POC: devShell interface

pkgs/stdenv/adapters.nix

@@ -6,7 +6,7 @@
 
 let
   # N.B. Keep in sync with default arg for stdenv/generic.
-  defaultMkDerivationFromStdenv = import ./generic/make-derivation.nix { inherit lib config; };
+  defaultMkDerivationFromStdenv = import ./generic/make-derivation.nix { inherit lib config; inherit (pkgs) defaultDevShell; };
 
   # Low level function to help with overriding `mkDerivationFromStdenv`. One
   # gives it the old stdenv arguments and a "continuation" function, and

pkgs/stdenv/cross/default.nix

@@ -1,5 +1,6 @@
 { lib
 , localSystem, crossSystem, config, overlays, crossOverlays ? []
+, defaultDevShell
 }:
 
 let
@@ -11,6 +12,8 @@ let
 
     # Ignore custom stdenvs when cross compiling for compatability
     config = builtins.removeAttrs config [ "replaceStdenv" ];
+
+    inherit defaultDevShell;
   };
 
 in lib.init bootStages ++ [

pkgs/stdenv/darwin/default.nix

@@ -34,6 +34,7 @@
       cpio = fetch { file = "cpio"; sha256 = "sha256-SWkwvLaFyV44kLKL2nx720SvcL4ej/p2V/bX3uqAGO0="; };
       tarball = fetch { file = "bootstrap-tools.cpio.bz2"; sha256 = "sha256-kRC/bhCmlD4L7KAvJQgcukk7AinkMz4IwmG1rqlh5tA="; executable = false; };
     }
+, defaultDevShell
 }:
 
 assert crossSystem == localSystem;
@@ -149,7 +150,7 @@ rec {
       thisStdenv = import ../generic {
         name = "${name}-stdenv-darwin";
 
-        inherit config shell extraBuildInputs;
+        inherit config shell extraBuildInputs defaultDevShell;
 
         extraNativeBuildInputs = extraNativeBuildInputs ++ lib.optionals doUpdateAutoTools [
           last.pkgs.updateAutotoolsGnuConfigScriptsHook
@@ -668,7 +669,7 @@ rec {
     import ../generic rec {
       name = "stdenv-darwin";
 
-      inherit config;
+      inherit config defaultDevShell;
       inherit (pkgs.stdenv) fetchurlBoot;
 
       buildPlatform = localSystem;

pkgs/stdenv/default.nix

@@ -8,6 +8,7 @@
   lib
   # Args to pass on to the pkgset builder, too
 , localSystem, crossSystem, config, overlays, crossOverlays ? []
+, defaultDevShell
 } @ args:
 
 let

pkgs/stdenv/devShell.nix

@@ -0,0 +1,30 @@
+{ pkgs }:
+{ drv, ... }:
+
+# stdenvDevShell only supports simple derivations, not generalized packages or anything else.
+assert drv?drvPath && drv.type or null == "derivation";
+
+# TODO: fork and improve nix-shell logic
+(pkgs.buildPackages.writeScriptBin "devShell" ''
+  #!${pkgs.buildPackages.runtimeShell}
+
+  # TODO replicate in bash
+  exec ${pkgs.buildPackages.nix}/bin/nix-shell ${builtins.unsafeDiscardOutputDependency drv.drvPath}
+
+'').overrideAttrs (prevAttrs: {
+  buildCommand = ''
+    # Write the bin/devShell command
+    ${prevAttrs.buildCommand}
+    mkdir -p $out
+
+    # environment.sh exposes the environment, but no bash functions
+    cp $inputDerivation $out/environment.sh
+
+    # TODO implement this and use it in the devShell command
+    #      should this have a different name?
+    # setup.sh loads the derivation-like environment variables and stdenv/setup.sh
+    echo '# TODO' >$out/setup.sh
+  '';
+  # TODO not sure if these must be equal; may want to reimplement this, maybe?
+  inherit (drv) inputDerivation;
+})

pkgs/stdenv/generic/default.nix

@@ -52,7 +52,10 @@ argsStdenv@{ name ? "stdenv", preHook ? "", initialPath
 
 , # The implementation of `mkDerivation`, parameterized with the final stdenv so we can tie the knot.
   # This is convient to have as a parameter so the stdenv "adapters" work better
-  mkDerivationFromStdenv ? import ./make-derivation.nix { inherit lib config; }
+  mkDerivationFromStdenv ? import ./make-derivation.nix { inherit lib config defaultDevShell; }
+
+, # See ./make-derivation.nix
+  defaultDevShell ? _: null
 }:
 
 let

pkgs/stdenv/generic/make-derivation.nix

@@ -1,4 +1,8 @@
-{ lib, config }:
+{ lib,
+  config,
+  # Function to construct the default devShell attribute; when not set via passthru.
+  defaultDevShell ? _: null,
+}:
 
 stdenv:
 
@@ -473,6 +477,8 @@ else let
                    else true);
     };
 
+  drv = derivation derivationArg;
+
 in
 
 lib.extendDerivation
@@ -503,13 +509,18 @@ lib.extendDerivation
        args = [ "-c" "export > $out" ];
      });
 
+     devShell = defaultDevShell {
+       # TODO bring `finalPackage` into scope here.
+       drv = overrideAttrs (o: {});
+     };
+
      inherit meta passthru overrideAttrs;
    } //
    # Pass through extra attributes that are not inputs, but
    # should be made available to Nix expressions using the
    # derivation (e.g., in assertions).
    passthru)
-  (derivation derivationArg);
+  drv;
 
 in
   fnOrAttrs:

pkgs/stdenv/linux/default.nix

@@ -40,6 +40,7 @@
   files = archLookupTable.${localSystem.system} or (if getCompatibleTools != null then getCompatibleTools
     else (abort "unsupported platform for the pure Linux stdenv"));
   in files
+, defaultDevShell
 }:
 
 assert crossSystem == localSystem;
@@ -461,6 +462,8 @@ in
         inherit (prevStage) binutils binutils-unwrapped;
         gcc = cc;
       };
+
+      inherit defaultDevShell;
     };
   })
 

pkgs/top-level/all-packages.nix

@@ -112,6 +112,10 @@ with pkgs;
 
   tests = callPackages ../test {};
 
+  stdenvDevShell = import ../stdenv/devShell.nix { inherit pkgs; };
+
+  defaultDevShell = stdenvDevShell;
+
   ### Nixpkgs maintainer tools
 
   nix-generate-from-cpan = callPackage ../../maintainers/scripts/nix-generate-from-cpan.nix { };

pkgs/top-level/default.nix

@@ -124,6 +124,7 @@ in let
 
   stages = stdenvStages {
     inherit lib localSystem crossSystem config overlays crossOverlays;
+    inherit (pkgs) defaultDevShell;
   };
 
   pkgs = boot stages;