structuredmerge · pboling · Sep 14, 2026 · Sep 14, 2026 · Sep 14, 2026
diff --git a/.github/workflows/current.yml b/.github/workflows/current.yml
@@ -149,6 +149,9 @@ jobs:
         env:
           K_JEM_TEMPLATING: true
           STRUCTUREDMERGE_DEV: ${{ github.workspace }}/gems
+          # Current represents what is available today: require the published
+          # Rust host gem, which fails until structuredmerge_host_prototype is released.
+          STRUCTUREDMERGE_RUST_HOST_PUBLISHED: true
         run: |
           bundle config set frozen false
           for attempt in 1 2 3; do
@@ -168,8 +171,261 @@ jobs:
           K_JEM_TEMPLATING: true
           K_SOUP_COV_DO: false
           STRUCTUREDMERGE_DEV: ${{ github.workspace }}/gems
+          STRUCTUREDMERGE_RUST_HOST_PUBLISHED: true
         run: timeout 12m bundle exec kettle-test
 
+  rust-host:
+    name: Rust host @ HEAD
+    needs: detect
+    if: ${{ needs.detect.outputs.count != '0' && needs.detect.outputs.release_mode == '' }}
+    runs-on: ubuntu-latest
+    steps:
+      - name: Clone structuredmerge-rust HEAD
+        shell: bash
+        run: |
+          set -euo pipefail
+          git clone --depth 1 https://github.com/structuredmerge/structuredmerge-rust.git "${RUNNER_TEMP}/structuredmerge-rust"
+          echo "structuredmerge-rust HEAD: $(git -C "${RUNNER_TEMP}/structuredmerge-rust" rev-parse HEAD)"
+      - name: Setup Rust
+        uses: dtolnay/rust-toolchain@6c977a6ca4077a0ceb28ffbe03f59d46e9ac8772
+        with:
+          toolchain: stable
+      # Build exactly as structuredmerge-rust's release-ruby-host.yml does (including
+      # CARGO_FEATURE_LINK_RUBY), so Deps @ HEAD tests the gem end users will install.
+      - name: Setup Ruby
+        uses: ruby/setup-ruby@9eb537ca036ebaed86729dcb9309076e4c5c3b74 # v1.314.0
+        with:
+          ruby-version: "4.0"
+          bundler-cache: false
+      - name: Install Rust host package dependencies
+        shell: bash
+        working-directory: ${{ runner.temp }}/structuredmerge-rust/packages/ruby
+        run: bundle install --jobs 4 --retry 8
+      - name: Install Alef
+        shell: bash
+        working-directory: ${{ runner.temp }}/structuredmerge-rust
+        run: |
+          cargo install --git https://github.com/structuredmerge/alef.git \
+            --rev "$(cat workspace-scripts/alef-source-revision)" --locked
+      - name: Build platform gem
+        shell: bash
+        working-directory: ${{ runner.temp }}/structuredmerge-rust
+        env:
+          CARGO_BUILD_TARGET: x86_64-unknown-linux-gnu
+          CARGO_FEATURE_LINK_RUBY: "1"
+          PLATFORM: x86_64-linux
+          RUST_TARGET: x86_64-unknown-linux-gnu
+          TARGET: x86_64-unknown-linux-gnu
+        run: |
+          set -euo pipefail
+          mkdir -p dist
+          alef publish build --lang ruby
+          alef publish package --lang ruby --target "${TARGET}" --output dist
+          test "$(find dist -maxdepth 1 -name "*-${PLATFORM}.gem" -print | wc -l)" -eq 1
+      - name: Upload Rust host gem
+        uses: actions/upload-artifact@043fb46d1a93c77aae656e7c1c64a875d1fc6a0a # v7.0.1
+        with:
+          name: structuredmerge-host-prototype-head
+          path: ${{ runner.temp }}/structuredmerge-rust/dist/*-x86_64-linux.gem
+          if-no-files-found: error
+          retention-days: 7
+
+  dep-heads:
+    name: Deps @ HEAD (${{ matrix.gem }})
+    needs:
+      - detect
+      - rust-host
+    if: ${{ needs.detect.outputs.count != '0' && needs.detect.outputs.release_mode == '' }}
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix: ${{ fromJson(needs.detect.outputs.matrix) }}
+    steps:
+      - name: Checkout
+        uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
+      - name: Clone sibling fixtures repo
+        shell: bash
+        run: |
+          set -euo pipefail
+          fixtures_repository="$(ruby -ryaml -e 'puts YAML.load_file(".structuredmerge/fixtures.lock").fetch("repository")')"
+          fixtures_tag="$(ruby -ryaml -e 'puts YAML.load_file(".structuredmerge/fixtures.lock").fetch("tag")')"
+          fixtures_revision="$(ruby -ryaml -e 'puts YAML.load_file(".structuredmerge/fixtures.lock").fetch("revision")')"
+          git clone --filter=blob:none --no-checkout "${fixtures_repository}" ../fixtures
+          git -C ../fixtures fetch --depth 1 origin "refs/tags/${fixtures_tag}:refs/tags/${fixtures_tag}"
+          git -C ../fixtures checkout --detach "${fixtures_revision}"
+          test "$(git -C ../fixtures rev-parse HEAD)" = "${fixtures_revision}"
+          test "$(git -C ../fixtures rev-parse "refs/tags/${fixtures_tag}^{commit}")" = "${fixtures_revision}"
+      - name: Download Rust host gem
+        uses: actions/download-artifact@3e5f45b2cfb9172054b4087a40e8e0b5a5461e7c # v8.0.1
+        with:
+          name: structuredmerge-host-prototype-head
+          path: ${{ runner.temp }}/structuredmerge-host
+      - name: Setup Ruby
+        uses: appraisal-rb/setup-ruby-flash@925395edf973d2dc0a629919f407f3547a03d4b5 # v2.1
+        with:
+          ruby-version: ruby
+          bundler-cache: false
+          working-directory: ${{ matrix.gem }}
+          pre-bundle-gems: |
+            nomono --source https://gem.coop --source https://rubygems.org
+      - name: Unpack Rust host gem
+        shell: bash
+        run: |
+          set -euo pipefail
+          host_root="${RUNNER_TEMP}/structuredmerge-host"
+          gem_file="$(find "${host_root}" -maxdepth 1 -name '*-x86_64-linux.gem' -print -quit)"
+          test -n "${gem_file}"
+          gem unpack "${gem_file}" --target "${host_root}/unpacked"
+          host_dir="$(find "${host_root}/unpacked" -mindepth 1 -maxdepth 1 -type d -print -quit)"
+          gem specification "${gem_file}" --ruby > "${host_dir}/structuredmerge_host_prototype.gemspec"
+          echo "STRUCTUREDMERGE_RUST_HOST_DIR=${host_dir}" >> "${GITHUB_ENV}"
+      - name: Compose dep-heads bundle
+        shell: bash
+        working-directory: ${{ matrix.gem }}
+        run: |
+          set -euo pipefail
+          cat > dep_heads.gemfile <<'RUBY'
+          # frozen_string_literal: true
+
+          # CI-only dep-heads bundle: the Rust host built from structuredmerge-rust HEAD,
+          # this gem's Gemfile, and the HEAD versions of its runtime dependencies.
+          # Like the dep-heads appraisal, HEAD declarations replace the Gemfile's
+          # released declarations of the same gems instead of conflicting with them.
+          runtime_heads = File.expand_path('gemfiles/modular/runtime_heads.gemfile', __dir__)
+          head_gem_names = Bundler::Dsl.new.tap { |dsl| dsl.eval_gemfile(runtime_heads) }.dependencies.map(&:name)
+
+          gem 'structuredmerge_host_prototype', path: ENV.fetch('STRUCTUREDMERGE_RUST_HOST_DIR')
+          eval_gemfile File.expand_path('Gemfile', __dir__)
+          instance_variable_get(:@dependencies).reject! { |dependency| head_gem_names.include?(dependency.name) }
+          eval_gemfile runtime_heads
+          RUBY
+      - name: Install dependencies
+        working-directory: ${{ matrix.gem }}
+        env:
+          BUNDLE_GEMFILE: ${{ github.workspace }}/${{ matrix.gem }}/dep_heads.gemfile
+          K_JEM_TEMPLATING: true
+          # Bundle for spec subprocesses (e.g. ast-merge-git Git drivers) that reset BUNDLE_GEMFILE.
+          KETTLE_FAMILY_BUNDLE_GEMFILE: ${{ github.workspace }}/${{ matrix.gem }}/dep_heads.gemfile
+          STRUCTUREDMERGE_DEV: ${{ github.workspace }}/gems
+        run: |
+          bundle config set frozen false
+          for attempt in 1 2 3; do
+            if bundle install --jobs 4 --retry 8; then
+              exit 0
+            fi
+
+            if [[ "${attempt}" -lt 3 ]]; then
+              sleep "$((attempt * 5))"
+            fi
+          done
+
+          exit 1
+      - name: Verify Rust host loads
+        working-directory: ${{ matrix.gem }}
+        env:
+          BUNDLE_GEMFILE: ${{ github.workspace }}/${{ matrix.gem }}/dep_heads.gemfile
+          K_JEM_TEMPLATING: true
+          STRUCTUREDMERGE_DEV: ${{ github.workspace }}/gems
+        shell: bash
+        run: |
+          set -euo pipefail
+          # Gems that declare the host must be able to load the release-built host on this
+          # standard rv Ruby; failing here keeps host specs from silently skipping.
+          if ! grep -q 'structuredmerge_host_prototype' Gemfile; then
+            echo "This gem does not declare structuredmerge_host_prototype; nothing to verify."
+            exit 0
+          fi
+          bundle exec ruby -e 'require "structuredmerge_host_prototype"; puts "structuredmerge_host_prototype #{StructuredmergeHostPrototype::VERSION} loaded"'
+      - name: Run checks
+        working-directory: ${{ matrix.gem }}
+        env:
+          BUNDLE_GEMFILE: ${{ github.workspace }}/${{ matrix.gem }}/dep_heads.gemfile
+          K_JEM_TEMPLATING: true
+          K_SOUP_COV_DO: false
+          KETTLE_FAMILY_BUNDLE_GEMFILE: ${{ github.workspace }}/${{ matrix.gem }}/dep_heads.gemfile
+          STRUCTUREDMERGE_DEV: ${{ github.workspace }}/gems
+        run: timeout 12m bundle exec kettle-test
+
+  coverage:
+    name: Coverage (${{ matrix.gem }})
+    needs: detect
+    if: ${{ needs.detect.outputs.count != '0' && needs.detect.outputs.release_mode == '' }}
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix: ${{ fromJson(needs.detect.outputs.matrix) }}
+    steps:
+      - name: Checkout
+        uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
+      - name: Clone sibling fixtures repo
+        shell: bash
+        run: |
+          set -euo pipefail
+          fixtures_repository="$(ruby -ryaml -e 'puts YAML.load_file(".structuredmerge/fixtures.lock").fetch("repository")')"
+          fixtures_tag="$(ruby -ryaml -e 'puts YAML.load_file(".structuredmerge/fixtures.lock").fetch("tag")')"
+          fixtures_revision="$(ruby -ryaml -e 'puts YAML.load_file(".structuredmerge/fixtures.lock").fetch("revision")')"
+          git clone --filter=blob:none --no-checkout "${fixtures_repository}" ../fixtures
+          git -C ../fixtures fetch --depth 1 origin "refs/tags/${fixtures_tag}:refs/tags/${fixtures_tag}"
+          git -C ../fixtures checkout --detach "${fixtures_revision}"
+          test "$(git -C ../fixtures rev-parse HEAD)" = "${fixtures_revision}"
+          test "$(git -C ../fixtures rev-parse "refs/tags/${fixtures_tag}^{commit}")" = "${fixtures_revision}"
+      - name: Setup Ruby
+        uses: appraisal-rb/setup-ruby-flash@925395edf973d2dc0a629919f407f3547a03d4b5 # v2.1
+        with:
+          ruby-version: ruby
+          bundler-cache: false
+          working-directory: ${{ matrix.gem }}
+          pre-bundle-gems: |
+            nomono --source https://gem.coop --source https://rubygems.org
+      - name: Install dependencies
+        working-directory: ${{ matrix.gem }}
+        env:
+          K_JEM_TEMPLATING: true
+          STRUCTUREDMERGE_DEV: ${{ github.workspace }}/gems
+          # Coverage runs against the published Rust host gem, for maximum coverage once it
+          # is released; until then this fails like current.
+          STRUCTUREDMERGE_RUST_HOST_PUBLISHED: true
+        run: |
+          bundle config set frozen false
+          for attempt in 1 2 3; do
+            if bundle install --jobs 4 --retry 8; then
+              exit 0
+            fi
+
+            if [[ "${attempt}" -lt 3 ]]; then
+              sleep "$((attempt * 5))"
+            fi
+          done
+
+          exit 1
+      - name: Load coverage thresholds
+        shell: bash
+        working-directory: ${{ matrix.gem }}
+        run: |
+          set -euo pipefail
+          for key in K_SOUP_COV_MIN_BRANCH K_SOUP_COV_MIN_LINE K_SOUP_COV_MIN_HARD; do
+            value="$(sed -nE "s/^${key}[[:space:]]*=[[:space:]]*\"([^\"]*)\".*/\\1/p" mise.toml 2>/dev/null | head -1)"
+            if [[ -n "${value}" ]]; then
+              echo "${key}=${value}" >> "${GITHUB_ENV}"
+            fi
+          done
+      - name: Run checks with coverage
+        working-directory: ${{ matrix.gem }}
+        env:
+          K_JEM_TEMPLATING: true
+          K_SOUP_COV_COMMAND_NAME: Test Coverage
+          K_SOUP_COV_DO: true
+          K_SOUP_COV_FORMATTERS: xml,rcov,lcov,tty
+          K_SOUP_COV_MULTI_FORMATTERS: true
+          STRUCTUREDMERGE_DEV: ${{ github.workspace }}/gems
+          STRUCTUREDMERGE_RUST_HOST_PUBLISHED: true
+        run: timeout 20m bundle exec kettle-test
+      - name: Verify coverage reports
+        working-directory: ${{ matrix.gem }}
+        run: |
+          test -s coverage/lcov.info
+          test -s coverage/coverage.xml
+
   family-suite:
     name: StructuredMerge family suite
     needs: detect
@@ -424,6 +680,9 @@ jobs:
     needs:
       - detect
       - gem-suite
+      - rust-host
+      - dep-heads
+      - coverage
       - family-suite
       - benchmark-dev
       - rbs
@@ -438,6 +697,9 @@ jobs:
           RELEASE_MODE: ${{ needs.detect.outputs.release_mode }}
           DETECT_RESULT: ${{ needs.detect.result }}
           GEM_SUITE_RESULT: ${{ needs.gem-suite.result }}
+          RUST_HOST_RESULT: ${{ needs.rust-host.result }}
+          DEP_HEADS_RESULT: ${{ needs.dep-heads.result }}
+          COVERAGE_RESULT: ${{ needs.coverage.result }}
           FAMILY_SUITE_RESULT: ${{ needs.family-suite.result }}
           BENCHMARK_DEV_RESULT: ${{ needs.benchmark-dev.result }}
           RBS_RESULT: ${{ needs.rbs.result }}
@@ -447,6 +709,9 @@ jobs:
           echo "Selected gem suites: ${SELECTED_GEMS}"
           echo "Detect result: ${DETECT_RESULT}"
           echo "Gem suite result: ${GEM_SUITE_RESULT}"
+          echo "Rust host @ HEAD result: ${RUST_HOST_RESULT}"
+          echo "Deps @ HEAD result: ${DEP_HEADS_RESULT}"
+          echo "Coverage result: ${COVERAGE_RESULT}"
           echo "Family suite result: ${FAMILY_SUITE_RESULT}"
           echo "Dev benchmark result: ${BENCHMARK_DEV_RESULT}"
           echo "RBS result: ${RBS_RESULT}"
@@ -462,6 +727,9 @@ jobs:
 
           if [[ "${FAMILY_SUITE_RESULT}" == "success" ]]; then
             [[ "${GEM_SUITE_RESULT}" == "skipped" ]] || exit 1
+            [[ "${RUST_HOST_RESULT}" == "skipped" ]] || exit 1
+            [[ "${DEP_HEADS_RESULT}" == "skipped" ]] || exit 1
+            [[ "${COVERAGE_RESULT}" == "skipped" ]] || exit 1
             [[ "${RBS_RESULT}" == "skipped" ]] || exit 1
             [[ "${BENCHMARK_DEV_RESULT}" == "skipped" ]] || exit 1
             [[ "${TSLP_COLD_CACHE_RESULT}" == "skipped" ]] || exit 1
@@ -472,10 +740,12 @@ jobs:
             [[ "${result}" == "success" ]] || exit 1
           done
 
-          case "${GEM_SUITE_RESULT}" in
-            success|skipped)
-              ;;
-            *)
-              exit 1
-              ;;
-          esac
+          for result in "${GEM_SUITE_RESULT}" "${RUST_HOST_RESULT}" "${DEP_HEADS_RESULT}" "${COVERAGE_RESULT}"; do
+            case "${result}" in
+              success|skipped)
+                ;;
+              *)
+                exit 1
+                ;;
+            esac
+          done
diff --git a/gems/ast-crispr/Gemfile b/gems/ast-crispr/Gemfile
@@ -26,6 +26,12 @@ if !structuredmerge_rust_dev.empty? && !%w[false 0 no off].include?(structuredme
   gem 'structuredmerge_host_prototype', path: File.join(structuredmerge_rust_dev, 'packages/ruby')
 end
 
+# CI current and coverage jobs require the published Rust host gem; this fails until it is released.
+if ENV.fetch('STRUCTUREDMERGE_RUST_HOST_PUBLISHED', 'false').casecmp('true').zero? &&
+   instance_variable_get(:@dependencies).none? { |dependency| dependency.name == 'structuredmerge_host_prototype' }
+  gem 'structuredmerge_host_prototype', '~> 0.2'
+end
+
 # Local workspace dependency wiring for *_local.gemfile overrides
 gem 'nomono', '~> 1.1', '>= 1.1.5', require: false # ruby >= 3.2.0
 

diff --git a/gems/ast-merge-git/Gemfile b/gems/ast-merge-git/Gemfile
@@ -13,6 +13,12 @@ if !structuredmerge_rust_dev.empty? && !%w[false 0 no off].include?(structuredme
   gem 'structuredmerge_host_prototype', path: File.join(structuredmerge_rust_dev, 'packages/ruby')
 end
 
+# CI current and coverage jobs require the published Rust host gem; this fails until it is released.
+if ENV.fetch('STRUCTUREDMERGE_RUST_HOST_PUBLISHED', 'false').casecmp('true').zero? &&
+   instance_variable_get(:@dependencies).none? { |dependency| dependency.name == 'structuredmerge_host_prototype' }
+  gem 'structuredmerge_host_prototype', '~> 0.2'
+end
+
 git_source(:codeberg) { |repo_name| "https://codeberg.org/#{repo_name}" }
 git_source(:gitlab) { |repo_name| "https://gitlab.com/#{repo_name}" }
 

diff --git a/gems/ast-merge-git/spec/real_git_integration_spec.rb b/gems/ast-merge-git/spec/real_git_integration_spec.rb
@@ -556,6 +556,8 @@ def text_git_baseline(base:, ours:, theirs:)
     }
   ].each do |provider|
     it "runs the explicit #{provider.fetch(:label)} selector through the installed Git-driver path" do
+      skip 'compiled Rust host is unavailable' unless Ast::Merge::Git::RustHostProvider.available?
+
       base = provider.fetch(:source)
       ours = provider.fetch(:ours)
       theirs = provider.fetch(:theirs)

diff --git a/gems/ast-template/Gemfile b/gems/ast-template/Gemfile
@@ -34,6 +34,12 @@ if !structuredmerge_rust_dev.empty? && !%w[false 0 no off].include?(structuredme
   gem 'structuredmerge_host_prototype', path: File.join(structuredmerge_rust_dev, 'packages/ruby')
 end
 
+# CI current and coverage jobs require the published Rust host gem; this fails until it is released.
+if ENV.fetch('STRUCTUREDMERGE_RUST_HOST_PUBLISHED', 'false').casecmp('true').zero? &&
+   instance_variable_get(:@dependencies).none? { |dependency| dependency.name == 'structuredmerge_host_prototype' }
+  gem 'structuredmerge_host_prototype', '~> 0.2'
+end
+
 # The default adapter registry is exercised by the release suite with local
 # sibling wiring disabled, so its released adapter dependencies must be present
 # in the ordinary development bundle as well as in the templating bundle.