aya: Add cargo-public-api

Adds cargo-public-api. This allows for public API changes to get caught
by cargo test, requiring new changes to be "blessed" by using:

   UPDATE_EXPECT=1 cargo test

When this file is changed, Alessandro will need to review the PR.

Signed-off-by: Dave Tucker <dave@dtucker.co.uk>

.cargo/config.toml

@@ -9,3 +9,6 @@ linker = "arm-linux-gnueabihf-gcc"
 
 [target.aarch64-unknown-linux-musl]
 linker = "aarch64-linux-musl-gcc"
+
+[env]
+CARGO_WORKSPACE_DIR = { value = "", relative = true }

aya/Cargo.toml

@@ -29,7 +29,11 @@ tokio = { workspace = true, features = ["rt"], optional = true }
 
 [dev-dependencies]
 assert_matches = { workspace = true }
+expect-test = "1.4.1"
 futures = { workspace = true }
+public-api = "0.31.2"
+rustdoc-json = "0.8.6"
+rustup-toolchain = "0.1.5"
 tempfile = { workspace = true }
 
 [features]

aya/src/lib.rs

@@ -58,3 +58,27 @@ pub mod util;
 pub use bpf::*;
 pub use obj::btf::{Btf, BtfError};
 pub use object::Endianness;
+
+#[cfg(test)]
+mod tests {
+    #[test]
+    #[cfg_attr(miri, ignore)]
+    fn public_api() {
+        // Install a compatible nightly toolchain if it is missing
+        rustup_toolchain::install(public_api::MINIMUM_NIGHTLY_RUST_VERSION).unwrap();
+
+        // Build rustdoc JSON
+        let rustdoc_json = rustdoc_json::Builder::default()
+            .toolchain(public_api::MINIMUM_NIGHTLY_RUST_VERSION)
+            .build()
+            .unwrap();
+
+        // Derive the public API from the rustdoc JSON
+        let public_api = public_api::Builder::from_rustdoc_json(rustdoc_json)
+            .build()
+            .unwrap();
+
+        // Assert that the public API looks correct
+        expect_test::expect_file!["./public-api.txt"].assert_eq(&public_api.to_string());
+    }
+}

aya/src/maps/mod.rs

@@ -224,7 +224,7 @@ fn maybe_warn_rlimit() {
         let limit = unsafe { limit.assume_init() };
 
         let limit: RlimitSize = RlimitSize(limit.rlim_cur.try_into().unwrap());
-        if limit.0 == RLIM_INFINITY.try_into().unwrap() {
+        if limit.0 == TryInto::<usize>::try_into(RLIM_INFINITY).unwrap() {
             return;
         }
         warn!(