Require building with GHC 9.10

.github/workflows/haskell-ci.yml

@@ -8,9 +8,9 @@
 #
 # For more information, see https://github.com/haskell-CI/haskell-ci
 #
-# version: 0.18.1
+# version: 0.19.20240512
 #
-# REGENDATA ("0.18.1",["github","cabal.project"])
+# REGENDATA ("0.19.20240512",["github","cabal.project"])
 #
 name: Haskell-CI
 on:
@@ -23,29 +23,29 @@ jobs:
     timeout-minutes:
       60
     container:
-      image: buildpack-deps:bionic
+      image: buildpack-deps:jammy
     continue-on-error: ${{ matrix.allow-failure }}
     strategy:
       matrix:
         include:
-          - compiler: ghcjs-8.4
-            compilerKind: ghcjs
-            compilerVersion: "8.4"
-            setup-method: hvr-ppa
+          - compiler: ghc-9.10.1
+            compilerKind: ghc
+            compilerVersion: 9.10.1
+            setup-method: ghcup
             allow-failure: false
-          - compiler: ghc-9.8.1
+          - compiler: ghc-9.8.2
             compilerKind: ghc
-            compilerVersion: 9.8.1
+            compilerVersion: 9.8.2
             setup-method: ghcup
             allow-failure: false
-          - compiler: ghc-9.6.2
+          - compiler: ghc-9.6.5
             compilerKind: ghc
-            compilerVersion: 9.6.2
+            compilerVersion: 9.6.5
             setup-method: ghcup
             allow-failure: false
-          - compiler: ghc-9.4.5
+          - compiler: ghc-9.4.8
             compilerKind: ghc
-            compilerVersion: 9.4.5
+            compilerVersion: 9.4.8
             setup-method: ghcup
             allow-failure: false
           - compiler: ghc-9.2.7
@@ -66,99 +66,64 @@ jobs:
           - compiler: ghc-8.8.4
             compilerKind: ghc
             compilerVersion: 8.8.4
-            setup-method: hvr-ppa
+            setup-method: ghcup
             allow-failure: false
           - compiler: ghc-8.6.5
             compilerKind: ghc
             compilerVersion: 8.6.5
-            setup-method: hvr-ppa
+            setup-method: ghcup
             allow-failure: false
           - compiler: ghc-8.4.4
             compilerKind: ghc
             compilerVersion: 8.4.4
-            setup-method: hvr-ppa
+            setup-method: ghcup
             allow-failure: false
           - compiler: ghc-8.2.2
             compilerKind: ghc
             compilerVersion: 8.2.2
-            setup-method: hvr-ppa
+            setup-method: ghcup
             allow-failure: false
           - compiler: ghc-8.0.2
             compilerKind: ghc
             compilerVersion: 8.0.2
-            setup-method: hvr-ppa
+            setup-method: ghcup
             allow-failure: false
       fail-fast: false
     steps:
-      - name: Set GHCJS environment variables
-        run: |
-          if [ $HCKIND = ghcjs ]; then
-          echo "GHCJS=true" >> "$GITHUB_ENV"
-          echo "GHCJSARITH=1" >> "$GITHUB_ENV"
-          else
-          echo "GHCJS=false" >> "$GITHUB_ENV"
-          echo "GHCJSARITH=0" >> "$GITHUB_ENV"
-          fi
-        env:
-          HCKIND: ${{ matrix.compilerKind }}
-          HCNAME: ${{ matrix.compiler }}
-          HCVER: ${{ matrix.compilerVersion }}
       - name: apt
         run: |
           apt-get update
-          apt-get install -y --no-install-recommends gnupg ca-certificates dirmngr curl git software-properties-common libtinfo5
-          if [ "${{ matrix.setup-method }}" = ghcup ]; then
-            mkdir -p "$HOME/.ghcup/bin"
-            curl -sL https://downloads.haskell.org/ghcup/0.1.20.0/x86_64-linux-ghcup-0.1.20.0 > "$HOME/.ghcup/bin/ghcup"
-            chmod a+x "$HOME/.ghcup/bin/ghcup"
-            "$HOME/.ghcup/bin/ghcup" install ghc "$HCVER" || (cat "$HOME"/.ghcup/logs/*.* && false)
-            "$HOME/.ghcup/bin/ghcup" install cabal 3.10.2.0 || (cat "$HOME"/.ghcup/logs/*.* && false)
-          else
-            apt-add-repository -y 'ppa:hvr/ghc'
-            if [ $((GHCJSARITH)) -ne 0 ] ; then apt-add-repository -y 'ppa:hvr/ghcjs' ; fi
-            if [ $((GHCJSARITH)) -ne 0 ] ; then curl -sSL "https://deb.nodesource.com/gpgkey/nodesource.gpg.key" | apt-key add - ; fi
-            if [ $((GHCJSARITH)) -ne 0 ] ; then apt-add-repository -y 'deb https://deb.nodesource.com/node_10.x bionic main' ; fi
-            apt-get update
-            if [ $((GHCJSARITH)) -ne 0 ] ; then apt-get install -y "$HCNAME" ghc-8.4.4 nodejs ; else apt-get install -y "$HCNAME" ; fi
-            mkdir -p "$HOME/.ghcup/bin"
-            curl -sL https://downloads.haskell.org/ghcup/0.1.20.0/x86_64-linux-ghcup-0.1.20.0 > "$HOME/.ghcup/bin/ghcup"
-            chmod a+x "$HOME/.ghcup/bin/ghcup"
-            "$HOME/.ghcup/bin/ghcup" install cabal 3.10.2.0 || (cat "$HOME"/.ghcup/logs/*.* && false)
-          fi
+          apt-get install -y --no-install-recommends gnupg ca-certificates dirmngr curl git software-properties-common libtinfo5 libnuma-dev
+          mkdir -p "$HOME/.ghcup/bin"
+          curl -sL https://downloads.haskell.org/ghcup/0.1.20.0/x86_64-linux-ghcup-0.1.20.0 > "$HOME/.ghcup/bin/ghcup"
+          chmod a+x "$HOME/.ghcup/bin/ghcup"
+          "$HOME/.ghcup/bin/ghcup" install ghc "$HCVER" || (cat "$HOME"/.ghcup/logs/*.* && false)
+          "$HOME/.ghcup/bin/ghcup" install cabal 3.10.2.0 || (cat "$HOME"/.ghcup/logs/*.* && false)
         env:
           HCKIND: ${{ matrix.compilerKind }}
           HCNAME: ${{ matrix.compiler }}
           HCVER: ${{ matrix.compilerVersion }}
       - name: Set PATH and environment variables
         run: |
           echo "$HOME/.cabal/bin" >> $GITHUB_PATH
-          if [ $((GHCJSARITH)) -ne 0 ] ; then echo "/opt/ghc/8.4.4/bin" >> $GITHUB_PATH ; fi
           echo "LANG=C.UTF-8" >> "$GITHUB_ENV"
           echo "CABAL_DIR=$HOME/.cabal" >> "$GITHUB_ENV"
           echo "CABAL_CONFIG=$HOME/.cabal/config" >> "$GITHUB_ENV"
           HCDIR=/opt/$HCKIND/$HCVER
-          if [ "${{ matrix.setup-method }}" = ghcup ]; then
-            HC=$("$HOME/.ghcup/bin/ghcup" whereis ghc "$HCVER")
-            HCPKG=$(echo "$HC" | sed 's#ghc$#ghc-pkg#')
-            HADDOCK=$(echo "$HC" | sed 's#ghc$#haddock#')
-            echo "HC=$HC" >> "$GITHUB_ENV"
-            echo "HCPKG=$HCPKG" >> "$GITHUB_ENV"
-            echo "HADDOCK=$HADDOCK" >> "$GITHUB_ENV"
-            echo "CABAL=$HOME/.ghcup/bin/cabal-3.10.2.0 -vnormal+nowrap" >> "$GITHUB_ENV"
-          else
-            HC=$HCDIR/bin/$HCKIND
-            echo "HC=$HC" >> "$GITHUB_ENV"
-            echo "HCPKG=$HCDIR/bin/$HCKIND-pkg" >> "$GITHUB_ENV"
-            echo "HADDOCK=$HCDIR/bin/haddock" >> "$GITHUB_ENV"
-            echo "CABAL=$HOME/.ghcup/bin/cabal-3.10.2.0 -vnormal+nowrap" >> "$GITHUB_ENV"
-          fi
-
+          HC=$("$HOME/.ghcup/bin/ghcup" whereis ghc "$HCVER")
+          HCPKG=$(echo "$HC" | sed 's#ghc$#ghc-pkg#')
+          HADDOCK=$(echo "$HC" | sed 's#ghc$#haddock#')
+          echo "HC=$HC" >> "$GITHUB_ENV"
+          echo "HCPKG=$HCPKG" >> "$GITHUB_ENV"
+          echo "HADDOCK=$HADDOCK" >> "$GITHUB_ENV"
+          echo "CABAL=$HOME/.ghcup/bin/cabal-3.10.2.0 -vnormal+nowrap" >> "$GITHUB_ENV"
           HCNUMVER=$(${HC} --numeric-version|perl -ne '/^(\d+)\.(\d+)\.(\d+)(\.(\d+))?$/; print(10000 * $1 + 100 * $2 + ($3 == 0 ? $5 != 1 : $3))')
           echo "HCNUMVER=$HCNUMVER" >> "$GITHUB_ENV"
           echo "ARG_TESTS=--enable-tests" >> "$GITHUB_ENV"
           echo "ARG_BENCH=--enable-benchmarks" >> "$GITHUB_ENV"
-          if [ $((! GHCJSARITH && HCNUMVER >= 90800)) -ne 0 ] ; then echo "HEADHACKAGE=true" >> "$GITHUB_ENV" ; else echo "HEADHACKAGE=false" >> "$GITHUB_ENV" ; fi
+          if [ $((HCNUMVER >= 91000)) -ne 0 ] ; then echo "HEADHACKAGE=true" >> "$GITHUB_ENV" ; else echo "HEADHACKAGE=false" >> "$GITHUB_ENV" ; fi
           echo "ARG_COMPILER=--$HCKIND --with-compiler=$HC" >> "$GITHUB_ENV"
+          echo "GHCJSARITH=0" >> "$GITHUB_ENV"
         env:
           HCKIND: ${{ matrix.compilerKind }}
           HCNAME: ${{ matrix.compiler }}
@@ -194,7 +159,6 @@ jobs:
                         26021a13b401500c8eb2761ca95c61f2d625bfef951b939a8124ed12ecf07329
                         f76d08be13e9a61a377a85e2fb63f4c5435d40f8feb3e12eb05905edb8cdea89
              key-threshold: 3
-          active-repositories: hackage.haskell.org, head.hackage.ghc.haskell.org:override
           EOF
           fi
           cat >> $CABAL_CONFIG <<EOF
@@ -207,8 +171,6 @@ jobs:
           $HC --version || true
           $HC --print-project-git-commit-id || true
           $CABAL --version || true
-          if [ $((GHCJSARITH)) -ne 0 ] ; then node --version ; fi
-          if [ $((GHCJSARITH)) -ne 0 ] ; then echo $GHCJS ; fi
       - name: update cabal index
         run: |
           $CABAL v2-update -v
@@ -222,15 +184,15 @@ jobs:
           chmod a+x $HOME/.cabal/bin/cabal-plan
           cabal-plan --version
       - name: checkout
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
         with:
           path: source
       - name: initial cabal.project for sdist
         run: |
           touch cabal.project
           echo "packages: $GITHUB_WORKSPACE/source/./singletons" >> cabal.project
-          if [ $((! GHCJSARITH && HCNUMVER >= 90800)) -ne 0 ] ; then echo "packages: $GITHUB_WORKSPACE/source/./singletons-th" >> cabal.project ; fi
-          if [ $((! GHCJSARITH && HCNUMVER >= 90800)) -ne 0 ] ; then echo "packages: $GITHUB_WORKSPACE/source/./singletons-base" >> cabal.project ; fi
+          if [ $((HCNUMVER >= 91000)) -ne 0 ] ; then echo "packages: $GITHUB_WORKSPACE/source/./singletons-th" >> cabal.project ; fi
+          if [ $((HCNUMVER >= 91000)) -ne 0 ] ; then echo "packages: $GITHUB_WORKSPACE/source/./singletons-base" >> cabal.project ; fi
           cat cabal.project
       - name: sdist
         run: |
@@ -252,14 +214,14 @@ jobs:
           touch cabal.project
           touch cabal.project.local
           echo "packages: ${PKGDIR_singletons}" >> cabal.project
-          if [ $((! GHCJSARITH && HCNUMVER >= 90800)) -ne 0 ] ; then echo "packages: ${PKGDIR_singletons_th}" >> cabal.project ; fi
-          if [ $((! GHCJSARITH && HCNUMVER >= 90800)) -ne 0 ] ; then echo "packages: ${PKGDIR_singletons_base}" >> cabal.project ; fi
-          if [ $((GHCJSARITH || ! GHCJSARITH && HCNUMVER >= 80200)) -ne 0 ] ; then echo "package singletons" >> cabal.project ; fi
-          if [ $((GHCJSARITH || ! GHCJSARITH && HCNUMVER >= 80200)) -ne 0 ] ; then echo "    ghc-options: -Werror=missing-methods" >> cabal.project ; fi
-          if [ $((! GHCJSARITH && HCNUMVER >= 90800)) -ne 0 ] ; then echo "package singletons-th" >> cabal.project ; fi
-          if [ $((! GHCJSARITH && HCNUMVER >= 90800)) -ne 0 ] ; then echo "    ghc-options: -Werror=missing-methods" >> cabal.project ; fi
-          if [ $((! GHCJSARITH && HCNUMVER >= 90800)) -ne 0 ] ; then echo "package singletons-base" >> cabal.project ; fi
-          if [ $((! GHCJSARITH && HCNUMVER >= 90800)) -ne 0 ] ; then echo "    ghc-options: -Werror=missing-methods" >> cabal.project ; fi
+          if [ $((HCNUMVER >= 91000)) -ne 0 ] ; then echo "packages: ${PKGDIR_singletons_th}" >> cabal.project ; fi
+          if [ $((HCNUMVER >= 91000)) -ne 0 ] ; then echo "packages: ${PKGDIR_singletons_base}" >> cabal.project ; fi
+          if [ $((HCNUMVER >= 80200)) -ne 0 ] ; then echo "package singletons" >> cabal.project ; fi
+          if [ $((HCNUMVER >= 80200)) -ne 0 ] ; then echo "    ghc-options: -Werror=missing-methods" >> cabal.project ; fi
+          if [ $((HCNUMVER >= 91000)) -ne 0 ] ; then echo "package singletons-th" >> cabal.project ; fi
+          if [ $((HCNUMVER >= 91000)) -ne 0 ] ; then echo "    ghc-options: -Werror=missing-methods" >> cabal.project ; fi
+          if [ $((HCNUMVER >= 91000)) -ne 0 ] ; then echo "package singletons-base" >> cabal.project ; fi
+          if [ $((HCNUMVER >= 91000)) -ne 0 ] ; then echo "    ghc-options: -Werror=missing-methods" >> cabal.project ; fi
           cat >> cabal.project <<EOF
           source-repository-package
             type:     git
@@ -277,7 +239,7 @@ jobs:
           $CABAL v2-build $ARG_COMPILER $ARG_TESTS $ARG_BENCH --dry-run all
           cabal-plan
       - name: restore cache
-        uses: actions/cache/restore@v3
+        uses: actions/cache/restore@v4
         with:
           key: ${{ runner.os }}-${{ matrix.compiler }}-${{ github.sha }}
           path: ~/.cabal/store
@@ -291,20 +253,20 @@ jobs:
           $CABAL v2-build $ARG_COMPILER $ARG_TESTS $ARG_BENCH all --write-ghc-environment-files=always
       - name: tests
         run: |
-          if [ $((! GHCJSARITH)) -ne 0 ] ; then $CABAL v2-test $ARG_COMPILER $ARG_TESTS $ARG_BENCH all --test-show-details=direct ; fi
+          $CABAL v2-test $ARG_COMPILER $ARG_TESTS $ARG_BENCH all --test-show-details=direct
       - name: cabal check
         run: |
           cd ${PKGDIR_singletons} || false
           ${CABAL} -vnormal check
-          if [ $((! GHCJSARITH && HCNUMVER >= 90800)) -ne 0 ] ; then cd ${PKGDIR_singletons_th} || false ; fi
-          if [ $((! GHCJSARITH && HCNUMVER >= 90800)) -ne 0 ] ; then ${CABAL} -vnormal check ; fi
-          if [ $((! GHCJSARITH && HCNUMVER >= 90800)) -ne 0 ] ; then cd ${PKGDIR_singletons_base} || false ; fi
-          if [ $((! GHCJSARITH && HCNUMVER >= 90800)) -ne 0 ] ; then ${CABAL} -vnormal check ; fi
+          if [ $((HCNUMVER >= 91000)) -ne 0 ] ; then cd ${PKGDIR_singletons_th} || false ; fi
+          if [ $((HCNUMVER >= 91000)) -ne 0 ] ; then ${CABAL} -vnormal check ; fi
+          if [ $((HCNUMVER >= 91000)) -ne 0 ] ; then cd ${PKGDIR_singletons_base} || false ; fi
+          if [ $((HCNUMVER >= 91000)) -ne 0 ] ; then ${CABAL} -vnormal check ; fi
       - name: haddock
         run: |
-          if [ $((! GHCJSARITH)) -ne 0 ] ; then $CABAL v2-haddock --disable-documentation $ARG_COMPILER --with-haddock $HADDOCK $ARG_TESTS $ARG_BENCH all ; fi
+          $CABAL v2-haddock --disable-documentation $ARG_COMPILER --with-haddock $HADDOCK $ARG_TESTS $ARG_BENCH all
       - name: save cache
-        uses: actions/cache/save@v3
+        uses: actions/cache/save@v4
         if: always()
         with:
           key: ${{ runner.os }}-${{ matrix.compiler }}-${{ github.sha }}

README.md

@@ -56,16 +56,14 @@ Compatibility
 windows for requirements on the compiler version needed to build each library:
 
 * `singletons` is a minimal library, and as such, it has a relatively
-   wide support window. `singletons` must be built with one of the following
-   compilers:
-
-   * GHC 8.0 or greater
-   * GHCJS
+   wide support window. `singletons` must be built with GHC 8.0 or later.
+   `singletons` aims to support cross-compilers as well (e.g., GHC's JavaScript
+   backend).
 * `singletons-th` and `singletons-base` require use of many bleeding-edge
   GHC language extensions, even more so than `singletons` itself. As such, it
   is difficult to maintain support for multiple GHC versions in any given
   release of either library, so they only support the latest major GHC version
-  (currently GHC 9.8).
+  (currently GHC 9.10).
 
 Any code that uses the singleton-generation functionality from `singletons-th`
 or `singletons-base` needs to enable a long list of GHC extensions. This list
@@ -850,6 +848,7 @@ The following constructs are partially supported:
 * type families
 * `TypeApplications`
 * wildcard types
+* inferred type variable binders
 
 See the following sections for more details.
 
@@ -1229,6 +1228,72 @@ any other context. Ultimately, this is due to a GHC restriction, as GHC itself
 will forbid using wildcards in most kind-level contexts. For example, GHC will
 permit `f :: _` but reject `type F :: _`.
 
+## Inferred type variable binders
+
+`singletons-th` supports promoting inferred type variable binders in most
+circumstances. For example, `singletons-th` can promote this definition:
+
+```hs
+konst :: forall a {b}. a -> b -> a
+konst x _ = x
+```
+
+To this type family:
+
+```hs
+type Konst :: forall a {b}. a -> b -> a
+type family Konst @a x y where
+  Konst @a (x :: a) (_ :: b) = x
+```
+
+There is one (somewhat obscure) corner case that `singletons-th` cannot handle,
+which requires both of the following criteria to be met:
+
+* A definition must not have any visible arguments.
+* A definition must have an inferred type variable binder as the last type
+  variable in an outermost `forall`.
+
+For instance, `singletons-th` cannot promote this definition:
+
+```hs
+bad :: forall {a}. Either a Bool
+bad = Right True
+```
+
+This is because `singletons-th` will attempt to generate this type family:
+
+```hs
+type Bad :: forall {a}. Either a Bool
+type family Bad where
+  Bad = Right True
+```
+
+GHC will not kind-check `Bad`, however. GHC will kind-check the standalone kind
+signature and conclude that `Bad` has arity 0, i.e., that it does not bind any
+arguments (visible or invisible). However, the definition of `Bad` requires an
+arity of 1, as it implicitly binds an argument:
+
+```hs
+Bad @{a} = Right @{a} @Bool True
+```
+
+In order to make this kind-check, we would need to be able to generate something
+like this:
+
+```hs
+type Bad :: forall {a}. Either a Bool
+type family Bad @{a} where
+  Bad = Right True
+```
+
+However, GHC does not allow users to things like `@{a}`, and this is by design.
+(See [this
+part](https://github.com/ghc-proposals/ghc-proposals/blob/10290a668608d608c3f6c6010be265cf7a02e1fc/proposals/0425-decl-invis-binders.rst#alternatives)
+of the relevant GHC proposal about invisible binders in type declarations.) As
+such, there is no way for `singletons-th` to promote this definition exactly as
+written. As a workaround, you can change the `forall {a}` to `forall a`, or you
+can remove the standalone kind signature.
+
 ## Support for promotion, but not singling
 
 The following constructs are supported for promotion but not singleton generation:

cabal.haskell-ci

@@ -1,8 +1,9 @@
-distribution:           bionic
+distribution:           jammy
 no-tests-no-benchmarks: False
 unconstrained:          False
 jobs-selection:         any
 -- Needed to avoid https://github.com/haskell/cabal/issues/5423
 haddock-components:     libs
--- Temporarily use head.hackage for GHC 9.8 until the ecosystem catches up
-head-hackage:           >= 9.8
+-- Using `active-repositories: ..., head.hackage.ghc.haskell.org:override`
+-- tends not to work well with singletons-base's custom Setup script.
+head-hackage-override:  False

singletons-base/CHANGES.md

@@ -1,6 +1,10 @@
 Changelog for the `singletons-base` project
 ===========================================
 
+3.4 [????.??.??]
+----------------
+* Require building with GHC 9.10.
+
 3.3 [2023.10.13]
 ----------------
 * Require building with GHC 9.8.