ci: add api diff

.github/workflows/lint.yml

@@ -40,7 +40,7 @@ jobs:
 
       - uses: giraffate/[email protected]
         with:
-          reporter: 'github-pr-check'
+          reporter: "github-pr-check"
           github_token: ${{ secrets.GITHUB_TOKEN }}
           clippy_flags: --workspace --all-features --tests --examples --bins -- -Dclippy::todo -Aunknown_lints
 
@@ -67,3 +67,31 @@ jobs:
 
       - name: check external types
         run: just check-external-types-all +${{ vars.RUST_VERSION_EXTERNAL_TYPES }}
+
+  public-api-diff:
+    name: Public API Diff
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout main branch
+        uses: actions/checkout@v4
+        with:
+          ref: ${{ github.base_ref }}
+
+      - name: Checkout PR branch
+        uses: actions/checkout@v4
+
+      - name: Install Rust (${{ vars.RUST_VERSION_API_DIFF }})
+        uses: actions-rust-lang/[email protected]
+        with:
+          toolchain: ${{ vars.RUST_VERSION_API_DIFF }}
+
+      - name: Install cargo-public-api
+        uses: taiki-e/[email protected]
+        with:
+          tool: cargo-public-api
+
+      - name: Generate API diff
+        run: |
+          for f in $(find -mindepth 2 -maxdepth 2 -name Cargo.toml); do
+            cargo public-api --manifest-path "$f" --simplified diff ${{ github.event.pull_request.base.sha }}..${{ github.sha }}
+          done

bytestring/src/lib.rs

@@ -506,13 +506,13 @@ mod test {
     }
 
     #[test]
-    #[should_panic]
+    #[should_panic = "byte index 1 is not a char boundary;"]
     fn split_at_invalid_code_point() {
         ByteString::from_static("µ").split_at(1);
     }
 
     #[test]
-    #[should_panic]
+    #[should_panic = "byte index 9 is out of bounds"]
     fn split_at_outside_string() {
         ByteString::from_static("foo").split_at(9);
     }