ci: add cargo-check-external-types

.github/workflows/rust.yml

@@ -80,3 +80,17 @@ jobs:
         uses: actions/checkout@v4
       - name: Check semver
         uses: obi1kenobi/cargo-semver-checks-action@v2
+
+  check-external-types:
+    name: Validate external types appearing in public API
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout sources
+        uses: actions/checkout@v4
+      - name: Install rust toolchain
+        uses: dtolnay/rust-toolchain@master
+        with:
+          toolchain: nightly-2024-02-07
+          # ^ sync with https://github.com/awslabs/cargo-check-external-types/blob/main/rust-toolchain.toml
+      - run: cargo install cargo-check-external-types
+      - run: cargo check-external-types

Cargo.toml

@@ -21,3 +21,9 @@ rusticata-macros = "4.0"
 cookie-factory = { version = "0.3", optional = true }
 num-bigint = { version = "0.4", optional = true }
 num-traits = { version = "0.2", optional = true }
+
+[package.metadata.cargo_check_external_types]
+allowed_external_types = [
+    "nom",
+    "nom::*",
+]