bake: pass variables explicitly to buildx

.github/workflows/.test-bake.yml

@@ -599,13 +599,20 @@ jobs:
       contents: read
       id-token: write
     with:
-      setup-qemu: true
-      artifact-upload: false
       context: test
-      output: local
-      target: go
+      output: image
+      push: false
+      target: vars
       vars: |
         XX_VERSION=1.9.0
+        DOCKER_METADATA_OUTPUT_VERSION=caller-version
+      meta-images: example/app
+      meta-tags: |
+        type=raw,value=vars-one
+        type=raw,value=vars-two
+      meta-labels: |
+        org.example.vars.one=one
+        org.example.vars.two=two
 
   bake-auth-scope:
     uses: ./.github/workflows/bake.yml

.github/workflows/bake.yml

@@ -347,6 +347,7 @@ jobs:
             const { GitHub } = require('@docker/github-builder-runtime/lib/github/github');
             const { RunnerMapping } = require('@docker/github-builder-runtime/lib/github-builder/runner-mapping');
             const { BakeTargets } = require('@docker/github-builder-runtime/lib/github-builder/bake-targets');
+            const { BakeVars } = require('@docker/github-builder-runtime/lib/github-builder/bake-vars');
             const { Util } = require('@docker/github-builder-runtime/lib/util');
 
             const inpSbomImage = core.getInput('sbom-image');
@@ -359,7 +360,7 @@ jobs:
             const inpArtifactUpload = core.getBooleanInput('artifact-upload');
             const inpJobNamePrefix = core.getInput('job-name-prefix');
             const inpContext = core.getInput('context');
-            const inpVars = Util.getInputList('vars');
+            const inpVars = Util.getInputList('vars', {ignoreComma: true, quote: false});
             const inpFiles = Util.getInputList('files');
             const inpOutput = core.getInput('output');
             const inpPush = core.getBooleanInput('push');
@@ -409,21 +410,12 @@ jobs:
             }
             const registryLogin = inpRegistryLogin === 'auto' ? inpOutput === 'image' && inpPush : inpRegistryLogin === 'true';
 
-            const envs = Object.assign({},
-              inpVars ? inpVars.reduce((acc, curr) => {
-                const idx = curr.indexOf('=');
-                if (idx !== -1) {
-                  acc[curr.substring(0, idx)] = curr.substring(idx + 1);
-                }
-                return acc;
-              }, {}) : {},
-              {
-                BUILDKIT_MULTI_PLATFORM: '1',
-                BUILDX_BAKE_GIT_AUTH_TOKEN: inpGitHubToken
-              }
-            );
-            await core.group(`Set envs`, async () => {
-              core.info(JSON.stringify(Object.keys(envs).sort(), null, 2));
+            const bakeVars = BakeVars.resolve(inpVars);
+            await core.group(`Set bake vars`, async () => {
+              core.info(JSON.stringify(bakeVars.map(value => {
+                const idx = value.indexOf('=');
+                return idx === -1 ? '<invalid>' : value.substring(0, idx);
+              }).sort(), null, 2));
             });
 
             const metaImages = inpMetaImages.map(image => image.toLowerCase());
@@ -448,9 +440,14 @@ jobs:
                   overrides: [...validationOverrides, '*.secrets='],
                   sbom: inpSbom ? `generator=${inpSbomImage}` : 'false',
                   source: bakeSource,
-                  targets: [inpTarget]
+                  targets: [inpTarget],
+                  vars: bakeVars,
+                  githubToken: inpGitHubToken
                 }, {
-                  env: Object.keys(envs).length > 0 ? envs : undefined
+                  env: {
+                    BUILDKIT_MULTI_PLATFORM: '1',
+                    BUILDX_BAKE_DISABLE_VARS_ENV_LOOKUP: '1'
+                  }
                 });
                 if (!def) {
                   throw new Error('Bake definition not set');
@@ -857,6 +854,7 @@ jobs:
             const os = require('os');
             const { Build } = require('@docker/github-builder-runtime/lib/buildx/build');
             const { BuildSecrets } = require('@docker/github-builder-runtime/lib/github-builder/build-secrets');
+            const { BakeVars } = require('@docker/github-builder-runtime/lib/github-builder/bake-vars');
             const { GitHub } = require('@docker/github-builder-runtime/lib/github/github');
             const { Util } = require('@docker/github-builder-runtime/lib/util');
 
@@ -879,7 +877,7 @@ jobs:
             const inpSbom = core.getBooleanInput('sbom');
             const inpSet = Util.getInputList('set', {ignoreComma: true, quote: false});
             const inpTarget = core.getInput('target');
-            const inpVars = Util.getInputList('vars');
+            const inpVars = Util.getInputList('vars', {ignoreComma: true, quote: false});
             const inpBuildkitProxyNetwork = core.getBooleanInput('buildkit-proxy-network');
 
             const inpMetaImages = core.getMultilineInput('meta-images');
@@ -924,27 +922,15 @@ jobs:
             }
             core.setOutput('secret-dir', buildSecrets.directory);
 
-            const envs = Object.assign({},
-              inpVars ? inpVars.reduce((acc, curr) => {
-                const idx = curr.indexOf('=');
-                if (idx !== -1) {
-                  acc[curr.substring(0, idx)] = curr.substring(idx + 1);
-                }
-                return acc;
-              }, {}) : {},
-              {
-                BUILDKIT_MULTI_PLATFORM: '1'
-              }
-            );
-
-            // Git authentication is supplied directly to the Bake action.
-            delete envs.BUILDX_BAKE_GIT_AUTH_TOKEN;
-
-            await core.group(`Set envs`, async () => {
-              core.info(JSON.stringify(Object.keys(envs).sort(), null, 2));
-              core.setOutput('envs', JSON.stringify(envs));
+            const bakeVars = BakeVars.resolve(inpVars);
+            await core.group(`Set bake vars`, async () => {
+              core.info(JSON.stringify(bakeVars.map(value => {
+                const idx = value.indexOf('=');
+                return idx === -1 ? '<invalid>' : value.substring(0, idx);
+              }).sort(), null, 2));
+              core.setOutput('vars', JSON.stringify(bakeVars));
             });
-            
+
             let bakeFiles = inpFiles;
             await core.group(`Set bake files`, async () => {
               if (bakeFiles.length === 0) {
@@ -1019,8 +1005,11 @@ jobs:
           targets: ${{ steps.prepare.outputs.target }}
           sbom: ${{ steps.prepare.outputs.sbom }}
           set: ${{ steps.prepare.outputs.overrides }}
+          vars: ${{ steps.prepare.outputs.vars }}
           github-token: ${{ secrets.github-token || github.token }}
-        env: ${{ fromJson(steps.prepare.outputs.envs || '{}') }}
+        env:
+          BUILDKIT_MULTI_PLATFORM: '1'
+          BUILDX_BAKE_DISABLE_VARS_ENV_LOOKUP: '1'
       -
         name: Remove build secrets
         if: ${{ always() && steps.prepare.outputs.secret-dir != '' }}

README.md

@@ -377,6 +377,14 @@ jobs:
 | `meta-flavor`             | List   |                                       | [Flavor](https://github.com/docker/metadata-action?tab=readme-ov-file#flavor-input) defines a global behavior for `meta-tags`                                                                                                                                                                        |
 | `buildkit-proxy-network`  | Bool   | `false`                               | Enable BuildKit proxy network mode for default Dockerfile `RUN` networking. See [BuildKit proxy network](#buildkit-proxy-network).                                                                                                                                                                   |
 
+> [!NOTE]
+> The `vars` input is passed to Buildx as explicit Bake variables. Ambient
+> environment lookup for Bake variables is disabled. The `CI` environment variable
+> and variables with `GITHUB_`, `RUNNER_`, or `DOCKER_METADATA_OUTPUT_` prefixes
+> are forwarded as explicit vars for workflows that declare them in their Bake
+> definition. Multiline metadata values are preserved. Caller-provided vars take
+> precedence over these forwarded values.
+
 ### Secrets
 
 | Name             | Default               | Description                                                                             |

test/docker-bake.hcl

@@ -15,6 +15,34 @@ variable "XX_VERSION" {
   default = null
 }
 
+variable "BUILDX_VERSION" {
+  default = "not-leaked"
+}
+
+variable "CI" {
+  default = ""
+}
+
+variable "GITHUB_SHA" {
+  default = ""
+}
+
+variable "RUNNER_OS" {
+  default = ""
+}
+
+variable "DOCKER_METADATA_OUTPUT_VERSION" {
+  default = ""
+}
+
+variable "DOCKER_METADATA_OUTPUT_TAGS" {
+  default = ""
+}
+
+variable "DOCKER_METADATA_OUTPUT_LABELS" {
+  default = ""
+}
+
 target "go" {
   inherits = ["docker-metadata-action"]
   args = {
@@ -23,6 +51,20 @@ target "go" {
   dockerfile = "go.Dockerfile"
 }
 
+target "vars" {
+  args = {
+    BUILDX_VERSION                 = BUILDX_VERSION
+    CI                             = CI
+    GITHUB_SHA                     = GITHUB_SHA
+    RUNNER_OS                      = RUNNER_OS
+    XX_VERSION                     = XX_VERSION
+    DOCKER_METADATA_OUTPUT_VERSION = DOCKER_METADATA_OUTPUT_VERSION
+    DOCKER_METADATA_OUTPUT_TAGS    = DOCKER_METADATA_OUTPUT_TAGS
+    DOCKER_METADATA_OUTPUT_LABELS  = DOCKER_METADATA_OUTPUT_LABELS
+  }
+  dockerfile = "vars.Dockerfile"
+}
+
 target "go-cross" {
   inherits = ["go"]
   platforms = ["linux/amd64", "linux/arm64"]

test/vars.Dockerfile

@@ -0,0 +1,25 @@
+# syntax=docker/dockerfile:1
+
+FROM alpine
+ARG BUILDX_VERSION
+ARG CI
+ARG GITHUB_SHA
+ARG RUNNER_OS
+ARG XX_VERSION
+ARG DOCKER_METADATA_OUTPUT_VERSION
+ARG DOCKER_METADATA_OUTPUT_TAGS
+ARG DOCKER_METADATA_OUTPUT_LABELS
+RUN test "$BUILDX_VERSION" = "not-leaked"
+RUN test "$CI" = "true"
+RUN test -n "$GITHUB_SHA"
+RUN test -n "$RUNNER_OS"
+RUN test "$XX_VERSION" = "1.9.0"
+RUN test "$DOCKER_METADATA_OUTPUT_VERSION" = "caller-version"
+RUN printf '%s\n' "$DOCKER_METADATA_OUTPUT_TAGS" | grep -Fx 'example/app:vars-one' \
+    && printf '%s\n' "$DOCKER_METADATA_OUTPUT_TAGS" | grep -Fx 'example/app:vars-two'
+RUN printf '%s\n' "$DOCKER_METADATA_OUTPUT_LABELS" | grep -Fx 'org.example.vars.one=one' \
+    && printf '%s\n' "$DOCKER_METADATA_OUTPUT_LABELS" | grep -Fx 'org.example.vars.two=two'
+RUN mkdir -p /out && printf 'ok\n' > /out/vars.txt
+
+FROM scratch
+COPY --from=0 /out /