From f536901693ef6128cc61030ee74eb4433793b174 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?J=C3=B6rg=20Thalheim?= <joerg@thalheim.io>
Date: Fri, 14 Aug 2020 07:25:50 +0100
Subject: [PATCH] nixos/filesystems: don't allow mountpoints with trailing
 slash

They are semantically the same as the non-slash version and therefore
are potential source of duplicates.

Also fixes https://github.com/NixOS/nixpkgs/issues/78951
---
 nixos/modules/tasks/filesystems.nix | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/nixos/modules/tasks/filesystems.nix b/nixos/modules/tasks/filesystems.nix
index 96f57fc80b0c..5388fc738e31 100644
--- a/nixos/modules/tasks/filesystems.nix
+++ b/nixos/modules/tasks/filesystems.nix
@@ -7,8 +7,9 @@ let
 
   addCheckDesc = desc: elemType: check: types.addCheck elemType check
     // { description = "${elemType.description} (with check: ${desc})"; };
-  nonEmptyStr = addCheckDesc "non-empty" types.str
-    (s: (builtins.match ".*[^ \t]+.*" s) != null);
+
+  isNonEmpty = s: (builtins.match ".*[^ \t]+.*" s) != null;
+  nonEmptyStr = addCheckDesc "non-empty" types.str isNonEmpty;
 
   fileSystems' = toposort fsBefore (attrValues config.fileSystems);
 
@@ -28,10 +29,10 @@ let
   coreFileSystemOpts = { name, config, ... }: {
 
     options = {
-
       mountPoint = mkOption {
         example = "/mnt/usb";
-        type = nonEmptyStr;
+        type = addCheckDesc "non-empty without trailing slash" types.str
+          (s: isNonEmpty s && (builtins.match "(/|/.*[^/])" s) != null);
         description = "Location of the mounted the file system.";
       };