From ab8bf8c35beb13d6d3d1ac9cfe1ea30d29894e53 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Sandro=20J=C3=A4ckel?= <sandro.jaeckel@gmail.com>
Date: Fri, 30 Aug 2024 11:31:26 +0200
Subject: [PATCH] lib/modules: improve error message when option is being
 accessed that isn't defined

---
 lib/modules.nix                                 | 2 +-
 lib/tests/modules.sh                            | 8 ++++----
 pkgs/tools/nix/nixos-option/src/nixos-option.cc | 2 +-
 3 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/lib/modules.nix b/lib/modules.nix
index b9e9ca1e5d78..c097f947cc4b 100644
--- a/lib/modules.nix
+++ b/lib/modules.nix
@@ -861,7 +861,7 @@ let
       else
         # (nixos-option detects this specific error message and gives it special
         # handling.  If changed here, please change it there too.)
-        throw "The option `${showOption loc}' is used but not defined.";
+        throw "The option `${showOption loc}' was accessed but has no value defined. Try setting the option.";
 
     isDefined = defsFinal != [];
 
diff --git a/lib/tests/modules.sh b/lib/tests/modules.sh
index 3301a3d987ee..68b192294076 100755
--- a/lib/tests/modules.sh
+++ b/lib/tests/modules.sh
@@ -304,7 +304,7 @@ checkConfigOutput '^".*Hello.*"$' options.namedPackage.description ./declare-mkP
 checkConfigOutput '^"hello"$' config.pathPackage.pname ./declare-mkPackageOption.nix
 checkConfigOutput '^"pkgs\.hello\.override \{ stdenv = pkgs\.clangStdenv; \}"$' options.packageWithExample.example.text ./declare-mkPackageOption.nix
 checkConfigOutput '^".*Example extra description\..*"$' options.packageWithExtraDescription.description ./declare-mkPackageOption.nix
-checkConfigError 'The option .undefinedPackage. is used but not defined' config.undefinedPackage ./declare-mkPackageOption.nix
+checkConfigError 'The option .undefinedPackage. was accessed but has no value defined. Try setting the option.' config.undefinedPackage ./declare-mkPackageOption.nix
 checkConfigOutput '^null$' config.nullablePackage ./declare-mkPackageOption.nix
 checkConfigOutput '^"null or package"$' options.nullablePackageWithDefault.type.description ./declare-mkPackageOption.nix
 checkConfigOutput '^"myPkgs\.hello"$' options.packageWithPkgsText.defaultText.text ./declare-mkPackageOption.nix
@@ -402,7 +402,7 @@ checkConfigOutput '^null$' config.foo ./freeform-attrsOf.nix ./freeform-str-dep-
 checkConfigOutput '^"24"$' config.foo ./freeform-attrsOf.nix ./freeform-str-dep-unstr.nix ./define-value-string.nix
 # Check whether an freeform-typed value can depend on a declared option, this can only work with lazyAttrsOf
 checkConfigError 'infinite recursion encountered' config.foo ./freeform-attrsOf.nix ./freeform-unstr-dep-str.nix
-checkConfigError 'The option .* is used but not defined' config.foo ./freeform-lazyAttrsOf.nix ./freeform-unstr-dep-str.nix
+checkConfigError 'The option .* was accessed but has no value defined. Try setting the option.' config.foo ./freeform-lazyAttrsOf.nix ./freeform-unstr-dep-str.nix
 checkConfigOutput '^"24"$' config.foo ./freeform-lazyAttrsOf.nix ./freeform-unstr-dep-str.nix ./define-value-string.nix
 # submodules in freeformTypes should have their locations annotated
 checkConfigOutput '/freeform-submodules.nix"$' config.fooDeclarations.0 ./freeform-submodules.nix
@@ -461,8 +461,8 @@ checkConfigOutput "{}" config.attrs.a ./emptyValues.nix
 checkConfigOutput "null" config.null.a ./emptyValues.nix
 checkConfigOutput "{}" config.submodule.a ./emptyValues.nix
 # These types don't have empty values
-checkConfigError 'The option .int.a. is used but not defined' config.int.a ./emptyValues.nix
-checkConfigError 'The option .nonEmptyList.a. is used but not defined' config.nonEmptyList.a ./emptyValues.nix
+checkConfigError 'The option .int.a. was accessed but has no value defined. Try setting the option.' config.int.a ./emptyValues.nix
+checkConfigError 'The option .nonEmptyList.a. was accessed but has no value defined. Try setting the option.' config.nonEmptyList.a ./emptyValues.nix
 
 # types.unique
 #   requires a single definition
diff --git a/pkgs/tools/nix/nixos-option/src/nixos-option.cc b/pkgs/tools/nix/nixos-option/src/nixos-option.cc
index eab727bc1db5..658b836d491a 100644
--- a/pkgs/tools/nix/nixos-option/src/nixos-option.cc
+++ b/pkgs/tools/nix/nixos-option/src/nixos-option.cc
@@ -465,7 +465,7 @@ void printValue(Context & ctx, Out & out, std::variant<Value, std::exception_ptr
             v.print(ctx.state.symbols, out.ostream);
         }
     } catch (ThrownError & e) {
-        if (e.msg() == "The option `" + path + "' is used but not defined.") {
+        if (e.msg() == "The option `" + path + "' was accessed but has no value defined. Try setting the option.") {
             // 93% of errors are this, and just letting this message through would be
             // misleading.  These values may or may not actually be "used" in the
             // config.  The thing throwing the error message assumes that if anything