0 +1,9 @@
+#!/bin/sh
+
+set -eux -o pipefail
+
+export CFLAGS="-coverage -ftest-coverage -fprofile-arcs"
+
+meson setup --buildtype=debug --prefix /usr _build .
+meson compile -C _build
+meson test -C _build

.gitlab-ci/gen-coverage.sh

@@ -0,0 +1,14 @@
+#!/bin/sh
+
+set -eux -o pipefail
+
+mkdir -p public
+grcov _build --source-dir ./ --prefix-dir ../ --output-type cobertura --branch --ignore-not-existing -o public/coverage.xml
+grcov _build --source-dir ./ --prefix-dir ../ --output-type html --branch --ignore-not-existing -o public/coverage
+
+# Print "Coverage: 42.42" so .gitlab-ci.yml will pick it up with a regex
+#
+# We scrape this from the HTML report, not the JSON summary, because coverage.json
+# uses no decimal places, just something like "42%".
+
+grep -Eo 'abbr title.* %' public/coverage/index.html | head -n 1 | grep -Eo '[0-9.]+ %' | grep -Eo '[0-9.]+' | awk '{ print "Coverage:", $1 }'

.gitlab-ci/install-grcov.sh

@@ -0,0 +1,9 @@
+#!/bin/bash
+
+set -eux -o pipefail
+
+wget https://github.com/mozilla/grcov/releases/download/v0.10.0/grcov-x86_64-unknown-linux-gnu.tar.bz2
+tar xvf grcov-x86_64-unknown-linux-gnu.tar.bz2
+mkdir -p /usr/local/bin
+mv grcov /usr/local/bin/grcov
+