sellout · sellout · Feb 10, 2026 · Feb 10, 2026 · Feb 2, 2026
diff --git a/flake.lock b/flake.lock
diff --git a/templates/haskell/.config/flake/outputs.nix b/templates/haskell/.config/flake/outputs.nix
@@ -102,15 +102,17 @@ in
       ## one via GitHub workflow. Additionally, check any revisions that have
       ## explicit conditionalization. And check whatever version `pkgs.ghc`
       ## maps to in the nixpkgs we depend on.
-      testedGhcVersions = system: [
-        self.lib.defaultGhcVersion
-        "9.4.8"
-        "9.6.7"
-        "9.8.4"
-        "9.10.2"
-        "9.12.2"
-        # "ghcHEAD" # doctest doesn’t work on current HEAD
-      ];
+      testedGhcVersions = system:
+        [
+          self.lib.defaultGhcVersion
+          "9.4.8"
+          "9.6.7"
+          "9.8.4"
+          "9.10.2"
+        ]
+        ++ nixpkgs.lib.optionals (system != "i686-linux") [
+          "9.12.2" # GHC fails to build on i686-linux
+        ];
 
       ## The versions that are older than those supported by Nix that we
       ## prefer to test against.
@@ -170,7 +172,12 @@ in
         [self.projectConfigurations.${system}.packages.path]
         ## NB: Haskell Language Server no longer supports GHC <9.6.
         ++ nixpkgs.lib.optional
-        (nixpkgs.lib.versionAtLeast hpkgs.ghc.version "9.6")
+        (nixpkgs.lib.versionAtLeast hpkgs.ghc.version "9.6"
+          ## TODO: With Nixpkgs 25.11, HLS complains about conflicting package
+          ##       versions in these combinations, so skip it.
+          && !(pkgs.stdenv.hostPlatform.isLinux
+            && nixpkgs.lib.versionAtLeast hpkgs.ghc.version "9.8"
+            && nixpkgs.lib.versionOlder hpkgs.ghc.version "9.10"))
         hpkgs.haskell-language-server);
 
     projectConfigurations =

diff --git a/templates/haskell/.config/project/default.nix b/templates/haskell/.config/project/default.nix
@@ -35,16 +35,39 @@
         "check-licenses"
       ]
       ++ lib.concatMap (sys:
-        lib.concatMap (ghc: [
-          "build (${ghc}, ${sys})"
-          "build (--prefer-oldest, ${ghc}, ${sys})"
-        ])
+        lib.concatMap (ghc:
+          ## Don’t add `exclude`d matrix entries to the required list
+          ##
+          ## TODO: Make this less manual (like the `include` component).
+            if
+              ## GHC before 8.4 needs an older Ubuntu
+              lib.versionOlder ghc "8.4"
+              && sys == "ubuntu-24.04"
+              ## GHC doesn’t support ARM before GHC 9.2.
+              || lib.versionOlder ghc "9.2"
+              && builtins.elem sys ["macos-15" "ubuntu-24.04-arm"]
+              ## GHC 9.2.1 relied on libnuma at runtime for aarch64
+              || ghc == "9.2.1" && sys == "ubuntu-24.04-arm"
+            then []
+            else [
+              "build (${ghc}, ${sys})"
+              "build (--prefer-oldest, ${ghc}, ${sys})"
+            ])
         self.lib.nonNixTestedGhcVersions)
-      config.services.haskell-ci.systems);
+      config.services.haskell-ci.systems
+      ## Add `include`d matrix entries to the required list.
+      ++ map (
+        entry:
+          if entry.bounds == ""
+          then "build (${entry.ghc}, ${entry.os})"
+          else "build (${entry.bounds}, ${entry.ghc}, ${entry.os})"
+      )
+      config.services.haskell-ci.include);
   services.haskell-ci = {
     inherit (self.lib) defaultGhcVersion;
     ghcVersions = self.lib.nonNixTestedGhcVersions;
     cabalPackages = {"${config.project.name}" = "core";};
+    ## The latest Stackage LTS that we also build on GitHub for.
     latestGhcVersion = "9.10.1";
   };
 

diff --git a/templates/haskell/.config/project/hlint.nix b/templates/haskell/.config/project/hlint.nix
@@ -27,11 +27,19 @@
       };
     }
 
-    {ignore = {name = "Eta reduce";};}
-    {ignore = {name = "Evaluate";};}
-    {ignore = {name = "Reduce duplication";};}
-    {ignore = {name = "Use list comprehension";};}
-    {ignore = {name = "Use section";};}
+    {
+      ignore.name = [
+        ## This can be removed once we no longer support ≤ base 4.18, which
+        ## doesn’t yet export `Data.Functor.unzip`.
+        "Avoid NonEmpty.unzip"
+        ## This complains when we use a common import and then import from the
+        ## same module under a CPP conditional. Since Ormolu handles combinig
+        ## imports when possible anyway, this warning isn’t helpful.
+        "Use fewer imports"
+        ## I just don’t like them (even the monadic variant).
+        "Use list comprehension"
+      ];
+    }
 
     {
       package = {

diff --git a/templates/haskell/core/CHANGELOG.md b/templates/haskell/core/CHANGELOG.md
@@ -11,4 +11,6 @@ and this project adheres to the [Haskell Package Versioning Policy](https://pvp.
 
 - initial release of this package
 
-[0.0.1.0]: https://github.com/{{project.repo}}/releases/tag/v0.0.1.0
+<!-- NB: The version on the left is the Haskell package version (PVP), the version on the right is the repo (tag) version (SemVer). Their only relationship is that a change of any severity on the left implies a change of at least that severity on the right. -->
+
+[0.0.1.0]: https://github.com/{{project.repo}}/releases/tag/v0.1.0
diff --git a/templates/haskell/core/README.md b/templates/haskell/core/README.md
@@ -1,6 +1,6 @@
 # {{project.name}}
 
-[![Hackage Version](https://img.shields.io/hackage/v/{{project.name}})](https://hackage.haskell.org/package/{{project-name}})
+[![Hackage Version](https://img.shields.io/hackage/v/{{project.name}})](https://hackage.haskell.org/package/{{project.name}})
 [![Packaging status](https://repology.org/badge/tiny-repos/haskell:{{project.name}}.svg)](https://repology.org/project/haskell:{{project.name}}/versions)
 [![latest packaged versions](https://repology.org/badge/latest-versions/haskell:{{project.name}}.svg)](https://repology.org/project/haskell:{{project.name}}/versions)
 

diff --git a/templates/haskell/core/{{project.name}}.cabal b/templates/haskell/core/{{project.name}}.cabal
@@ -44,11 +44,19 @@ tested-with:
 
 homepage: https://github.com/{{project.repo}}#readme
 bug-reports: https://github.com/{{project.repo}}/issues
+
 source-repository head
   type: git
   location: https://github.com/{{project.repo}}.git
   subdir: core
 
+source-repository this
+  type: git
+  location: https://github.com/{{project.repo}}.git
+  subdir: core
+  -- NB: This is the repo version, which is distinct from the package version.
+  tag: v0.1.0
+
 custom-setup
   setup-depends:
     -- TODO: Due to haskell/cabal#3751, `Cabal` has to be specified even though
@@ -139,7 +147,11 @@ common defaults
   import: GHC2024
   build-depends:
     base ^>= {4.8.2, 4.9.0, 4.10.0, 4.11.0, 4.12.0, 4.13.0, 4.14.0, 4.15.0, 4.16.0, 4.17.0, 4.18.0, 4.19.0, 4.20.0, 4.21.0},
+    ghc-compat-plugin ^>= {0.1.0},
   ghc-options:
+    -fplugin GhcCompat
+    -fplugin-opt GhcCompat:minVersion=7.10.3
+    -fplugin-opt GhcCompat:reportIncompatibleExtensions=error
   if impl(ghc >= 8.0.1)
     ghc-options:
       -Weverything
@@ -157,20 +169,14 @@ common defaults
   else
     ghc-options:
       -Wall
-  -- remove if the oldest supported version is GHC 8.10.1+
-  if impl(ghc >= 8.10.1)
-    ghc-options:
-      -Wno-prepositive-qualified-module
-  -- remove if the oldest supported version is GHC 9.2.1+
-  if impl(ghc >= 9.2.1)
+  if impl(ghc >= 8.6.1)
     ghc-options:
-      -Wno-missing-kind-signatures
-  if impl(ghc >= 9.8.1)
+      -- remove if oldest supported version is GHC 8.6.1
+      -Wno-star-is-type
+  if impl(ghc >= 8.8.1)
     ghc-options:
-      -- remove if the oldest supported version is GHC 9.2.1+
-      -Wno-missing-poly-kind-signatures
-      -- Inference good.
-      -Wno-missing-role-annotations
+      -- remove if oldest supported version is GHC 8.2.1
+      -Wno-missing-deriving-strategies
   default-extensions:
     -- BlockArguments - uncomment if the oldest supported version is GHC 8.6.1+
     DefaultSignatures