From ed94388c2e622f28cb45108a4e73c9d2b2a796da Mon Sep 17 00:00:00 2001
From: Sridhar Ratnakumar <3998+srid@users.noreply.github.com>
Date: Mon, 2 Sep 2024 18:08:10 -0400
Subject: [PATCH] Add `meta.description` to flake apps (#356)

---
 CHANGELOG.md                    |  5 +++++
 nix/modules/project/outputs.nix | 15 +++++++++------
 nix/types/app-type.nix          | 11 +++++++++++
 3 files changed, 25 insertions(+), 6 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index e1036a51..be1701f6 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,10 @@
 # Revision history for haskell-flake
 
+## Unreleased
+
+- Enhancements
+  - Support `meta.description` in flake apps. Requires newer version of flake-parts.
+
 ## 0.5.0 (Jun 24, 2024)
 
 - Breaking changes
diff --git a/nix/modules/project/outputs.nix b/nix/modules/project/outputs.nix
index a489d186..16c70419 100644
--- a/nix/modules/project/outputs.nix
+++ b/nix/modules/project/outputs.nix
@@ -54,7 +54,7 @@ let
       exes = mkOption {
         type = types.lazyAttrsOf appType;
         description = ''
-          Attrset of executables from `.cabal` file.  
+          Attrset of executables from `.cabal` file.
 
           If the associated Haskell project has a separate bin output
           (cf. `enableSeparateBinOutput`), then this exe will refer
@@ -90,15 +90,19 @@ in
 
       finalPackages = config.basePackages.extend finalOverlay;
 
-      buildPackageInfo = name: value: {
+      buildPackageInfo = name: value: rec {
         package = finalPackages.${name};
         exes =
           lib.listToAttrs
             (map
               (exe:
-                lib.nameValuePair exe {
-                  program = "${lib.getBin finalPackages.${name}}/bin/${exe}";
-                }
+                lib.nameValuePair exe ({
+                  program = "${lib.getBin package}/bin/${exe}";
+                  meta.description =
+                    if lib.hasAttrByPath [ "meta" "description" ] package
+                    then "${if exe != name then "[${exe}] " else ""}${package.meta.description}"
+                    else "Executable ${if exe != name then "${exe} from " else "for "}package ${name}";
+                })
               )
               value.cabal.executables
             );
@@ -122,4 +126,3 @@ in
       };
     };
 }
-
diff --git a/nix/types/app-type.nix b/nix/types/app-type.nix
index b1ebcdd3..3a4b70db 100644
--- a/nix/types/app-type.nix
+++ b/nix/types/app-type.nix
@@ -24,6 +24,17 @@ let
           A path to an executable or a derivation with `meta.mainProgram`.
         '';
       };
+      meta = lib.mkOption {
+        type = lib.types.lazyAttrsOf lib.types.raw;
+        default = { };
+        # TODO refer to Nix manual 2.25
+        description = ''
+          Metadata information about the app.
+          Standardized in Nix at <https://github.com/NixOS/nix/pull/11297>.
+
+          Note: `nix flake check` is only aware of the `description` attribute in `meta`.
+        '';
+      };
     };
   };
 in