[bazel] Setup workflow to publish to BCR

.bcr/bazel/metadata.template.json

@@ -0,0 +1,16 @@
+{
+  "homepage": "https://emscripten.org",
+  "maintainers": [
+    {
+      "name": "Sam Clegg",
+      "email": "sbc@chromium.org",
+      "github": "sbc100",
+      "github_user_id": 515813
+    }
+  ],
+  "repository": [
+    "github:emscripten-core/emsdk"
+  ],
+  "versions": [],
+  "yanked_versions": {}
+}

.bcr/bazel/presubmit.yml

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+matrix:
+  platform:
+    - debian13
+    - ubuntu2204
+    - windows
+  bazel:
+    - 7.x
+    - 8.x
+    - 9.x
+tasks:
+  verify_targets:
+    name: Verify build targets
+    platform: ${{ platform }}
+    bazel: ${{ bazel }}
+    build_targets:
+      - '@emsdk//hello-world:hello-world-wasm'
+      - '@emsdk//hello-world:hello-world-wasm-simd'
+bcr_test_module:
+  module_path: test_external
+  matrix:
+    platform:
+    - debian13
+    - ubuntu2204
+    - windows
+    bazel:
+    - 7.x
+    - 8.x
+    - 9.x
+  tasks:
+    run_test_module:
+      name: Run test module
+      platform: ${{ platform }}
+      bazel: ${{ bazel }}
+      build_targets:
+      - //:hello-world-wasm
+      - //long_command_line:long_command_line_wasm

.bcr/bazel/source.template.json

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+{
+  "integrity": "",
+  "strip_prefix": "{REPO}-{TAG}/bazel",
+  "url": "https://github.com/{OWNER}/{REPO}/archive/refs/tags/{TAG}.tar.gz"
+}

.bcr/config.yml

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+# See https://github.com/bazel-contrib/publish-to-bcr#a-note-on-release-automation
+
+fixedReleaser:
+  login: sbc100
+  email: sbc@chromium.org
+
+moduleRoots:
+  - bazel

.github/workflows/publish-to-bcr.yml

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+name: Publish to BCR
+on:
+  push:
+    tags:
+      - '*'
+
+jobs:
+  publish:
+    uses: bazel-contrib/publish-to-bcr/.github/workflows/publish.yaml@v1.0.0
+    with:
+      tag_name: ${{ inputs.tag_name || github.ref_name }}
+      registry_fork: emscripten-core/bazel-central-registry
+      # see note on Attestation Support
+      attest: true
+    permissions:
+      contents: write
+      # Necessary if attest:true
+      id-token: write
+      # Necessary if attest:true
+      attestations: write
+    secrets:
+      # Necessary to push to the BCR fork, and to open a pull request against a registry
+      publish_token: ${{ secrets.BCR_PUBLISH_TOKEN }}