CI: Add a basic test coverage job

Later we'll add one coverage job per backend, and aggregate all of the
results at the end for the coverage report.

.gitlab-ci.yml

@@ -477,3 +477,28 @@ macOS x86 host:
     - export CAIRO_TEST_IGNORE_quartz_rgb24=$(tr '\n' ',' < .gitlab-ci/ignore-quartz-rgb24.txt)
     - export CAIRO_TEST_TARGET=quartz
     - (cd build/test && srcdir=../../test ./cairo-test-suite)
+
+coverage:
+  stage: 'analysis'
+  extends:
+    - '.fdo.distribution-image@fedora'
+  needs:
+    - job: 'fedora image'
+      artifacts: false
+  script:
+    - source ./.gitlab-ci/env.sh
+    - bash -x ./.gitlab-ci/build-with-coverage.sh
+    - bash -x ./.gitlab-ci/gen-coverage.sh
+  coverage: '/Coverage: \d+\.\d+/'
+  artifacts:
+    name: "cairo-${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
+

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

@@ -0,0 +1,17 @@
+#!/bin/sh
+
+set -eux -o pipefail
+
+export CFLAGS="-coverage -ftest-coverage -fprofile-arcs"
+
+export CAIRO_TEST_IGNORE_image_argb32=$(tr '\n' ',' < .gitlab-ci/ignore-image-argb32.txt)
+export CAIRO_TEST_IGNORE_image_rgb24=$(tr '\n' ',' < .gitlab-ci/ignore-image-rgb24.txt)
+export CAIRO_TEST_IGNORE_image16_rgb24=$(tr '\n' ',' < .gitlab-ci/ignore-image16-rgb24.txt)
+export CAIRO_TEST_TARGET=image,image16
+
+meson setup --buildtype=debug _build .
+meson compile -C _build
+
+export srcdir=../../test
+cd _build/test
+xvfb-run ./cairo-test-suite

.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 }'