From c5b82e49b33e95a17a675ad4c60da30c168ff020 Mon Sep 17 00:00:00 2001
From: Emily <vcs@emily.moe>
Date: Mon, 27 Oct 2025 19:05:09 +0000
Subject: [PATCH] aliases: add `warnAlias`

---
 maintainers/scripts/remove-old-aliases.py |  8 ++++----
 pkgs/top-level/aliases.nix                | 25 +++++++++++++++++++++++
 2 files changed, 29 insertions(+), 4 deletions(-)

diff --git a/maintainers/scripts/remove-old-aliases.py b/maintainers/scripts/remove-old-aliases.py
index c7d1292b3e1e..bceee1074844 100755
--- a/maintainers/scripts/remove-old-aliases.py
+++ b/maintainers/scripts/remove-old-aliases.py
@@ -98,8 +98,8 @@ def get_date_lists(
             date_too_complex_list.append(f"{lineno:>5} {line}")
         elif "= with " in line:
             date_too_complex_list.append(f"{lineno:>5} {line}")
-        elif "lib.warnOnInstantiate" in line or "warning" in line:
-            if 'lib.warnOnInstantiate "' in line:
+        elif "warnAlias" in line or "warning" in line:
+            if 'warnAlias "' in line:
                 date_older_warning_list.append(line)
             else:
                 date_too_complex_list.append(f"{lineno:>5} {line}")
@@ -140,7 +140,7 @@ def convert(lines: list[str], convert_to: str) -> list[tuple[str, str]]:
                 before_equal, after_equal = (
                     x.strip() for x in line.split("=", maxsplit=2)
                 )
-                if after_equal.startswith("lib.warnOnInstantiate"):
+                if after_equal.startswith("warnAlias"):
                     after_equal = after_equal.split("\"", maxsplit=3)[2].strip()
             except ValueError as err:
                 print(err, line, "\n")
@@ -162,7 +162,7 @@ def convert(lines: list[str], convert_to: str) -> list[tuple[str, str]]:
             converted_lines[line] = converted
         elif convert_to == "warnings":
             converted = (
-                f"{indent}{alias} = lib.warnOnInstantiate \"'{alias_unquoted}' has been"
+                f"{indent}{alias} = warnAlias \"'{alias_unquoted}' has been"
                 f" renamed to/replaced by '{replacement}'\" {replacement};"
                 f" # Converted to warning {datetime.today().strftime('%Y-%m-%d')}"
             )
diff --git a/pkgs/top-level/aliases.nix b/pkgs/top-level/aliases.nix
index a2fe24a88240..764164c20131 100644
--- a/pkgs/top-level/aliases.nix
+++ b/pkgs/top-level/aliases.nix
@@ -231,6 +231,31 @@ let
     aliases: lib.mapAttrs (n: alias: removeRecurseForDerivations (checkInPkgs n alias)) aliases;
 
   plasma5Throws = mapAliases (lib.mapAttrs (k: _: makePlasma5Throw k) deprecatedPlasma5Packages);
+
+  warnAlias =
+    msg: v:
+    if lib.isDerivation v then
+      lib.warnOnInstantiate msg v
+    else if lib.isAttrs v then
+      lib.mapAttrs (lib.warn msg) v
+    else if lib.isFunction v then
+      arg: lib.warn msg (v arg)
+    else if lib.isList v then
+      map (lib.warn msg) v
+    else if lib.isString v then
+      # Unlike the other cases, this changes the type of the value and
+      # is therefore a breaking change for some code, but it’s the best
+      # we can do.
+      { __toString = lib.warn msg (lib.const v); }
+    else
+      # Can’t do better than this, and a `throw` would be more
+      # disruptive for users…
+      #
+      # `nix search` flags up warnings already, so hopefully this won’t
+      # make things much worse until we have proper CI for aliases,
+      # especially since aliases of paths and numbers are presumably
+      # not common.
+      lib.warn msg v;
 in
 
 mapAliases {