enable packagesFrom

README.md

@@ -34,7 +34,7 @@ new environment variables, which then need to be unset. The `stdenv` itself
 contains either GCC or Clang which makes it hard to select a specific C
 compiler.
 
-This is why `mkDevShell` builds its environment from a `builtins.derivation`.
+This is why `mkShell` builds its environment from a `builtins.derivation`.
 
 direnv loads will change from:
 ```
@@ -65,11 +65,10 @@ those are useful yet:
 When entering a random project, it's useful to get a quick view of what
 commands are available.
 
-When running `nix-shell` or `nix develop`, `mkDevShell` prints a welcome
-message:
+When running `nix-shell` or `nix develop`, `mkShell` prints a welcome message:
 
 ```
-### 🔨 Welcome to mkDevShell ####
+🔨 Welcome to devshell
 
 # Commands
 
@@ -90,13 +89,12 @@ handle 80% of the use-cases and falling back on Nix is always possible.
 Life is not complete otherwise. Huhu.
 
 Packages that contain bash completions will automatically be loaded by
-`mkDevShell` in `nix-shell` or `nix develop` modes.
+`mkShell` in `nix-shell` or `nix develop` modes.
 
 ### Capture development dependencies in CI
 
 With a CI + Binary cache setup, one often wants to be able to capture all the
-build inputs of a `shell.nix`. Before, `pkgs.mkShell` would even refuse to
-build! (my fault really). With `pkgs.mkDevShell`, capturing all of the
+build inputs of a `shell.nix`. With `mkShell` capturing all of the
 development dependencies is as easy as:
 
 ```sh

devshell.toml

@@ -25,6 +25,11 @@ packages = [
   "hyperfine",
 ]
 
+# Expose all the dependencies from a package to the environment.
+packagesFrom = [
+  "direnv"
+]
+
 # Declare commands that are available in the environment.
 [[commands]]
 help = "prints hello"

modules/back-compat.nix

@@ -37,12 +37,19 @@ with lib;
       type = types.listOf strOrPackage;
       default = [ ];
     };
+
+    packagesFrom = mkOption {
+      internal = true;
+      type = types.listOf strOrPackage;
+      default = [ ];
+    };
   };
 
   # Copy the values over to the devshell module
   config.devshell =
     {
       packages = config.packages;
+      packagesFrom = config.packagesFrom;
       startup.bash_extra = noDepEntry config.bash.extra;
       interactive.bash_interactive = noDepEntry config.bash.interactive;
     }

modules/devshell.nix

@@ -196,6 +196,14 @@ let
     '';
   };
 
+  # Returns a list of all the input derivation ... for a derivation.
+  inputsOf = drv:
+    (drv.buildInputs or [ ]) ++
+    (drv.nativeBuildInputs or [ ]) ++
+    (drv.propagatedBuildInputs or [ ]) ++
+    (drv.propagatedNativeBuildInputs or [ ])
+  ;
+
 in
 {
   options.devshell = {
@@ -291,6 +299,15 @@ in
       '';
     };
 
+    packagesFrom = mkOption {
+      type = types.listOf strOrPackage;
+      default = [ ];
+      description = ''
+        Add all the build dependencies from the listed packages to the
+        environment.
+      '';
+    };
+
     shell = mkOption {
       internal = true;
       type = types.package;
@@ -331,6 +348,8 @@ in
   config.devshell = {
     package = devshell_dir;
 
+    packages = foldl' (sum: drv: sum ++ (inputsOf drv)) [ ] cfg.packagesFrom;
+
     startup = {
       motd = noDepEntry ''
         __devshell-motd() {

overlay.nix

@@ -1,4 +1,4 @@
-# Import this overlay in your project to add devshell and mkDevShell
+# Import this overlay in your project to add devshell
 final: prev:
 {
   devshell = import ./. { nixpkgs = final; };