mkShell: add builder (#30975)

doc/default.nix

@@ -49,6 +49,10 @@ pkgs.stdenv.mkDerivation {
       outputFile = "introduction.xml";
       useChapters = true;
     }
+  + toDocbook {
+      inputFile = ./shell.md;
+      outputFile = "shell.xml";
+    }
   + toDocbook {
       inputFile = ./languages-frameworks/python.md;
       outputFile = "./languages-frameworks/python.xml";

doc/shell.md

@@ -0,0 +1,20 @@
+---
+title: stdenv.mkShell
+author: zimbatm
+date: 2017-10-30
+---
+
+stdenv.mkShell is a special kind of derivation that is only useful when using
+it combined with nix-shell. It will in fact fail to instantiate when invoked
+with nix-build.
+
+## Usage
+
+```nix
+{ pkgs ? import <nixpkgs> {} }:
+pkgs.mkShell {
+  # this will make all the build inputs from hello and gnutar available to the shell environment
+  inputsFrom = with pkgs; [ hello gnutar ];
+  buildInputs = [ pkgs.gnumake ];
+}
+```

pkgs/build-support/mkshell/default.nix

@@ -0,0 +1,46 @@
+{ lib, stdenv }:
+
+# A special kind of derivation that is only meant to be consumed by the
+# nix-shell.
+{
+  inputsFrom ? [], # a list of derivations whose inputs will be made available to the environment
+  buildInputs ? [],
+  nativeBuildInputs ? [],
+  propagatedBuildInputs ? [],
+  propagatedNativeBuildInputs ? [],
+  ...
+}@attrs:
+let
+  mergeInputs = name:
+    let
+      op = item: sum: sum ++ item."${name}" or [];
+      nul = [];
+      list = [attrs] ++ inputsFrom;
+    in
+      lib.foldr op nul list;
+
+  rest = builtins.removeAttrs attrs [
+    "inputsFrom"
+    "buildInputs"
+    "nativeBuildInputs"
+    "propagatedBuildInputs"
+    "propagatedNativeBuildInputs"
+  ];
+in
+
+stdenv.mkDerivation ({
+  name = "nix-shell";
+  phases = ["nobuildPhase"];
+
+  buildInputs = mergeInputs "buildInputs";
+  nativeBuildInputs = mergeInputs "nativeBuildInputs";
+  propagatedBuildInputs = mergeInputs "propagatedBuildInputs";
+  propagatedNativeBuildInputs = mergeInputs "propagatedNativeBuildInputs";
+
+  nobuildPhase = ''
+    echo
+    echo "This derivation is not meant to be built, aborting";
+    echo
+    exit 1
+  '';
+} // rest)

pkgs/top-level/all-packages.nix

@@ -311,6 +311,8 @@ with pkgs;
       inherit kernel rootModules allowMissing;
     };
 
+  mkShell = callPackage ../build-supports/mkshell { };
+
   nixBufferBuilders = import ../build-support/emacs/buffer.nix { inherit (pkgs) lib writeText; inherit (emacsPackagesNg) inherit-local; };
 
   pathsFromGraph = ../build-support/kernel/paths-from-graph.pl;