ci: add macOS jobs to GitLab CI

Add a job to GitLab CI which runs tests on macOS, which matches the
equivalent "osx-clang" job that we have for GitHub Workflows. One
significant difference though is that this new job runs on Apple M1
machines and thus uses the "arm64" architecture. As GCC does not yet
support this comparatively new architecture we cannot easily include an
equivalent for the "osx-gcc" job that exists in GitHub Workflows.

Note that one test marked as `test_must_fail` is surprisingly passing:

  t7815-grep-binary.sh                             (Wstat: 0 Tests: 22 Failed: 0)
    TODO passed:   12

This seems to boil down to an unexpected difference in how regcomp(3P)
works when matching NUL bytes. Cross-checking with the respective GitHub
job shows that this is not an issue unique to the GitLab CI job as it
passes in the same way there.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

.gitlab-ci.yml

@@ -7,7 +7,7 @@ workflow:
     - if: $CI_COMMIT_TAG
     - if: $CI_COMMIT_REF_PROTECTED == "true"
 
-test:
+test:linux:
   image: $image
   before_script:
     - ./ci/install-docker-dependencies.sh
@@ -52,6 +52,38 @@ test:
       - t/failed-test-artifacts
     when: on_failure
 
+test:osx:
+  image: $image
+  tags:
+    - saas-macos-medium-m1
+  variables:
+    TEST_OUTPUT_DIRECTORY: "/Volumes/RAMDisk"
+  before_script:
+    # Create a 4GB RAM disk that we use to store test output on. This small hack
+    # significantly speeds up tests by more than a factor of 2 because the
+    # macOS runners use network-attached storage as disks, which is _really_
+    # slow with the many small writes that our tests do.
+    - sudo diskutil apfs create $(hdiutil attach -nomount ram://8192000) RAMDisk
+    - ./ci/install-dependencies.sh
+  script:
+    - ./ci/run-build-and-tests.sh
+  after_script:
+    - |
+      if test "$CI_JOB_STATUS" != 'success'
+      then
+        ./ci/print-test-failures.sh
+        mv "$TEST_OUTPUT_DIRECTORY"/failed-test-artifacts t/
+      fi
+  parallel:
+    matrix:
+      - jobname: osx-clang
+        image: macos-13-xcode-14
+        CC: clang
+  artifacts:
+    paths:
+      - t/failed-test-artifacts
+    when: on_failure
+
 static-analysis:
   image: ubuntu:22.04
   variables:

ci/lib.sh

@@ -252,7 +252,14 @@ then
 	CI_COMMIT="$CI_COMMIT_SHA"
 	case "$CI_JOB_IMAGE" in
 	macos-*)
-		CI_OS_NAME=osx;;
+		# GitLab CI has Python installed via multiple package managers,
+		# most notably via asdf and Homebrew. Ensure that our builds
+		# pick up the Homebrew one by prepending it to our PATH as the
+		# asdf one breaks tests.
+		export PATH="$(brew --prefix)/bin:$PATH"
+
+		CI_OS_NAME=osx
+		;;
 	alpine:*|fedora:*|ubuntu:*)
 		CI_OS_NAME=linux;;
 	*)