ci: Cache LLVM downloads separately

.github/workflows/main.yaml

@@ -9,6 +9,7 @@ env:
   RUSTDOCFLAGS: -Dwarnings
   RUSTFLAGS: -Dwarnings
   RUST_BACKTRACE: full
+  LLVM_DOWNLOAD_DIR: "${{ github.workspace }}/llvm-downloads"
 
 jobs:
   test:
@@ -31,8 +32,15 @@ jobs:
     - uses: Swatinem/rust-cache@v2
       with:
         key: ${{ matrix.target }}
+
+    - name: Cache LLVM source
+      uses: actions/cache@v6
+      with:
+        path: llvm-downloads
+        key: llvm-downloads-${{ hashFiles('Cargo.toml', 'etc/download-llvm.sh') }}
     - name: Download llvm source
       run: ./etc/download-llvm.sh
+
     - name: Build and run tests
       run: cargo test --workspace
 

etc/download-llvm.sh

@@ -12,7 +12,7 @@ version="$(
 llvm_hash="${version##*-}"
 
 target_dir="${CARGO_TARGET_DIR:-target}"
-out_dir="$target_dir/llvm-downloads"
+out_dir="${LLVM_DOWNLOAD_DIR:-$target_dir/llvm-downloads}"
 mkdir -p "$out_dir"
 
 if [ -d "$out_dir/llvm-project-$llvm_hash" ] && [ "${1:-}" != "-f" ]; then

fuzz/build.rs

@@ -47,11 +47,15 @@ fn main() -> io::Result<()> {
     let target_dir = env::var_os("CARGO_TARGET_DIR")
         .map(PathBuf::from)
         .unwrap_or_else(|| manifest_dir.parent().unwrap().join("target"));
-    let llvm_root = target_dir.join(format!("llvm-downloads/llvm-project-{llvm_commit_hash}"));
+    let version_dir = format!("llvm-project-{llvm_commit_hash}");
+    let llvm_root = match env::var_os("LLVM_DOWNLOAD_DIR") {
+        Some(dir) => PathBuf::from(dir).join(version_dir),
+        None => target_dir.join("llvm-downloads").join(version_dir),
+    };
 
     if !llvm_root.try_exists().is_ok_and(|val| val) {
         panic!(
-            "llvm dir `{llvm_root:?}` does not exist or cannot be reached. \
+            "llvm dir {llvm_root:?} does not exist or cannot be reached. \
             Perhaps you need to run etc/download-llvm.sh?"
         )
     }