From add81e270cf5be0dae19ef1baf557c18fa3bc479 Mon Sep 17 00:00:00 2001
From: Eman Resu <78693624+quatquatt@users.noreply.github.com>
Date: Sat, 16 May 2026 14:09:45 -0400
Subject: [PATCH] lib.systems.doubles: only typecheck in CI

---
 ci/OWNERS               |  2 +-
 lib/systems/doubles.nix | 22 +++++++++++++++++++---
 lib/systems/parse.nix   |  6 ++++--
 lib/tests/systems.nix   | 16 ++++++++++++++++
 4 files changed, 40 insertions(+), 6 deletions(-)

diff --git a/ci/OWNERS b/ci/OWNERS
index 43ef6f666651..463c546e695b 100644
--- a/ci/OWNERS
+++ b/ci/OWNERS
@@ -39,6 +39,7 @@
 /lib/derivations.nix        @NixOS/stdenv
 /lib/fetchers.nix           @alyssais @NixOS/stdenv
 /lib/meta.nix               @alyssais @NixOS/stdenv
+/lib/meta-types.nix         @infinisil @adisbladis @NixOS/stdenv
 /lib/source-types.nix       @alyssais @NixOS/stdenv
 /lib/systems                @alyssais @NixOS/stdenv
 ## Libraries / Module system
@@ -67,7 +68,6 @@
 /pkgs/stdenv/generic/problems.nix                @infinisil
 /pkgs/test/problems                              @infinisil
 /pkgs/stdenv/generic/check-meta.nix              @infinisil @Ericson2314 @adisbladis @NixOS/stdenv
-/pkgs/stdenv/generic/meta-types.nix              @infinisil @adisbladis @NixOS/stdenv
 /pkgs/stdenv/cross                               @Ericson2314 @NixOS/stdenv
 /pkgs/build-support                              @philiptaron
 /pkgs/build-support/cc-wrapper                   @Ericson2314
diff --git a/lib/systems/doubles.nix b/lib/systems/doubles.nix
index e9fa908dfc88..d3e184320fbd 100644
--- a/lib/systems/doubles.nix
+++ b/lib/systems/doubles.nix
@@ -1,7 +1,15 @@
 { lib }:
 let
-  inherit (lib) lists;
+  inherit (lib)
+    lists
+    splitString
+    ;
   inherit (lib.systems) parse;
+  inherit (parse)
+    mkSystemFromSkeleton
+    mkSkeletonFromList
+    doubleFromSystem
+    ;
   inherit (lib.systems.inspect) predicates;
   inherit (lib.attrsets) matchAttrs;
 
@@ -117,9 +125,17 @@ let
     "x86_64-uefi"
   ];
 
-  allParsed = map parse.mkSystemFromString all;
+  uncheckedSystemFromString =
+    let
+      systemType = {
+        _type = "system";
+      };
+    in
+    s: mkSystemFromSkeleton (mkSkeletonFromList (splitString "-" s)) // systemType;
 
-  filterDoubles = f: map parse.doubleFromSystem (lists.filter f allParsed);
+  allParsed = map uncheckedSystemFromString all;
+
+  filterDoubles = f: map doubleFromSystem (lists.filter f allParsed);
 
 in
 {
diff --git a/lib/systems/parse.nix b/lib/systems/parse.nix
index e8e5a7799014..cdfeafe7c18d 100644
--- a/lib/systems/parse.nix
+++ b/lib/systems/parse.nix
@@ -903,6 +903,8 @@ rec {
     or (throw "system string '${lib.concatStringsSep "-" l}' has invalid number of hyphen-separated components");
 
   # This should revert the job done by config.guess from the gcc compiler.
+  # Note: this does _not_ verify that the system is valid
+  # `mkSystemFromString` is recommended for external use
   mkSystemFromSkeleton =
     let
       getCpu = name: cpuTypes.${name} or (throw "Unknown CPU type: ${name}");
@@ -960,9 +962,9 @@ rec {
       };
 
     in
-    mkSystem parsed;
+    parsed;
 
-  mkSystemFromString = s: mkSystemFromSkeleton (mkSkeletonFromList (splitString "-" s));
+  mkSystemFromString = s: mkSystem (mkSystemFromSkeleton (mkSkeletonFromList (splitString "-" s)));
 
   kernelName =
     kernel: if kernel ? version then kernel.name + toString kernel.version else kernel.name;
diff --git a/lib/tests/systems.nix b/lib/tests/systems.nix
index 3feef87d97c0..e2b9093511c6 100644
--- a/lib/tests/systems.nix
+++ b/lib/tests/systems.nix
@@ -215,6 +215,22 @@ lib.runTests (
   })
 
   // {
+    test_platforms_pass_typecheck = {
+      # To improve performance, the result of parsing all 70+ systems in
+      # `lib.platforms` into their attrset representations aren't typechecked.
+      # The results are expected to be constant, and avoiding the slow
+      # validation gives a meaningful improvement to evaluation speed. We ensure
+      # that all systems pass validation here
+      expr = builtins.filter (
+        system:
+        let
+          evalResult = builtins.tryEval (lib.systems.parse.mkSystemFromString system);
+        in
+        evalResult.success == false
+      ) lib.platforms.all;
+
+      expected = [ ];
+    };
     test_equals_example_x86_64-linux = {
       expr = lib.systems.equals (lib.systems.elaborate "x86_64-linux") (
         lib.systems.elaborate "x86_64-linux"