From ab54d6e45044ebabcfb0d6e77173229b050ce5e7 Mon Sep 17 00:00:00 2001
From: Sergey Gulin <sergeygulin96@gmail.com>
Date: Mon, 29 Jan 2024 02:22:13 +0300
Subject: [PATCH] [Chore] Add weeder check

Problem: We want to be able to check our Haskell applications for dead
code. This can be done using weeder.

Solution: Use weeder check from serokell.nix.
---
 haskell.nix/README.md                               | 4 +++-
 haskell.nix/application/.github/workflows/check.yml | 4 ++++
 haskell.nix/application/.gitlab-ci.yml              | 5 +++++
 haskell.nix/application/flake.nix                   | 8 ++++++++
 haskell.nix/application/weeder.toml                 | 1 +
 5 files changed, 21 insertions(+), 1 deletion(-)
 create mode 100644 haskell.nix/application/weeder.toml

diff --git a/haskell.nix/README.md b/haskell.nix/README.md
index bf80568..0c45d65 100644
--- a/haskell.nix/README.md
+++ b/haskell.nix/README.md
@@ -26,7 +26,9 @@ Haskell application and library templates for Buildkite, Gitlab or GitHub CI usi
          - For GitHub, copy `.github/workflows/check-outdated.yml` or `.github/workflows/check-nightly.yml` to your library repository.
          - For Gitlab, configure the schedule in the repository settings and uncomment `check-outdated` and `report-outdated` or `check-nightly` and `report-nightly-failure` in `.gitlab-ci.yml`. For nightly checks, you will also need to enable gitlab hosted runners in the repository settings.
 
-    5. Make sure to clean up your `flake.nix` and pipeline configuration files by removing any optional code that is left commented out.
+    5. You might want to add a [`weeder`](https://github.com/ocharles/weeder/) check to check for dead code in your application. To do this uncomment the related lines in both `flake.nix` (do not forget to uncomment `writeHieFiles = true;`) and pipeline configuration files, then copy `weeder.toml` (for more advanced setup, please refer to the [corresponding section](https://github.com/ocharles/weeder/?tab=readme-ov-file#calling-weederUsually) of the `weeder` README) to your repository. For a library, code is usually considered dead unless it is exported; such cases are already detected by GHC warnings, so no `weeder` is required.
+
+    6. Make sure to clean up your `flake.nix` and pipeline configuration files by removing any optional code that is left commented out.
 
 - Enjoy working CI!
 
diff --git a/haskell.nix/application/.github/workflows/check.yml b/haskell.nix/application/.github/workflows/check.yml
index c5ba080..40f160b 100644
--- a/haskell.nix/application/.github/workflows/check.yml
+++ b/haskell.nix/application/.github/workflows/check.yml
@@ -44,6 +44,10 @@ jobs:
       #   run: nix build -L .#checks.x86_64-linux.hpack
       #   if: success() || failure()
 
+      # - name: check-weeder
+      #   run: nix build -L .#checks.x86_64-linux.weeder
+      #   if: success() || failure()
+
   build:
     runs-on: [self-hosted, nix]
     steps:
diff --git a/haskell.nix/application/.gitlab-ci.yml b/haskell.nix/application/.gitlab-ci.yml
index 29fa8fe..59da321 100644
--- a/haskell.nix/application/.gitlab-ci.yml
+++ b/haskell.nix/application/.gitlab-ci.yml
@@ -47,6 +47,11 @@ check-trailing-whitespace:
 #   script:
 #     - nix build -L .#checks.x86_64-linux.hpack
 
+# check-weeder:
+#   stage: validate
+#   script:
+#     - nix build -L .#checks.x86_64-linux.weeder
+
 # build haskell components
 build-all:
   stage: build
diff --git a/haskell.nix/application/flake.nix b/haskell.nix/application/flake.nix
index 52f7e0f..f00a5e5 100644
--- a/haskell.nix/application/flake.nix
+++ b/haskell.nix/application/flake.nix
@@ -18,6 +18,7 @@
     stackage = {
       flake = false;
     };
+    serokell-nix.inputs.haskell-nix.follows = "haskell-nix";
   };
 
   outputs = { self, nixpkgs, haskell-nix, hackage, stackage, serokell-nix, flake-compat, flake-utils, ... }:
@@ -43,6 +44,8 @@
         # haskell.nix configuration
         modules = [
           (serokell-nix.lib.haskell.optionsLocalPackages {
+            # Uncomment if your project uses weeder check
+            # writeHieFiles = true;
             ghcOptions = [
               # fail on warnings
               "-Werror"
@@ -91,6 +94,11 @@
         # cabal-check = pkgs.build.haskell.cabal-check ./.;
         # Uncomment if your project uses hpack to generate cabal files
         # hpack = pkgs.build.haskell.hpack ./.;
+        # Uncomment to check for dead code
+        # weeder = pkgs.build.haskell.weeder {
+        #   weederToml = ./weeder.toml;
+        #   inherit hs-pkgs;
+        # };
       };
     });
 }
diff --git a/haskell.nix/application/weeder.toml b/haskell.nix/application/weeder.toml
new file mode 100644
index 0000000..ba93bd5
--- /dev/null
+++ b/haskell.nix/application/weeder.toml
@@ -0,0 +1 @@
+roots = [ "^Main.main$", "^Paths_.*" ]