fix: stamp a real version into the docker latest image (#930)

The push_to_docker_latest job had no checkout step, so
docker/build-push-action built from the remote Git context, which
BuildKit materializes without a .git directory. Inside the image
`git describe --tags` then failed with "fatal: not a git repository" and
main.airVersion was stamped empty, and hack/check.sh's `git diff --cached`
failed the same way.

Check out the repo with full history and build from the local context so
git works, and fall back to "dev" in the Makefile so any other
git-less build still produces a usable version string.

Co-authored-by: Claude Opus 5 <noreply@anthropic.com>

Author: xiantang

.github/workflows/build.yml

@@ -73,6 +73,13 @@ jobs:
     if: github.event_name == 'push' && github.ref == 'refs/heads/master'
     runs-on: ubuntu-latest
     steps:
+      # Without a checkout, build-push-action builds from the remote Git
+      # context, which has no .git directory, so `git describe --tags` inside
+      # the image cannot stamp a version. Fetch tags for the same reason.
+      - name: Check out code
+        uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
       - name: Set up QEMU
         uses: docker/setup-qemu-action@v3
       - name: Set up Docker Buildx
@@ -92,6 +99,7 @@ jobs:
         id: docker_build
         uses: docker/build-push-action@v5
         with:
+          context: .
           push: true
           platforms: linux/amd64,linux/arm64
           tags: |

Makefile

@@ -1,4 +1,6 @@
-AIRVER := $(shell git describe --tags)
+# Builds outside a git checkout (e.g. a Docker build context without .git) have
+# no tags to describe, so fall back instead of stamping an empty version.
+AIRVER ?= $(shell git describe --tags 2>/dev/null || echo dev)
 LDFLAGS += -X "main.BuildTimestamp=$(shell date -u "+%Y-%m-%d %H:%M:%S")"
 LDFLAGS += -X "main.airVersion=$(AIRVER)"
 LDFLAGS += -X "main.goVersion=$(shell go version | sed -r 's/go version go(.*)\ .*/\1/')"