Try #783:

Author: bors[bot]

.github/bors.toml

@@ -1,3 +1,3 @@
-block_labels = ["I-needs-decision", "S-blocked"]
+block_labels = ["status: postponed", "status: wontfix"]
 delete_merged_branches = true
-status = ["ci"]
+status = ["full-ci"]

.github/composite/llvm/action.yml

@@ -0,0 +1,26 @@
+name: llvm
+description: "Install LLVM + Clang, with caching"
+
+#inputs:
+#  llvm:
+#    required: false
+#    default: 'true'
+#    description: "Whether LLVM should be installed ('true' by default)"
+
+runs:
+  using: "composite"
+  steps:
+    - name: Cache LLVM and Clang
+      id: cache-llvm
+      # Note: conditionals not yet supported; see https://github.com/actions/runner/issues/834
+      # if: ${{ inputs.llvm == 'true' }}
+      uses: actions/cache@v2
+      with:
+        path: ${{ runner.temp }}/llvm
+        key: llvm-10.0
+    - uses: KyleMayes/install-llvm-action@v1
+      # if: ${{ inputs.llvm == 'true' }}
+      with:
+        version: "10.0"
+        directory: ${{ runner.temp }}/llvm
+        cached: ${{ steps.cache-llvm.outputs.cache-hit }}

.github/composite/rust/action.yml

@@ -0,0 +1,26 @@
+
+name: rust
+description: "Install Rust toolchain, with caching"
+
+inputs:
+  rust:
+    required: false
+    description: "Rust toolchain, e.g. 'stable' or 'nightly'"
+    default: stable
+  components:
+    required: false
+    description: "Components array"
+    default: ''
+
+runs:
+  using: "composite"
+  steps:
+    - uses: actions-rs/toolchain@v1
+      with:
+        profile: minimal
+        toolchain: ${{ inputs.rust }}
+        override: true # use selected toolchain for remainder of this step
+        components: ${{ inputs.components }}
+
+    # For notes about the cache, see 'Full CI' workflow
+    - uses: Swatinem/rust-cache@v1