ci: build microbenchmarks

Fixes #10682

Signed-off-by: Etienne Millon <[email protected]>

.github/workflows/workflow.yml

@@ -271,3 +271,11 @@ jobs:
           ocaml-compiler: ${{ matrix.ocaml-compiler }}
       - uses: actions/checkout@v4
       - run: opam switch create . -y
+
+  build-microbench:
+    name: Build microbenchmarks
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: cachix/install-nix-action@v22
+      - run: nix develop .#microbench -c make dune build bench/micro

flake.nix

@@ -222,6 +222,15 @@
                 that can build Dune and the Coq testsuite.
               '';
             };
+          microbench = makeDuneDevShell {
+            extraBuildInputs = with pkgs.ocamlPackages; [
+              core_bench
+            ];
+            meta.description = ''
+              Provides a minimal shell environment that can build the
+              microbenchmarks.
+            '';
+          };
 
           scope = makeDuneDevShell {
             duneFromScope = true;