From 360fd2099de0f6ca84d825eff4e5a1541f233fd5 Mon Sep 17 00:00:00 2001
From: Archit Gupta <archit@accelbread.com>
Date: Sun, 25 Feb 2024 18:40:05 -0800
Subject: [PATCH] Allow devShells to be directly set to derivations

---
 API_GUIDE.md                 |  8 ++++----
 builtinModules/devShells.nix |  7 +++++--
 tests/default.nix            | 17 +++++++++++++++--
 3 files changed, 24 insertions(+), 8 deletions(-)

diff --git a/API_GUIDE.md b/API_GUIDE.md
index b6fde0d..ecb9a3b 100644
--- a/API_GUIDE.md
+++ b/API_GUIDE.md
@@ -439,7 +439,7 @@ To use the first example, but manually specify the package name:
 
 ```
 Type:
-  devShell: Cfg | (Pkgs -> Cfg) | PackageDef
+  devShell: Cfg | (Pkgs -> Cfg) | PackageDef | Derivation | (Pkgs -> Derivation)
   Cfg.packages: [Derivation] | (Pkgs -> [Derivation])
   Cfg.inputsFrom: [Derivation] | (Pkgs -> [Derivation])
   Cfg.shellHook: Str | (Pkgs -> Str)
@@ -451,11 +451,11 @@ The devshell options allow you to configure `devShells.${system}.default`. It is
 split up into options in order to enable multiple modules to contribute to its
 configuration.
 
-`devShell` can alternatively be set to a package definition, which is then used
-as the default shell, overriding other options.
+`devShell` can alternatively be set to a package definition or derivation, which
+is then used as the default shell, overriding other options.
 
 `devShell` can also be set to a function that takes the package set and returns
-an attrSet of the devShell configuration options.
+an attrSet of the devShell configuration options or a derivation.
 
 The options available are as follows:
 
diff --git a/builtinModules/devShells.nix b/builtinModules/devShells.nix
index 751e02e..7c07655 100644
--- a/builtinModules/devShells.nix
+++ b/builtinModules/devShells.nix
@@ -47,10 +47,13 @@ let
     let val = pkgs.callPackage fn { }; in
     if (functionArgs fn == { }) || !(package.check val)
     then fn pkgs
-    else { overrideShell = val; };
+    else val;
+
+  packageOverride = p: { overrideShell = p; };
 
   devShellType = coercedTo function wrapFn
-    (optFunctionTo (submodule devShellModule));
+    (optFunctionTo (coercedTo package packageOverride
+      (submodule devShellModule)));
 
   genDevShell = pkgs: cfg:
     if cfg.overrideShell != null then cfg.overrideShell
diff --git a/tests/default.nix b/tests/default.nix
index eab35f8..bd773d1 100644
--- a/tests/default.nix
+++ b/tests/default.nix
@@ -324,13 +324,13 @@ in
     })
     (f: lib.isDerivation f.devShells.x86_64-linux.default);
 
-  devShell-override = test
+  devShell-pkgDef = test
     (flakelight ./empty {
       devShell = { mkShell }: mkShell { };
     })
     (f: lib.isDerivation f.devShells.x86_64-linux.default);
 
-  devShell-override-empty = test
+  devShell-pkgDef-empty = test
     (flakelight ./empty {
       disabledModules = [ "builtinFormatters.nix" ];
       devShell = { mkShell }: mkShell { };
@@ -365,6 +365,19 @@ in
     })
     (f: lib.isDerivation f.devShells.x86_64-linux.default);
 
+  devShell-pkg = test
+    (flakelight ./empty ({ inputs, ... }: {
+      systems = [ "x86_64-linux" ];
+      devShell = inputs.nixpkgs.legacyPackages.x86_64-linux.hello;
+    }))
+    (f: lib.isDerivation f.devShells.x86_64-linux.default);
+
+  devShell-pkg-fn = test
+    (flakelight ./empty {
+      devShell = pkgs: pkgs.hello;
+    })
+    (f: lib.isDerivation f.devShells.x86_64-linux.default);
+
   devShells = test
     (flakelight ./empty {
       devShell.inputsFrom = pkgs: [ pkgs.emacs ];