From eb312d499ca61639a2f73d7c8b46846527389dca Mon Sep 17 00:00:00 2001
From: lassulus <git@lassul.us>
Date: Tue, 12 Sep 2023 18:19:18 +0200
Subject: [PATCH] lib/types: init taggedSubmodules

---
 lib/types.nix                                 | 17 +++++++
 .../development/option-types.section.md       | 51 +++++++++++++++++++
 2 files changed, 68 insertions(+)

diff --git a/lib/types.nix b/lib/types.nix
index 5ffbecda5db39..9bf3fc4989908 100644
--- a/lib/types.nix
+++ b/lib/types.nix
@@ -710,6 +710,23 @@ rec {
         in mergedOption.type;
     };
 
+    # A type that is one of several submodules, similiar to types.oneOf but is usable inside attrsOf or listOf
+    # submodules need an option with a type str which is used to find the corresponding type
+    taggedSubmodules =
+      { types
+      , specialArgs ? {}
+      }: mkOptionType rec {
+      name = "taggedSubmodules";
+      description = "one of ${concatStringsSep "," (attrNames types)}";
+      check = x: if x ? type then types.${x.type}.check x else throw "No type option set in:\n${lib.generators.toPretty {} x}";
+      merge = loc: foldl'
+        (res: def: types.${def.value.type}.merge loc [
+          (lib.recursiveUpdate { value._module.args = specialArgs; } def)
+        ])
+        { };
+      nestedTypes = types;
+    };
+
     submoduleWith =
       { modules
       , specialArgs ? {}
diff --git a/nixos/doc/manual/development/option-types.section.md b/nixos/doc/manual/development/option-types.section.md
index 44bb3b4782e19..1ef6711bf205d 100644
--- a/nixos/doc/manual/development/option-types.section.md
+++ b/nixos/doc/manual/development/option-types.section.md
@@ -213,6 +213,57 @@ Submodules are detailed in [Submodule](#section-option-types-submodule).
     options. This is equivalent to
     `types.submoduleWith { modules = toList o; shorthandOnlyDefinesConfig = true; }`.
 
+`types.taggedSubmodules` { *`types`*, *`specialArgs`* ? {} }
+
+:   Like `types.oneOf`, but takes an attrsSet of submodule in types. Those need to have a type option
+    which is used to find the correct submodule.
+
+::: {#ex-tagged-submodules .example}
+### Tagged submodules
+```nix
+let
+  submoduleA = submodule {
+    options = {
+      type = mkOption {
+        type = str;
+      };
+      foo = mkOption {
+        type = int;
+      };
+    };
+  };
+  submoduleB = submodule {
+    options = {
+      type = mkOption {
+        type = str;
+      };
+      bar = mkOption {
+        type = int;
+      };
+    };
+  };
+in
+options.mod = mkOption {
+  type = attrsOf (taggedSubmodule {
+    types = {
+      a = submoduleA;
+      b = submoduleB;
+    };
+  });
+};
+config.mod = {
+  someA = {
+    type = "a";
+    foo = 123;
+  };
+  someB = {
+    type = "b";
+    foo = 456;
+  };
+};
+```
+:::
+
 `types.submoduleWith` { *`modules`*, *`specialArgs`* ? {}, *`shorthandOnlyDefinesConfig`* ? false }
 
 :   Like `types.submodule`, but more flexible and with better defaults.