Flakify the development shell

.github/workflows/ci.yaml

@@ -24,26 +24,26 @@ jobs:
           ~/.cabal/packages
           ~/.cabal/store
           dist-newstyle
-        key: cabal-deps-${{ runner.os }}-${{ hashFiles('nix/sources.json') }}-${{ matrix.ghc-version }}-v${{ env.cache-invalidation-key }}-${{ hashFiles('linear-base.cabal') }}-${{ github.sha }}
-        restore-keys: cabal-deps-${{ runner.os }}-${{ hashFiles('nix/sources.json') }}-${{ matrix.ghc-version }}-v${{ env.cache-invalidation-key }}-${{ hashFiles('linear-base.cabal') }}-
+        key: cabal-deps-${{ runner.os }}-${{ hashFiles('flake.lock') }}-${{ matrix.ghc-version }}-v${{ env.cache-invalidation-key }}-${{ hashFiles('linear-base.cabal') }}-${{ github.sha }}
+        restore-keys: cabal-deps-${{ runner.os }}-${{ hashFiles('flake.lock') }}-${{ matrix.ghc-version }}-v${{ env.cache-invalidation-key }}-${{ hashFiles('linear-base.cabal') }}-
     - name: Build Nix dependencies
-      run: nix-shell --arg ghcVersion '"${{ matrix.ghc-version }}"' --arg installHls 'false' --pure --run "echo '=== Nix dependencies installed ==='"
+      run: nix develop .#devShells.x86_64-linux.ci-"${{ matrix.ghc-version }}" --command echo '=== Nix dependencies installed ==='
     - name: Init Cabal's config file
-      run: nix-shell --arg ghcVersion '"${{ matrix.ghc-version }}"' --arg installHls 'false' --pure --run "cabal --config-file=/home/runner/.cabal/config user-config -f init"
+      run: nix develop .#devShells.x86_64-linux.ci-"${{ matrix.ghc-version }}" --command cabal --config-file=/home/runner/.cabal/config user-config -f init
     - name: Update Cabal's database
-      run: nix-shell --arg ghcVersion '"${{ matrix.ghc-version }}"' --arg installHls 'false' --pure --run "cabal update"
+      run: nix develop .#devShells.x86_64-linux.ci-"${{ matrix.ghc-version }}" --command cabal update
     - name: Build Cabal's dependencies
-      run: nix-shell --arg ghcVersion '"${{ matrix.ghc-version }}"' --arg installHls 'false' --pure --run "cabal build --dependencies-only"
+      run: nix develop .#devShells.x86_64-linux.ci-"${{ matrix.ghc-version }}" --command cabal build --dependencies-only
     - name: Build
-      run: nix-shell --arg ghcVersion '"${{ matrix.ghc-version }}"' --arg installHls 'false' --pure --run "cabal build"
+      run: nix develop .#devShells.x86_64-linux.ci-"${{ matrix.ghc-version }}" --command cabal build
     - name: Haddock
-      run: nix-shell --arg ghcVersion '"${{ matrix.ghc-version }}"' --arg installHls 'false' --pure --run "cabal haddock"
+      run: nix develop .#devShells.x86_64-linux.ci-"${{ matrix.ghc-version }}" --command cabal haddock
     - name: cabal-docspec
-      run: nix-shell --arg ghcVersion '"${{ matrix.ghc-version }}"' --arg installHls 'false' --pure --run "cabal-docspec"
+      run: nix develop .#devShells.x86_64-linux.ci-"${{ matrix.ghc-version }}" --command cabal-docspec
     - name: Build benchmarks
-      run: nix-shell --arg ghcVersion '"${{ matrix.ghc-version }}"' --arg installHls 'false' --pure --run "cabal build linear-base:bench:bench"
+      run: nix develop .#devShells.x86_64-linux.ci-"${{ matrix.ghc-version }}" --command cabal build linear-base:bench:bench
     - name: Run benchmarks
-      run: nix-shell --arg ghcVersion '"${{ matrix.ghc-version }}"' --arg installHls 'false' --pure --run "cabal bench 2>&1 | tee benchmark_ghc${{ matrix.ghc-version }}.txt"
+      run: nix develop .#devShells.x86_64-linux.ci-"${{ matrix.ghc-version }}" --command cabal bench 2>&1 | tee benchmark_ghc${{ matrix.ghc-version }}.txt
     - name: Upload benchmark results
       uses: actions/upload-artifact@v4
       with:
@@ -60,16 +60,10 @@ jobs:
     - uses: cachix/install-nix-action@v15
       with:
         nix_path: "${{ env.nixpkgs-url }}"
-    - name: Cache Stack dependencies
-      uses: actions/cache@v4
-      with:
-        path: ~/.stack
-        key: stack-deps-ormolu-${{ runner.os }}-${{ hashFiles('nix/sources.json') }}-v${{ env.cache-invalidation-key }}-${{ hashFiles('stack.yaml.lock') }}-${{ github.sha }}
-        restore-keys: stack-deps-ormolu-${{ runner.os }}-${{ hashFiles('nix/sources.json') }}-v${{ env.cache-invalidation-key }}-${{ hashFiles('stack.yaml.lock') }}-
     - name: Build Nix dependencies
-      run: nix-shell --arg installHls 'false' --pure --run "echo '=== Nix dependencies installed ==='"
+      run: nix develop .#devShells.x86_64-linux.ci-stack --command echo '=== Nix dependencies installed ==='
     - name: check formatting
-      run: nix-shell --arg installHls 'false' --pure --run 'stack build ormolu && stack exec ormolu -- -m check $(find . -type f -name "*.hs-boot" -o -name "*.hs")'
+      run: nix develop .#devShells.x86_64-linux.ci-stack --command ormolu -m check $(find . -type f -name "*.hs-boot" -o -name "*.hs")
 
   stack-build:
     name: stack build
@@ -83,9 +77,9 @@ jobs:
       uses: actions/cache@v4
       with:
         path: ~/.stack
-        key: stack-deps-${{ runner.os }}-${{ hashFiles('nix/sources.json') }}-v${{ env.cache-invalidation-key }}-${{ hashFiles('stack.yaml.lock', 'linear-base.cabal') }}-${{ github.sha }}
-        restore-keys: stack-deps-${{ runner.os }}-${{ hashFiles('nix/sources.json') }}-v${{ env.cache-invalidation-key }}-${{ hashFiles('stack.yaml.lock', 'linear-base.cabal') }}-
+        key: stack-deps-${{ runner.os }}-${{ hashFiles('flake.lock') }}-v${{ env.cache-invalidation-key }}-${{ hashFiles('stack.yaml.lock', 'linear-base.cabal') }}-${{ github.sha }}
+        restore-keys: stack-deps-${{ runner.os }}-${{ hashFiles('flake.lock') }}-v${{ env.cache-invalidation-key }}-${{ hashFiles('stack.yaml.lock', 'linear-base.cabal') }}-
     - name: Build Nix dependencies
-      run: nix-shell --arg installHls 'false' --pure --run "echo '=== Nix dependencies installed ==='"
+      run: nix develop .#devShells.x86_64-linux.ci-stack --command echo '=== Nix dependencies installed ==='
     - name: Build
-      run: nix-shell --arg installHls 'false' --pure --run "stack build --pedantic --test --bench --no-run-benchmarks"
+      run: nix develop .#devShells.x86_64-linux.ci-stack --command stack build --pedantic --test --bench --no-run-benchmarks

bench/Data/Mutable/HashMap.hs

@@ -22,7 +22,7 @@ import qualified Data.HashMap.Strict as Map
 import qualified Data.HashTable.ST.Basic as BasicST
 import qualified Data.HashTable.ST.Cuckoo as CuckooST
 import Data.Hashable (Hashable (..), hashWithSalt)
-import Data.List (foldl')
+import qualified Data.List as List
 import qualified Data.Unrestricted.Linear as Linear
 import GHC.Generics (Generic)
 import qualified Prelude.Linear as Linear
@@ -199,7 +199,7 @@ vanilla_hashmap_strict inp@(BenchInput {pairs = kvs}) =
       bench (descriptions !! n) $ nf (\xs -> f xs Map.empty) kvs
 
     foldlx :: (b -> a -> b) -> [a] -> b -> b
-    foldlx f xs b = foldl' f b xs
+    foldlx f xs b = List.foldl' f b xs
 
     look :: Map.HashMap Key Int -> Key -> Map.HashMap Key Int
     look m k = case m Map.!? k of
@@ -208,7 +208,7 @@ vanilla_hashmap_strict inp@(BenchInput {pairs = kvs}) =
 
     bench1 :: Benchmark
     bench1 = mkBench 0 $
-      \xs hm -> foldl' (\m (k, v) -> Map.delete k (Map.insert k v m)) hm xs
+      \xs hm -> List.foldl' (\m (k, v) -> Map.delete k (Map.insert k v m)) hm xs
 
     bench2 :: Benchmark
     bench2 = mkBench 1 $

cabal.project

@@ -3,4 +3,4 @@ packages: *.cabal
 tests: True
 benchmarks: True
 allow-newer: all
-index-state: 2024-09-13T13:31:57Z
+index-state: 2026-05-12T09:26:21Z

flake.nix

@@ -0,0 +1,86 @@
+{
+  description = "Linear-base";
+
+  inputs.nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
+  inputs.flake-utils.url = "github:numtide/flake-utils";
+
+  outputs = { self, nixpkgs, flake-utils }:
+    flake-utils.lib.eachDefaultSystem (system:
+      let
+        pkgs = import nixpkgs { inherit system; inherit overlays; };
+
+        # need to match Stackage LTS version from stack.yaml snapshot
+        stack-ghc-version = "ghc9103";
+
+        # Versions used by CI's Cabal-based matrix
+        ci-ghc-versions = ["96" "98" "910" "912"];
+
+        cabal-docspec = import ./nix/cabal-docspec.nix { inherit pkgs; };
+
+        buildTools = ghc-ver:
+          let hask = pkgs.haskell.packages."${ghc-ver}"; in
+          [
+            hask.ghc
+            pkgs.cabal-install
+            stack-wrapped
+            cabal-docspec
+            pkgs.ormolu # Haskell formatter
+          ];
+
+        devTools = ghc-ver:
+          let hask = pkgs.haskell.packages."${ghc-ver}"; in
+          [
+            hask.ghcid # Continuous terminal Haskell compile checker
+            hask.haskell-language-server # LSP server for editor
+          ];
+
+        mkCIShellFor = ghc-ver: pkgs.mkShell {
+          # Set UTF-8 local so that run-tests can parse GHC's unicode output.
+          LANG="C.UTF-8";
+
+          buildInputs = buildTools "${ghc-ver}";
+        };
+
+        ci-shells = builtins.listToAttrs (map (ver:
+          { name = "ci-${ver}"; value = mkCIShellFor "ghc${ver}"; }
+          ) ci-ghc-versions);
+
+        mkDevShellFor = ghc-ver: pkgs.mkShell {
+          # Set UTF-8 local so that run-tests can parse GHC's unicode output.
+          LANG="C.UTF-8";
+
+          buildInputs = buildTools "${ghc-ver}" ++ devTools "${ghc-ver}";
+
+        };
+
+        cabal-dev-shells = builtins.listToAttrs (map (ver:
+          { name = "dev-${ver}"; value = mkDevShellFor "ghc${ver}"; }
+          ) ci-ghc-versions);
+
+        # See https://docs.haskellstack.org/en/stable/topics/nix_integration/
+        stack-wrapped = pkgs.symlinkJoin {
+          name = "stack"; # will be available as the usual `stack` in terminal
+          paths = [ pkgs.stack ];
+          buildInputs = [ pkgs.makeWrapper ];
+          postBuild = ''
+            wrapProgram $out/bin/stack \
+              --add-flags "\
+                --no-nix \
+                --system-ghc \
+                --no-install-ghc \
+              "
+          '';
+        };
+
+        overlays = [
+        ];
+
+      in {
+
+        devShells = ci-shells // cabal-dev-shells // {
+          default = mkDevShellFor stack-ghc-version;
+
+          ci-stack = mkCIShellFor stack-ghc-version;};
+      }
+    );
+}

format.sh

@@ -1,14 +1,10 @@
 #!/usr/bin/env bash
-# Format linear-base using the version of Ormolu specified in stack.yaml.
+# Format linear-base using the version of Ormolu from the PATH. It's recommended
+# using the version provided by `flake.nix`, since it's the one used by the CI
+# to enforce formatting.
 
 set -e
 
 export LANG="C.UTF-8"
 
-stack build ormolu
-## We can't format cabal at the moment because `cabal format` inlines
-## common stanzas, which is very much something that we don't want. See
-## https://github.com/haskell/cabal/issues/5734
-#
-# cabal format
-stack exec ormolu -- -m inplace $(find . -type f -name "*.hs-boot" -o -name "*.hs")
+ormolu -m inplace $(find . -type f -name "*.hs-boot" -o -name "*.hs")