lib/modules: Add context to the "option does not exist" error

Add trace items that provide context for a failed definition that
can not be caught within the Nix language.

This also adds a test for the `tryEval` behavior of `showDefs`.

lib/modules.nix

@@ -284,7 +284,18 @@ rec {
         if config._module.check && config._module.freeformType == null && merged.unmatchedDefns != [] then
           let
             firstDef = head merged.unmatchedDefns;
-            baseMsg = "The option `${showOption (prefix ++ firstDef.prefix)}' does not exist. Definition values:${showDefs [ firstDef ]}";
+            baseMsg =
+              let
+                optText = showOption (prefix ++ firstDef.prefix);
+                defText =
+                  builtins.addErrorContext
+                    "while evaluating the error message for definitions for `${optText}', which is an option that does not exist"
+                    (builtins.addErrorContext
+                      "while evaluating a definition from `${firstDef.file}'"
+                      ( showDefs [ firstDef ])
+                    );
+              in
+                "The option `${optText}' does not exist. Definition values:${defText}";
           in
             if attrNames options == [ "_module" ]
               then

lib/tests/modules.sh

@@ -64,6 +64,9 @@ checkConfigOutput '^"one two"$' config.result ./shorthand-meta.nix
 # Check boolean option.
 checkConfigOutput '^false$' config.enable ./declare-enable.nix
 checkConfigError 'The option .* does not exist. Definition values:\n\s*- In .*: true' config.enable ./define-enable.nix
+checkConfigError 'The option .* does not exist. Definition values:\n\s*- In .*' config.enable ./define-enable-throw.nix
+checkConfigError 'while evaluating a definition from `.*/define-enable-abort.nix' config.enable ./define-enable-abort.nix
+checkConfigError 'while evaluating the error message for definitions for .enable., which is an option that does not exist' config.enable ./define-enable-abort.nix
 
 checkConfigOutput '^1$' config.bare-submodule.nested ./declare-bare-submodule.nix ./declare-bare-submodule-nested-option.nix
 checkConfigOutput '^2$' config.bare-submodule.deep ./declare-bare-submodule.nix ./declare-bare-submodule-deep-option.nix

lib/tests/modules/define-enable-abort.nix

@@ -0,0 +1,3 @@
+{
+  config.enable = abort "oops";
+}

lib/tests/modules/define-enable-throw.nix

@@ -0,0 +1,3 @@
+{
+  config.enable = throw "oops";
+}