lib/types: always use `<function body>` instead of `[function body]` to indicate a function inside an option structure

The motivation is to have a single identifier for that. Useful for the
next commit where I'll try to escape option-parts correctly (options can
be any kind of strings, but unless these are Nix identifiers, they must
be quoted).

Since `<function body>` (or `<name>`/`*`) are special identifiers in
error messages and the manual, we need a unique way to mark an option
part as function call because these are not to be quoted.

lib/tests/modules.sh

@@ -302,11 +302,11 @@ checkConfigOutput '^"baz"$' config.value.nested.bar.baz ./types-anything/mk-mods
 ## types.functionTo
 checkConfigOutput '^"input is input"$' config.result ./functionTo/trivial.nix
 checkConfigOutput '^"a b"$' config.result ./functionTo/merging-list.nix
-checkConfigError 'A definition for option .fun.\[function body\]. is not of type .string.. Definition values:\n\s*- In .*wrong-type.nix' config.result ./functionTo/wrong-type.nix
+checkConfigError 'A definition for option .fun.<function body>. is not of type .string.. Definition values:\n\s*- In .*wrong-type.nix' config.result ./functionTo/wrong-type.nix
 checkConfigOutput '^"b a"$' config.result ./functionTo/list-order.nix
 checkConfigOutput '^"a c"$' config.result ./functionTo/merging-attrs.nix
 checkConfigOutput '^"a bee"$' config.result ./functionTo/submodule-options.nix
-checkConfigOutput '^"fun.\[function body\].a fun.\[function body\].b"$' config.optionsResult ./functionTo/submodule-options.nix
+checkConfigOutput '^"fun.<function body>.a fun.<function body>.b"$' config.optionsResult ./functionTo/submodule-options.nix
 
 # moduleType
 checkConfigOutput '^"a b"$' config.resultFoo ./declare-variants.nix ./define-variant.nix

lib/types.nix

@@ -616,8 +616,8 @@ rec {
       descriptionClass = "composite";
       check = isFunction;
       merge = loc: defs:
-        fnArgs: (mergeDefinitions (loc ++ [ "[function body]" ]) elemType (map (fn: { inherit (fn) file; value = fn.value fnArgs; }) defs)).mergedValue;
-      getSubOptions = prefix: elemType.getSubOptions (prefix ++ [ "[function body]" ]);
+        fnArgs: (mergeDefinitions (loc ++ [ "<function body>" ]) elemType (map (fn: { inherit (fn) file; value = fn.value fnArgs; }) defs)).mergedValue;
+      getSubOptions = prefix: elemType.getSubOptions (prefix ++ [ "<function body>" ]);
       getSubModules = elemType.getSubModules;
       substSubModules = m: functionTo (elemType.substSubModules m);
       functor = (defaultFunctor "functionTo") // { wrapped = elemType; };