ci: add no-panic check for the custom backend (#517)

Author: newpavlov

.github/workflows/nopanic.yaml

@@ -47,6 +47,13 @@ jobs:
     - name: Check (rdrand.rs)
       run: ret=$(grep panic target/release/libgetrandom_wrapper.so; echo $?); [ $ret -eq 1 ]
 
+    - name: Build (custom.rs)
+      env:
+        RUSTFLAGS: -Dwarnings --cfg getrandom_backend="custom"
+      run: cargo build --release
+    - name: Check (custom.rs)
+      run: ret=$(grep panic target/release/libgetrandom_wrapper.so; echo $?); [ $ret -eq 1 ]
+
     - name: Build (wasi.rs, preview 1)
       run: cargo build --release --target wasm32-wasip1
     - name: Check (wasi.rs, preview 1)

nopanic_check/Cargo.toml

@@ -14,3 +14,9 @@ getrandom = { path = ".." }
 
 [profile.release]
 panic = "abort"
+
+[lints.rust.unexpected_cfgs]
+level = "warn"
+check-cfg = [
+  'cfg(getrandom_backend, values("custom"))',
+]

nopanic_check/src/lib.rs

@@ -16,3 +16,15 @@ pub extern "C" fn getrandom_wrapper(buf_ptr: *mut u8, buf_len: usize) -> u32 {
     let res = getrandom::getrandom_uninit(buf).map(|_| ());
     unsafe { core::mem::transmute(res) }
 }
+
+#[cfg(getrandom_backend = "custom")]
+#[no_mangle]
+unsafe extern "Rust" fn __getrandom_custom(
+    dest: *mut u8,
+    len: usize,
+) -> Result<(), getrandom::Error> {
+    for i in 0..len {
+        core::ptr::write(dest.add(i), i as u8);
+    }
+    Ok(())
+}