CI: Fetch and cache Sapling parameters for tests

.github/workflows/ci.yml

@@ -50,6 +50,21 @@ jobs:
         with:
           toolchain: 1.40.0
           override: true
+
+      - name: Fetch path to Zcash parameters
+        working-directory: ./zcash_proofs
+        run: echo "::set-env name=ZCASH_PARAMS::$(cargo run --release --example get-params-path --features directories)"
+      - name: Cache Zcash parameters
+        id: cache-params
+        uses: actions/cache@v2
+        with:
+          path: ${{ env.ZCASH_PARAMS }}
+          key: ${{ runner.os }}-params
+      - name: Fetch Zcash parameters
+        if: steps.cache-params.outputs.cache-hit != 'true'
+        working-directory: ./zcash_proofs
+        run: cargo run --release --example download-params --features download-params
+
       - name: cargo fetch
         uses: actions-rs/cargo@v1
         with:

zcash_proofs/Cargo.toml

@@ -31,6 +31,10 @@ download-params = ["minreq"]
 local-prover = ["directories"]
 multicore = ["bellman/multicore"]
 
+[[example]]
+name = "get-params-path"
+required-features = ["directories"]
+
 [[example]]
 name = "download-params"
 required-features = ["download-params"]

zcash_proofs/examples/get-params-path.rs

@@ -0,0 +1,7 @@
+fn main() {
+    if let Some(path) = zcash_proofs::default_params_folder() {
+        if let Some(path) = path.to_str() {
+            println!("{}", path);
+        }
+    }
+}

zcash_proofs/src/lib.rs

@@ -39,7 +39,7 @@ const DOWNLOAD_URL: &str = "https://download.z.cash/downloads";
 
 /// Returns the default folder that the Zcash proving parameters are located in.
 #[cfg(feature = "directories")]
-fn default_params_folder() -> Option<PathBuf> {
+pub fn default_params_folder() -> Option<PathBuf> {
     BaseDirs::new().map(|base_dirs| {
         if cfg!(any(windows, target_os = "macos")) {
             base_dirs.data_dir().join("ZcashParams")