skip ifds in nix flake show instead of throwing

tests/functional/flakes/common.sh

@@ -88,6 +88,19 @@ writeDependentFlake() {
 EOF
 }
 
+writeIfdFlake() {
+    local flakeDir="$1"
+    cat > "$flakeDir/flake.nix" <<EOF
+{
+  outputs = { self }: {
+    packages.$system.default = import ./ifd.nix;
+  };
+}
+EOF
+
+    cp -n ../ifd.nix ../dependencies.nix ../dependencies.builder0.sh "${config_nix}" "$flakeDir/"
+}
+
 writeTrivialFlake() {
     local flakeDir="$1"
     cat > "$flakeDir/flake.nix" <<EOF

tests/functional/flakes/show.sh

@@ -6,7 +6,7 @@ flakeDir=$TEST_ROOT/flake
 mkdir -p "$flakeDir"
 
 writeSimpleFlake "$flakeDir"
-cd "$flakeDir"
+pushd "$flakeDir"
 
 
 # By default: Only show the packages content for the current system and no
@@ -87,3 +87,18 @@ assert show_output.legacyPackages.${builtins.currentSystem}.AAAAAASomeThingsFail
 assert show_output.legacyPackages.${builtins.currentSystem}.simple.name == "simple";
 true
 '
+
+# Test that nix flake show doesn't fail if one of the outputs contains
+# an IFD
+popd
+writeIfdFlake $flakeDir
+pushd $flakeDir
+
+
+nix flake show --json > show-output.json
+nix eval --impure --expr '
+let show_output = builtins.fromJSON (builtins.readFile ./show-output.json);
+in
+assert show_output.packages.${builtins.currentSystem}.default == { };
+true
+'