From 0530d6bd0498e6f554cc9070a163ac9aec5819c8 Mon Sep 17 00:00:00 2001
From: Valentin Gagarin <valentin.gagarin@tweag.io>
Date: Mon, 13 Nov 2023 20:59:15 +0100
Subject: [PATCH] doc: add explanatory code comment

---
 pkgs/build-support/mkshell/default.nix | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/pkgs/build-support/mkshell/default.nix b/pkgs/build-support/mkshell/default.nix
index 3517e949f67a..5369301ea105 100644
--- a/pkgs/build-support/mkshell/default.nix
+++ b/pkgs/build-support/mkshell/default.nix
@@ -16,6 +16,10 @@
 let
   mergeInputs = name:
     (attrs.${name} or [ ]) ++
+    # 1. get all `{build,nativeBuild,...}Inputs` from the elements of `inputsFrom`
+    # 2. since that is a list of lists, `flatten` that into a regular list
+    # 3. filter out of the result everything that's in `inputsFrom` itself
+    # this leaves actual dependencies of the derivations in `inputsFrom`, but never the derivations themselves
     (lib.subtractLists inputsFrom (lib.flatten (lib.catAttrs name inputsFrom)));
 
   rest = builtins.removeAttrs attrs [