test GHC 9.0.1 on CI (not final)

.github/workflows/master.yml

@@ -13,15 +13,15 @@ jobs:
     strategy:
       matrix:
         os: [ubuntu-latest]
-        cabal: ["3.2"]
+        cabal: ["3.4"]
         ghc:
           - "8.0.2"
           - "8.2.2"
           - "8.4.4"
           - "8.6.5"
           - "8.8.4"
           - "8.10.2"
-
+          - "9.0.1"
     steps:
     - uses: actions/checkout@v2
 
@@ -34,6 +34,7 @@ jobs:
 
     - name: Freeze
       run: |
+        if [[ ${{ matrix.ghc }} == "9.0.1" ]]; then cat cabal.project.ghc-9.0 >> cabal.project; fi
         cabal configure --enable-tests --enable-benchmarks --test-show-details=direct
         cabal freeze
 
@@ -49,7 +50,7 @@ jobs:
 
     - name: Configure
       run: |
-        cabal install --ignore-project -j2 doctest --constraint='doctest ^>=0.17'
+        cabal install --ignore-project -j2 doctest --constraint='doctest ^>=0.18'
 
     - name: Build
       run: |

cabal.project.ghc-9.0

@@ -0,0 +1,24 @@
+with-compiler: ghc-9.0.1
+
+index-state: 2021-05-09T12:34:06Z
+
+allow-newer: base, template-haskell, Cabal
+allow-newer: lens, optics-core, optics-th, optics-extra
+allow-newer: servant-auth-server:memory
+
+source-repository-package
+  type: git
+  location: https://github.com/snapframework/io-streams
+  tag: ae692fee732adea9fe843fb3efe0dd43a6993844
+source-repository-package
+  type: git
+  location: https://github.com/GetShopTV/swagger2
+  tag: 51f2108826dff2a0c31b581025e8f9f9b29accb1
+source-repository-package
+  type: git
+  location: https://github.com/jwaldmann/blaze-textual
+  tag: d8ee6cf80e27f9619d621c936bb4bda4b99a183f
+source-repository-package
+  type: git
+  location: https://github.com/amesgen/servant-quickcheck
+  tag: 11d05b51f2b33bc1b19d4904561074ec4366a99c