make: add docker-dev-* targets for building dev images

Adds three make targets that wrap dev.Dockerfile:

- docker-dev-build builds an lnd dev image, tagged $(DOCKER_DEV_IMAGE)
(default lnd-dev:<short-hash>).
- docker-dev-lndinit-build layers an lndinit image on top, tagged
$(LNDINIT_REPO):lnd-dev-<short-hash> (default lndinit:...).
- docker-dev-lndinit-build-push builds and pushes the lndinit image.

All three targets go through `docker buildx build` so the BuildKit
cache mounts added in 20e6518 are used.

Author: ZZiigguurraatt

Makefile

@@ -213,6 +213,58 @@ docker-tools:
 	@$(call print, "Building tools docker image.")
 	docker build -q -t lnd-tools $(TOOLS_DIR)
 
+# Short commit hash of the working tree, with a `-dirty` suffix if there are
+# uncommitted changes. Unlike $(COMMIT), this never picks up submodule tags
+# like `kvdb/v1.5.1` — `/` is not a valid character in a docker image tag.
+# `--match='__no_such_tag__'` forces `git describe` to ignore all tags so
+# `--always` falls back to the short hash.
+DOCKER_DEV_COMMIT := $(shell git describe --always --dirty --match='__no_such_tag__')
+
+# Image (name:tag) produced by `docker-dev-build`. Also consumed by
+# `docker-dev-lndinit-build` so the lndinit image is always layered on
+# whatever `docker-dev-build` just built. Defaults to `lnd-dev:<short-hash>`
+# (e.g. `lnd-dev:f5a093c1f` on commit f5a093c1f).
+DOCKER_DEV_IMAGE ?= lnd-dev:$(DOCKER_DEV_COMMIT)
+
+# Repository name for the lndinit dev image; the tag is always
+# `lnd-dev-$(DOCKER_DEV_COMMIT)` so it's obvious which docker-dev-build image
+# the lndinit image was layered on.
+LNDINIT_REPO ?= lndinit
+
+# Build context (path or git URL with optional #ref) for lndinit's dev.Dockerfile.
+# NOTE: `#` is escaped as `\#` so make doesn't treat the ref as a comment.
+LNDINIT_CONTEXT ?= https://github.com/lightninglabs/lndinit.git\#main
+
+# Full lndinit image name:tag, derived from LNDINIT_REPO and DOCKER_DEV_COMMIT.
+LNDINIT_IMAGE := $(LNDINIT_REPO):lnd-dev-$(DOCKER_DEV_COMMIT)
+
+# dev.Dockerfile uses BuildKit cache mounts unconditionally, so these targets
+# always go through `docker buildx build`.
+#? docker-dev-build: Build a development docker image from dev.Dockerfile (override DOCKER_DEV_IMAGE=<name:tag>)
+docker-dev-build:
+	@$(call print, "Building dev docker image $(DOCKER_DEV_IMAGE).")
+	docker buildx build -t $(DOCKER_DEV_IMAGE) -f dev.Dockerfile .
+
+#? docker-dev-lndinit-build: Build an lndinit dev image layered on the docker-dev-build image (override LNDINIT_REPO=<name>, LNDINIT_CONTEXT=<git ref or path>)
+docker-dev-lndinit-build: docker-dev-build
+	@$(call print, "Building lndinit docker image $(LNDINIT_IMAGE) on top of $(DOCKER_DEV_IMAGE).")
+	IMG='$(DOCKER_DEV_IMAGE)'; \
+	CTX='$(LNDINIT_CONTEXT)'; \
+	if [ -d "$$CTX" ]; then \
+	    DOCKERFILE="$$CTX/dev.Dockerfile"; \
+	else \
+	    DOCKERFILE=dev.Dockerfile; \
+	fi; \
+	docker buildx build \
+	    --build-arg BASE_IMAGE="$${IMG%:*}" \
+	    --build-arg BASE_IMAGE_VERSION="$${IMG##*:}" \
+	    -t $(LNDINIT_IMAGE) -f "$$DOCKERFILE" "$$CTX"
+
+#? docker-dev-lndinit-build-push: Build the lndinit dev image (via docker-dev-lndinit-build) and push $(LNDINIT_IMAGE). `docker login` to that registry must already be done.
+docker-dev-lndinit-build-push: docker-dev-lndinit-build
+	@$(call print, "Pushing lndinit docker image $(LNDINIT_IMAGE).")
+	docker push $(LNDINIT_IMAGE)
+
 scratch: build
 
 
@@ -551,4 +603,7 @@ clean-docker-volumes:
 	android \
 	mobile \
 	clean \
-	clean-docker-volumes
+	clean-docker-volumes \
+	docker-dev-build \
+	docker-dev-lndinit-build \
+	docker-dev-lndinit-build-push

docs/DOCKER.md

@@ -10,11 +10,45 @@ There are two flavors of Dockerfiles available:
 
 ## Development/testing
 
-To build a standalone development image from the local source directory, use the
-following command:
+To build a standalone development image from the local source directory:
 
 ```shell
-$  docker build --tag=myrepository/lnd-dev -f dev.Dockerfile .
+$  make docker-dev-build
+```
+
+The image is tagged `lnd-dev:<short-hash>` by default (with a `-dirty`
+suffix if the working tree has uncommitted changes); override with
+`make docker-dev-build DOCKER_DEV_IMAGE=myrepository/lnd-dev:mytag`.
+
+To additionally build an `lndinit` image layered on top of the dev image
+(pulling `lndinit`'s `dev.Dockerfile` from upstream main):
+
+```shell
+$  make docker-dev-lndinit-build
+```
+
+The image is tagged `<LNDINIT_REPO>:lnd-dev-<short-hash>` (e.g.
+`lndinit:lnd-dev-f5a093c1f`) so the tag makes it obvious which
+`docker-dev-build` image it was layered on. `LNDINIT_REPO` defaults to
+`lndinit`; override to push to a registry, e.g. `myrepository/lndinit`.
+`LNDINIT_CONTEXT` is the build context that `docker buildx` pulls
+`lndinit`'s `dev.Dockerfile` from — defaults to
+`https://github.com/lightninglabs/lndinit.git#main`, but can be a local path
+(e.g. `../lndinit`) or any other git URL with an optional `#<ref>` suffix
+(branch, tag, or commit SHA). For example, to build lndinit from a local
+checkout under the `myrepository/lndinit` repo name:
+
+```shell
+$  make docker-dev-lndinit-build \
+     LNDINIT_REPO=myrepository/lndinit \
+     LNDINIT_CONTEXT=../lndinit
+```
+
+To build the `lndinit` image and push it to a registry you're already logged
+into in one step:
+
+```shell
+$  make docker-dev-lndinit-build-push
 ```
 
 There is also a `docker-compose` setup available for development or testing that

docs/release-notes/release-notes-0.22.0.md

@@ -111,6 +111,19 @@
   the build context is a remote git repository because COPY layers are more
   smartly compared to cache.
 
+* [New `make` targets for `dev.Dockerfile`](https://github.com/lightningnetwork/lnd/pull/TBD):
+  `docker-dev-build` builds a development image from `dev.Dockerfile`
+  (tagged `lnd-dev:<short-hash>` by default; override with
+  `DOCKER_DEV_IMAGE=`). `docker-dev-lndinit-build` layers an
+  [`lndinit`](https://github.com/lightninglabs/lndinit) image on top of it
+  (using `lndinit`'s upstream `dev.Dockerfile`; tagged
+  `<LNDINIT_REPO>:lnd-dev-<short-hash>` so the tag reflects the underlying
+  dev image — override the repo name with `LNDINIT_REPO=` and the build
+  context with `LNDINIT_CONTEXT=`). `docker-dev-lndinit-build-push` builds
+  and then pushes the lndinit image. All three go through
+  `docker buildx build` so BuildKit cache mounts are used. See
+  [`docs/DOCKER.md`](../DOCKER.md) for examples.
+
 # Contributors (Alphabetical Order)
 
 * bitromortac