chore(ffi): run gen_header.sh in CI environment (#2488)

Clean up the script so that any unexpected error terminates the
script, and stop suppressing errors that may contain useful
information (for example, that you are using the stable version but
need to use the nightly).

This is useful because if hyper.h is not up to date going forward the
CI should flag it. As is, there are a bunch of changes to hyper.h that
have not been checked in (or were generated by a newer version of the
cbindgen script.)

Fixes #2483.

.github/workflows/CI.yml

@@ -17,6 +17,7 @@ jobs:
       - test
       - features
       - ffi
+      - ffi-header
       - doc
     steps:
       - run: exit 0
@@ -119,9 +120,7 @@ jobs:
   ffi:
     name: Test C API (FFI)
     needs: [style]
-
     runs-on: ubuntu-latest
-
     steps:
       - name: Checkout
         uses: actions/checkout@v1
@@ -147,10 +146,6 @@ jobs:
           command: build
           args: --features client,http1,http2,ffi
 
-      # TODO: re-enable check once figuring out how to get it working in CI
-      # - name: Verify cbindgen
-      #   run: ./capi/gen_header.sh --verify
-
       - name: Make Examples
         run: cd capi/examples && make client
 
@@ -162,6 +157,39 @@ jobs:
           command: test
           args: --features full,ffi --lib
 
+  ffi-header:
+    name: Verify hyper.h is up to date
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v1
+
+      - name: Install Rust
+        uses: actions-rs/toolchain@v1
+        with:
+          profile: minimal
+          toolchain: nightly
+          default: true
+          override: true
+          components: cargo
+
+      - name: Install cbindgen
+        uses: actions-rs/cargo@v1
+        with:
+          command: install
+          args: cbindgen
+
+      - name: Build FFI
+        uses: actions-rs/cargo@v1
+        env:
+          RUSTFLAGS: --cfg hyper_unstable_ffi
+        with:
+          command: build
+          args: --features client,http1,http2,ffi
+
+      - name: Ensure that hyper.h is up to date
+        run: ./capi/gen_header.sh --verify
+
   doc:
     name: Build docs
     needs: [style, test]