Rescue stack windows build (#954)

* Revert "Drop stack Windows CI"

This reverts commit 919d3bce57.

* Fix stack Windows build

I finally figured this puzzle out

.azure/windows-stack.yml

@@ -0,0 +1,41 @@
+jobs:
+- job: ghcide_stack_windows
+  timeoutInMinutes: 120
+  pool:
+    vmImage: 'windows-2019'
+  variables:
+      STACK_ROOT: "C:\\sr"
+  steps:
+  - checkout: self
+  - task: Cache@2
+    inputs:
+      key: stack-root-cache | $(Agent.OS) | $(Build.SourcesDirectory)/stack-windows.yaml | $(Build.SourcesDirectory)/ghcide.cabal
+      path: $(STACK_ROOT)
+      cacheHitVar: STACK_ROOT_CACHE_RESTORED
+    displayName: "Cache stack root"
+  - task: Cache@2
+    inputs:
+      key: stack-work-cache | $(Agent.OS) | $(Build.SourcesDirectory)/stack-windows.yaml | $(Build.SourcesDirectory)/ghcide.cabal
+      path: .stack-work
+      cacheHitVar: STACK_WORK_CACHE_RESTORED
+    displayName: "Cache stack work"
+  - bash: |
+      ./fmt.sh
+    displayName: "HLint via ./fmt.sh"
+  - bash: |
+      curl -sSkL http://www.stackage.org/stack/windows-x86_64 -o /usr/bin/stack.zip
+      unzip -o /usr/bin/stack.zip -d /usr/bin/
+      mkdir -p "$STACK_ROOT"
+    displayName: 'Install Stack'
+  - bash: stack setup --stack-yaml stack-windows.yaml
+    displayName: 'stack setup'
+  - bash: |
+      # Installing happy and alex standalone to avoid error "strip.exe: unable to rename ../*.exe; reason: File exists"
+      stack install happy --stack-yaml stack-windows.yaml
+      stack install alex --stack-yaml stack-windows.yaml
+      choco install -y cabal --version=$CABAL_VERSION
+      $(cygpath $ProgramData)/chocolatey/bin/RefreshEnv.cmd
+      # GHC 8.10.1 fails with ghc segfaults, using -fexternal-interpreter seems to make it working
+      # There are other transient errors like timeouts downloading from stackage so we retry 3 times
+        stack build --test --no-run-tests --stack-yaml stack-windows.yaml --ghc-options="-fexternal-interpreter" || stack build --test --no-run-tests --stack-yaml stack-windows.yaml --ghc-options="-fexternal-interpreter" || stack build --test --no-run-tests --stack-yaml stack-windows.yaml  --ghc-options="-fexternal-interpreter"
+    displayName: 'stack build --test'

azure-pipelines.yml

@@ -15,3 +15,4 @@ pr:
 
 jobs:
   - template: ./.azure/linux-stack.yml
+  - template: ./.azure/windows-stack.yml

stack-windows.yaml

@@ -37,10 +37,11 @@ nix:
   packages: [zlib]
 
 configure-options:
+    ghcide:
+        - --disable-library-for-ghci
     heapsize:
         - --disable-library-for-ghci
-        - --disable-library-stripping
-# Otherwise the ghcide will fail with:
+# Otherwise the ghcide build will fail with:
 # ```
 # ghcide                           > ghc.exe: unable to load package `heapsize-0.2'
 # ghcide                           > ghc-iserv:  | D:\a\1\s\.stack-work\install\52d658b2\lib\x86_64-windows-ghc-8.10.1\heapsize-0.2-KCPoGpPDcevACNftTTY2at\HSheapsize-0.2-KCPoGpPDcevACNftTTY2at.o: unknown symbol `heap_view_closurePtrs'
@@ -48,7 +49,12 @@ configure-options:
 # Cause:
 # The pre-linked object file is missing the heapsize_prim.o symbols table (from the cbits object)
 #
-# Reason: The ld invocation is stripping too much
+# Reason: Not sure, maybe the ld invocation is stripping too much
+#
+# Fix: do not generate the pre-linked object to prevent ghc from using it at link time.
+#      There are two instances where this must be prevented:
+#         1. When linking the ghcide library (using the heapsize pre-linked object)
+#         2. When linking the ghcide executable (using the ghcide pre-linked object)
 #
 # Quoting https://downloads.haskell.org/ghc/latest/docs/html/users_guide/packages.html
 #