Re-enable doctests on CI

.github/workflows/main.yml

@@ -12,7 +12,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        os: [ubuntu-latest, macOS-latest]
+        os: [ubuntu-latest]
         cabal: ["3.2"]
         ghc:
           - "8.8.4"
@@ -40,6 +40,7 @@ jobs:
     - name: Configure
       run: |
         cabal configure --enable-tests --enable-benchmarks --test-show-details=direct
+        cabal install --ignore-project -j2 doctest --constraint='doctest ^>=0.17'
 
     - name: Freeze
       run: |
@@ -59,6 +60,30 @@ jobs:
       run: |
         cabal test all
 
+    - name: Run doctests
+      run: |
+        # Necessary for doctest to be found in $PATH
+        export PATH="$HOME/.cabal/bin:$PATH"
+
+        # Filter out base-compat-batteries from .ghc.environment.*, as its modules
+        # conflict with those of base-compat.
+        #
+        # FIXME: This is an ugly hack. Ultimately, we'll want to use cabal-doctest
+        # (or cabal v2-doctest, if it ever lands) to provide a clean GHC environment.
+        # This might allow running doctests in GHCJS build as well.
+        perl -i -e 'while (<ARGV>) { print unless /package-id\s+(base-compat-batteries)-\d+(\.\d+)*/; }' .ghc.environment.*
+
+        (cd servant && doctest src)
+        (cd servant-client && doctest src)
+        (cd servant-client-core && doctest src)
+        (cd servant-http-streams && doctest src)
+        (cd servant-docs && doctest src)
+        (cd servant-foreign && doctest src)
+        (cd servant-server && doctest src)
+        (cd servant-machines && doctest src)
+        (cd servant-conduit && doctest src)
+        (cd servant-pipes && doctest src)
+
   stack:
     name: stack / ghc ${{ matrix.ghc }}
     runs-on: ubuntu-latest