From de108e05f0b3df48efff93a8bec15e6ff8333f09 Mon Sep 17 00:00:00 2001
From: Trevor Gross <tg@trevorgross.com>
Date: Sat, 19 Sep 2026 06:19:01 -0500
Subject: [PATCH] ci: Cache LLVM downloads separately

rust-cache made some changes (presumably [1]) that delete most non-Rust
files before caching, including the LLVM source, but leave the
directories. This causes `download-llvm.sh` to think the source exists
and skip a re-download, but the build fails because the needed files are
missing. It's not clear whether the download was being cached
previously, or if rust-cache deleted the directories so it was always
re-downloaded.

Move the directory in CI and set up a separate cache step so rust-cache
isn't responsible for these files anymore.

[1]: https://github.com/Swatinem/rust-cache/commit/3bf42ac996de475743278f3187c4fd89f23b8630
---
 .github/workflows/main.yaml | 8 ++++++++
 etc/download-llvm.sh        | 2 +-
 fuzz/build.rs               | 8 ++++++--
 3 files changed, 15 insertions(+), 3 deletions(-)

diff --git a/.github/workflows/main.yaml b/.github/workflows/main.yaml
index 20044d7..4fec031 100644
--- a/.github/workflows/main.yaml
+++ b/.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
 
diff --git a/etc/download-llvm.sh b/etc/download-llvm.sh
index 4dd4d23..68bcf0a 100755
--- a/etc/download-llvm.sh
+++ b/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
diff --git a/fuzz/build.rs b/fuzz/build.rs
index 5c049e3..a119af6 100644
--- a/fuzz/build.rs
+++ b/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?"
         )
     }