From 577b48177488b96a25b45a735ce63648cc309d8f Mon Sep 17 00:00:00 2001
From: Eman Resu <78693624+quatquatt@users.noreply.github.com>
Date: Mon, 27 Apr 2026 00:37:00 -0400
Subject: [PATCH 1/5] lib.systems.parse: use `builtins.head foo` instead of
 `elemAt foo 0`

---
 lib/systems/parse.nix | 23 ++++++++++++-----------
 1 file changed, 12 insertions(+), 11 deletions(-)

diff --git a/lib/systems/parse.nix b/lib/systems/parse.nix
index 626b5bcb41ac..0e3a6c2a1239 100644
--- a/lib/systems/parse.nix
+++ b/lib/systems/parse.nix
@@ -24,6 +24,7 @@ let
     elem
     elemAt
     hasPrefix
+    head
     id
     length
     mapAttrs
@@ -68,7 +69,7 @@ let
     let
       found = match "(.*)e?abi.*" x;
     in
-    if found == null then x else elemAt found 0;
+    if found == null then x else head found;
 
 in
 
@@ -791,9 +792,9 @@ rec {
     l:
     {
       "1" =
-        if elemAt l 0 == "avr" then
+        if head l == "avr" then
           {
-            cpu = elemAt l 0;
+            cpu = head l;
             kernel = "none";
             abi = "unknown";
           }
@@ -802,7 +803,7 @@ rec {
       "2" = # We only do 2-part hacks for things Nix already supports
         if elemAt l 1 == "cygwin" then
           mkSkeletonFromList [
-            (elemAt l 0)
+            (head l)
             "pc"
             "cygwin"
           ]
@@ -812,20 +813,20 @@ rec {
         # hack-in MSVC for the non-MinGW case right here.
         else if elemAt l 1 == "windows" then
           {
-            cpu = elemAt l 0;
+            cpu = head l;
             kernel = "windows";
             abi = "msvc";
           }
         else if (elemAt l 1) == "elf" then
           {
-            cpu = elemAt l 0;
+            cpu = head l;
             vendor = "unknown";
             kernel = "none";
             abi = elemAt l 1;
           }
         else
           {
-            cpu = elemAt l 0;
+            cpu = head l;
             kernel = elemAt l 1;
           };
       "3" =
@@ -840,7 +841,7 @@ rec {
           ]
         then
           {
-            cpu = elemAt l 0;
+            cpu = head l;
             kernel = elemAt l 1;
             abi = elemAt l 2;
             vendor = "unknown";
@@ -862,7 +863,7 @@ rec {
           || hasPrefix "wasm32" (elemAt l 0)
         then
           {
-            cpu = elemAt l 0;
+            cpu = head l;
             vendor = elemAt l 1;
             kernel =
               if elemAt l 2 == "mingw32" then
@@ -873,14 +874,14 @@ rec {
         # lots of tools expect a triplet for Cygwin, even though the vendor is just "pc"
         else if elemAt l 2 == "cygwin" then
           {
-            cpu = elemAt l 0;
+            cpu = head l;
             vendor = elemAt l 1;
             kernel = "cygwin";
           }
         else
           throw "system string '${lib.concatStringsSep "-" l}' with 3 components is ambiguous";
       "4" = {
-        cpu = elemAt l 0;
+        cpu = head l;
         vendor = elemAt l 1;
         kernel = elemAt l 2;
         abi = elemAt l 3;

From 7fcbff801da7e94701efd93369f090e025ee85dd Mon Sep 17 00:00:00 2001
From: Eman Resu <78693624+quatquatt@users.noreply.github.com>
Date: Mon, 27 Apr 2026 00:37:30 -0400
Subject: [PATCH 2/5] lib.systems.parse: only check condition once

---
 lib/systems/parse.nix | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/lib/systems/parse.nix b/lib/systems/parse.nix
index 0e3a6c2a1239..3f636442ee9d 100644
--- a/lib/systems/parse.nix
+++ b/lib/systems/parse.nix
@@ -418,10 +418,8 @@ rec {
   gnuNetBSDDefaultExecFormat =
     cpu:
     if
-      (cpu.family == "arm" && cpu.bits == 32)
-      || (cpu.family == "sparc" && cpu.bits == 32)
-      || (cpu.family == "m68k" && cpu.bits == 32)
-      || (cpu.family == "x86" && cpu.bits == 32)
+      cpu.bits == 32
+      && (cpu.family == "arm" || cpu.family == "sparc" || cpu.family == "m68k" || cpu.family == "x86")
     then
       execFormats.aout
     else

From a9c0a094f7e4a530b4681d654d78c087b9441d52 Mon Sep 17 00:00:00 2001
From: Eman Resu <78693624+quatquatt@users.noreply.github.com>
Date: Sun, 26 Apr 2026 21:12:16 -0400
Subject: [PATCH 3/5] lib.systems.elaborate: avoid optionalAttrs merge

---
 lib/systems/default.nix | 29 +++++++++++++----------------
 1 file changed, 13 insertions(+), 16 deletions(-)

diff --git a/lib/systems/default.nix b/lib/systems/default.nix
index f60ece0c8f5c..31bf8367462f 100644
--- a/lib/systems/default.nix
+++ b/lib/systems/default.nix
@@ -11,7 +11,6 @@ let
     isList
     mapAttrs
     optional
-    optionalAttrs
     optionalString
     removeSuffix
     replaceString
@@ -178,21 +177,19 @@ let
             if final.isx86_64 || final.isMips64 || final.isPower64 then "lib64" else "lib"
           else
             null;
-        extensions =
-          optionalAttrs final.hasSharedLibraries {
-            sharedLibrary =
-              if final.isDarwin then
-                ".dylib"
-              else if (final.isWindows || final.isCygwin) then
-                ".dll"
-              else
-                ".so";
-          }
-          // {
-            staticLibrary = if final.isWindows then ".lib" else ".a";
-            library = if final.isStatic then final.extensions.staticLibrary else final.extensions.sharedLibrary;
-            executable = if (final.isWindows || final.isCygwin) then ".exe" else "";
-          };
+        extensions = {
+          staticLibrary = if final.isWindows then ".lib" else ".a";
+          library = if final.isStatic then final.extensions.staticLibrary else final.extensions.sharedLibrary;
+          executable = if (final.isWindows || final.isCygwin) then ".exe" else "";
+
+          ${if final.hasSharedLibraries then "sharedLibrary" else null} =
+            if final.isDarwin then
+              ".dylib"
+            else if (final.isWindows || final.isCygwin) then
+              ".dll"
+            else
+              ".so";
+        };
         # Misc boolean options
         useAndroidPrebuilt = false;
         useiOSPrebuilt = false;

From 833f05d0994512c721c035c3874078973a2698f6 Mon Sep 17 00:00:00 2001
From: Eman Resu <78693624+quatquatt@users.noreply.github.com>
Date: Mon, 27 Apr 2026 00:40:11 -0400
Subject: [PATCH 4/5] lib.systems.elaborate: prevent unnecessary attrset merges

---
 lib/systems/default.nix | 80 +++++++++++++++++++----------------------
 1 file changed, 37 insertions(+), 43 deletions(-)

diff --git a/lib/systems/default.nix b/lib/systems/default.nix
index 31bf8367462f..fd4ed9777b52 100644
--- a/lib/systems/default.nix
+++ b/lib/systems/default.nix
@@ -83,6 +83,29 @@ let
       # TODO: deprecate args.rustc in favour of args.rust after 23.05 is EOL.
       rust = args.rust or args.rustc or { };
 
+      selectEmulator =
+        pkgs:
+        let
+          wine = (pkgs.winePackagesFor "wine${toString final.parsed.cpu.bits}").minimal;
+        in
+        # Note: we guarantee that the return value is either `null` or a path
+        # to an emulator program. That is, if an emulator requires additional
+        # arguments, a wrapper should be used.
+        if pkgs.stdenv.hostPlatform.canExecute final then
+          lib.getExe (pkgs.writeShellScriptBin "exec" ''exec "$@"'')
+        else if final.isWindows then
+          "${wine}/bin/wine"
+        else if final.isLinux && pkgs.stdenv.hostPlatform.isLinux && final.qemuArch != null then
+          "${pkgs.qemu-user}/bin/qemu-${final.qemuArch}"
+        else if final.isWasi then
+          "${pkgs.wasmtime}/bin/wasmtime"
+        else if final.isGhcjs then
+          "${pkgs.nodejs-slim}/bin/node"
+        else if final.isMmix then
+          "${pkgs.mmixware}/bin/mmix"
+        else
+          null;
+
       final = {
         # Prefer to parse `config` as it is strictly more informative.
         parsed = parse.mkSystemFromString (args.config or allArgs.system);
@@ -370,48 +393,21 @@ let
         # Handle Android SDK and NDK versions.
         androidSdkVersion = args.androidSdkVersion or null;
         androidNdkVersion = args.androidNdkVersion or null;
+
+        emulatorAvailable = pkgs: selectEmulator pkgs != null;
+
+        # whether final.emulator pkgs.pkgsStatic works
+        staticEmulatorAvailable =
+          pkgs: final.emulatorAvailable pkgs && (final.isLinux || final.isWasi || final.isMmix);
+
+        emulator =
+          pkgs:
+          if (final.emulatorAvailable pkgs) then
+            selectEmulator pkgs
+          else
+            throw "Don't know how to run ${final.config} executables.";
+
       }
-      // (
-        let
-          selectEmulator =
-            pkgs:
-            let
-              wine = (pkgs.winePackagesFor "wine${toString final.parsed.cpu.bits}").minimal;
-            in
-            # Note: we guarantee that the return value is either `null` or a path
-            # to an emulator program. That is, if an emulator requires additional
-            # arguments, a wrapper should be used.
-            if pkgs.stdenv.hostPlatform.canExecute final then
-              lib.getExe (pkgs.writeShellScriptBin "exec" ''exec "$@"'')
-            else if final.isWindows then
-              "${wine}/bin/wine"
-            else if final.isLinux && pkgs.stdenv.hostPlatform.isLinux && final.qemuArch != null then
-              "${pkgs.qemu-user}/bin/qemu-${final.qemuArch}"
-            else if final.isWasi then
-              "${pkgs.wasmtime}/bin/wasmtime"
-            else if final.isGhcjs then
-              "${pkgs.nodejs-slim}/bin/node"
-            else if final.isMmix then
-              "${pkgs.mmixware}/bin/mmix"
-            else
-              null;
-        in
-        {
-          emulatorAvailable = pkgs: (selectEmulator pkgs) != null;
-
-          # whether final.emulator pkgs.pkgsStatic works
-          staticEmulatorAvailable =
-            pkgs: final.emulatorAvailable pkgs && (final.isLinux || final.isWasi || final.isMmix);
-
-          emulator =
-            pkgs:
-            if (final.emulatorAvailable pkgs) then
-              selectEmulator pkgs
-            else
-              throw "Don't know how to run ${final.config} executables.";
-
-        }
-      )
       // mapAttrs (n: v: v final.parsed) inspect.predicates
       // mapAttrs (n: v: v final.gcc.arch or "default") architectures.predicates
       // args
@@ -553,8 +549,6 @@ let
             "-uefi"
           ];
         };
-      }
-      // {
         go = {
           # See https://pkg.go.dev/internal/platform for a list of known platforms
           GOARCH =

From acd5585a3ba8481395f5897ba6060af176ef7539 Mon Sep 17 00:00:00 2001
From: Eman Resu <78693624+quatquatt@users.noreply.github.com>
Date: Sun, 3 May 2026 16:48:10 -0400
Subject: [PATCH 5/5] lib.systems.parse: check if cpus are equal first

Rather than doing this last, we do it first. Saves a little time if
we're comparing to an identical platform
---
 lib/systems/parse.nix | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/lib/systems/parse.nix b/lib/systems/parse.nix
index 3f636442ee9d..98db2595235f 100644
--- a/lib/systems/parse.nix
+++ b/lib/systems/parse.nix
@@ -444,7 +444,8 @@ rec {
   isCompatible =
     with cpuTypes;
     a: b:
-    any id [
+    b == a
+    || any id [
       # x86
       (b == i386 && isCompatible a i486)
       (b == i486 && isCompatible a i586)
@@ -482,9 +483,6 @@ rec {
 
       # SPARC
       (b == sparc && isCompatible a sparc64)
-
-      # identity
-      (b == a)
     ];
 
   ################################################################################