From 91551c09d48583230b36cf759ad703b5f1d83d9a Mon Sep 17 00:00:00 2001
From: Robert Helgesson <robert@rycee.net>
Date: Sat, 2 May 2020 01:06:41 +0200
Subject: [PATCH] files: add helper function `mkOutOfStoreSymlink`

Using this function it is possible to make `home.file` create a
symlink to a path outside the Nix store. For example, a Home Manager
configuration containing

    home.file."foo".source = config.lib.file.mkOutOfStoreSymlink ./bar;

would upon activation create a symlink `~/foo` that points to the
absolute path of the `bar` file relative the configuration file.

PR #1211
---
 modules/files.nix                            |  7 +++++
 tests/modules/files/default.nix              |  1 +
 tests/modules/files/out-of-store-symlink.nix | 29 ++++++++++++++++++++
 3 files changed, 37 insertions(+)
 create mode 100644 tests/modules/files/out-of-store-symlink.nix

diff --git a/modules/files.nix b/modules/files.nix
index 0b87d539..ae48e30d 100644
--- a/modules/files.nix
+++ b/modules/files.nix
@@ -39,6 +39,13 @@ in
   };
 
   config = {
+    lib.file.mkOutOfStoreSymlink = path:
+      let
+        pathStr = toString path;
+        name = hm.strings.storeFileName (baseNameOf pathStr);
+      in
+        pkgs.runCommandLocal name {} ''ln -s ${escapeShellArg pathStr} $out'';
+
     # This verifies that the links we are about to create will not
     # overwrite an existing file.
     home.activation.checkLinkTargets = hm.dag.entryBefore ["writeBoundary"] (
diff --git a/tests/modules/files/default.nix b/tests/modules/files/default.nix
index 04c61d3b..77743a76 100644
--- a/tests/modules/files/default.nix
+++ b/tests/modules/files/default.nix
@@ -1,6 +1,7 @@
 {
   files-executable = ./executable.nix;
   files-hidden-source = ./hidden-source.nix;
+  files-out-of-store-symlink = ./out-of-store-symlink.nix;
   files-source-with-spaces = ./source-with-spaces.nix;
   files-text = ./text.nix;
 }
diff --git a/tests/modules/files/out-of-store-symlink.nix b/tests/modules/files/out-of-store-symlink.nix
new file mode 100644
index 00000000..af274aae
--- /dev/null
+++ b/tests/modules/files/out-of-store-symlink.nix
@@ -0,0 +1,29 @@
+{ config, lib, ... }:
+
+with lib;
+
+let
+
+  filePath = ./. + "/source with spaces!";
+
+in {
+  config = {
+    home.file."oos".source = config.lib.file.mkOutOfStoreSymlink filePath;
+
+    nmt.script = ''
+      assertLinkExists "home-files/oos"
+
+      storePath="$(readlink $TESTED/home-files/oos)"
+
+      if [[ ! -L $storePath ]]; then
+        fail "Expected $storePath to be a symbolic link, but it was not."
+      fi
+
+      actual="$(readlink "$storePath")"
+      expected="${toString filePath}"
+      if [[ $actual != $expected ]]; then
+        fail "Symlink home-files/oos should point to $expected via the Nix store, but it actually points to $actual."
+      fi
+    '';
+  };
+}