From d4428d00ae05cd21c256f9490c7f089ec04fd962 Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <edolstra@gmail.com>
Date: Tue, 22 Feb 2022 14:19:39 +0100
Subject: [PATCH] nix flake check: Warn about deprecated flake outputs

---
 src/nix/flake.cc | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/src/nix/flake.cc b/src/nix/flake.cc
index 303edb9fe..14a235501 100644
--- a/src/nix/flake.cc
+++ b/src/nix/flake.cc
@@ -501,6 +501,17 @@ struct CmdFlakeCheck : FlakeCommand
 
                         state->forceValue(vOutput, pos);
 
+                        std::string_view replacement =
+                            name == "defaultPackage" ? "packages.<system>.default" :
+                            name == "defaultApps" ? "apps.<system>.default" :
+                            name == "defaultTemplate" ? "templates.default" :
+                            name == "defaultBundler" ? "bundlers.<system>.default" :
+                            name == "overlay" ? "overlays.default" :
+                            name == "devShell" ? "devShells.<system>.default" :
+                            "";
+                        if (replacement != "")
+                            warn("flake output attribute '%s' is deprecated; use '%s' instead", name, replacement);
+
                         if (name == "checks") {
                             state->forceAttrs(vOutput, pos);
                             for (auto & attr : *vOutput.attrs) {