improve cirrus build time by properly using cabal cache

.cirrus.yml

@@ -2,54 +2,32 @@ freebsd_instance:
   image: freebsd-12-1-release-amd64
 
 build_task:
-  env:
-    ASSUME_ALWAYS_YES: YES
+  # caches the freebsd package downloads
+  # saves probably just a couple of seconds, but hey...
+  pkg_cache:
+    folder: /var/cache/pkg
+
   install_script:
-    ## TODO: Some of these workaround steps might be unneeded now
-    ## gmake required, otherwise bsd make is used and some cryptic "No operator" errors are shown
-    - pkg install -y gmake
-    ## gcc required, otherwise warning: macro expansion producing 'defined' has undefined behavior [-Wexpansion-to-defined]
-    - pkg install -y gcc
-    - pkg install -y libiconv
-    - pkg install -y gmp
-    - pkg install -y postgresql95-client
-    - pkg install -y pkgconf
-    - pkg install -y ghc
-    - pkg install -y hs-cabal-install
-  cabal_cache:
-    folder: ~/.cabal
+    - pkg install -y postgresql95-client ghc hs-cabal-install
+  
+  # cache the hackage index file and downloads which are
+  # cabal v2-update downloads an incremental update, so we don't need to keep this up2date
+  packages_cache:
+    # warning: don't use ~/.cabal here, this will break the cache
+    folder: /.cabal/packages
+    reupload_on_changes: false
+
+  # cache the dependencies built by cabal
+  # they have to be uploaded on every change to make the next build fast
+  store_cache:
+    # warning: don't use ~/.cabal here, this will break the cache
+    folder: /.cabal/store
     fingerprint_script: cat postgrest.cabal
+    reupload_on_changes: true
+
   build_script:
     - cabal v2-update
     - cabal v2-build
+
   binaries_artifacts:
     path: "dist-newstyle/build/x86_64-freebsd/ghc-8.6.5/postgrest-7.0.1/x/postgrest/build/postgrest/*"
-  #binary_script:
-    #- mkdir bin
-    ## cabal v2-install --installdir=.
-    ## the installdir option is not working on this cabal version(form hs-cabal-install), so the binary must be extrated from the path
-    ## this is too brittle so for now we don't use it
-    #- ldd /tmp/cirrus-ci-build/dist-newstyle/build/x86_64-freebsd/ghc-8.6.5/postgrest-7.0.1/x/postgrest/build/postgrest/postgrest
-    #- mv /tmp/cirrus-ci-build/dist-newstyle/build/x86_64-freebsd/ghc-8.6.5/postgrest-7.0.1/x/postgrest/build/postgrest/postgrest bin/
-  ## https://cirrus-ci.org/guide/writing-tasks/#artifacts-instruction
-  #binaries_artifacts:
-    #path: bin/
-  cleanup_script:
-    - rm -rf ~/.cabal/logs
-    - rm  ~/.cabal/config
-
-#publish_task:
-  #skip: $CIRRUS_TAG == ""
-  #env:
-    #TOKEN: ENCRYPTED[c99babbf04e8a33962ffbbc75bf20d3abe408f9bede5ed5d8956cd24da6fdb34266c920984cc43f8106ef3423fba0e98]
-  #depends_on:
-    #- build
-  #script:
-    ## https://cirrus-ci.org/guide/writing-tasks/#artifacts-instruction
-    #- wget https://api.cirrus-ci.com/v1/artifact/github/$CIRRUS_REPO_FULL_NAME/build/binaries/bin/postgrest
-    #- tar cvJf postgrest-$CIRRUS_TAG-freebsd.tar.xz -C ~/project/result/bin postgrest
-    ### The CIRRUS_RELEASE env var is not the same as the tag. It's an id for the release.
-    #- curl -X POST --data-binary @$NAME \
-      #-H "Authorization:token ${TOKEN}" \
-      #-H "Content-Type:application/octet-stream" \
-      #"https://uploads.github.com/repos/$CIRRUS_REPO_FULL_NAME/releases/${CIRRUS_RELEASE}/assets?name=${NAME}"