fix(cabal): cabal-fmt and cabal-gild discover module

examples/formatter-cabal-fmt.toml

@@ -1,6 +1,19 @@
 # Example generated by ../examples.sh
 [formatter.cabal-fmt]
-command = "cabal-fmt"
+command = "cabal-fmt-wrapper"
 excludes = []
-includes = ["*.cabal"]
-options = ["--inplace"]
+includes = [
+    "*.cabal",
+    "*.chs",
+    "*.cpphs",
+    "*.gc",
+    "*.hs",
+    "*.hsc",
+    "*.hsig",
+    "*.lhs",
+    "*.lhsig",
+    "*.ly",
+    "*.x",
+    "*.y",
+]
+options = []

examples/formatter-cabal-gild.toml

@@ -2,5 +2,20 @@
 [formatter.cabal-gild]
 command = "cabal-gild-wrapper"
 excludes = []
-includes = ["*.cabal", "cabal.project", "cabal.project.local"]
+includes = [
+    "*.cabal",
+    "cabal.project",
+    "cabal.project.local",
+    "*.chs",
+    "*.cpphs",
+    "*.gc",
+    "*.hs",
+    "*.hsc",
+    "*.hsig",
+    "*.lhs",
+    "*.lhsig",
+    "*.ly",
+    "*.x",
+    "*.y",
+]
 options = []

programs/cabal-fmt.nix

@@ -1,4 +1,13 @@
-{ mkFormatterModule, ... }:
+{
+  lib,
+  config,
+  pkgs,
+  mkFormatterModule,
+  ...
+}:
+let
+  cfg = config.programs.cabal-fmt;
+in
 {
   meta.maintainers = [ ];
 
@@ -9,8 +18,38 @@
         "haskellPackages"
         "cabal-fmt"
       ];
-      args = [ "--inplace" ];
-      includes = [ "*.cabal" ];
+      includes = [
+        "*.cabal"
+        # Include Haskell source files to detect changes
+        # for cabal-fmt's module discovery feature
+        "*.chs"
+        "*.cpphs"
+        "*.gc"
+        "*.hs"
+        "*.hsc"
+        "*.hsig"
+        "*.lhs"
+        "*.lhsig"
+        "*.ly"
+        "*.x"
+        "*.y"
+      ];
     })
   ];
+
+  config = lib.mkIf cfg.enable {
+    settings.formatter.cabal-fmt = {
+      # Override command to filter out non-cabal files
+      command = pkgs.writeShellApplication {
+        name = "cabal-fmt-wrapper";
+        # The cabal file needs to be formatted by a formatter along with other Haskell source code.
+        # For example, module completion by `cabal-fmt: discover`.
+        # It is difficult to determine this strictly.
+        # Since formatting with cabal-fmt doesn't take much time, we execute it speculatively.
+        text = ''${pkgs.git}/bin/git ls-files -z "*.cabal"|${pkgs.parallel}/bin/parallel --null "${lib.getExe cfg.package} --inplace {}"'';
+      };
+      # Clear args since we're handling them in the wrapper
+      options = lib.mkForce [ ];
+    };
+  };
 }

programs/cabal-gild.nix

@@ -1,8 +1,8 @@
 {
-  mkFormatterModule,
   lib,
   config,
   pkgs,
+  mkFormatterModule,
   ...
 }:
 
@@ -23,6 +23,19 @@ in
         "*.cabal"
         "cabal.project"
         "cabal.project.local"
+        # Include Haskell source files to detect changes
+        # for cabal-gild's module discovery feature
+        "*.chs"
+        "*.cpphs"
+        "*.gc"
+        "*.hs"
+        "*.hsc"
+        "*.hsig"
+        "*.lhs"
+        "*.lhsig"
+        "*.ly"
+        "*.x"
+        "*.y"
       ];
     })
   ];
@@ -33,11 +46,11 @@ in
       # https://github.com/tfausak/cabal-gild/issues/35
       command = pkgs.writeShellApplication {
         name = "cabal-gild-wrapper";
-        text = ''
-          for file in "$@"; do
-            ${lib.getExe cfg.package} --io="$file"
-          done
-        '';
+        # The cabal file needs to be formatted by a formatter along with other Haskell source code.
+        # For example, module completion by `cabal-gild: discover`.
+        # It is difficult to determine this strictly.
+        # Since formatting with cabal-gild doesn't take much time, we execute it speculatively.
+        text = ''${pkgs.git}/bin/git ls-files -z "*.cabal"|${pkgs.parallel}/bin/parallel --null "${lib.getExe cfg.package} --io {}"'';
       };
     };
   };