tests.build-environment-info: add more information

The user information would have helped diagnose the empty GECOS issue
we had with the Hydra Darwin builders recently and the OS information
seems generally nice to have.

pkgs/test/build-environment-info/default.nix

@@ -1,11 +1,39 @@
-{ runCommand }:
+{
+  lib,
+  stdenv,
+  runCommand,
+  getent,
+  xcbuild,
+}:
 
 # Prints information about the state of the build environment for
 # assistance debugging Hydra. Feel free to add anything you would find
 # useful to this.
-runCommand "build-environment-info" { } ''
-  ulimit -a
+runCommand "build-environment-info"
+  {
+    nativeBuildInputs = [ getent ] ++ lib.optionals stdenv.buildPlatform.isDarwin [ xcbuild ];
+  }
+  ''
+    # It’s useful to get more info even if a command fails.
+    set +e
+
+    run() {
+      echoCmd : "$@"
+      "$@"
+    }
+
+    run uname -a
+
+    ${lib.optionalString stdenv.buildPlatform.isDarwin ''
+      run env SYSTEM_VERSION_COMPAT=0 plutil -p /System/Library/CoreServices/SystemVersion.plist
+    ''}
+
+    run id
+
+    run getent passwd "$(id -un)"
+
+    run ulimit -a
 
     # Always fail so that this job can easily be restarted.
-  exit 1
-''
+    run exit 1
+  ''