lib.types.attrsWith

The following is the current implementation of this function.

{
      elemType,
      lazy ? false,
      placeholder ? "name",
    }:
    mkOptionType rec {
      name = if lazy then "lazyAttrsOf" else "attrsOf";
      description =
        (if lazy then "lazy attribute set" else "attribute set")
        + " of ${optionDescriptionPhrase (class: class == "noun" || class == "composite") elemType}";
      descriptionClass = "composite";
      check = {
        __functor = _self: isAttrs;
        isV2MergeCoherent = true;
      };
      merge = {
        __functor =
          self: loc: defs:
          (self.v2 { inherit loc defs; }).value;
        v2 =
          { loc, defs }:
          let
            evals =
              if lazy then
                zipAttrsWith (name: defs: mergeDefinitions (loc ++ [ name ]) elemType defs) (pushPositions defs)
              else
                # Filtering makes the merge function more strict
                # Meaning it is less lazy
                filterAttrs (n: v: v.optionalValue ? value) (
                  zipAttrsWith (name: defs: mergeDefinitions (loc ++ [ name ]) elemType defs) (pushPositions defs)
                );
          in
          {
            headError = checkDefsForError check loc defs;
            value = mapAttrs (
              n: v:
              if lazy then
                v.optionalValue.value or elemType.emptyValue.value or v.mergedValue
              else
                v.optionalValue.value
            ) evals;
            valueMeta.attrs = mapAttrs (n: v: v.checkedAndMerged.valueMeta) evals;
          };
      };

      emptyValue = {
        value = { };
      };
      getSubOptions = prefix: elemType.getSubOptions (prefix ++ [ "<${placeholder}>" ]);
      getSubModules = elemType.getSubModules;
      substSubModules =
        m:
        attrsWith {
          elemType = elemType.substSubModules m;
          inherit lazy placeholder;
        };
      functor =
        (elemTypeFunctor "attrsWith" {
          inherit elemType lazy placeholder;
        })
        // {
          # Custom type merging required because of the "placeholder" attribute
          inherit binOp;
        };
      nestedTypes.elemType = elemType;
    }