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.

The change to aya/src/maps/mod.rs is due to public-api requiring
serde_json, which has cause the following type issue:

type annotations needed
multiple `impl`s satisfying `usize: std::cmp::PartialEq<_>`
  found in the following crates: `core`, `serde_json`:
- impl std::cmp::PartialEq for usize;
- impl std::cmp::PartialEq<serde_json::value::Value> for usize;

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

Cargo.toml

@@ -73,8 +73,10 @@ num_enum = { version = "0.6", default-features = false }
 object = { version = "0.31", default-features = false }
 parking_lot = { version = "0.12.0", default-features = false }
 proc-macro2 = { version = "1", default-features = false }
+public-api = { version = "0.31.2", default-features = false }
 quote = { version = "1", default-features = false }
 rbpf = { version = "0.2.0", default-features = false }
+rustdoc-json = { version = "0.8.6", default-features = false }
 syn = { version = "2", default-features = false }
 tempfile = { version = "3", default-features = false }
 testing_logger = { version = "0.1.1", default-features = false }

aya/Cargo.toml

@@ -29,7 +29,10 @@ tokio = { workspace = true, features = ["rt"], optional = true }
 
 [dev-dependencies]
 assert_matches = { workspace = true }
+cargo_metadata = { workspace = true }
 futures = { workspace = true }
+public-api = { workspace = true }
+rustdoc-json = { workspace = true }
 tempfile = { workspace = true }
 
 [features]

aya/src/lib.rs

@@ -58,3 +58,47 @@ pub mod util;
 pub use bpf::*;
 pub use obj::btf::{Btf, BtfError};
 pub use object::Endianness;
+
+#[cfg(test)]
+mod tests {
+    use cargo_metadata::{Metadata, MetadataCommand};
+    use std::{
+        env,
+        fs::{read_to_string, File},
+        io::Write,
+    };
+
+    #[test]
+    #[cfg_attr(miri, ignore = "uses open() which is not supported by miri")]
+    fn public_api() {
+        let rustdoc_json = rustdoc_json::Builder::default()
+            .toolchain("nightly")
+            .package("aya")
+            .all_features(true)
+            .build()
+            .unwrap();
+
+        let public_api = public_api::Builder::from_rustdoc_json(rustdoc_json)
+            .build()
+            .unwrap();
+
+        let metadata = MetadataCommand::new()
+            .no_deps()
+            .exec()
+            .expect("failed to run cargo metadata");
+        let Metadata { workspace_root, .. } = &metadata;
+
+        let path = workspace_root.join("aya/src/public-api.txt");
+
+        if env::var("UPDATE_EXPECT").is_ok() {
+            let mut f = File::create(&path).expect("failed to create aya/src/public-api.txt");
+            f.write_all(public_api.to_string().as_bytes())
+                .expect("failed to write aya/src/public-api.txt");
+        }
+        let current_api = read_to_string(path).expect("failed to read aya/src/public-api.txt");
+
+        if current_api != public_api.to_string() {
+            panic!("public api has changed. please bless by re-running tests with UPDATE_EXPECT=1");
+        }
+    }
+}

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 == usize::try_from(RLIM_INFINITY).unwrap() {
             return;
         }
         warn!(