bake: shared session for local context

With the latest Buildx, BuildKit, and Dockerfile, bake can detect when
multiple targets use the same local context, and deduplicate context
transfer.

Signed-off-by: David Karlsson <35727626+dvdksn@users.noreply.github.com>

Dockerfile

@@ -1,4 +1,4 @@
-# syntax=docker/dockerfile:1
+# syntax=docker/dockerfile-upstream:master
 
 # ALPINE_VERSION sets the Alpine Linux version for all Alpine stages
 ARG ALPINE_VERSION=3.20
@@ -26,14 +26,11 @@ WORKDIR /tmp/hugo
 RUN wget -O "hugo.tar.gz" "https://github.com/gohugoio/hugo/releases/download/v${HUGO_VERSION}/hugo_extended_${HUGO_VERSION}_linux-${TARGETARCH}.tar.gz"
 RUN tar -xf "hugo.tar.gz" hugo
 
-FROM scratch AS ctx
-COPY --link . .
-
 # build-base is the base stage for building the site
 FROM base AS build-base
 COPY --from=hugo /tmp/hugo/hugo /bin/hugo
 COPY --from=node /src/node_modules /src/node_modules
-COPY --from=ctx . .
+COPY . .
 
 # dev is for local development with Docker Compose
 FROM build-base AS dev
@@ -49,7 +46,7 @@ RUN hugo --gc --minify -d /out -e $HUGO_ENV -b $DOCS_URL
 # lint lints markdown files
 FROM davidanson/markdownlint-cli2:v0.12.1 AS lint
 USER root
-RUN --mount=type=bind,from=ctx,target=. \
+RUN --mount=type=bind,target=. \
     /usr/local/bin/markdownlint-cli2 \
     "content/**/*.md" \
     "#content/engine/release-notes/*.md" \
@@ -106,7 +103,7 @@ RUN htmltest
 FROM alpine:${ALPINE_VERSION} AS unused-media
 RUN apk add --no-cache fd ripgrep
 WORKDIR /test
-RUN --mount=type=bind,from=ctx,target=. <<"EOT"
+RUN --mount=type=bind,target=. <<"EOT"
 set -ex
 ./scripts/test_unused_media.sh
 EOT
@@ -115,7 +112,7 @@ EOT
 FROM base AS pagefind
 ARG PAGEFIND_VERSION=1.1.0
 COPY --from=build /out ./public
-RUN --mount=type=bind,from=ctx,src=pagefind.yml,target=pagefind.yml \
+RUN --mount=type=bind,src=pagefind.yml,target=pagefind.yml \
     npx pagefind@v${PAGEFIND_VERSION} --output-path "/pagefind"
 
 # index generates a Pagefind index
@@ -127,7 +124,7 @@ FROM alpine:${ALPINE_VERSION} AS test-go-redirects
 WORKDIR /work
 RUN apk add yq
 COPY --from=build /out ./public
-RUN --mount=type=bind,from=ctx,target=. <<"EOT"
+RUN --mount=type=bind,target=. <<"EOT"
 set -ex
 ./scripts/test_go_redirects.sh
 EOT

docker-bake.hcl

@@ -14,21 +14,7 @@ group "default" {
   targets = ["release"]
 }
 
-target "ctx" {
-  target = "ctx"
-  context = "."
-  output = ["type=cacheonly"]
-  provenance = false
-}
-
-target "_common" {
-  contexts = {
-    ctx = "target:ctx"
-  }
-}
-
 target "index" {
-  inherits = ["_common"]
   # generate a new local search index
   target = "index"
   output = ["type=local,dest=static/pagefind"]
@@ -36,7 +22,6 @@ target "index" {
 }
 
 target "release" {
-  inherits = ["_common"]
   args = {
     HUGO_ENV = HUGO_ENV
     DOCS_URL = DOCS_URL
@@ -52,28 +37,24 @@ group "validate" {
 
 target "test" {
   target = "test"
-  inherits = ["_common"]
   output = ["type=cacheonly"]
   provenance = false
 }
 
 target "lint" {
   target = "lint"
-  inherits = ["_common"]
   output = ["type=cacheonly"]
   provenance = false
 }
 
 target "unused-media" {
   target = "unused-media"
-  inherits = ["_common"]
   output = ["type=cacheonly"]
   provenance = false
 }
 
 target "test-go-redirects" {
   target = "test-go-redirects"
-  inherits = ["_common"]
   output = ["type=cacheonly"]
   provenance = false
 }