Continuous integration on Windows and Linux

3 files changed, 74 insertions, 11 deletions

diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index 9253d60..4e2b7c3 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -1,20 +1,55 @@
+# This Github Actions workflow is modified from
+# https://kodimensional.dev/github-actions
 name: 'CI'
-on: ['push']
+
+# Trigger the workflow on push or pull request, but only for the master branch
+on: [push, pull_request]
+
 jobs:
   build:
+
     strategy:
       matrix:
         os: [ubuntu-latest, windows-latest]
+
+    env:
+      ARGS: --no-terminal --fast
       
     name: ${{ matrix.os }}
-    runs-on: $${{ matrix.os }}
+    runs-on: ${{ matrix.os }}
     
     steps:
-    - uses: 'actions/checkout@v1'
-    - uses: 'mstksg/setup-stack@v1'
-    - uses: 'actions/cache@v1'
+    - uses: actions/checkout@v2
+      if: github.event.action == 'opened' || github.event.action == 'synchronize' || github.event.ref == 'refs/heads/master'
+
+    # https://github.com/actions/setup-haskell
+    - uses: actions/setup-haskell@v1.1
+      name: Setup Haskell Stack
       with:
-        path: '~/.stack'
-        key: "${{ runner.os }}-v3-stack-${{ hashFiles('stack.yaml.lock') }}"
-        restore-keys: '${{ runner.os }}-v3-stack'
-    - run: 'stack build --test'
+        stack-version: "latest"
+        enable-stack: true
+        stack-no-global: true
+    
+    # https://github.com/actions/cache
+    - uses: actions/cache@v2
+      name: Cache ~/.stack
+      with:
+        path: ~/.stack
+        key: ${{ runner.os }}-${{ hashFiles('stack.yaml') }}
+
+    # There are strange problems with CI on Windows, where builds with GHC 8.8.*
+    # always fail. Therefore, we distinguish between builds on Ubuntu and Windows
+    # and use an older compiler on Windows.
+    # See here for bug reports:
+    #   https://gitlab.haskell.org/ghc/ghc/issues/17599
+    #   https://gitlab.haskell.org/ghc/ghc/issues/17926
+    
+    - name: Test (Ubuntu)
+      run: |
+        stack test $ARGS --stack-yaml stack.yaml
+      if: ${{ runner.os == 'Linux' }}
+
+    - name: Test (Windows)
+      run: |
+        stack test $ARGS --stack-yaml stack.yaml --compiler ghc-8.6.5
+      if: ${{ runner.os == 'Windows' }} 
diff --git a/hakyll.cabal b/hakyll.cabal
index 4be61bc..6607ebf 100644
--- a/hakyll.cabal
+++ b/hakyll.cabal
@@ -173,7 +173,7 @@ Library
     cryptonite           >= 0.25     && < 0.27,
     data-default         >= 0.4      && < 0.8,
     deepseq              >= 1.3      && < 1.5,
-    directory            >= 1.0      && < 1.4,
+    directory            >= 1.2.7.0  && < 1.4,
     file-embed           >= 0.0.10.1 && < 0.0.12,
     filepath             >= 1.0      && < 1.5,
     lrucache             >= 1.1.1    && < 1.3,
diff --git a/lib/Hakyll/Core/Util/File.hs b/lib/Hakyll/Core/Util/File.hs
index 9db6b11..02b8ece 100644
--- a/lib/Hakyll/Core/Util/File.hs
+++ b/lib/Hakyll/Core/Util/File.hs
@@ -1,3 +1,5 @@
+{-# LANGUAGE ScopedTypeVariables #-}
+{-# LANGUAGE CPP                 #-}
 --------------------------------------------------------------------------------
 -- | A module containing various file utility functions
 module Hakyll.Core.Util.File
@@ -8,10 +10,12 @@ module Hakyll.Core.Util.File
 
 
 --------------------------------------------------------------------------------
+import           Control.Concurrent  (threadDelay)
+import           Control.Exception   (SomeException, catch)
 import           Control.Monad       (filterM, forM, when)
 import           System.Directory    (createDirectoryIfMissing,
                                       doesDirectoryExist, getDirectoryContents,
-                                      removeDirectoryRecursive)
+                                      removeDirectoryRecursive, removePathForcibly)
 import           System.FilePath     (takeDirectory, (</>))
 
 
@@ -51,6 +55,30 @@ getRecursiveContents ignore top = go ""
 
 --------------------------------------------------------------------------------
 removeDirectory :: FilePath -> IO ()
+#ifndef mingw32_HOST_OS
 removeDirectory fp = do
     e <- doesDirectoryExist fp
     when e $ removeDirectoryRecursive fp
+#else
+-- Deleting files on Windows is unreliable. If a file/directory is open by a program (e.g. antivirus),
+-- then removing related directories *quickly* may fail with strange messages.
+-- See here for discussions:
+--      https://github.com/haskell/directory/issues/96
+--      https://github.com/haskell/win32/pull/129
+--
+-- The hacky solution is to retry deleting directories a few times, 
+-- with a delay, on Windows only.
+removeDirectory = retryWithDelay 10 . removePathForcibly
+#endif
+
+
+--------------------------------------------------------------------------------
+-- | Retry an operation at most /n/ times (/n/ must be positive).
+--   If the operation fails the /n/th time it will throw that final exception.
+--   A delay of 100ms is introduced between every retry.
+retryWithDelay :: Int -> IO a -> IO a
+retryWithDelay i x 
+    | i <= 0    = error "Hakyll.Core.Util.File.retry: retry count must be 1 or more"
+    | i == 1    = x
+    | otherwise = catch x $ \(_::SomeException) -> threadDelay 100 >> retryWithDelay (i-1) x
+