Split benchmarks out of CI into separate action.

The benchmark action is only run on manual dispatch.

Rationale: this action dramatically slows down CI.
It is nice to run benchmarks, but we don't need them all the time.

We add (non-optimized) testing of benchmark compilation to one of
the CI builds.

.github/workflows/benchmark.yml

@@ -0,0 +1,58 @@
+name: benchmarks
+
+on: workflow_dispatch
+
+permissions:
+  contents: read
+
+jobs:
+  benchmark:
+
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: true
+      matrix:
+        versions:
+          - ghc: '8.10.7'
+            cabal: '3.2'
+          - ghc: '9.2.2'
+            cabal: '3.6'
+    steps:
+    - uses: actions/checkout@v3
+
+    - name: Install cabal/ghc
+      run: |
+        ghcup install ghc --set ${{ matrix.versions.ghc }}
+        ghcup install cabal ${{ matrix.versions.cabal }}
+
+    # declare/restore cached things
+
+    - name: Cache cabal global package db
+      id:   cabal-global
+      uses: actions/cache@v3
+      with:
+        path: |
+          ~/.cabal
+        key: benchmark-${{ runner.os }}-${{ matrix.versions.ghc }}-${{ matrix.versions.cabal }}-cabal-global-${{ secrets.CACHE_VERSION }}
+
+    - name: Cache cabal work
+      id:   cabal-local
+      uses: actions/cache@v3
+      with:
+        path: |
+          dist-newstyle
+        key: benchmark-${{ runner.os }}-${{ matrix.versions.ghc }}-${{ matrix.versions.cabal }}-cabal-local-${{ secrets.CACHE_VERSION }}
+
+    - name: Install dependencies
+      run: |
+          v2=$([ "${{ matrix.versions.cabal }}" = "2.2" ] && printf 'new' || printf 'v2')
+          cabal $v2-update
+          cabal $v2-build --dependencies-only --enable-optimization=1 --enable-benchmarks --disable-tests
+
+    - name: Build and test
+      run: |
+          v2=$([ "${{ matrix.versions.cabal }}" = "2.2" ] && printf 'new' || printf 'v2')
+          cabal $v2-build --enable-optimization=1 --enable-benchmarks --disable-tests 2>&1 | tee build.log
+          # fail if warnings in local build
+          ! grep -q ": *[Ww]arning:" build.log || exit 1
+          cabal $v2-bench --enable-optimization=1 --benchmark-options='--timeout=6 +RTS -T -RTS'

.github/workflows/ci.yml

@@ -52,7 +52,7 @@ jobs:
             testopts: '--test-option=--hide-successes --test-option=--ansi-tricks=false'
           - ghc: '8.8.4'
             cabal: '3.2'
-            cabalopts: '-f-server'
+            cabalopts: '-f-server --enable-benchmarks'
             testopts: '--test-option=--hide-successes --test-option=--ansi-tricks=false'
           - ghc: '8.10.7'
             cabal: '3.2'
@@ -191,53 +191,3 @@ jobs:
           ! grep -q ": *[Ww]arning:" build.log || exit 1
           cabal v2-test --disable-optimization --test-option=--hide-successes --test-option=--ansi-tricks=false
 
-  benchmark:
-
-    runs-on: ubuntu-18.04
-    strategy:
-      fail-fast: true
-      matrix:
-        versions:
-          - ghc: '8.10.7'
-            cabal: '3.2'
-          - ghc: '9.2.2'
-            cabal: '3.6'
-    steps:
-    - uses: actions/checkout@v3
-
-    - name: Install cabal/ghc
-      run: |
-        ghcup install ghc --set ${{ matrix.versions.ghc }}
-        ghcup install cabal ${{ matrix.versions.cabal }}
-
-    # declare/restore cached things
-
-    - name: Cache cabal global package db
-      id:   cabal-global
-      uses: actions/cache@v3
-      with:
-        path: |
-          ~/.cabal
-        key: benchmark-${{ runner.os }}-${{ matrix.versions.ghc }}-${{ matrix.versions.cabal }}-cabal-global-${{ secrets.CACHE_VERSION }}
-
-    - name: Cache cabal work
-      id:   cabal-local
-      uses: actions/cache@v3
-      with:
-        path: |
-          dist-newstyle
-        key: benchmark-${{ runner.os }}-${{ matrix.versions.ghc }}-${{ matrix.versions.cabal }}-cabal-local-${{ secrets.CACHE_VERSION }}
-
-    - name: Install dependencies
-      run: |
-          v2=$([ "${{ matrix.versions.cabal }}" = "2.2" ] && printf 'new' || printf 'v2')
-          cabal $v2-update
-          cabal $v2-build --dependencies-only --enable-optimization=1 --enable-benchmarks --disable-tests
-
-    - name: Build and test
-      run: |
-          v2=$([ "${{ matrix.versions.cabal }}" = "2.2" ] && printf 'new' || printf 'v2')
-          cabal $v2-build --enable-optimization=1 --enable-benchmarks --disable-tests 2>&1 | tee build.log
-          # fail if warnings in local build
-          ! grep -q ": *[Ww]arning:" build.log || exit 1
-          cabal $v2-bench --enable-optimization=1 --benchmark-options='--timeout=6 +RTS -T -RTS'