From b3cc29c288b6ac5e2fa71477cabb2d088f568001 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Domen=20Ko=C5=BEar?= <domen@dev.si>
Date: Thu, 9 Feb 2023 07:25:50 +0000
Subject: [PATCH 1/2] types: explicitly state unique options are expected to be
 unique

---
 lib/options.nix | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/options.nix b/lib/options.nix
index d14d209a8347..22eb6c2eeb1d 100644
--- a/lib/options.nix
+++ b/lib/options.nix
@@ -184,7 +184,7 @@ rec {
     if length defs == 1
     then (head defs).value
     else assert length defs > 1;
-      throw "The option `${showOption loc}' is defined multiple times.\n${message}\nDefinition values:${showDefs defs}";
+      throw "The option `${showOption loc}' is defined multiple times while it's expected to be unique.\n${message}\nDefinition values:${showDefs defs}";
 
   /* "Merge" option definitions by checking that they all have the same value. */
   mergeEqualOption = loc: defs:

From fe734efc9c2c0a42b9c34dfd6280d82558744a06 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Domen=20Ko=C5=BEar?= <domen@dev.si>
Date: Thu, 9 Feb 2023 07:38:40 +0000
Subject: [PATCH 2/2] types: suggest how to resolve the conflict

---
 lib/options.nix | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/lib/options.nix b/lib/options.nix
index 22eb6c2eeb1d..5e8f4ca4bb95 100644
--- a/lib/options.nix
+++ b/lib/options.nix
@@ -36,6 +36,9 @@ let
   inherit (lib.types)
     mkOptionType
     ;
+  prioritySuggestion = ''
+   Use `lib.mkForce value` or `lib.mkDefault value` to change the priority on any of these definitions.
+  '';
 in
 rec {
 
@@ -184,7 +187,7 @@ rec {
     if length defs == 1
     then (head defs).value
     else assert length defs > 1;
-      throw "The option `${showOption loc}' is defined multiple times while it's expected to be unique.\n${message}\nDefinition values:${showDefs defs}";
+      throw "The option `${showOption loc}' is defined multiple times while it's expected to be unique.\n${message}\nDefinition values:${showDefs defs}\n${prioritySuggestion}";
 
   /* "Merge" option definitions by checking that they all have the same value. */
   mergeEqualOption = loc: defs:
@@ -195,7 +198,7 @@ rec {
     else if length defs == 1 then (head defs).value
     else (foldl' (first: def:
       if def.value != first.value then
-        throw "The option `${showOption loc}' has conflicting definition values:${showDefs [ first def ]}"
+        throw "The option `${showOption loc}' has conflicting definition values:${showDefs [ first def ]}\n${prioritySuggestion}"
       else
         first) (head defs) (tail defs)).value;