From 45ecf43c516fb899d639be0b73c85b013be0ba9c Mon Sep 17 00:00:00 2001
From: Ben Siraphob <bensiraphob@gmail.com>
Date: Fri, 3 Jul 2026 14:09:30 -0700
Subject: [PATCH] lib.meta-types: add binary either/both combinators

Every in-tree union/intersection use has exactly two members, and the
binary form verifies without allocating a closure or calling the any/all
primop per check. check-meta.nix switches to either/both; union and
intersection are kept for potential future use.

Assisted-by: Claude Code (Claude Fable 5)
---
 lib/meta-types.nix                 | 26 ++++++++++++++++++++++++
 pkgs/stdenv/generic/check-meta.nix | 32 +++++++-----------------------
 2 files changed, 33 insertions(+), 25 deletions(-)

diff --git a/lib/meta-types.nix b/lib/meta-types.nix
index 1d67f5f063e8..264c921eb54e 100644
--- a/lib/meta-types.nix
+++ b/lib/meta-types.nix
@@ -160,6 +160,32 @@ lib.fix (self: {
       verify = v: all (func: func v) funcs;
     };
 
+  either =
+    t1: t2:
+    assert isTypeDef t1 && isTypeDef t2;
+    let
+      # Store the functions directly so we don't have to pay the cost of attrset lookups at runtime.
+      v1 = t1.verify;
+      v2 = t2.verify;
+    in
+    {
+      name = "either<${t1.name},${t2.name}>";
+      verify = v: v1 v || v2 v;
+    };
+
+  both =
+    t1: t2:
+    assert isTypeDef t1 && isTypeDef t2;
+    let
+      # Store the functions directly so we don't have to pay the cost of attrset lookups at runtime.
+      v1 = t1.verify;
+      v2 = t2.verify;
+    in
+    {
+      name = "both<${t1.name},${t2.name}>";
+      verify = v: v1 v && v2 v;
+    };
+
   not =
     t:
     assert isTypeDef t;
diff --git a/pkgs/stdenv/generic/check-meta.nix b/pkgs/stdenv/generic/check-meta.nix
index 049be19b4e6a..f834ebcb37c6 100644
--- a/pkgs/stdenv/generic/check-meta.nix
+++ b/pkgs/stdenv/generic/check-meta.nix
@@ -304,21 +304,18 @@ let
       types = import ../../../lib/meta-types.nix { inherit lib; };
       inherit (types)
         str
-        union
+        either
         int
         attrs
         any
         listOf
         bool
         record
-        intersection
+        both
         not
         derivation
         ;
-      platforms = listOf (union [
-        str
-        attrs
-      ]); # see lib.meta.platformMatch
+      platforms = listOf (either str attrs); # see lib.meta.platformMatch
     in
     record {
       # These keys are documented
@@ -326,31 +323,16 @@ let
       mainProgram = str;
       longDescription = str;
       branch = str;
-      homepage = union [
-        (listOf str)
-        str
-      ];
+      homepage = either str (listOf str);
       donationPage = str;
       downloadPage = str;
-      changelog = union [
-        (listOf str)
-        str
-      ];
+      changelog = either str (listOf str);
       license =
         let
           # TODO disallow `str` licenses, use a module
-          licenseType = union [
-            (intersection [
-              attrs
-              (not derivation)
-            ])
-            str
-          ];
+          licenseType = either (both attrs (not derivation)) str;
         in
-        union [
-          (listOf licenseType)
-          licenseType
-        ];
+        either licenseType (listOf licenseType);
       sourceProvenance = listOf attrs;
       maintainers = listOf attrs; # TODO use the maintainer type from lib/tests/maintainer-module.nix
       nonTeamMaintainers = listOf attrs; # TODO use the maintainer type from lib/tests/maintainer-module.nix