From 7d4eb3f1b7c74b3812c1873b6136a18387310bb8 Mon Sep 17 00:00:00 2001
From: Silvan Mosberger <silvan.mosberger@tweag.io>
Date: Wed, 13 Sep 2023 22:26:16 +0200
Subject: [PATCH] lib.fileset.toSource: Evaluate fileset even for empty
 directories

---
 lib/fileset/default.nix  | 4 +++-
 lib/fileset/internal.nix | 1 +
 lib/fileset/tests.sh     | 3 +++
 3 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/lib/fileset/default.nix b/lib/fileset/default.nix
index b30125265520..51002332a319 100644
--- a/lib/fileset/default.nix
+++ b/lib/fileset/default.nix
@@ -92,6 +92,7 @@ The only way to change which files get added to the store is by changing the `fi
       fileset = _coerce "lib.fileset.toSource: `fileset`" filesetPath;
       rootFilesystemRoot = (splitRoot root).root;
       filesetFilesystemRoot = (splitRoot fileset._internalBase).root;
+      filter = _toSourceFilter fileset;
     in
     if ! isPath root then
       if isStringLike root then
@@ -123,9 +124,10 @@ The only way to change which files get added to the store is by changing the `fi
             - Set `root` to ${toString fileset._internalBase} or any directory higher up. This changes the layout of the resulting store path.
             - Set `fileset` to a file set that cannot contain files outside the `root` ${toString root}. This could change the files included in the result.''
     else
+      builtins.seq filter
       cleanSourceWith {
         name = "source";
         src = root;
-        filter = _toSourceFilter fileset;
+        inherit filter;
       };
 }
diff --git a/lib/fileset/internal.nix b/lib/fileset/internal.nix
index ae8eb20e3ed2..946ea1014f30 100644
--- a/lib/fileset/internal.nix
+++ b/lib/fileset/internal.nix
@@ -294,6 +294,7 @@ rec {
     in
     # Special case because the code below assumes that the _internalBase is always included in the result
     # which shouldn't be done when we have no files at all in the base
+    # This also forces the tree before returning the filter, leads to earlier error messages
     if tree == null then
       empty
     else
diff --git a/lib/fileset/tests.sh b/lib/fileset/tests.sh
index e27610573a86..5bd798ae7942 100755
--- a/lib/fileset/tests.sh
+++ b/lib/fileset/tests.sh
@@ -246,6 +246,9 @@ expectFailure 'toSource { root = ./a; fileset = ./a; }' 'lib.fileset.toSource: `
 \s*- If you want to import the file into the store _with_ a containing directory, set `root` to the containing directory, such as '"$work"', and set `fileset` to the file path.'
 rm -rf *
 
+# The fileset argument should be evaluated, even if the directory is empty
+expectFailure 'toSource { root = ./.; fileset = abort "This should be evaluated"; }' 'evaluation aborted with the following error message: '\''This should be evaluated'\'
+
 # Only paths under `root` should be able to influence the result
 mkdir a
 expectFailure 'toSource { root = ./a; fileset = ./.; }' 'lib.fileset.toSource: `fileset` could contain files in '"$work"', which is not under the `root` '"$work"'/a. Potential solutions: